Pye Mozart HF10 stereo pair

[helma]

I already made a thread about this when I first got it back in March or so, though at the time of purchase I mistook it for HFS20. It came in a small cabinet also housing a Garrard HF4 record player. What we have here is a pair of Pye Mozart HF10. The twist is the left one has stereo pots and switches with wires going to the 2nd unit, which obviously doesn't have any controls of it's own then. It seems this was a factory job, since the amp with the faceplate has "Stereophonic" engraved on it in place of the "High Fidelity" regular of regular HF10 faceplace. Also the 2nd unit has the chassis made smaller so there's no empty space where the pots would normally be. I've yet to build a proper case for it, they've been just strapped to this piece of wooden board. On the second photo the other unit is missing one of it's preamp valves since I was taking some measurements from the socket. A couple (bad) photos:

http://i.imgur.com/170PVMd.jpg

http://i.imgur.com/ngzW5a7.jpg


At the top right on each unit you see an empty valve socket - that's for an EF88 for the phonostage, this is not normal and I'm not sure if it was a Pye Factory job, or made by whoever sold this console or a later modification by someone. The date code on the valves reads D0J which I assume would mean they were made by Valvo in Hamburg in October 1960. All the original capacitors and stock Mullard valves were dated 1958, so I'm assuming this was made then and the EF88 is a later addition by someone or the company who made the cabin and bundled it all together.

Never seen anything like this trying to dig up information on these old Pye Mozart series amps, I suppose if Pye made more like this it didn't made a whole lot, seems like it could maybe be a 'transitional' stereo setup before HFS20 was introduced. Anyone seen anything like this before? I guess I should try some forum specializing on old British valve stuff :)

I've recapped them, changed all paper caps and electrolytics, replacing the smaller ones with film caps and Nichicons for the big cans. Hum was reduced and the sound cleared up, with the 60 year old stock caps the treble was a bit rolled off. Surprisingly all the changed caps still measured within spec at the small test voltage at least, but don't know how they'd behave with the high voltages they see in actual use.

Sound is awesome to my ears, very full without getting overly warm and fuzzy and both frequency extremes are surprisingly good as well. Would like to try out some a bit more efficient speakers, I've been driving a pair of Kef 104aB and JBL 120Ti, both of which are rather ineffecient. Sounds great but don't get very loud. The Kefs are not that great at high volumes anyway, though I never realized that before I got the JBLs. Stereo imaging
with the PYE is not the greatest, I mean not that it's horribad or anything, it's very stable but it's more a "broad brush" version as opposed to pinpoint etching. Still it has become my go to amp for most listening. Competition has been some better 80s japanese amps.

[Firebottle]

Wow. Thanks for posting the details and photos.

[Arkless Electronics]

A strange find there.... I've renovated a few of the stereo version (pre amp and stereo power amp) but never seen that set up you have. I was pleasantly surprised by the power amp. I was expecting it to be awful but indeed it sounds pretty good and surprisingly modern. A very unusual and intriguing design, it uses an EL34 pentode single ended with cathode windings as well as anode and loads of feedback.

If you are not already doing so I would use it as a power amp only to get the best results from it.

[Barry]

A strange find there.... I've renovated a few of the stereo version (pre amp and stereo power amp) but never seen that set up you have. I was pleasantly surprised by the power amp. I was expecting it to be awful but indeed it sounds pretty good and surprisingly modern. A very unusual and intriguing design, it uses an EL34 pentode single ended with cathode windings as well as anode and loads of feedback.

If you are not already doing so I would use it as a power amp only to get the best results from it.

http://www.valve-radio.co.uk/literature/pye-mozart-hf10-amplifier-service-manual/

http://www.valve-radio.co.uk/wp-content/uploads/2014/05/HF10-10.jpg

[helma]

I've been currently using the Pye from the tape-outs of an 80s Yamaha A-700 (with an upgraded phonostage), so the signal goes through the preamp. Power-amp inputs are in the plans, kind of waiting for putting together the enclosure which will be a good opportunity to do other work as well. With some tweaking of the bass & treble knobs the preamp gives a reasonably even response, but I can certainly imagine it being a weak link. The tone control section has the paper caps replaced, but the ceramics are still originals. I'll be changing those as well at some point.

I'm wondering if I should just do a complete rebuild, I measured some of the resistors and they were nothing close to modern tolerances, some of the values were pretty far from spec, but on the other hand they were same for both units so I guess there was at least some effort to match the channels. Modern resistors would surely sound different though. Also the rectifiers are still the original selenium ones, I've read those to be pretty unreliable. I've got modern bridges waiting but I like listening to my kit more than working on it, so haven't got around to it.

