re-capping an old UREI 1176 LN ??

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matthias

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Jun 4, 2004
Messages
768
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germany / frankfurt
I had not used my 1176 (F-Rev) for some time...
last night I wanted to set it up again and after I finished that
terrible cableing on the back I switched it on,
but there was only a big and loud hum at the output... 50/60 hz at +6db

I disconnected all cables, but the meter still shows the 6db hum..

I opened it and recognized that the silver power filtering caps
are looking "leaky"...


1176-1.JPG


1176-2.JPG



can that be the reason for this error??

can I replace them with usual electrolytic caps of the same or bigger value??


thanks,
mat
 

Steve Jones

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Joined
Jun 3, 2004
Messages
506
Location
Sydney
definately replace them, keep the same values and voltages - although if you go a little higher with the voltages that is OK. I wouldn't suggest going too much higher with the capacitance rating, as this increases the turn on surge which could be a bit too much for the rectifiers if they are getting old.

As for the other electro's (and tantalums if your unit uses 3 of them) I would replace the tantalums with new ones, replace any electros that are used for power supply shunting. It is a matter of choice if you want to replace any audio coupling electros, there are 2 schools of thought on that one when it comes to old gear.
 

matthias

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Joined
Jun 4, 2004
Messages
768
Location
germany / frankfurt
thank you for the fast reply !!


when I look at the schematic C25 (the big blue cap) should be 1000µ
but it's a 2300µ cap in my comp... can I just put in a 2200µ 63V cap ???

(btw: the UA 1176 reissue has also the same big caps as the old one, is there any reason for that, except the the look??)


there are only 2 tantalium caps in my comp ( c19 and c20, each 6,8µ )
in the gr-control-amp section... are that the tants you suggested to replace ???

tant.JPG



are there any other parts that I should replace to ensure stability in the future??
maybe C15 the 470µ cap that leads into the output transformer..??

cap.JPG
 

Steve Jones

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Joined
Jun 3, 2004
Messages
506
Location
Sydney
If it's got bigger value filter caps in there, then it should be fine to replace them with the same ones as were there. Tantalums are unreliable, so yes, replace them as they do terrible damage when they fail. Don't forget that they are polarised, or else you will be picking bits of capacitor out of your hair after you turn the unit on. I don't have a schematic in front of me to tell you specifically which other caps to replace though.

Other good things to do are to get some deoxit into the transistor sockets and work the legs in and out a few times, and then get some isopropyl alcohol from the pharmacist and an old toothbrush and scrub the PC board around and under the end of the board that has the socketed FET's on it, as this is a high impedence circuit, and dust and cigarette smoke on the board will cause the compressor and meter circuit to drift with humidity if the board is dirty.

If you have an RMS multimeter, you can easily calibrate the unit to factory spec, except for the distortion trimmer, which you shouldn't touch if you don't have a distortion meter. If you don't have a test oscillator, there are several free and shareware PC and Mac programs that allow you to generate a 1K test tone, and burn it to a CD, and viola! instant test tone. just burn 10 minutes of 1k tone, put it in your diskman, and use the voume control to set your level. Buy a cheap true RMS multimeter, and you can calibrate away.
 

PRR

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Jan 30, 2010
Messages
11,144
Location
Maine USA
> a big and loud hum.... the silver power filtering caps are looking "leaky"... can that be the reason for this error??

Yes. They used to be capacitors. Now they are just cans full of aluminum foil. (The magic juice got out.) Since they were filter capacitors, and aren't anymore, you have zero filtering. The "DC" goes from 15V to zero volts 100 times a second (twice the supply frequency, in Germany usually 50Hz). The amp can't make steady output with grossly unsteady supply voltage.

> can I replace them with usual electrolytic caps of the same or bigger value??

Yes. In an emergency, you could even go a little smaller. 680uFd instead of 1,000uFd. In "small" boxes like limiters, you can go bigger, probably 2 or 3 times bigger if you have the space (and there is a lot of space there).
 
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