Marantz CD67 Upgraded clock and valve preamp views / advice please.

[DarrenHW]

A couple of weeks ago I picked up a CD63MKII, I was so impressed by this I bought a CD67 with an upgraded clock and a CD63 with a valve preamp from another member on here with the plan to turn 3 into 1. I now have the valve preamp temporarily hooked up to the CD67 and would like some advice and opinions on the best way forward with this before I install everything into a CD67SE I picked up on eBay the other day.

12198

This shows the Trichord clock installation, this is how it arrived, I haven’t touched it but I do have a few questions;
The ground (circled in red) is not connected to anything. Is this right / does the ground on the right hand site mitigate the need for an additional ground?
Is this the best location for the clock or should it be moved and mounted on the enclosure?

12199

This shows my “stealing points” for the signal to the valve preamp, I just used a bit of scrap wire to do this, what wire should I use for this / does it matter?

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These show the valve preamp externalised, I did this as a test bed for the preamp with the intention of installing it in the CD67 but now I’d like to leave it in a separate enclosure, is this a good idea (or at least not a necessarily bad one) or should the preamp be as near to the CD PCB as possible? If it’s okay to leave the preamp external is there any harm in terminating the wire’s taking the signal from the CDP in female RCA’s and using male RCA’s to connect the preamp?

And one final question, I have a pair of ECC83 valves can I try these in place of the ECC82 valves installed in the preamp, everything I’ve read seems to say yes, but as this is my first venture into valve’s I’d like clarification before trying a bit of “tube rolling”.

All input greatly appreciated, thanks.

[Firebottle]

Hi Darren,

The ECC82 and 83 valves are quite different in their characteristics, the 83 is a high gain device whilst the 82 is low gain.

Shouldn't cause any damage, as the pinout is the same, but will probably sound awful depending on the actual circuit configuration.

:cool: Alan

[DarrenHW]

Hi Alan.

Thanks for the clarification, read your post then swapped the 82's for the 83's with excellent results! :) The CDP's now more transparent, the treble is far sweeter, bass is softer but more musical, stereo imagining has improved dramatically, in short they're far more musical. The ECC83's I have are a pair of unmatched Mullards, (1 made in GB, 1 in Holland) the ECC82's are Tungsram's I don't know whether the imrpovement is due to the different manufacturer or valve type but I like it, thanks :fingers:

[Firebottle]

Good result. Any idea what make the valve buffer board is?

[NRG]

Re the clock connection: Curious, it seems from the TriChord instruction page http://www.trichordresearch.co.uk/clock-fitting-instructions/ the gnd wire should be connected....can you contact the previous owner to find out why its not with yours? Presumably the CD player works OK as it is?

[Firebottle]

If the power is being sourced from the general supply rail the instructions state:

'2) Do not connect the black twisted wire, but cut it just short of the length of the red wire and make sure that its end does not short against any component or PCB track.'

Leave the clock board where it is, the black and white wires are quite short, which is desirable.

:cool: Alan

[DarrenHW]

Good result. Any idea what make the valve buffer board is?

Great result!!! The board is DIY and has been repaired a few time, my plan is to copy the layout onto perfboard. I do have a few more photo's of it that I took whilst removing and refitting it. Apparently these were modded by a guy who sold them on eBay but doesn't appear to be doing so any more?

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12203


Re the clock connection: Curious, it seems from the TriChord instruction page http://www.trichordresearch.co.uk/clock-fitting-instructions/ the gnd wire should be connected....can you contact the previous owner to find out why its not with yours? Presumably the CD player works OK as it is?

RTFM again :doh: I promise before I post again asking for info, I'll track down any instructions / manuals I can find and make sure I read and follow them :spank:

Thanks for the link to the instructions, I'll read up and get the clock grounded, soldering iron has stopped working so I need to order a new one, all soldering is on hold until I have a replacement :(.

The previous owner bought it second hand with a view to doing what I have done but never got round to it. Yes, the CDP works OK, hard to compare what difference the clock makes as before I started chopping things up I had a stock CD63MKII, CD63 with Valve Pre and CD67 with Trichord clock and AD826AN OPAMP's. I would say the CD63 with valve's sounded "nicer" but the CD67 sounded more accurate, the CD67 is supposed to be a less "coloured" CDP in stock form so it could have been the difference's between the two CDP's or just placebo? It is easily the best CDP I've had, previously I had a B&O Beogram CD 6500, which I thought was good until hearing the CD63 in stock form.

