Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Fresh_Start on October 28, 2018, 08:18:58 am

Title: Troubleshooting Amp with HT Short
Post by: Fresh_Start on October 28, 2018, 08:18:58 am

A Super Reverb I built almost 10 years ago has returned. The Standby switch came loose and rotated to the point where the tab connected to the filter caps touched the chassis. The fuse blew, and the owner put in some odd ceramic fuse he found at Radio Shack.  Apparently he’d blown through the fuses I included with the amp.

I had not included lock washers on the power or standby switches!!!!! :BangHead:
 :w2:
The amp powers up ok. I only have a 2 amp fuse at the moment but I can’t turn the volume above 3 in my small workshop anyway.


Obviously I need to compare voltages with my build notes. Might as well re-bias the power tubes while I’m at it.


Is there anything else I need to pay special attention to?  Any specific parts like maybe filter caps that I should be worried about?


P.S. anyone use Locktite on switches to prevent this possibility?  The amp and I both live in Maine now, so I guess it’s possible the nut came loose due to temperature changes.

Title: Re: Troubleshooting Amp with HT Short
Post by: PRR on October 28, 2018, 01:15:14 pm

Get more fuses. Always start with a Lamp Limiter. Weber has low-Amp circuit breakers which are much more tamper-resistant than fuses; cost more, but may save the amp's life.

I would worry about the rectifiers. However you say it works now? The rects would either be good or no-fooling bad.

Locktite works in Maine. I don't think Locktite alone is enough for a part which can rotate HV into the chassis. Go to NAPA, get "thin gasket paper, small". This is tough stuff and close kin to electrical insulation for large motors. Make a "U" with a 3/8" hole in the middle to cover the sides of the switch. (_I_ would go as far as ShoeGoo-ing this to the chassis; it will stick but can be scraped-out if even needed.)

Title: Re: Troubleshooting Amp with HT Short
Post by: Fresh_Start on October 28, 2018, 01:41:10 pm

Thanks PRR - started with limiter bulb initially.  Off to NAPA shortly. 

That stuff sounds good for under the Fender pilot light assembly too.  I recently helped a friend who had a short there and I've certainly had problems with those in the past.