[Arkless Electronics]

I've been currently using the Pye from the tape-outs of an 80s Yamaha A-700 (with an upgraded phonostage), so the signal goes through the preamp. Power-amp inputs are in the plans, kind of waiting for putting together the enclosure which will be a good opportunity to do other work as well. With some tweaking of the bass & treble knobs the preamp gives a reasonably even response, but I can certainly imagine it being a weak link. The tone control section has the paper caps replaced, but the ceramics are still originals. I'll be changing those as well at some point.

I'm wondering if I should just do a complete rebuild, I measured some of the resistors and they were nothing close to modern tolerances, some of the values were pretty far from spec, but on the other hand they were same for both units so I guess there was at least some effort to match the channels. Modern resistors would surely sound different though. Also the rectifiers are still the original selenium ones, I've read those to be pretty unreliable. I've got modern bridges waiting but I like listening to my kit more than working on it, so haven't got around to it.

The resistors will have drifted by roughly the same amount rather than been chosen to match!! Almost always high. I don't really buy into resistors sounding different to any great extent personally. I replaced the selenium rectifiers in ones I've renovated but be careful to add extra series resistance as silicon rectifiers will result in considerably higher output voltage.

[helma]

The resistors will have drifted by roughly the same amount rather than been chosen to match!! Almost always high. I don't really buy into resistors sounding different to any great extent personally. I replaced the selenium rectifiers in ones I've renovated but be careful to add extra series resistance as silicon rectifiers will result in considerably higher output voltage.

I finally got around to replacing the selenium rectifiers. The reference voltages were down something like 25V from spec, getting 225 where there should be 250V etc. By contrast using modern silicone rectifiers the voltages were up by roughly similar amount. Had to add 330R series resistance after the rectifiers, now it's about spec, generally around 5V low so could maybe finetune that resistance a bit, but on the other hand my mains was a bit lower than usual last night, so maybe I'll just leave it be. Didn't hook it up yet to speakers, just checked everything with a dummy load, so don't know how much the sound was affected. At the moment the rectifiers and resistors are hooked up using screw terminals, wanted to make sure everything works as it should before I solder them and also need to figure out where to install them physically.

I've been using the whole thing, eventually I'd like to add pre-out/main-in jacks once I figure out how to best do it, so it could be hooked either way. For now the preamp is very much in the picture. What did you find disagreeable about it and the sound and do you personally think the pre is just a poor design? Obviously the signal passes through a set of tone controls and some very old pots and switches, however these in my unit seem to be in tip-top shape and didn't really even need a clean, no symptoms what so ever. I've recapped the tone controls, but to get flat frequence response (judged by ear), treble needs to be bumped up to about +1 and bass needs to be cut back to about -2 . Dialed in right it sounds quite neutral though, albeit perhaps not the last word on audiophile qualities, however very engaging and musical nonetheless.

Btw. most of the original caps were also in very good shape, at least measured with the tiny voltages the cheap ebay tester I have uses, but it could be they behave differently under high voltages and subjectively the sound was improved a lot by the recap. The damping adjustment pots are in a rough shape, to the point they are really not to be adjusted while the unit is powered on for all the screetches and loud noises they make, should replace those at some point.

Also still haven't got around to ordering a new set of power tubes, the original Mullards seem fine as far as I can tell, but I can't tell much for not having a tested new pair as a reference...

[spendorman]

Good that you got rid of the selenium rectifiers, my experience of them (decades ago) was that they were not reliable, and emitted a horrible (understatement) smell when they went wrong.

Perhaps new EL34's, just to preserve the Mullards, I have used JJ EL34's and JJ KT77's to good effect in my Radford STA25 III.

[Arkless Electronics]

Good that you got rid of the selenium rectifiers, my experience of them (decades ago) was that they were not reliable, and emitted a horrible (understatement) smell when they went wrong.

Perhaps new EL34's, just to preserve the Mullards, I have used JJ EL34's and JJ KT77's to good effect in my Radford STA25 III.

Foul indeed and IIRC toxic so it's open window and out of room when it's happened to me...

I've heard rumours that JJ quality control has vastly improved in recent years but when I was dealing with loads of valved guitar amps I found JJ to be the most unreliable as regards catastrophic failures...

[spendorman]

Yes, JJ quality increased from the early days, it probably had to!