Any thoughts on whether external is detrimental to SQ (i.e. wire length) and any recommendations on wiring? I am thinking of just using an interconnect chopped in half with the preamp soldered in the middle of it, any thoughts?

[DarrenHW]

If the power is being sourced from the general supply rail the instructions state:

'2) Do not connect the black twisted wire, but cut it just short of the length of the red wire and make sure that its end does not short against any component or PCB track.'

Leave the clock board where it is, the black and white wires are quite short, which is desirable.

:cool: Alan

Just posted, then saw your post. Thanks Alan. Now I'm off to read the instructions!

[NRG]

If the power is being sourced from the general supply rail the instructions state:

'2) Do not connect the black twisted wire, but cut it just short of the length of the red wire and make sure that its end does not short against any component or PCB track.'

Leave the clock board where it is, the black and white wires are quite short, which is desirable.

:cool: Alan

Helps to fully RTFM ! LOL! Good catch... :)

[DarrenHW]

Sifting through my box of salvaged valves I've now come across an (unmatched) pair of Mullard EF86's (a quick google brings up an article referring to them as pre amp valves but does also show a preference for ECC83's) and a matched pair of Tungsram EL84 valves (seem to be popular with guitar amps) am I safe to try these?

[Firebottle]

Oh no, they are totally different valves, both pentodes.

The ECC83/82s are double triodes.

Have a look at this site for valve data http://www.mif.pg.gda.pl/homepages/frank/vs.html, tis very good.

:cool: Alan

[DarrenHW]

Thanks for the link Alan, very informative :thumbsup:

[Naughty Nigel]

ECC82's and ECC83 are both double triodes, but as others have said, their characteristics are very different.

ECC82's are generally used in RF (radio frequency) circuits rather than audio. ECC83's have much higher gain than ECC82's and are generally preferred for audio preamp stages.

EF86's are small signal pentodes commonly used in audio preamps. EF86's have higher gain than ECC83's but some would say the ECC83 sounds better.

The EL84 is an output pentode often used in low power valve amplifiers. Maximum output power is about five watts in a single ended circuit, or 12 ~ 14 watts in push pull on a good day. For higher power EL34's or KT66/KT88's are much preferred.

As a matter of interest, there is a certain logic to the codes used on valves.

If we take the ECC83, E refers to the heater voltage which is 6.3 volts. C denotes a small signal triode so ECC indicates a double triode with a heater voltage of 6.3 volts!

'L' denotes an power pentode such as the EL84 or EL34.

'Z' is a rectifier valve, such as the GZ32 or GZ34. These have a heater voltage of 5.0 volts, hence 'G' rather than 'E'.

Some valves combined several elements in one envelope, such as the ECL82. This combined a preamp triode with an output pentode and was popular in low cost radio sets in the 1960s'.

The number (82, 83, 86, etc.) is just a design number and doesn't usually refer to any physical characteristics.

The name diode, triode, pentode, etc. refers to the number of electrodes in the valve.

A diode will only have an anode and cathode. Elections can only flow from the cathode (which is heated) to the anode, so this is useful as a power rectifier or as a 'detector' diode in radio receives.

A triode has three electrodes; an anode, cathode and control grid. The voltage applied to the control grid controls whether and how many electrons can flow from the cathode to the anode, and is therefore useful for amplification.

A pentode has five electrodes; an anode, cathode and three grids. These provide higher gain than simple triodes, but with lower quality. However, by applying negative feedback via the supplementary grids quality is improved whilst maintaining efficiency.

Then there are beam tetrodes (KT66, KT88, etc.) which provide the gain of a pentode with the quality of a triode.

Oh, and in case anyone wonders, electrons flow from negative to positive, and not from positive to negative as convention dictates.

Nigel.

[DarrenHW]

Having only had 1 day off since my last post the CDP and Pre have both sat on the rack powered off, which for the Pre in it's current prototype form means being completely unplugged from the mains. I powered everything on yesterday and I only have music through 1 speaker and it's distorted. I swapped back from the ECC83's to ECC82's with the same result but with slightly less distortion. I have checked and swapped amps and interconnects nothing changed but what I did discover is that if the RCA's are only just connected (like so)

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I have music through both speakers, also if the pre is powered off I have music through both speakers (all be it very quiet) even with both RCA's firmly seated. Due to this my thoughts are that this is related to a grounding issue with one or both of the valve sockets? As previously mentioned I bought this second hand and it is a DIY board that has had a number of repairs. I am currently awaiting delivery of a new soldering iron so cannot really investigate any further, I've tried wiggling things but without any change.

