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Old 3rd Nov 2017, 8:25 pm   #41
ms660
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Default Re: Looking for help please with 1964 Trio W-41 stereo valve amp

With everything working normally the output valves will be pretty much at their dissipation limit due to the value of the HT voltage that feeds them coupled with the fact that the cathode current has to be enough to supply the preamp valve heaters.

Lawrence.
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Old 3rd Nov 2017, 9:05 pm   #42
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Default Re: Looking for help please with 1964 Trio W-41 stereo valve amp

Hi Tim,
Lawrence is perfectly correct, but his comments might strike you as a bit odd! To have the output valves running at maximum dissipation all the time, even with the volume at minimum seems counter- intuitive!! You only expect things to get hot when you are creating a lot of racket
The output stage works in 'class A' mode. This means the valves are biassed to work on a nice linear portion of their transfer curve, so even with no signal, they are both conducting a constant current near to their maximum limits.
That's why you get a steady voltage on the cathodes sufficient to power the preamp valve heaters.
Class A gets round some of the flaws of push pull output stages and gives really good quality sound but is very inefficient: that's the down side of it. On the plus side, it will keep your room warm!!
Hope that answers a question that you may not have considered yet!
Right, time to do a bit of circuit tracing.
All the best
Nick

Last edited by 1100 man; 3rd Nov 2017 at 9:06 pm. Reason: missing word
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Old 4th Nov 2017, 12:15 am   #43
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Default Re: Looking for help please with 1964 Trio W-41 stereo valve amp

Phew, that was fun!! I enjoy tracing out circuits, although this was a lot easier than a PCB. I should probably get out more though
It's usually what I do when I get a new piece of equipment to rebuild. It is very instructive and I find it really familiarises me with the circuit and also the layout. As you have found, components are often not where you expect them to be!
I've had this amp for well over 20 years and never even looked at it to find out what it was I now feel, after the last 2 1/2 hours, well acquainted with it and am now keen to give it an overhaul and a new set of output valves!
I also discovered that the tone controls have been rewired which I will have to attend to.

As regards to your actual phono preamp fault, I would suggest the following checks which will prove the switching and wiring. We'll concentrate on the right hand channel which uses V2. This is more accessible as it doesn't have as many components crammed over it!

The following is done with the amp UNPLUGGED

1) Insert a lead with a phono plug on the end into the RH 'phono' input jack.
2) Set selector on front panel to 'phono'.
3) Work out which is pin 7 on V2.
4) Measure continuity (0 ohms on your meter) between the input lead (inserted in 1 above) and pin 7.

This will prove that signals will get from the input jack to the input (pin7 grid) of the preamp via the selector switch.

The next test will verify the wiring & switching between the output of the preamp and V3.


1) In picture 2, one end of C104 (a 0.1 mfd wax covered cap) goes to a piece of tagstrip and a yellow wire. Point 1 in picture 2.
2) On picture 3, look at the wiring on the balance control and find point 'A'.
3)Set front panel selector to 'Phono'.
4) Set 'tape monitor' switch to 'off'.
5) Set 'mono/ stereo' switch to 'stereo'.
You should now get continuity between point '1' and point 'A'.
This will verify the wiring/ switching between the output of the phono preamp and V3.

I hope you can make some sense of my drawings but if you need any clarification, please ask!
I also note that your amp looks much more shiny and non rusty than mine: but then it probably hasn't been stored in my damp loft for 20 years!!

All the best
Nick
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Old 4th Nov 2017, 1:12 pm   #44
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Default Re: Looking for help please with 1964 Trio W-41 stereo valve amp

I have a new development for you kind folk...

I was advised along the way in this journey by a very knowledgeable chap to replace the 2 rather shabby looking wax coated caps of 0.1uf across v1 and v2

My order of parts arrived this morning and I'm not convinced they are a suitable replacement? The wax caps I believe have polarity and as far as I can ascertain these tiny replacements don't. Have I goofed?
Could you tell me what I should have ordered please?

pictures attached
Thank you.
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Old 4th Nov 2017, 1:14 pm   #45
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Default Re: Looking for help please with 1964 Trio W-41 stereo valve amp

Wax caps don't have polarity. They will work either way round. The marked end (if there is one) denotes the outer foil, which is generally connected to the earthy side of the circuit.