[helma]

AFAIK JJ EL34 quality is fine these days, at least a well respected Finnish vendor seems happy about selling them, which apparently isn't the case with JJ KT77 which they still don't recommend because of quality control issues, though I recall reading somewhere the KT77 have also gotten better. They also offer a "hifi graded" version of the JJ EL34, which they have ran in and tested extensively, apparently about 5-10% of product they get their hands on meets their criteria of specs. Adds 10 euros to the price per valve, so a pair would run about 50 euros, but they do throw in an extended (6 months) warranty, so might as well go with that. Haven't yet put in the order though and also noticed a NOS pair of Svetlana EL34 wouldn't cost that much more, so wondering if that would be a better value for money.

[Arkless Electronics]

AFAIK JJ EL34 quality is fine these days, at least a well respected Finnish vendor seems happy about selling them, which apparently isn't the case with JJ KT77 which they still don't recommend because of quality control issues, though I recall reading somewhere the KT77 have also gotten better. They also offer a "hifi graded" version of the JJ EL34, which they have ran in and tested extensively, apparently about 5-10% of product they get their hands on meets their criteria of specs. Adds 10 euros to the price per valve, so a pair would run about 50 euros, but they do throw in an extended (6 months) warranty, so might as well go with that. Haven't yet put in the order though and also noticed a NOS pair of Svetlana EL34 wouldn't cost that much more, so wondering if that would be a better value for money.

I'd take Svetlana ("winged C") over JJ all day long;) At the time when I was getting loads of faulty JJ valves, most valve suppliers in UK were strongly recommending them! Call me cynical... but this makes me think the suppliers were getting a good mark up on them... I do hope that QA has indeed improved since then (about 10 years ago).

Just an aside but it amazes me that Mullard are so sought after over Brimar, Mazda etc... All of the "BVA" British and European valves from the golden age were of good quality and I sometimes find Brimar to be better than Mullard!

[mik_rik]

Try some Russian 6p3s-e,[gold grid] a lot cheaper than n.o.s Mullard .I have used them and can recommend them,although they are not quite the bargain they used to be.I agree with Jez about Brimar and Mazda rivalling Mullard,at this moment I have a set of Mazda's in my amp which I prefer to Mullard's I had previously. Mick

[Arkless Electronics]

Try some Russian 6p3s-e,[gold grid] a lot cheaper than n.o.s Mullard .I have used them and can recommend them,although they are not quite the bargain they used to be.I agree with Jez about Brimar and Mazda rivalling Mullard,at this moment I have a set of Mazda's in my amp which I prefer to Mullard's I had previously. Mick

I wouldn't recommend this! It's a 6L6 near equivalent (lower max ratings than 6L6... bit of a weedy version) and not entirely compatible with EL34. It's a beam tetrode whilst the EL34 is a pentode for a start... It should work but requires different bias and screen grid voltages for proper operation. How it would react to the cathode windings in the Pye is any ones guess!

[spendorman]

I'm no expert on valves, but I thought Brimmar and Mazda were often Mullards in disguise.

[mik_rik]

A helluva lot of guitar and audio people use the 6p3s-e [not 6p3s which is a totally different valve] built for Russian military and are not "weedy" in their experience.Nothing wrong with trying them after reading other peoples experience .A kt66 is a kinkless tetrode and was GEC'S way around 6l6 patents and is different again ,and people sub 5881 6l6 ,el34 etc in amps up to Quad11 for them.Different construction does not mean they are not able to be used .I can only talk from experience and have used 6p3s-e in a Radford STA 15 ,no red plating ,have took said amp to NEBO's , no issues that anyone heard.I would definately trust them a lot more than other el34's on sale from some ,even reputable vendors.YMMV Mick

[mik_rik]

I'm no expert on valves, but I thought Brimmar and Mazda were often Mullards in disguise.

Mullards are recognisable by a code etched onto the glass[usually starting with the letter b denoting Blackburn plant,a double seam on top ,and a hole in the locating spigot.Towards the end of valve production,there was quite a bit of cross buying going on but I have no Brimar or Mazda Mullard made,including Ecc and Ef types. Mick

[Arkless Electronics]

A helluva lot of guitar and audio people use the 6p3s-e [not 6p3s which is a totally different valve] built for Russian military and are not "weedy" in their experience.Nothing wrong with trying them after reading other peoples experience .A kt66 is a kinkless tetrode and was GEC'S way around 6l6 patents and is different again ,and people sub 5881 6l6 ,el34 etc in amps up to Quad11 for them.Different construction does not mean they are not able to be used .I can only talk from experience and have used 6p3s-e in a Radford STA 15 ,no red plating ,have took said amp to NEBO's , no issues that anyone heard.I would definately trust them a lot more than other el34's on sale from some ,even reputable vendors.YMMV Mick

I haven't heard your Radford but other than that I strongly disagree with everything you said I'm afraid...

