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Old 3rd Dec 2021, 2:09 pm   #28
DonaldStott
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Join Date: Aug 2015
Location: Glasgow, UK.
Posts: 1,840
Default Re: Bush DAC90A hum - AGAIN!

Quote:
Originally Posted by theredhouseinn View Post
Disconnect the end of R17 the heater dropper, the connection that goes to the rectifier heater, the first one in the chain, whilst the set is switched on. If the hum goes, then it is a heater chain problem. If the hum dies as the cathodes go cold then the hum is coming from elsewhere. Don't try this if you are not used to working on live sets.
John.
Just a quick update to mention that I tried this suggestion from John (theredhouseinn) whilst taking suitable precautions as I was working on a live set!

The hum very gradually faded once the first link in the heater chain was disconnected which corresponds with the cathodes going cold - so it's not the heater chain either?

Quote:
Originally Posted by Kentode View Post
I feel disappointed for you Donald, l just hope you didn't buy the fader lube just for this one problem as I've just been looking for it and it's £21! Once I've got over the shock l think I'll ask Santa to put some in my stocking as l do tend to blast all my pots with Servisol D5, which I'm thinking might be a bit unkind.
Don't worry Ken (Kentode) - I already had DeoxIT Fader F5 as I'd had some bad experiences previously when spraying pots with D5 which is fine for switches.

See here:-

https://www.youtube.com/watch?v=0ADYRx2jQSE
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Last edited by DonaldStott; 3rd Dec 2021 at 2:19 pm.
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