Has anyone encountered a problem like this before / is my best place to start by checking the board for a broken solder joint?

Thanks.

P.S. Thanks for the info Nigel, very informative :thumbsup:

[Naughty Nigel]

If the distortion is on both channels, and was improved by fitting ECC82's it sounds to me as if the HT voltage may be too low, or the grid bias is somehow forcing the valves to conduct.

Is it possible that your CD player is presenting a positive voltage on the preamp control grids? Does the preamp have suitable value grid bias resistors to drain any voltage from the CD player?

Grid bias resistors in preamp inputs are usually 470,000 Ω to 1 MΩ, but a lower value might be better in a transistor circuit, especially if some DC leakage voltage is present. Better still, decouple the input by using a suitable value capacitor (say 1 µF polystyrene).

Clearly the circuit diagram would help here.

Nigel.

[DarrenHW]

Hi Nigel,

Thanks for the response, I'll need to read through it a couple of times and with the help of Google I'll hopefully be able to get my head around what you've written. I believe this is the circuit diagram, I need to remove the board to confirm but cannot do this until the new soldering iron arrives.

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Grateful for any input.

Thanks,

[Firebottle]

The 5963 shown on the circuit is a near equivalent with ECC82, so stick with '82.

For a quick check of circuit conditions measure the voltage on R12 and 22 to ground, ONLY if you are confident to do so.
It should be around half the supply voltage, 85V or so.

Cheers, Alan

[Naughty Nigel]

Is it possible that your CD player is presenting a positive voltage on the preamp control grids? Does the preamp have suitable value grid bias resistors to drain any voltage from the CD player?

Grid bias resistors in preamp inputs are usually 470,000 Ω to 1 MΩ, but a lower value might be better in a transistor circuit, especially if some DC leakage voltage is present. Better still, decouple the input by using a suitable value capacitor (say 1 µF polystyrene).

Clearly the circuit diagram would help here.

Nigel.

Firstly, ignore what I said above as I had not seen the circuit diagram at the time.

Secondly, as Firebottle says, check the voltage on voltage on R12 and R22 with reference to ground if you feel confident to do this. If you can, check the HT voltage as well to see if this is around the value shown on the circuit diagram.

You might also check the voltage across R14 and R24 (connected to the cathodes of V1B and V2B) as this will give some idea of anode current, but will vary depending on the valve used. The cathode voltage for an ECC83 should be about 2 volts, whereas the ECC82 will be about 8.5 volts, as the latter has a much higher anode current, but much lower gain.

The circuit is slightly unusual in that the first triode in each valve (V1A and V2A) is used as a constant current source for V1B and V2B rather than the more usual anode load resistor. This probably works better with the low-ish HT rail voltage, and helps to stabilise operation with varying supply voltages.

This circuit relies on both triodes in each valve working properly if it is to work as intended, which could make fault finding tricky for the uninitiated.

I also wonder whether your experiments with different valves might have damaged (overheated) some of the resistors in the circuit, increasing their resistance? This might have reduced anode current and will cause distortion.

Also, if possible, try listening to the CD player without the valve preamp connected to make sure that it really is the preamp that is causing the problems!

Nigel

[Naughty Nigel]

Grateful for any input.

Indeed; as long as it has the correct sensitivity, equalisation curve and impedance. :lol:

Nigel.

[DarrenHW]

Indeed; as long as it has the correct sensitivity, equalisation curve and impedance. :lol:

Nigel.

:lol:

Thanks for the suggestions, I've started with the easiest test, measuring the resistors. I get no reading from R13 or R23 all other resistors check out within spec. Could these be the culprit? If so can these be changed to different values to allow the use of ECC83's or just replace and use the ECC82's?

Thanks,

[Naughty Nigel]

Resistors R13 and R23 are 240 KΩ, which may not register on some [less sensitive] multimeters. However, if you are in any doubt there would be no harm in changing them for good quality replacements.

R13 and R23 are known as grid bias or grid leak resistors. If these have gone open circuit (I cannot think why) then you would get a very distorted output, as the control grids would go positive allowing the second triodes (V1B and V2B) to conduct heavily.