[Arkless Electronics]

I'm no expert on valves, but I thought Brimmar and Mazda were often Mullards in disguise.

As Mick said, towards the later period all sorts of things were marked as being a different make... there were even things like Tesla's etc marked Mullard...

[mik_rik]

At present ,the GZ34 rectifier valve I am using is branded Zaerix but is Mullard [I would not use anything else,to me more important than the pre and power o/p valves]Goes to show you don't always know who made what.I would use any of the old makes before I would risk losing a mains t/x or an o/p t/x to some of the modern ,cheap Chinese valves. Again ymmv but just my 2pennorth Mick

[mik_rik]

I haven't heard your Radford but other than that I strongly disagree with everything you said I'm afraid...

Fair enough,agree to disagree ,can't remember if I took it to NEBO AT Seaton Carew ,if I did ,good chance you heard it there.Again ,just my experience of valve rolling...cheers

[spendorman]

Mullards are recognisable by a code etched onto the glass[usually starting with the letter b denoting Blackburn plant,a double seam on top ,and a hole in the locating spigot.Towards the end of valve production,there was quite a bit of cross buying going on but I have no Brimar or Mazda Mullard made,including Ecc and Ef types. Mick

Yes, I remember about the hole in the end of the spigot. Anyone remember Bentley Acoustic? Supplied many makers valves under their own name.

[Arkless Electronics]

Yes, I remember about the hole in the end of the spigot. Anyone remember Bentley Acoustic? Supplied many makers valves under their own name.

Yep and "Zearux valve mail order" (not sure about spelling), Pinnacle, Edicron and there were a few others.. some of these (most!) were dodgy as fuck! I've gone through a pile of Pinnacle EL84's sticking em in a Leak stereo 20 and watching them self immolate within a minute when fitted as sets of four! Some however were Mullards remarked as these brands! Or Tungsram etc.. I reckon it all depended on what they could get their hands on at the time!

About 6 months ago I needed a new GZ34 for my Stereo 20 (the Mullard hadn't failed.. I'd been made an offer I couldn't refuse for it by a guitar player!) so i turned to a bag of Edicron ones I'd picked up for next to nowt .. and found out why.... 5 failed. Some lasting as long as 2 days... otherss little as 2 minutes... the sixth is giving sterling service after 6 months... Caveat emptor;)

[Arkless Electronics]

Fair enough,agree to disagree ,can't remember if I took it to NEBO AT Seaton Carew ,if I did ,good chance you heard it there.Again ,just my experience of valve rolling...cheers

No offence intended Mick. I'm just blunt as you will have realised... The 6p3s is roughly equivalent to the 6L6 but has much reduced ratings. It would be fine in a 6L6 based amp giving 20-25W but in one giving 40 it would have a life in single digit hours probably. they are though (or were) very cheap. Yes there are other rated types available that get near to USA types in rating. The e or b (Russian e or V) normally mean long life rating or harsh environment rating and are often (if you're lucky!) military NOS, which if you get the pukka thing are as good as Mullard. I wouldn't trust the "OTK" in purple on the envelope much any more as resellers/charlatans have cottoned on to it and it's easy to fake!

Philips (Dutch owners of Mullard since about 1930-ish IIRC) had a patent on the pentode well before RCA came up with their answer in the "beam power tetrode". Their "new big thing" was the 807, which was a top anode RF rated valve that did sterling service in WW2 for us and the yanks and was knocking on a bit by then... The 6l6 was a cheapened version optimised for audio amps but based closely on the 807. There are loads of variants of the 6L6! probably more so than any other valve. The KT66 is indeed a "kinkless tetrode" ie beam power tube by a different name to get round RCA's copyright. It's a further improved and higher rated SQ version of the 6L6 but British basically.. The KT77 is a GEC/Marconi/Osram answer to the EL34 and although a beam tetrode is optimised to be as pentode like.. and EL34 to be specific.. as possible, and again was intended as a higher rated better quality version of the commonly used EL34 of course.

5881 is a military spec version of 6L6 and there is a lovely Russian version of this which may be based on the 6p3s.. it has a very thin "button base" to cut down on the height of the valve... rumours are they were used in the servo of the bomb doors of Russian cold war era bombers and they had to be reduced in height to fit in the available space... possibly apocryphal! These, if pukka, are superb and I'd take them in preference to non military spec/SQ/selected Brimar, GEC (USA GEC of course. Unrelated to UK GEC AFAIK) etc..

