Valves for Croft Micro 25/Series 7 [Archive]

keiths

18-12-2013, 10:51

I recently picked up a second-hand Croft Micro 25 Pre and a Series 7 power amp on another forum. The units are both in mint condition, but I don't know how many hours the valves have on them. As I'm hoping to do lots of listening over the Christmas break, it occurs to me that it may be prudent for me to obtain some spare valves now 'just in case'.

As these amps are my first foray into valve gear, I know little about valves and am looking for some advice as to which ECC83 valves to buy and where to buy from. Obviously, time is getting a bit tight as I want these here before the Christmas break, so I need a recommendation for a reliable supplier who can post them to me first class within the next couple of days.

As for which brands to buy, I'm not really interested in tube rolling for now and am just looking to have a spare set of 'cooking quality' values that are at least as good as the stock ones currently fitted.

Also, the pre-amp gain is very high and I'm currently using a pair of Rothwell attenuators (-10dB) on the power amp input. The gain is still somewhat high even now. Can anyone confirm that replacing just the single line-stage ECC83 with a 5751 instead will result in 30dB less gain on all inputs and if so which 5751 tube I should buy?

Cheers,
Keith

rubber duck

18-12-2013, 11:37

Also, the pre-amp gain is very high and I'm currently using a pair of Rothwell attenuators (-10dB) on the power amp input. The gain is still somewhat high even now. Can anyone confirm that replacing just the single line-stage ECC83 with a 5751 instead will result in 30dB less gain on all inputs and if so which 5751 tube I should buy?

I would not use any attenuators as these roll off the highs and kill the sound. You can try an ECC82 in the line stage which will reduce the gain. If the amps sound fine I wouldn't worry too much about replacing valves at this stage. There's little that can go wrong with the 25 and the S7 only uses one valve in the input stage. Welcome to Croft and enjoy!

keiths

18-12-2013, 11:57

I would not use any attenuators as these roll off the highs and kill the sound.

Thanks Jeff - I'm only using the attenuators as a stop-gap. Without them, I can only use about 10-degrees of the volume control range, which makes matching the channels nigh-on impossible.

You can try an ECC82 in the line stage which will reduce the gain.

I wasn't aware I could swap-in an ECC82. Does that give less gain than using an 5751 in that position?

If the amps sound fine I wouldn't worry too much about replacing valves at this stage. There's little that can go wrong with the 25 and the S7 only uses one valve in the input stage. Welcome to Croft and enjoy!

Cheers - the amps sound great and I am not trying to 'improve' them by tube-rolling at this stage. I just want to have some spare valves sitting in a draw just in case one blows over the Christmas period and leaves me without any music.

rubber duck

18-12-2013, 12:18

worrasf

18-12-2013, 12:21

Hi Keith
I have a Croft 25R (and Series 4s) and have spent many hours tube rolling. There is no such thing as a "perfect" tube as they really do alter the sound but for me the "best" tubes in the preamp are GE 5-star triple mica 5751's (slightly lower gain than standard 12ax7/ECC83). "Runner up" are Mazda silver ecc83 and Siemens Halske 12ax7 but others will give you other suggestions.
In my preamp I use the GE's in the phono stage, a Amperex 12BH7 in the line stage and 2 Siemens Halske 12ax7 in the power stage. After multi- swaps this gives me the sound I like.
In the S4S I use the Mazda ecc83's (plus all the other tubes).

If you get any of the above they will be very good and "better" than the stock new issue Sovteks or JJ's but whether you like what they do is another matter.
For new issue tubes I use watford Valves - not the cheapest but reliable and good quality control.

Steve

Tarzan

18-12-2013, 13:02

Hi Keith, why not try to get used the sond of the amps as you have just picked them up?:)

Disregard the above statement if you are already used to the sound of the stocktubes.:)

keiths

18-12-2013, 13:49

Hi Keith, I think the 5751 is the equivalent of the ECC83. Glenn recommended me the ECC82 as a lower gain alternative. I do think you're being a little too concerned about tube failure, especially as there are no output tubes involved. But for peace of mind try the JJ-Teslas from Watford Valves.

Thanks again Jeff. I'm sure you're right about me being unnecessarily worried about valve failure, but I'd still rather have a couple of inexpensive replacements on hand 'just-in-case'. Looking at the specs, the ECC83 has an amplification factor of 100, whilst the 5751 would appear to have a factor of 70.

I've ordered two JJ Tesla ECC83s to keep as emergency spares and a GE 5751 to try from Watford Valves. Thanks for your help.

Another quick question - how do I identify the line stage valve in the pre?

Cheers,
Keith

keiths

18-12-2013, 13:51

...If you get any of the above they will be very good and "better" than the stock new issue Sovteks or JJ's but whether you like what they do is another matter.
For new issue tubes I use watford Valves - not the cheapest but reliable and good quality control.