If the circuit was designed for ECC82's and you have a pair of good ECC82's to hand I cannot think of any reason to change to ECC83's.

The ECC83 has much higher gain than the ECC82 which might not be helpful in this application as I suspect the designer wanted a low gain preamp with low output impedance, which is what you would usually expect from a CD player.

In my view the higher gain of ECC83's would give far too high an output voltage for this application, and would not drive a low impedance circuit well unless the circuit design was substantially modified. You would also need to change resistors R12, R14, R22 and R24 to higher values so that anode current is reduced to about one milliamp, rather than ten milliamps for the ECC82. This would also mean that the HT voltage would be a little higher than intended.

Nigel.

[DarrenHW]

Problems now all resolved, there has been a change I've failed to mention which is that the CDP had been plugged into the Home Cinema amp (an Onkyo TX-SR607) as the Yamaha stereo amp it was connected too has a dirty switch so I've removed it ready for cleaning. Plugging the CDP back into a stereo amp and all is good, even with the ECC83's installed (which I use as to me they sound far nicer than the ECC82's). I guess they gain from the SRPP (at least I've learnt a new abbreviation today!) is too high for the Onkyo?

Sorry to waste everyone's time with this, I really should have tried connecting back up to the stereo amp before anything else :doh:

Thanks again,

[Naughty Nigel]

All's well that ends well. And it exercised my brain a little too which is never a bad thing! :)

Nigel.

[DarrenHW]

As the gain from the SRPP (from my searching yesterday this seems to be what it's actually called, is this the correct way to refer to it?) has caused an issue with the Onkyo (and concerns have been expressed in the above posts) I feel that this should be addressed (it is bloody loud!). Whilst trying to find more info on the SRPP yesterday I came across this thread which is where I got the schematic from http://www.diyaudio.com/forums/tubes-valves/238718-reducing-gain-srpp-circuit-ecc82-6.html.

As previously mentioned I do plan on rebuilding the SRPP so would this be a worth while modification to make at the same time, especially as I'm hell bent on using the ECC83's.

On the subject of valve choice
If the circuit was designed for ECC82's and you have a pair of good ECC82's to hand I cannot think of any reason to change to ECC83's.

The ECC83's sound so much better
The CDP's now more transparent, the treble is far sweeter, bass is softer but more musical, stereo imagining has improved dramatically, in short they're far more musical. The ECC83's I have are a pair of unmatched Mullards, (1 made in GB, 1 in Holland) the ECC82's are Tungsram's I don't know whether the improvement is due to the different manufacturer or valve type but I like it So any thoughts as to whether this is due to type of valve / manufacturer or could this be a sign that the ECC82's are nearing the end of their life and a new pair would sound better, they're certainly cheaper than ECC83's!

[Naughty Nigel]

As the gain from the SRPP (from my searching yesterday this seems to be what it's actually called, is this the correct way to refer to it?) has caused an issue with the Onkyo (and concerns have been expressed in the above posts) I feel that this should be addressed (it is bloody loud!). Whilst trying to find more info on the SRPP yesterday I came across this thread which is where I got the schematic from http://www.diyaudio.com/forums/tubes-valves/238718-reducing-gain-srpp-circuit-ecc82-6.html.

As previously mentioned I do plan on rebuilding the SRPP so would this be a worth while modification to make at the same time, especially as I'm hell bent on using the ECC83's.

On the subject of valve choice

The ECC83's sound so much better So any thoughts as to whether this is due to type of valve / manufacturer or could this be a sign that the ECC82's are nearing the end of their life and a new pair would sound better, they're certainly cheaper than ECC83's!

How does it sound if you bypass the valve preamp altogether?

The cynic in me thinks this could be a valve preamp for the sake of using a valve preamp even though it isn't really needed. I can understand ECC83's sounding better as they were designed for audio use (rather than the ECC82 which was intended for RF circuits), but as I have said before the ECC83 has a huge amount of gain that you really don't need. You could always attenuate the signal somewhere, but what is the point of amplifying a signal unnecessarily only to attenuate it again? This will only add to the distortion at the output. :confused:

Nigel.

[NRG]

I don't see how you can substitute an '82 for an '83 or visa versa the characteristics are very different. If I where to guess given the improvement you found with the '83 that the circuit is really designed for an '83 ;) I would also expect to see an '82 used in the last or later stage of a preamp not the first...