All from memory, as google would be cheating.... and weds are pub night... hick... so if wrong I apologise:)

I've done loads of conversions from one type to the other on guitar amps in the past and for proper operation the screen grid resistor needs changing from 470R to 1K and the bias voltage is sufficiently different for optimum operation that only in some models of amp will it come within the adjustment range of the bias pot.. on some amps a resistor needs changing as well to get it in range. The Pye is fixed bias... sort of cathode bias ish I guess (you can't adjust it IIRC) but it's an interesting design! After rebuilding and modernising a pair a few years ago I was quite surprised by their sound... At reasonable levels quite SS like in many ways (in a good way), much more detail and precision than you may expect! However... it all went a bit Pete Tong well before they reached anywhere near clipping from memory. Rated at 10W (or was it 8?) I would not want to use them much above say 4W for best results. Leak Stereo 20 trounces them on max volume and slam etc but at low volumes I recall them being at least the equal of the Leak and maybe better;)

The transfer characteristics are fairly different and they therefore sound pretty different.... for good or bad depending on taste and amp model...

[spendorman]

I used to buy quite a lot of Zaerux (Z&I Aero Services), they were cheap, but not always good. Picked them up from their shop in Edgware Road (I think). Just picked one out of my (very large) box of spares. 21293

[spendorman]

When the Radford STA25 was reintroduced in 1984 (I think), the GEC KT77 was chosen, as good quality EL34's were difficult to obtain.

I have a set of these GEC KT 77's, they go for silly high prices these days.

[spendorman]

Surely it's the GE 5881, I have some of these as replacements for KT66's in my Quad II's, though I have not used them yet (in about 40 years!)

I believe that at one time Quad supplied these for the Quad II.

In the 80's I worked for GEC (Marconi), in the staff shop we could buy GEC products, including Hotpoint, as GEC owned them, strangely, GE (American) products became available too in the shop, there was some tie up between the two companies.

[Arkless Electronics]

Surely it's the GE 5881, I have some of these as replacements for KT66's in my Quad II's, though I have not used them yet (in about 40 years!)

I believe that at one time Quad supplied these for the Quad II.

In the 80's I worked for GEC (Marconi), in the staff shop we could buy GEC products, including Hotpoint, as GEC owned them, strangely, GE (American) products became available too in the shop, there was some tie up between the two companies.

Yes USA GE... I'd forgotten that they were often differentiated by the C being missed off the yank one... 6L6 and the mil equivalent 5881 are interchangeable with KT66 as KT66 was a later, British, improved answer to the 6L6....

[Arkless Electronics]

I used to buy quite a lot of Zaerux (Z&I Aero Services), they were cheap, but not always good. Picked them up from their shop in Edgware Road (I think). Just picked one out of my (very large) box of spares. 21293

That's the buggers yes!

[spendorman]

That's the buggers yes!

Their EL34's were a bit of a bomb, not all, but quite a lot.

[Arkless Electronics]

Their EL34's were a bit of a bomb, not all, but quite a lot.

Oh yes I can believe it. see my comments above about EL84's and GZ34's from some of these dubious brands... Whilst not common it was possible to get Mullard, Tesla, Tungsram etc remarked as these brands so it could work both ways... but 9 times out of 10 they were crap and it would take a dozen to find 2-3 that worked properly...

[spendorman]

7581A box
2129421295

I must have got the numbers wrong previously!

Also says 7581A on the valve.

[spendorman]

Oh yes I can believe it. see my comments above about EL84's and GZ34's from some of these dubious brands... Whilst not common it was possible to get Mullard, Tesla, Tungsram etc remarked as these brands so it could work both ways... but 9 times out of 10 they were crap and it would take a dozen to find 2-3 that worked properly...

Yes, I forgotten that I bought some rubbish EL84's from Zaerux.

[Arkless Electronics]

7581A box
2129421295

I must have got the numbers wrong previously!

Also says 7581A on the valve.

Very interesting! I did say earlier there are probably more variants of the 6L6 than any other valve... But I'd not heard of these! I wonder if they were the yanks answer to the British, improved version, of the 6L6, the KT66? The box markings would suggest this. I did resort to google on this for a quick search but mainly found reference to a modern "Tung-sol" version and old Ge plus Philips ecg JAN versions (later USA Sylvania in reality).

[spendorman]

I also have these.

21296

Can't be bothered with camera at the moment, used scanner, otherwise I would have included pics of the valves.