Steve

Many thanks Steve - I'll bear all this in mind when I try tube rolling.

keiths

18-12-2013, 13:55

Hi Keith, why not try to get used the sond of the amps as you have just picked them up?:)

Disregard the above statement if you are already used to the sound of the stocktubes.:)

Hi Andy - yes, I don't want to change the sound of the amps - I'm certainly not ready to start tube rolling yet. It's just a case of me wanting to lower the pre-amp's gain so I can ditch the Rothwell attenuators and use more of the volume control's range and also to have a set of valves 'in stock' in case one goes 'pop' especially over the Christmas period when I intend to do little other than chill out and listen to my system for an extended time and wouldn't want that ruined by a valve failure.

rubber duck

18-12-2013, 14:18

Another quick question - how do I identify the line stage valve in the pre?

It's the valve on the right.

PaulStewart

18-12-2013, 14:26

I would not use any attenuators as these roll off the highs and kill the sound

A properly designed attenuator at line level just reduces gain it does not alter frequency response. The Rothwell ones work really well in this respect, so Keith don't worry about using them if they work for your system.

The circuit you have is optimised for ECC83s so stick to them. I would not give JJs house room and Sovtek are the least I would use personally. FWIW the best new ECC83s I have heard lately are the Harma Retro ones from Watford Valves, I recently compared them to the original Mullard ones they are based on and they sound spot on to me and they are only £16 each. I now have all 5 ECC83s in my system running these.

Welcome to the wonderful world of thermionics.

Paul S

keiths

18-12-2013, 14:52

A properly designed attenuator at line level just reduces gain it does not alter frequency response. The Rothwell ones work really well in this respect, so Keith don't worry about using them if they work for your system.

Thanks for the reassurance Paul.

The circuit you have is optimised for ECC83s so stick to them. I would not give JJs house room and Sovtek are the least I would use personally. FWIW the best new ECC83s I have heard lately are the Harma Retro ones from Watford Valves, I recently compared them to the original Mullard ones they are based on and they sound spot on to me and they are only £16 each. I now have all 5 ECC83s in my system running these.

Welcome to the wonderful world of thermionics.

Paul S

Thanks for the recommendation. I did see the Harma Retro ECC83s on Watford Valve's site. I'll certainly consider those at some future point.

keiths

18-12-2013, 14:58

It's the valve on the right.

Thanks Jeff - you mean the one I've circled here?:

http://www.simister.com/public/croft_valves.jpg

Reffc

18-12-2013, 15:13

Hi Keith

I've had several sets of the Croft amps now and I'd stcik with the standard 83's as that is what they were deisgned for. The gain is altered (and set) by Glenn using feedback resistors. You can lower the gain by changing the value of the feedback resistors. Standard is 470K, intermediate gain is 220K and low gain is 100K.

picture from Glenn explaining this below:

https://mail.google.com/mail/?ui=2&ik=3709cf2481&view=fimg&th=13f2f0ddf039b3af&attid=0.1&disp=inline&safe=1&attbid=ANGjdJ_hmZnxFRqogVspwuYc6cMLI6Fez6NHF39sYW9 DIpGn8irC_CUrpvfm7FYZ5eAHWYIr6GDDIIEcIUOPo4_NPGzPY B3_y70s9f1uhhLD_PVz9osKTGa6FxkHBqQ&ats=1387379310932&rm=13f2f0ddf039b3af&zw&sz=w1808-h771

Glenn uses JJs and the new issue 803s is a cracking valve and a very reliable valve. I would recommend a set of the JJ803s gold pins if you can get them. There appears to be a snobbery thing against these valves but they sound great in Croft gear and are ultra reliable. JJ have been going an awful long time and know how to produce decent valves.

The amp didn't seem to sound vastly different rolling different valve brands but the 803s sounded the best of the bunch that I tested with the Micro 25 Pre and series 7R power (that included Mullards, Brimars, crappy EH 12ax7s and Tung Sols (same as EHs...in fact they are from the same factory))

rubber duck

18-12-2013, 15:37

Thanks Jeff - you mean the one I've circled here?:

Yes.

rubber duck

18-12-2013, 15:42

The circuit you have is optimised for ECC83s so stick to them.

I've had several sets of the Croft amps now and I'd stcik with the standard 83's as that is what they were deisgned for.

I don't disagree with this. But gain and hiss can be a problem, in which case substituting valves can be a solution. If in doubt you could always contact Glenn.

keiths

18-12-2013, 16:09

Hi Keith

I've had several sets of the Croft amps now and I'd stcik with the standard 83's as that is what they were deisgned for. The gain is altered (and set) by Glenn using feedback resistors. You can lower the gain by changing the value of the feedback resistors. Standard is 470K, intermediate gain is 220K and low gain is 100K.

picture from Glenn explaining this below:

https://mail.google.com/mail/?ui=2&ik=3709cf2481&view=fimg&th=13f2f0ddf039b3af&attid=0.1&disp=inline&safe=1&attbid=ANGjdJ_hmZnxFRqogVspwuYc6cMLI6Fez6NHF39sYW9 DIpGn8irC_CUrpvfm7FYZ5eAHWYIr6GDDIIEcIUOPo4_NPGzPY B3_y70s9f1uhhLD_PVz9osKTGa6FxkHBqQ&ats=1387379310932&rm=13f2f0ddf039b3af&zw&sz=w1808-h771

Thanks Paul - unfortunately the image isn't working for me.