[Naughty Nigel]

I don't see how you can substitute an '82 for an '83 or visa versa the characteristics are very different. If I where to guess given the improvement you found with the '83 that the circuit is really designed for an '83 ;) I would also expect to see an '82 used in the last or later stage of a preamp not the first...

I agree.

I would also like to quote from a post in the other place:


A piece of wire--

Is the most linear, low-noise Unity-Gain stage there is!

To be very honest, I cant see the point of adding this stage to the whole system,--just to render it so low gain....
Seems just a good way to add unnecessary distortion and noise to the signal....

--Thats just my simple and daft opinion!

Someone famous once said--Make it Simple--But No Simpler....

Having done some quick calculations, the recommended grid voltage for the ECC83 is -2.0 volts. The recommended anode current is 1.2 milliamps. The cathode resistor is 270Ω.

2.0 volts ÷ 270Ω = 7.4 milliamps.

The recommended grid voltage for the ECC82 is -8.5 volts. The recommended anode current is 10.5 milliamps.

8.5 volts ÷ 270Ω = 31.5 milliamps!

These figures are based on an anode voltage of 250 volts, and your circuit has an HT voltage of 170 ÷ 2 = 85 volts; so I would tend to agree with NRG that the circuit was almost certainly designed for the ECC83!

Perhaps the previous owner had an odd pair of ECC82's to hand and just plugged them in!

If you can, measure the voltage across the cathode resistors (R14 and R24) to see how much current is flowing through them (using Ohms Law).

Depending on what you find it might be advisable to increase the value of the cathode resistors to reduce anode current. That would improve sound quality as well as increasing valve life significantly.

However, I should point out that the ECC83 has a gain (gm) of 62,500 mA/V, so it really is a very sensitive valve!

Nigel.

[DarrenHW]

Thanks for the replies.

I've measure the voltage across (I hope) R14 & R24.

ECC83:

~ 275mV.

0.275 / 270 = 1 milliamp.

ECC82:

~ 1.3V

1.3 / 270 = 4.8 milliamp.

If my readings are correct it would seem that the current is low on both with the ECC83 being closer to the recommendation. So I guess (if the above is correct) that as speculated this was originally designed for ECC83's and ECC82's have been substituted?

Does it then follow that replacing R14 & R24 with 250 (0.275 / 250 = 1.1) would bring it closer to the recommendation or is it best left alone / have I got this all completely ass backwards?

Regarding the sound with / without the valves, it sounds far nicer (warmer, more musical and less fatiguing is the best my developing ears and vocabulary can provide), than it did previously with AD826AN OPAMP's and HDAM's bypassed.

Regarding the potential mod to the SRPP. From the tinkering I have done over the last few months it has certainly been my experience that the fewer components in the signal path the better, which I why I asked about the potential "mod", my thoughts are the same as yours, less is more.

Thanks,

[Naughty Nigel]

Thanks for the replies.

I've measure the voltage across (I hope) R14 & R24.

ECC83:

~ 275mV.

0.275 / 270 = 1 milliamp.

ECC82:

~ 1.3V

1.3 / 270 = 4.8 milliamp.

If my readings are correct it would seem that the current is low on both with the ECC83 being closer to the recommendation. So I guess (if the above is correct) that as speculated this was originally designed for ECC83's and ECC82's have been substituted?

Does it then follow that replacing R14 & R24 with 250 (0.275 / 250 = 1.1) would bring it closer to the recommendation or is it best left alone / have I got this all completely ass backwards?

Regarding the sound with / without the valves, it sounds far nicer (warmer, more musical and less fatiguing is the best my developing ears and vocabulary can provide), than it did previously with AD826AN OPAMP's and HDAM's bypassed.

Regarding the potential mod to the SRPP. From the tinkering I have done over the last few months it has certainly been my experience that the fewer components in the signal path the better, which I why I asked about the potential "mod", my thoughts are the same as yours, less is more.

Thanks,

If you are using a moving coil meter it will load the circuit slightly, so the true cathode voltage could be fractionally higher.

However, I would be inclined to leave the cathode resistors at the present values if the circuit works well.

Nigel.

[DarrenHW]

Excellent, so is it fair to assume this was designed for ECC83's? And if so would the ECC82's benefit from a reduction in resistance to something like 180 (1.3 / 180 = 7.2) I know this is not particularly relevant I only ask to satisfy my own curiosity as I think I may have learnt something today :).