[spendorman]

Pic of GE 7581A / KT6621297

[helma]

I've done loads of conversions from one type to the other on guitar amps in the past and for proper operation the screen grid resistor needs changing from 470R to 1K and the bias voltage is sufficiently different for optimum operation that only in some models of amp will it come within the adjustment range of the bias pot.. on some amps a resistor needs changing as well to get it in range. The Pye is fixed bias... sort of cathode bias ish I guess (you can't adjust it IIRC) but it's an interesting design! After rebuilding and modernising a pair a few years ago I was quite surprised by their sound... At reasonable levels quite SS like in many ways (in a good way), much more detail and precision than you may expect! However... it all went a bit Pete Tong well before they reached anywhere near clipping from memory. Rated at 10W (or was it 8?) I would not want to use them much above say 4W for best results. Leak Stereo 20 trounces them on max volume and slam etc but at low volumes I recall them being at least the equal of the Leak and maybe better;)


I can attest to this regarding the sound of the HF10 - I was really surprised how modern they sounded the first time I hooked the pair up. And this was with all original parts. Changing the caps only highlighted that. I'm not sure what I was expecting, something way more "50s sounding" I'm sure :) I also agree they don't seem to keep very well together at high volumes, but to my ears this happens at levels when there's already significantly increased distortion. It's possible though the original Mullards are tired and start breaking up earlier than they should. If not pushed near their limits, there's suprisingly solid and agile bass and nice snap to percussion etc. making drum kits really punch like they are supposed to. Unfortunately that just tempts me to crank it up some more and then they run out of juice.

This leads me to my dilemma - I can just about squeeze a nice listening level out of them with my fairly inefficient speakers, but with nothing left on the table, no cranking it up when feeling like it. It's just not enough power for my speakers and room, I think I would need speakers with a sensitivity of at least 93-96dB/W. So the question then becomes if I want to get new speakers or let the Pye go. This would be a perfect excuse for experimenting with some high efficiency full ranges or something, but another money sink. Will have to try with shiny new valves before making any decisions though. I've got quite a bit of hifi kit I need to get rid off and there are some other items I'd be willing to see go before the Mozart, so hopefully I'll find a way to talk myself into keeping it :) Also I have a history of flipping anything I got from a deal too good to be true, it would be nice to hang onto something for a change. It's usually not how I planned it, but then someone sees what I've got and makes an offer I can't refuse.

[spendorman]

It would be nice to try some highish efficiency speakers on the Pye before parting with it. I have a Chinese single ended EL34 amp that is pretty sweet on low volumes. I don't have any really efficient speakers, possibly the highest efficiency ones that I have are Tannoy HPD315's.

[mik_rik]

No offence intended Mick. I'm just blunt as you will have realised... The 6p3s is roughly equivalent to the 6L6 but has much reduced ratings. It would be fine in a 6L6 based amp giving 20-25W but in one giving 40 it would have a life in single digit hours probably. they are though (or were) very cheap. Yes there are other rated types available that get near to USA types in rating. The e or b (Russian e or V) normally mean long life rating or harsh environment rating and are often (if you're lucky!) military NOS, which if you get the pukka thing are as good as Mullard. I wouldn't trust the "OTK" in purple on the envelope much any more as resellers/charlatans have cottoned on to it and it's easy to fake!

Philips (Dutch owners of Mullard since about 1930-ish IIRC) had a patent on the pentode well before RCA came up with their answer in the "beam power tetrode". Their "new big thing" was the 807, which was a top anode RF rated valve that did sterling service in WW2 for us and the yanks and was knocking on a bit by then... The 6l6 was a cheapened version optimised for audio amps but based closely on the 807. There are loads of variants of the 6L6! probably more so than any other valve. The KT66 is indeed a "kinkless tetrode" ie beam power tube by a different name to get round RCA's copyright. It's a further improved and higher rated SQ version of the 6L6 but British basically.. The KT77 is a GEC/Marconi/Osram answer to the EL34 and although a beam tetrode is optimised to be as pentode like.. and EL34 to be specific.. as possible, and again was intended as a higher rated better quality version of the commonly used EL34 of course.

5881 is a military spec version of 6L6 and there is a lovely Russian version of this which may be based on the 6p3s.. it has a very thin "button base" to cut down on the height of the valve... rumours are they were used in the servo of the bomb doors of Russian cold war era bombers and they had to be reduced in height to fit in the available space... possibly apocryphal! These, if pukka, are superb and I'd take them in preference to non military spec/SQ/selected Brimar, GEC (USA GEC of course. Unrelated to UK GEC AFAIK) etc..