I can't see what that is you're holding in your hand. What is its capacitance and voltage rating?
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Old 4th Nov 2017, 1:24 pm   #46
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Default Re: Looking for help please with 1964 Trio W-41 stereo valve amp

Thanks Graham,
It's 0.1uf 200v which I thought would be a bit bigger!

ok to use?
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Old 4th Nov 2017, 1:40 pm   #47
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Default Re: Looking for help please with 1964 Trio W-41 stereo valve amp

These are what you should be ordering - see link below:-

https://www.cricklewoodelectronics.c...for-Audio.html
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Old 4th Nov 2017, 2:00 pm   #48
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Default Re: Looking for help please with 1964 Trio W-41 stereo valve amp

Ooh! thanks. That's exactly what I was expecting to find online, only didn't..
That site may come in very handy.

Tim
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Old 4th Nov 2017, 2:03 pm   #49
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Default Re: Looking for help please with 1964 Trio W-41 stereo valve amp

Quote:
Originally Posted by TimMills View Post
That site may come in very handy.
I've used them before and they're very good.
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Old 4th Nov 2017, 2:26 pm   #50
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Default Re: Looking for help please with 1964 Trio W-41 stereo valve amp

OH WOW. thanks Nick - That's given me a lot to go by!! there may be questions...

Tim
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Old 4th Nov 2017, 2:39 pm   #51
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Default Re: Looking for help please with 1964 Trio W-41 stereo valve amp

Quote:
Originally Posted by 1100 man View Post
As regards to your actual phono preamp fault, I would suggest the following checks which will prove the switching and wiring. We'll concentrate on the right hand channel which uses V2. This is more accessible as it doesn't have as many components crammed over it!

The following is done with the amp UNPLUGGED

1) Insert a lead with a phono plug on the end into the RH 'phono' input jack.
2) Set selector on front panel to 'phono'.
3) Work out which is pin 7 on V2.
4) Measure continuity (0 ohms on your meter) between the input lead (inserted in 1 above) and pin 7.

This will prove that signals will get from the input jack to the input (pin7 grid) of the preamp via the selector switch.

The next test will verify the wiring & switching between the output of the preamp and V3.


1) In picture 2, one end of C104 (a 0.1 mfd wax covered cap) goes to a piece of tagstrip and a yellow wire. Point 1 in picture 2.
2) On picture 3, look at the wiring on the balance control and find point 'A'.
3)Set front panel selector to 'Phono'.
4) Set 'tape monitor' switch to 'off'.
5) Set 'mono/ stereo' switch to 'stereo'.
You should now get continuity between point '1' and point 'A'.
This will verify the wiring/ switching between the output of the phono preamp and V3.

I hope you can make some sense of my drawings but if you need any clarification, please ask!
I also note that your amp looks much more shiny and non rusty than mine: but then it probably hasn't been stored in my damp loft for 20 years!!
This is excellent help Nick!
I'm hopefully going to have time to make these checks over the weekend, but it's a bit of a busy one..

in the mean time could I trouble you for another pic of the underside wiring, but a lot sharper image please? I'd love to be able to zoom in on photoshop and read it better. chuck plenty of light at it if you can. do you use a smart phone for pictures? they are pretty high resolution these days, just a bit tricky to get to focus on detail at times.
thank you!
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Old 4th Nov 2017, 3:40 pm   #52
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Default Re: Looking for help please with 1964 Trio W-41 stereo valve amp

Both those continuity test check out ok Nick.

...and your wiring looks a lot neater than mine! I think there's been some iffy component replacements in the past of this unit.

Tim
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Old 4th Nov 2017, 4:20 pm   #53
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Default Re: Looking for help please with 1964 Trio W-41 stereo valve amp

If I wanted to replace C205 a 40uf 150v cap... and 40uf is not found as standard, would you go for 32uf or 47uf? that are available, or does it make little difference in this application?
Or is there somewhere I don't yet know about that could supply a 40uf cap?