Thanks for the help and education :thumbsup:

[Naughty Nigel]

Excellent, so is it fair to assume this was designed for ECC83's? And if so would the ECC82's benefit from a reduction in resistance to something like 180 (1.3 / 180 = 7.2) I know this is not particularly relevant I only ask to satisfy my own curiosity as I think I may have learnt something today :).

Thanks for the help and education :thumbsup:

The ECC82 specifies a lower grid bias voltage than the ECC83 (-8.5 volts Vs. -2.0 volts), so you would actually need a higher value cathode load resistor. You have a very low effective HT voltage in this circuit so I would probably start out with 470Ω for R14, R24, R12 and R22 and then measure cathode voltages under running conditions to work out the anode current. Note that you would need to change R12 and R22 to the same values as R14 and R24 for the circuit to work. There is no harm in running valves at a lower anode current than specified, but if taken to excess it will reduce dynamic range.

The ECC82 would provide lower gain but with much lower output impedance (owing to the higher anode currents involved). If you are driving a typical low impedance CD input (100 KΩ) you would probably need to increase the value of the output coupling capacitors (C14 and it looks like C24) from 1 µF to 2.2 µF (or even 4.7 µF) to maintain bass response and to avoid LF distortion.

Nigel.

[DarrenHW]

Well, I guess I haven't learnt sh!t then :doh:

[Naughty Nigel]

Well, I guess I haven't learnt sh!t then :doh:

I would hope that you have learnt quite a lot, but you didn't take the different grid bias voltages of the two valves into account!

Thermionic valves, just like transistors, perform basic amplification functions in electronic circuits. However, to do this effectively and reliably they need to operate in the right electronic environment, which is set out in the devices' specifications. Understanding this environment and how it is achieved is an important part of understanding circuit designs. However, there are so many variables and circuit configurations that sometimes you just have to suck it and see. If you know what you are looking for a few simple tests (like measuring the voltage across a cathode resistor) can tell you a great deal, but you need to understand how the circuit functions for it to make any sense.

One of the reasons that I like valve circuits is because there are usually fewer stages than in solid state designs, so they are easier to understand! :)

Nigel.

[DarrenHW]

... but you need to understand how the circuit functions for it to make any sense.

And therein lies my biggest problem, I have no idea :rolleyes:. After re-reading your posts my cogs are starting to turn (hopefully in the right direction!) however without a new soldering iron (which will hopefully be delivered today) I cannot take any other measurements I was just lucky to be able to access the resistors I have taken measurements from.

Thank you for your patience and encouragement with this Nigel (although you may live to regret it!) hopefully over the weekend I'll be able to get this apart and take a full set of measurement with both valves and combining that data, the info above and the help of Google I hope to get my head around this :scratch:? I do still plan on rebuilding this circuit, primarily because the board has been repaired a number of times but also to design the board layout around a new enclosure, monkey see, monkey do is limit of my ability here (and I even get that wrong sometimes!) but I really would like to improve my knowledge. To that end as a learning tool I now plan to build 2 of these one optimised for ECC83's one for ECC82's, the better sounding will stay in the rack the other I'll give to my brother with one of the spare CD63's.

The plan for this weekend is to perform a partial recap on the crossovers in the Celestions (monkey see, monkey do!) so hopefully I'll be able to spend some time on the SRPP too.

Thanks again,

[Naughty Nigel]

There are plenty of good books to help you understand electronic circuits and electronic theory, but some of the best in my view were the old books from the 1930's onwards, which explain how simple circuits and components work.

One book I was given as a teenager was issued to radio operators during WW2 I think, and it explained exactly how radio transmitters and receivers worked. Some of the old books by Mullard and others were also very instructive so it might be worthwhile having a search around some second-hand book shops.

Interestingly, many of the old service manuals explained how circuits worked so that 'service engineers' of the day could work out what was wrong. Current service manuals only seem to provide flow charts to indicate which modules to replace. Presumably modern day 'service engineers' are unable to work out modern-day circuits, or maybe they just don't have the time?

Transistors are of course very different to valves, (particularly in terms of their working voltages), although their basic functions are similar.

Nigel.

[DarrenHW]

Will have to keep an eye open, I actually passed on an old Mullard book at a carboot a few weeks back. Saw the book, figured they'd be some valves knocking about,only to be disappointed and forgot all about the book, wish I'd picked it up. As I buy most of my books (mostly fiction) from carboot's I'll keep an eye out.