All from memory, as google would be cheating.... and weds are pub night... hick... so if wrong I apologise:)

I've done loads of conversions from one type to the other on guitar amps in the past and for proper operation the screen grid resistor needs changing from 470R to 1K and the bias voltage is sufficiently different for optimum operation that only in some models of amp will it come within the adjustment range of the bias pot.. on some amps a resistor needs changing as well to get it in range. The Pye is fixed bias... sort of cathode bias ish I guess (you can't adjust it IIRC) but it's an interesting design! After rebuilding and modernising a pair a few years ago I was quite surprised by their sound... At reasonable levels quite SS like in many ways (in a good way), much more detail and precision than you may expect! However... it all went a bit Pete Tong well before they reached anywhere near clipping from memory. Rated at 10W (or was it 8?) I would not want to use them much above say 4W for best results. Leak Stereo 20 trounces them on max volume and slam etc but at low volumes I recall them being at least the equal of the Leak and maybe better;)

The transfer characteristics are fairly different and they therefore sound pretty different.... for good or bad depending on taste and amp model...

Hi there Jez ,... no offence taken ,just to clarify ,it may be you thought I was referring to the 6p3s .The valve I was talking about was the 6p3s-e version which is totally different in construction and performance,much better imho.This is the one with the "coin" base and is much more rugged and is a very good sounding valve[I thought they were used in ballistic missile servo's,pleased they were not used in anger].When people talk about the sound of different valve types it is easy to use exaggerated terms to describe differences to make a point,these terms become gospel and so certain makes become must have and the price soon becomes inflated.Mullard are very good but not that other classic makes are rubbish in comparison hence as you say Brimar,Mazda are at least on a par. - and a lot cheaper! Cheers Mick

[Arkless Electronics]

Hi there Jez ,... no offence taken ,just to clarify ,it may be you thought I was referring to the 6p3s .The valve I was talking about was the 6p3s-e version which is totally different in construction and performance,much better imho.This is the one with the "coin" base and is much more rugged and is a very good sounding valve[I thought they were used in ballistic missile servo's,pleased they were not used in anger].When people talk about the sound of different valve types it is easy to use exaggerated terms to describe differences to make a point,these terms become gospel and so certain makes become must have and the price soon becomes inflated.Mullard are very good but not that other classic makes are rubbish in comparison hence as you say Brimar,Mazda are at least on a par. - and a lot cheaper! Cheers Mick

:)

[helma]

It would be nice to try some highish efficiency speakers on the Pye before parting with it. I have a Chinese single ended EL34 amp that is pretty sweet on low volumes. I don't have any really efficient speakers, possibly the highest efficiency ones that I have are Tannoy HPD315's.

Oh yeah, definitely not going to part with them before at least hearing them with more efficient speakers. I'm just a bit scared of that route because it has the potential for complete upheaval of the system once again. As it is, I'm in a pretty happy place with the setup and not really itching to change much. I do have a pair of Kef 104aB currently doing nothing and while very low sensitivity, together with the Pyes they would provide plenty enough volume for near field bedroom setup... or I could use the Pyes for desktop amp, but again seems a bit overkill :D I don't know, I have some hobby money tied up in surplus turntables and what not, once I get around to selling all that it would probably be plenty enough to get a decent pair of high sensitivity somethings, buying used there should be no risk with that even if I eventually decided to let the HF10s go.

[helma]

Little update - the Pye HF10s are still very much with me, I just did an easily reversible modification last night to turn the 'pick-up' input into a power-amp in, to allow bypassing the stock preamp. Only listened to an hour or so last night and now spinning something in the background. I think it did a world of good to the sound in terms of hifi qualities. Currently running with a simple passive volume control, last night I used a chinese hybrid pre. Either way, imaging is more precise and solid than it used to be. I think that was probably my biggest gripe about the sound stock. Imaging was a bit wishy-washy. That's a trait my JBLs share, so the end result was very broad strokes. Besides that the sound seems just more clear and neutral all around. The midrange is captivating, drums have a really tactile snap to them and saxophones have proper bite. There's a very euphonic 'liquidity' to the sound, I'm not sure what's that about but I suspect it's because I'm hearing a slightest amount of excess warmth/softness in the lower mids. I think I heard that trait last night also, but the passive pre might be highlighting it.

These are just first impressions and more listening is in order, but certainly sounds very very nice indeed at the moment. I also need to play around with the "damping" control more to find the best balance between control and midrange transparency. AFAIK it adjusts output impedance and amount of negative feedback.

[Firebottle]

That sounds like an excellent little mod.