Tim
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Old 4th Nov 2017, 5:00 pm   #54
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Default Re: Looking for help please with 1964 Trio W-41 stereo valve amp

Personally I would use a 47uf, rated @ 150v or Higher.
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Old 4th Nov 2017, 10:40 pm   #55
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Default Re: Looking for help please with 1964 Trio W-41 stereo valve amp

Yes that’s what I would do

http://cpc.farnell.com/vishay/mal204...rfnonsku=false
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Old 5th Nov 2017, 12:27 am   #56
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Default Re: Looking for help please with 1964 Trio W-41 stereo valve amp

Quote:
Originally Posted by TimMills View Post
in the mean time could I trouble you for another pic of the underside wiring, but a lot sharper image please? I'd love to be able to zoom in on photoshop and read it better. chuck plenty of light at it if you can. do you use a smart phone for pictures? they are pretty high resolution these days, just a bit tricky to get to focus on detail at times.
thank you!
Hi Tim,
Vintage electronics I can just about manage, but start mentioning words like 'smartphone' & 'photoshop' and my eyes just glaze over I'm pretty impressed that I can actually take a picture and get it uploaded onto the forum at all!! You've seen my level of CAD expertise
I'll try and take a better picture sometime tomorrow in the daylight. From what I could see of your amp in the picture, quite a few bits have been replaced.

Personally, I like to use modern components that at least look something like the originals. Most caps these days are meant for PCB's so have the leads coming out the bottom (like the tiny new one in your picture). The yellow caps on the Cricklewood site are much more suitable for old gear and are good quality. They usually come in 600 or 1000V rating which is enough for most things. It doesn't matter if you have a higher voltage rating than was originally fitted. Search for 'axial' capacitors which have a lead out of each end.
Farnell, CPC, and RS are also very useful for resistors and axial caps, but you will find you can't get everything from one place.
RS are particularly good as they don't have a minimum order so you can order 10 resistors which will be dispatched the same day with free carriage!
RS also do a nice looking range of resistors which look OK in old gear. A modern 1/4 W resistor looks silly as it's too small.

In view of the motley collection of bits in your amp, I would be inclined to give it a complete overhaul- replace any resistors which are too far out of spec with appropriate modern ones and various caps, again with nice looking ones.
You will then have an amp which will look nice underneath and work as it should. It will also give your new valves the best lifespan. It's not necessary or desirable to change every cap: only certain types in certain positions.
Over the next few days I'll come up with a list of caps that I would change and also where to source suitable replacements. I'll dig out the details of the RS range of resistors as well.

Could you also take a hi res picture of the underside of your amp- I can't quite see what has been changed.
All the best
Nick
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Old 5th Nov 2017, 5:26 pm   #57
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Default Re: Looking for help please with 1964 Trio W-41 stereo valve amp

Hi Tim,
I did take some more pictures for you today but forgot to change the camera to its highest res mode. So that was no good! The Forum software will reduce the resolution when the pictures are uploaded so if you PM me your email address, I'll email them to you.
Cheers
Nick
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Old 5th Nov 2017, 9:44 pm   #58
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Default Re: Looking for help please with 1964 Trio W-41 stereo valve amp

Sorry Nick I PM'd you before reading your longer post. That sounds like a great plan.
I have taken a 24 megapixel image ready to send to you without the compression of the forum software. If a gnat has met its end in there you'll be able to zoom in and see what sex it was.

b
Tim
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Old 5th Nov 2017, 10:11 pm   #59
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Default Re: Looking for help please with 1964 Trio W-41 stereo valve amp

So..

I've discovered a cap C109 that on schematic is .01u... but the one in my unit is .01mfd
I've been looking at conversion charts to see if they are the same thing under a different spec but have got confused again.
help!?

thank you
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Old 5th Nov 2017, 10:16 pm   #60
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Default Re: Looking for help please with 1964 Trio W-41 stereo valve amp

They're the same thing. One uses the 'mu' symbol (not u) to denote micro(farads). The other uses mfd to denote microfarads.

These days it might be called 10nF (nanofarad).
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