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TJ 22nd April 2003 01:01 PM

michaelson & austin tva 10
my friend give me this amp and when i turn it on i hear loud humming ! but if u play music the humming gone ! when u stop the music the hummiing back again ! what wrong with my amp ? please help ! thank

EC8010 22nd April 2003 08:16 PM

The TVA10 is a late 70s nightmare waiting to happen. I had one once. It oscillates if you leave its input open-circuit. It oscillates if you leave its output open-circuit. Each time, the EL34s glow red to let you know. It runs hot, so there are various things that could be dying. Have a look inside, and look for bulges on the ends of electrolytic capaitors.

fdegrove 22nd April 2003 11:05 PM


Oh dear...this amp is one example of those designs that gave valve amps a bad rep.

While it can sound fine, in the hands of the unaware it has been known to burn out its OPTs due to parasitic oscillation.

Sorry, but I feel this is one amp one shouldn't own.


TJ 23rd April 2003 01:20 PM

oh my god! sound like a nightmare for me ! !

i got a sch and i not sure the voltage ....... hope u guy can help me

when i measure the HT i only got 408 v and the sch show me 500 v !

EC8010 23rd April 2003 02:06 PM

Low HT
There are two main possibilities.

The 600uF capacitors were rather nasty RS types that lived near to the (hot) mains transformer. If they have gone leaky/low value, the HT will be low, and there will be hum.

The bias supply to the output valves is failing, and causing the output valves to draw too much current. Check the voltage on the grids of each output valve, it should be about -45V.

Finally, could you please type in the Queen's English? I don't imagine your tutors accept work typed in the style of a mobile phone text message, so don't use it on an international noticeboard. Replies to questions take time, and although everybody has tolerance for posters for whom English is not their first language, there is no excuse for a student in Britain to be sloppy.

TJ 24th April 2003 01:51 PM

I found the -ve bias caps is leaking and i change it and the hum is gone ! But went i turn the volume to 9 o'clock the sound start distort / broken ! The polarity on the -ve is connected right or wrong ? I've check the voltage .. Bias -44V HT 450V ..please help. thank !
ps thank for ur advice. i'll take into account

TJ 24th April 2003 01:56 PM

2 Attachment(s)
here the power supply

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