[helma]

I haven't been listening to CDs / digital for years much, unless I really want to hear the music. With the Pye I've found myself going through some old CDs with pleasure. Just for kicks I did a quick 3 amp shoot out last night, and yes, with my solid state amps that enjoyment was gone. With the Yamaha A-700 it became really grating, the Sherwood AM-8500 MOSFET amp was somewhat better but still more like "tolerable". Both sound fine with my vinyl frontend. So yeah, maybe I just need a better CD-player, then again I haven't yet heard one I really liked. Except with the Pye I was liking my 1 euro thrift store Philips CDR fine enough. It makes me think I should just set the system up around this. Yeah sure, it doesn't really leave me with much headroom or probably give as much "information" but then again I have hundreds of CDs which might get some regular play time again, maybe.

Oh, and I also think I heard a difference between the volume controls, but I can't test that, since the Yamaha doesn't have a pre-out. But in source direct mode the Yamaha preamp is totally passive, it's just a source selector and volume control. I think most of the difference in soud was due to the amps, but there was a certain thing going on with both the Sherwood and the Pye, which I think might be the potentiometer I'm using. I should probably build a new passive with better parts. Nothing too fancy/expensive, but at least a nice potentiometer or some chinese stepped attenuator. The one I'm using now I think softens up the sound. But it's a mostly pleasant coloration, so it doesn't get in the way. It would be interesting to test it side by side with something else to see if what I'm hearing is really the potentiometer or something else. But now that I think I've heard it, i'm imagining I can hear that coloration everywhere where that kind of carbon potentiometer is used... go figure :hmm:

[helma]

Well since then I've changed speakers, built some open baffles around a quad of Philips AD1200 12" fullranges w/ AD0163 tweeters coming in to help @*about 10kHz. 2nd pair of 12" drivers have 2nd order lowpass @*about 100Hz. So basically it's fullranges with a little help at both frequency extremes. Sensitivity is about 93dB/W I think, just enough of a boost in that regard to have the Pye operate in a more comfortable power range. I think sensitivity of > 96dB would be ideal, but this is enough.

I also finally got around to changing the valves, the original late 50s Mullards gave room to a pair of JJ EL34 & ECC83S. I think the original Mullards are still good, but would have to get them tested to be sure. In any case, putting the JJs in place of the Mullard Xf1, I was surprised how little difference there was. The Mullards have slightly cleaner and sweeter highs, the midrange is very similar with the Mullard probably having a slightly softer sound - if the JJ midrange is clear water, the Mullard is more like flowing translucent syrup :D Anyway both I feel are excellent in this respect, the JJ sounds perhaps a bit more "hifi". In any case the difference is small and I think matter of taste and most people I'm sure would be happy with either. I haven't tried, but I have a feeling for guitar applications where things are run into distortion, the Mullard would probably sound better, with a thicker and creamier tone. Bass is where I think the JJ has the upper hand, they just seem to have a tad more grip and control. Overall I would take the Mullard over the JJs, mainly for those sweeter and cleaner highs, but there's not that much to it and I'm perfectly happy with the JJs. Delighted to be honest, even after the extended run in and matching by Uraltone they are a 20 euro valve.

For the ECC83 it's a bit different story - here the late 50s long plate Mullard is clearly superior. Again, JJs lose out on the highs, they are coarser and less detailed, there's a little bit of "hash" to them. The JJ ECC83s were advertised as being slightly darker sounding than most and compared to the Mullards this certainly seems true. Also first impression was of a slight veil inserted between the listener and the music. It's not bad and only really noticeable when doing a direct comparison (plus the fullranges are NOT dark sounding, so it's not really a bad thing). Generally speaking, when listening to the setup with the JJs, I don't feel the presentation is veiled, but I know if I went back to the Mullards, there would be better clarity and tonality and more 3-dimensionality to the sound.

While the difference to the vintage Mullards is greater here, I still find the JJ good and enjoyable (which can't be said of the 90s Shuguangs I found in a box of guitar parts - no wonder I got rid of those ASAP - just horrible sounding despite tonality being very similar to the Mullards) and after getting used to the sound, I'm not really missing the Mullards much. I do have to say that the darkness of the tone needs to be taken into account, but in a proper setting these are fine sounding valves. I kinda wanna try their long plate ECC803s now to see how it fares.

What I love most about all this is now I have more peace of mind having the amp sit idle because I'm not wasting hours on the Mullards... reliability remains to be seen, though these were run in and tested pretty thoroughly I'm told, so at least there should be no lemons. I also think the Pye doesn't run the EL34 very hard, so I think they should be ok. We'll see.

[spendorman]

Looks like a very nice system, if you want to play with valves, you could try JJ KT77 to replace the EL34s. I run them in my Radford STA25 III.

I'm also preserving the original Mullard EL34s.