As for modern day service engineers, having managed a team of IT engineers I'd speculate most modern electrical repairs are considered economically unviable. I turned a failing "engineering" department of a medium sized IT company around to making annual (handsome) 6 figure profits by replacing instead of repairing, customers were happier too due to the fixed price and time frame. I know I'm probably considered the "enemy" to many engineers and I understand that but that's what I was employed to do. In hindsight I wish I'd spent those years concerned less with profit margins and learnt a little more but hindsight's supposedly a wonderful thing.

[Naughty Nigel]

Will have to keep an eye open, I actually passed on an old Mullard book at a carboot a few weeks back. Saw the book, figured they'd be some valves knocking about,only to be disappointed and forgot all about the book, wish I'd picked it up. As I buy most of my books (mostly fiction) from carboot's I'll keep an eye out.

As for modern day service engineers, having managed a team of IT engineers I'd speculate most modern electrical repairs are considered economically unviable. I turned a failing "engineering" department of a medium sized IT company around to making annual (handsome) 6 figure profits by replacing instead of repairing, customers were happier too due to the fixed price and time frame. I know I'm probably considered the "enemy" to many engineers and I understand that but that's what I was employed to do. In hindsight I wish I'd spent those years concerned less with profit margins and learnt a little more but hindsight's supposedly a wonderful thing.

All very true. Far too many devices cannot be repaired nowadays even if you can locate the fault. It's just a case of replacing 'this unit or that', or scrapping the whole thing. No wonder the earth is running out of natural resources whilst landfill sites are full.

I firmly believe this is why there is such a shortage of 'proper' engineers and scientists in this country as there is nothing for youngsters to tinker with and learn from any more. Motorbikes used to be the simplest things on wheels and could be taken apart at the roadside with an adjustable spanner and Swiss Army knife - but even they need to be plugged into a computer now. :(

Nigel

[NRG]

So true, I recently resurrected a dead Dell Server, the solution provided by the IT company servicing a small veterinary practice was to replace it as it was uneconomical to repair....I got it going with a full strip down, clean (it was truly truly filthy) and some component part replacements with a soldering iron...I would have charged a small fraction of what it cost them to purchase a replacement and transfer of data....I fear I'm becoming a dinosaur :D

[DarrenHW]

Further to my last post (and against your better advice!) I implemented the modification detailed in the diyAudio thread, needless to say (as you expected) it wasn't long before the iron was out again and the "modification" removed. I may as well have just stuck with the ECC82's as the mod stole all the magic of the ECC83's :(.

So moving on, my plan now is to try some ECC83 5751's for their lower gain, I also plan on reworking the circuit in 2 stages. Stage 1 is to rewire the "audio" section of the board keeping the PS section in tact and wiring out (sort of) point to point. I plan to make a tag board to mount the resistors and capacitors and wire to the sockets from here and build this into a new enclosure. I will do this with new components so that I don't have to dismantle the circuit. Stage 2 will be PS.

I have been endeavoring to improve my knowledge of valve circuits and have downloaded the Navy Electricity and Electronics Training Series Module 6, I'm slowly making my way through it (although I don't have much free time at the moment) and had intended on completing this before continuing with this project. However I need a pre amp and I'm so taken with valve's that I plan on buying a croft and want to have this circuit completed before ordering the pre to ensure the two will be compatible.

So a few questions if I may:

Components:

Capacitors C14/25 - C13/23.
I plan on using same value (0.33uf & 1uf) Jantzen Cross Caps in place of the Vishays. The reason I've chosen Jantzens is following the successful recap of my Celestion 44's with Jantzen caps I bought another pair of 44's which I will recap with electrolytics with the exception of the tweeter for which I'll use Jantzens again (so that I can compare the differences between a polyprop and electrolytic recap). So to save on postage I want to order from the same place and the Jatzens are dirt cheap!
http://www.europe-audio.com/Product.asp?Product_ID=8938
http://www.europe-audio.com/Product.asp?Product_ID=8931
Any thoughts on whether the Jantzens are a suitable replacement / upgrade / downgrade from the Vishays?

Resistors.
Do I just need bog standard 1/4W Metal Film resistors? Would there be any advantage in replacing these with better spec resistors, if so could you please make a recommendation?

B9A Sockets.
Any recommendations?

For the encloure I plan on making an oak (of which I have plenty) frame with 2mm copper top, bottom and back (for RCA & IEC sockets) plates similar to this:

12644

Any thoughts?

Thanks in advance.