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Old 1st Feb 2011, 12:13 am   #61
Trevor
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Default Re: Tuac Amplifier modules

Quote:
Originally Posted by Valvepower View Post
The THD is quoted as 0.031% which in not bad for a 1961 transistor amplifier
Not bad , ****** brilliant I did not realiise that such figures were obtained at that time with germanium
if I had a lottery win i would spend it on reproducing these jewels
regards trev
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Old 1st Feb 2011, 1:50 pm   #62
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Default Re: Tuac Amplifier modules

Hi Trevor

Here is an interesting article to complement what has already been discussed on this thread – The Bereskin amplifier. I like the way everything is explained and you are positively encouraged to build it yourself without having to win the lottery!

Eddie
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Old 3rd Feb 2011, 10:26 pm   #63
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Default Re: Tuac Amplifier modules

Hi Alan,

I’ve attached the circuit for a Fairchild amplifier. It could be the circuit for the amplifier the Fairchild Salesman left you all those years ago.

Terry.

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I learned that lesson a long time ago. The Fairchild Salesman gave me a couple of kits of brand new Silicon Planers and a (dc coupled) circuit to try. One whiff of oscilation or prod in the wrong place and it destroyed itself in microseconds. The only repair possible was to replace all the transistors.
Alan
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Old 3rd Feb 2011, 10:31 pm   #64
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Default Re: Tuac Amplifier modules

Hi,

The Bereskin amplifier is an interesting circuit. Seeing the driver transformer information has confirmed the turns ratio of the driver transformer used in nearly all the amplifiers I seen are around 3:1 to 5:1 giving current amplification.

Terry.
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Old 4th Feb 2011, 1:44 am   #65
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Default Re: Tuac Amplifier modules

Terry,
Similar, but mine was only about 5W output.
Somewhere in the attic I still have the T05 heatsinks - they look like motorbike cylinder heads - that I used to try to keep the OP transistors cool.
Alan
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Old 15th Feb 2011, 6:55 pm   #66
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Question Re: Tuac Amplifier modules

Hi everybody, hope someone is still checking this thread as I need a little help.

I have a Tuac 50w amp which I consider to be a guitar amp rather than Hi Fi (doesn't seem to like hi-fi as it seems to deteriorate the output transistors - 2n3055). I guess I must have bought it in the early 70's. Though many deride solid state amps I'd say it has a great clean crisp sound and I've always loved it. Basic, but one is supposed to hear the instrument more than the amp. I'd like it to still be in use 40 years on. I don't know whether any of the details of it are of interest to anyone in this thread?

Anyway, my question, bearing in mind I'm not a techie, when switched on for a little while and gets warmed up it starts to generate a hum and signal transmission stops. Everything seems to be cool and clean inside apart from one small silver transistor which gets extremely hot and I'm presuming is the cause of sound failure (in the power amp, not the pre-amp). It's one that has the triangular legs not the inline, if that means anything to anyone.

I've read that failure of one component often knocks out many others but I'm guessing that's not the case at the moment.

From what I've described does it sound likely that replacing this particular transistor is likely to resolve the problem?

If anyone wants to know any more about the amp just ask and I'll say what I can. Can't draw schematics but can certainly do photo's and things. The transformer on the output (power amp) board has a label which says Anglia A 5398 (seeing as transformers have been discussed here).

Hope some of this is of interest and hope someone can voice an opinion about my little problem.

Many thanks

Jim
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Old 16th Feb 2011, 12:46 am   #67
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Default Re: Tuac Amplifier modules

Hi Jim. I'm glad you've revived this thread as I found it very interesting. I love old amplifiers and have rather too many at the moment! But thats another story.
From what you describe, I would say there is a leaky capacitor in the signal chain passing DC to the transistor that gets hot. Usually transistors either work or don't, so it must be something else. A picture would be useful to point out suspect components. Others on here may have a circuit for the amp and be able to advise more.

David.
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Old 16th Feb 2011, 3:07 pm   #68
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Default Re: Tuac Amplifier modules

That transistor does get hot
Does it have a top hat heatsink?
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Old 16th Feb 2011, 4:47 pm   #69
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Default Re: Tuac Amplifier modules

Hi David and thanks for your reply, nice to hear from you. I hope I'm attaching a photo of the board, both sides, the bottom reversed so that the layout is identical and easy to read across. I've circled the underneath contacts for the 'hot' transistor. I imagine someone who knows what they're looking at will map this across pretty easily? To me a capacitor is a little circular disc, there aren't any haha. Not sure what those big green barrels are

It's a pretty basic circuit isn't it? What do you think, do see anything in the signal chain that might prompt this overheating? Let me know if you need any more info.

