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Old 2nd Nov 2017, 6:12 pm   #21
TimMills
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Default Re: Looking for help please with 1964 Trio W-41 stereo valve amp

Hi. yes the amp was powered off.... I'm happy to be asked any question.
and in the meantime I've removed all 4 resistors.

270k read 122k and 195k but neither give a reading that holds for more than a second on the screen.
The 68k ones read good at 69k but now they're out I'll replace all 4 and see where that gets me.

cheers

Tim
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Old 2nd Nov 2017, 6:16 pm   #22
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Default Re: Looking for help please with 1964 Trio W-41 stereo valve amp

OK. while those resistors are out the feedback loop will be broken, which presents an opportunity to check the other resistors in the preamp circuit.

I assume your meter gives steady readings when used to measure new resistors?
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Old 2nd Nov 2017, 6:28 pm   #23
TimMills
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Default Re: Looking for help please with 1964 Trio W-41 stereo valve amp

yes my meter does give steady readings on new resistors and those old 68k ones too.

I'll do some measuring a bit later. I have Dad taxi duties in store this evening.

thanks
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Old 2nd Nov 2017, 6:42 pm   #24
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Default Re: Looking for help please with 1964 Trio W-41 stereo valve amp

initially I've found all resistors directly connected to v1 and v2 are measuring ok appart from both 3.3m ohm which are across an old ceramic cap leg and the central post of the socket. they are just flashing up at 1.9m
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Old 2nd Nov 2017, 6:50 pm   #25
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Default Re: Looking for help please with 1964 Trio W-41 stereo valve amp

Hi
I find it's best, especially with high-value resistors, to remove one leg in order to measure them, especially as you're using a digital meter. Not only does this remove any influence from other components, it also saves you inadvertently blowing up your meter with a charged capacitor!
How silent is it on the phono inputs? Try inputting your source that you're using for the other inputs. It should be far too loud and very distorted, of course. Do you get anything at all? The valves appear to be working to an extent so it might be a simple switching fault.
I wonder if the method of heater voltage supply is to compensate in some way for ageing of the output valves? Just a thought.
Glyn
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Old 2nd Nov 2017, 6:55 pm   #26
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Default Re: Looking for help please with 1964 Trio W-41 stereo valve amp

Sorry Glyn I missed your reply.
now... when you say high value resistors are we talking m suffix?
input switching has been cleaned with servisol and that all seems ok. I'm hoping we're getting close to finding the problem with the failed 270k resistors and resulting voltage drop. I hope!
and yes, using higher output gear into phono in does distort the preamp valves..

there are other red ones underneath the output transformers that don't give good readings also. But I don't think I should go there right now...
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Old 2nd Nov 2017, 7:32 pm   #27
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Default Re: Looking for help please with 1964 Trio W-41 stereo valve amp

The suffix is 'M' denoting mega or millions of ohms, not 'm' denoting milli or thousandths of ohms.
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Old 3rd Nov 2017, 12:55 am   #28
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Default Re: Looking for help please with 1964 Trio W-41 stereo valve amp

Hi Tim,
Glad you've had a good response so far!!
High value resistors (greater than 100K) tend to go high in value especially the ones in British equipment. Whether Japanese one suffer the same problem, I don't know. However, they can also sometimes go low in value but that is less usual.
The actual values in most valve circuits are not usually that critical (exceptions apply of course!) and have to be pretty far out to stop a circuit from working at all.
When measuring resistors with a digital meter, don't stick your fingers on the probes to keep them in contact with the resistor. This can affect the reading. As has already been suggested, lifting a leg (of the resistor!) can be helpful.

I would suggest that you focus your efforts on just one channel rather than V1 & V2 at the same time. This might keep things a bit simpler.

As has also been noted, the anode voltages would suggest that both halves of V1 are doing roughly what they should. If they weren't conducting, the anode voltages would be much higher than they are.

This amp has weird type phono connectors : I'm not sure how well they take a modern plug. Are you sure that your input signal is actually connecting to the phono socket?

On a different note, how much repair work has the amp had? I note you have bought new valves for it. There are various capacitors that are critical for the survival of your new valves. These are any that are used between the anode of one valve and the grid of the next. If these are leaky, positive voltage will get through to the grid and cause more current to flow in the valve which it won't like.
For the left channel, these would be C16, C17, C9, C1, & C4. C8 a 25Mfd electrolytic may also be passed it's best. Also the corresponding components in the other channel.
This won't help your fault but your valves will be happy valves

My own amp needs a complete overhaul before it's powered up and a new set of output valves. The original 'Matsushita' 12AX7's are probably OK though.
I can look at/ photograph wiring etc. if you need anything.

Hope that helps,
All the best
Nick
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Old 3rd Nov 2017, 7:38 am   #29
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Default Re: Looking for help please with 1964 Trio W-41 stereo valve amp

Swap over the 2 valves (12AX7) with ones which do glow to prove the heaters are OK
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Old 3rd Nov 2017, 9:53 am   #30
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Default Re: Looking for help please with 1964 Trio W-41 stereo valve amp

Many thanks Nick!
That is a lot of great info.
The story behind this amp is that a local engineer did take it into his workshop Feb 2017. Where it sat collecting dust until October. I reminded him a few times I was waiting to see it working and eventually he got it back to me about 2 weeks ago with 4 new caps and 4 resistors... I've not yet worked out what caps they relate to on the schematic but they bridge the EL84s with the 3 ECC83 that aren't the preamp valves, you can see them in my picture with green legs. The 4 resistors should have been 2 but he decided to put two in series instead of one and I'm replacing them as soon as replacements come. I'm replacing the set of 4 across pin 2 and the centre post of each EL84 sockets. He's a nice guy and he's fixed amps for friends for a few years. He's just terribly slow at communication (almost non existent) and I'm reluctant to return it to him as I fear I may not see it again for months. He also told me I needed to buy an external phono preamp when I questioned why it wasn't working... I did . I spent 300 on one... and now I realise he was wrong.

