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Old 31st March 2014, 11:20 PM   #1
lexer98 is offline lexer98  Argentina
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Default Valve amp - maintenance

Hello valve guys ... i have a very old Ken Brown Stereo with valve amp, according to my calculations have more than 40yr old (My grandfather bought it when he married).
I would like to do a maintenance, because the only thing that was changed are the valves

1-Which things would have to change?

>Pots ... all pots add noise and the shaft does not slide smoothly
> Capacitors ?
>Valves ? ... two valves have burns marks
>Resistors ?

2-One transformer make a lot of noise when turn up the volumen,
in the video is barely noticeable but it is very annoying noise IRL ¿ any way to fix that ?

https://www.youtube.com/watch?v=k2P2Aa2CyHg

Thanks

Pics of the valves and interiors ... sorry for the quality

Valve 1

Click the image to open in full size.

Valve 2

Click the image to open in full size.

Click the image to open in full size.

Interiors

Click the image to open in full size.

Pots

Click the image to open in full size.



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Old 1st April 2014, 05:13 AM   #2
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hello ,

the amplificator is 1 way or 2 ways ?

so possible listing to all valve ?

they all résistor is not good to very performance , so possible change for news résistor !

possible change capacitor to risk burn !!!

look me old amplificator 2 ways , so first use is 1965 years

i me reconditioneded to old component for news perfs , change valve ( EZ81 , 12AX7S and 6P14P-EV )
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Old 1st April 2014, 06:44 AM   #3
lexer98 is offline lexer98  Argentina
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Thanks for the response jean ... is 2-way amplifier ... here is more specs
Power valves : 4X ECL82 ( Two per channel)
Pre-amp valve: 12AX7
AM valve: ECH81

The transformer makes noise when turn up the volumen to high (over 75%) or when a play music with much bass, i was think maybe the vanish is bad due the time and make the transformer plates vibrating ....
Here is one pic from internet , the transformer pointed is that make noise ...

Click the image to open in full size.
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Last edited by lexer98; 1st April 2014 at 06:50 AM.
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Old 1st April 2014, 07:36 AM   #4
Tesla88 is offline Tesla88  Italy
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About transformer noise, try tighten up the transformer laminations and transformer chassis screws.
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Old 1st April 2014, 07:39 AM   #5
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hello ,

so possible all problem !

1 = looking impédance primary OPT to not valve connected to 2 ways for comparate to Ohmeter .

2 = possible use corrector in Baxendall is very up perfomance to saturate OPT .

3 = looking in osscilloscope 2 ways for analyse the problem to 1 Khz in 4/8 Ohms HP ( or charge fictive ) .

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Old 1st April 2014, 08:09 AM   #6
lexer98 is offline lexer98  Argentina
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Quote:
Originally Posted by Tesla88 View Post
About transformer noise, try tighten up the transformer laminations and transformer chassis screws.
Quote:
Originally Posted by jean michel View Post
hello ,

so possible all problem !

1 = looking impédance primary OPT to not valve connected to 2 ways for comparate to Ohmeter .

2 = possible use corrector in Baxendall is very up perfomance to saturate OPT .

3 = looking in osscilloscope 2 ways for analyse the problem to 1 Khz in 4/8 Ohms HP ( or charge fictive ) .

Really thanks for the responses ! ... first i will check the transformer coils as sujected by jean and is all are good .. I'll varnish and tighten the transformer laminations
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Old 1st April 2014, 09:49 AM   #7
DF96 is offline DF96  England
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An amp built with 1970's components is likely to be fine, apart from any ageing electrolytic capacitors. Tropical fish caps last a long time. However, they are polyester dielectric - popular in guitar amps but can add a tiny amount of distortion. Up to you - I would leave them so the amp is authentic of its era.

The pots can be cleaned or replaced.

Valves can be replaced if necessary - check DC voltages.

Basically I would only change what is faulty, which may be nothing at all.
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Old 1st April 2014, 06:35 PM   #8
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Last time I had a transformer that made mechanical noise I took the steel frame off and fitted it back with a shot of silicone rubber.
It worked.
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Old 1st April 2014, 08:21 PM   #9
lexer98 is offline lexer98  Argentina
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Thanks DF96 and Refugee !! ... hand to the work !

Quote:
Originally Posted by DF96 View Post
An amp built with 1970's components is likely to be fine, apart from any ageing electrolytic capacitors. Tropical fish caps last a long time. However, they are polyester dielectric - popular in guitar amps but can add a tiny amount of distortion. Up to you - I would leave them so the amp is authentic of its era.

The pots can be cleaned or replaced.

Valves can be replaced if necessary - check DC voltages.

Basically I would only change what is faulty, which may be nothing at all.
How identify if a valve is bad measuring DC voltage ? can you explain me ?. Thanks
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Old 1st April 2014, 08:29 PM   #10
DF96 is offline DF96  England
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Compare the measured DC voltages with a service sheet. If within 20% then probably OK.
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