No, there's no heatsink, never was, and it's been running that way for probably 35 years I guess it must be something wearing a bit weary after all this time haha.

Hope someone's able to comment. Yes, I do appreciate that it should probably go for a refurb but ........

Thanks for any help.

Jim
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Old 16th Feb 2011, 7:18 pm   #70
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Default Re: Tuac Amplifier modules

Image attached this time?
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Old 16th Feb 2011, 8:18 pm   #71
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Default Re: Tuac Amplifier modules

Yes that is the driver transistor it may be leaky after running hot for so many years
Have you a voltmeter?
Regards Trev
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Old 16th Feb 2011, 8:37 pm   #72
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Default Re: Tuac Amplifier modules

Hi Trev

Yes, I am equipped with multi-meter (2), soldering irons (2, big and little) and all manner of other things Should I test with the transistor in or out and how do you suggest I do it?

And was this amp of any interest to you while you were doing your investigations?

Many hanks for your help.

Jim
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Old 16th Feb 2011, 11:47 pm   #73
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Default Re: Tuac Amplifier modules

I wish I had got a sample of your amp so it is of interest !I will need to look at the schematic and I will get back to you on what to check !
regards Trev
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Old 17th Feb 2011, 12:34 am   #74
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Default Re: Tuac Amplifier modules

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Not sure what those big green barrels are
They look like wirewound (power) resistors. At a guess the two big ones will be the emitter resistors for the output devices
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Old 17th Feb 2011, 3:34 pm   #75
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Default Re: Tuac Amplifier modules

Hi Chris

Well, power resistors kind of rings a bell, someone may have told me way back in the past. The big green one seems to have markers of NORMAN 15W 500J and the little one NORMAN 5W 68RJ. Does that clarify anything?

Jim
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Old 17th Feb 2011, 3:42 pm   #76
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Default Re: Tuac Amplifier modules

Hi Trev

All you guy's input is very much appreciated and I would very much like to try out some solutions. Would also like to help as much as poss so does it help if I put in some more photo's? Any close up's you'd like in particular? I'll try and a pic of the whole amp layout, if I can.

Many thanks

Jim
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Old 17th Feb 2011, 7:05 pm   #77
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Default Re: Tuac Amplifier modules

The big green resistors are part of the bias network for the output transistors used in conjunction with the driver transformer and the thermistors glued to the heatsink
The thin wires are the emitter resistors about 0.25 ohm this was a trick often used to save cost
There is every chance that the electrolytics are now leaky and as these determine the bias voltage/current for the driver stage its worth changing them!
There are a no of versions on the TUAC is your the later duel supply or the earlier single supply it looks like a dual to me?
regards Trev
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Old 17th Feb 2011, 7:46 pm   #78
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Default Re: Tuac Amplifier modules

Hi Trevor and thanks for your reply. Unfortunately you are talking to a relative imbecile It's nice to have some explanation of what things do. I've always thought those 2 thin wires a very strange arrangement haha. One is a bit rusty.

Well, I wouldn't have a clue what electrolytics might be. Can you tell me what they are and is there any way of testing them?

As regards dual supply, I wouldn't know one if it bit me on the bum Is there a way of telling, do they have distinctive features? I'm kind of presuming you're referring to the mains transformer?

Sorry to be a thicky but I play guitar more than mend amps

Many thanks.

Jim
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Old 18th Feb 2011, 8:47 pm   #79
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Default Re: Tuac Amplifier modules

Looking at the completed amplifier photo its a dual powered module that has spilt rails of about 35 volts each you can measure this dc voltage across the 2 large blue capacitors please advise me
The electrolytics are the black cylinders on the tuac pcb measure the voltage across each 1 and let me know
regards trev
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Old 18th Feb 2011, 10:26 pm   #80
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Default Re: Tuac Amplifier modules

Hi,

I agree with Trevor’s earlier posts saying the electrolytic capacitors (4x black ITT axial) on the power amp module are leaky upsetting the bias conditions of the driver stage.

Trevor, regarding the TUAC driver transformer I may well contact Anglia myself about getting a pair of transformers made, if that’s ok with you? Plus I want to talk to Anglia about other transformers as well.

Terry.
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