If you have any way of letting me know where I find those caps you list in the tangle of workings I'd love to see... like I mentioned my major issue is relating the schematic to the physical thing!
I'm also unsure where the 4x 40u 350v caps coming of hum balance on schematic are in real terms, as I can only find one at present... someone has done some work in it between 1964 and 2017 and the large blue DALY cap is marked 32u 350v and I think they've swapped that in... should I replace for 40u? will it make a difference? top left the large grey one is obvious to find but the other 2 escape me.
must dash...
thanks everyone...
Yes Peter I will do that once new Rs and Cs are in!
Tim
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Old 3rd Nov 2017, 10:10 am   #31
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Default Re: Looking for help please with 1964 Trio W-41 stereo valve amp

I'm confused about this thread, post#1 states that the phono section wasn't working at all, post #17 seems to imply that it is.....? What was the cause of the problem?

Lawrence.
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Old 3rd Nov 2017, 11:04 am   #32
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Default Re: Looking for help please with 1964 Trio W-41 stereo valve amp

Hi Lawrence,
Signal is getting through the phono stage to the speakers but no amplification is happening. It's very very quiet and thin, like putting an MM cart into a regular line level input. RIAA and preampfification does not seem to be occurring.
The cause of the problem is still under scrutiny.
Despite establishing voltage readings suggesting both 12AX7s are functioning ok, we have found both 270k resistors have failed, R3 and R103 and I'm awaiting components... I think we're in a 'watch this space' situation now although great advice is coming thick and fast.
I'm sure there are 1 or 2 who've looked at my pictures and thought... "I'd gut it and start again", and they may be right, but I'm keen to do what I can with my limited skills and equipment to try my best with the help of this forum - for now.

T
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Old 3rd Nov 2017, 11:24 am   #33
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Default Re: Looking for help please with 1964 Trio W-41 stereo valve amp

No need to gut it, may be worthwhile, as Nick has stated, to fix one channel at a time.
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Old 3rd Nov 2017, 11:47 am   #34
TimMills
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Default Re: Looking for help please with 1964 Trio W-41 stereo valve amp

Yes I like the idea of looking at one channel at a time. The draw back there for me is then having to order more components from the web and pay postage for both L and R channels. There may be a better way for me to source components of course and I'm open to suggestions...

I'm pretty convinced it'll be worthwhile.. and of course it's a great learning platform for me, if maybe a bit 'in at the deep end!'

Tim
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Old 3rd Nov 2017, 12:00 pm   #35
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Default Re: Looking for help please with 1964 Trio W-41 stereo valve amp

No problem measuring resistances in either channel and if proved faulty order at the same time but when fitting the new items just concentrate on one channel.
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Old 3rd Nov 2017, 3:16 pm   #36
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Default Re: Looking for help please with 1964 Trio W-41 stereo valve amp

Hi Tim,
Using my amp as a reference, I did a quick bit of circuit tracing this morning to find out where all the important R's & C's were.
I'll draw you a diagram and upload it tonight when I've got a bit more time. At least then you'll know where everything is!!
Cheers
Nick
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Old 3rd Nov 2017, 3:56 pm   #37
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Default Re: Looking for help please with 1964 Trio W-41 stereo valve amp

Thank you Nick,
That would be absolutely ace.

PS. today I have come to the conclusion my multimeter is faulty. I have a replacement coming tomorrow.
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Old 3rd Nov 2017, 7:54 pm   #38
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Default Re: Looking for help please with 1964 Trio W-41 stereo valve amp

I'm a little worried about posting this next bit of information in case I've done something dangerous or stupid or both....

but... as I've replaced all 4 valves and 4 x 470k resistors in the output stage today to make it all match up, I wanted to check I'd done it right and the solders and sound is good etc. so I powered it up having removed the preamp valves because there is currently 4 resistors removed from the preamp circuit R3 R5 R103 and R105. I put a line level into AUX from CD player and gave it an hour of exercise. It is sounding very sweet, very tight and really surprisingly quiet noise floor for an old bit of kit... The reason I'm telling you this is that I discovered that it seems to be generating about a quarter of the heat that it was generating when I first used it for a week when the preamp wasn't working but the valves and circuit were in place. Now I'm thinking is this the temperature it should be? it seems safer... was it getting so very hot before because something is very wrong in the preamp area?
If you could shed any light on this oddness I'd love to hear...
It seemed to be the 2 output transformers that were getting extremely hot before this test this evening.

thanks
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Old 3rd Nov 2017, 8:08 pm   #39
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Default Re: Looking for help please with 1964 Trio W-41 stereo valve amp

Basically you've increased the value of the resistance in the cathode circuit by removing the parallel resistive path in that circuit that's provided by the preamp valve heaters, less current flows, things run cooler.

Lawrence.
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Old 3rd Nov 2017, 8:13 pm   #40
TimMills
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Default Re: Looking for help please with 1964 Trio W-41 stereo valve amp

Thanks Lawrence
That makes sense. Not dangerous or damaging then?
I'll not run it again till I've got those resistors replaced.
It does sound so sweet though. All matched Sovtek EL84 have certainly tightened up that bottom end.
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