Glenn uses JJs and the new issue 803s is a cracking valve and a very reliable valve. I would recommend a set of the JJ803s gold pins if you can get them. There appears to be a snobbery thing against these valves but they sound great in Croft gear and are ultra reliable. JJ have been going an awful long time and know how to produce decent valves.

The amp didn't seem to sound vastly different rolling different valve brands but the 803s sounded the best of the bunch that I tested with the Micro 25 Pre and series 7R power (that included Mullards, Brimars, crappy EH 12ax7s and Tung Sols (same as EHs...in fact they are from the same factory))

Oh well. I've just changed my order at Watford Valves from gold pin Teslas to the Harma Retros. Never mind - as long as I've got a few spare valves 'just in case', I'll be happy.

Tarzan

18-12-2013, 17:33

Hi Andy - yes, I don't want to change the sound of the amps - I'm certainly not ready to start tube rolling yet. It's just a case of me wanting to lower the pre-amp's gain so I can ditch the Rothwell attenuators and use more of the volume control's range and also to have a set of valves 'in stock' in case one goes 'pop' especially over the Christmas period when I intend to do little other than chill out and listen to my system for an extended time and wouldn't want that ruined by a valve failure.

Sensible Keith.:)

Jimbo

18-05-2015, 19:30

Ok I know this is quite an old thread but still very current for us Croft owners.

Any thoughts on the Series 7 input valve ECC83. Anyone tried different valves in this position with better results rather than the standard JJ's?

For what its worth I run a GE JAN 5751 in this position which works well and reduces gain a little although I would like to try a NOS GE 5 star 5751 1960's tube if I can get hold of one. The JAN GE is a bit lean and etched.

Got a really nice NOS Tesla ECC83 Gold Pin 32 coming to try in the Series 7 this week so will report back once I have tried it.:)

Canetoad

19-05-2015, 00:41

I've just ordered a couple of NOS Tungsram ECC83s to be used in the line stage of my 25R and series 7. I'm currently using Harma retros, which can be a bit bright but seem to have a nice, wide soundstage. Before I use them I want to go back to the JJs for a comparison since using the Harmas for the last few months.

I'm always up for other's experiences tube rolling with the Crofts. :)

Jimbo

19-05-2015, 06:11

Hi Bernie, I have stuffed my Croft 25R with NOS Tesla ECC83. These are the gold pin 32's. Nothing I have tried sounds as good as these in my system. The regulation stage was the biggest revelation as I did not believe the valves here made much difference but they certainly do! The voltage reg valve is a NOS Mullard.

Jimbo

19-05-2015, 20:46

Ok so now tried a Tesla ECC83 32 gold pin valve in the Croft Series 7, replacing the JAN GE 5751. It is very good but a tad softer presentation than the GE. Detail, soundstage and transparency are all there but I think the GE has the edge, didn't think this would be the case:eek: The Tesla is a beautiful valve that excels with vocals and has a more liquid holographic sound in the Croft. The GE has more bite and detail and is more etched, probably a bit HIFI but it does seem to give a slightly clearer presentation.

slaba

17-03-2018, 12:16

I have stuffed my Croft 25R with NOS Tesla ECC83. These are the gold pin 32's. Nothing I have tried sounds as good as these in my system. The regulation stage was the biggest revelation as I did not believe the valves here made much difference but they certainly do! The voltage reg valve is a NOS Mullard.
Allow me to revive an old thread here as I'm trying to figure out which is which with the tube layout in my recently acquired Micro 25.
So far with the stock JJ ecc83s it can't come even close to my modulus pre but I'm sure I can fit better valves in the Croft, so before I go for the chinese fit and miss method to figure out which is which I thought I'd ask.

Looking at it from the front side and tracking the cables to the RCA plugs, left tube would be a regulator or a shared tube?, center tube for phono stage only and right tube for the line stage ? do we need a matched pair somewhere ? (I'm a moron with these things my modulus shares 2 balanced valves per stage hence my confused questioning)

Thanks for your … input :)

http://www.tonepublications.com/media/Croft-inside.jpg

OD1

16-04-2018, 18:47

Allow me to revive an old thread here as I'm trying to figure out which is which with the tube layout in my recently acquired Micro 25.
So far with the stock JJ ecc83s it can't come even close to my modulus pre but I'm sure I can fit better valves in the Croft, so before I go for the chinese fit and miss method to figure out which is which I thought I'd ask.

Looking at it from the front side and tracking the cables to the RCA plugs, left tube would be a regulator or a shared tube?, center tube for phono stage only and right tube for the line stage ? do we need a matched pair somewhere ? (I'm a moron with these things my modulus shares 2 balanced valves per stage hence my confused questioning)

Thanks for your … input :)

http://www.tonepublications.com/media/Croft-inside.jpg

Hi Mickael,

The two valves on the left are for the phonostage. The valve on the right is for the linestage.
Hope this helps ?