Any Electronic Gurus out there? Really need some help.

Arcturus · Jun 4, 2011

Unfortunately I think I just blew the power trans on my Sherwood S1000II. This is a mono 36 watt amp with 4 6BQ5 tube output.

I replaced a tube socket according to the schematic, and the amp was operational with no shorts. However, the bias rectifier a selenium unit with two leads connected to but when I put it back together, one of the leads broke off. The amp played fine for about an hour but then it started making popping noises coming from the area of the xformer, It was so hot that it almost left a first degree burn and smelled worse.

I quickly killed the power but popping noises continued after the amp was turned off.

I haven't had a chance to try it yet, and I now have diodes to replace the selenium rect.

Is my amp toast? :-(

I'm really upset about this because there's nothing sounds like this amp. It's unbelievably crisp and clear, and gives my 120 watt tube amps a run for their money.

Arcturus · Jun 4, 2011

Mods, could you move this to Tech Help please? Better suited for that forum.

whacko · Jun 4, 2011

Hey Arc,

Unless you know what you're doing I'd suggest getting somebody to test and inspect the amp.

It might be an idea to get them to fit the diode too because you also need to wire a resistor in series for surge protection.

On a brighter note - as your amp was working right up until you switched it off, it may well live again. So you'll still be able to annoy the neighbours.

Regards

Whacko

Arcturus · Jun 4, 2011

whacko said:
Hey Arc,

Unless you know what you're doing I'd suggest getting somebody to test and inspect the amp.

It might be an idea to get them to fit the diode too because you also need to wire a resistor in series for surge protection.

On a brighter note - as your amp was working right up until you switched it off, it may well live again. So you'll still be able to annoy the neighbours.

Regards

Whacko

Thank you, you've given me some hope. This amp is my center channel amp for my home theater, and I'm really bummed.

benbradley · Jun 4, 2011

For a moment I swear I thought I had hit some other book mark and I was on AudioKarma ... Check it out, http://audiokarma.org - I'm benb over there and on http://diyaudio.com.

The bad news is if it (the amp? the transformer?) was too hot, it's likely because something was some component(s) was getting too hot and possible got damaged. I'm guessing the transformer got hot by the bias winding being shorted - even if not, just not having the bias circuit working will cause excessive idle output tube current (the bias is a negative voltage and reduces the output tubes to a small quiescent current compared to when the signal runs them at full volume), heating up the tubes AND the transformer. The transformer and/or the output tubes may have become overheated. This could be especially bad for the transformer, as (not only will it not work right and be expensive to replace) overheated insulation between windings can cause them to short against each other, connecting line voltage to the amp's signal and speaker connections, causing a dangerous situation.

And whacko is right about replacing the selenium rectifier - like tubes, those things are neato historical items, but they're better replaced with a silicon rectifier (and a series resistor set to drop the same voltage as the forward voltage of the selenium). Put the selenium on your display shelf. The problem with selenium rectifiers is when they get an overload or short or go bad (overheat) they put out a really stinky substance into the air that is also supposed to be bad to breathe.

Arcturus · Jun 4, 2011

benbradley said:
For a moment I swear I thought I had hit some other book mark and I was on AudioKarma ... Check it out, http://audiokarma.org - I'm benb over there and on http://diyaudio.com.

The bad news is if it (the amp? the transformer?) was too hot, it's likely because something was some component(s) was getting too hot and possible got damaged. I'm guessing the transformer got hot by the bias winding being shorted - even if not, just not having the bias circuit working will cause excessive idle output tube current (the bias is a negative voltage and reduces the output tubes to a small quiescent current compared to when the signal runs them at full volume), heating up the tubes AND the transformer. The transformer and/or the output tubes may have become overheated. This could be especially bad for the transformer, as (not only will it not work right and be expensive to replace) overheated insulation between windings can cause them to short against each other, connecting line voltage to the amp's signal and speaker connections, causing a dangerous situation.

And whacko is right about replacing the selenium rectifier - like tubes, those things are neato historical items, but they're better replaced with a silicon rectifier (and a series resistor set to drop the same voltage as the forward voltage of the selenium). Put the selenium on your display shelf. The problem with selenium rectifiers is when they get an overload or short or go bad (overheat) they put out a really stinky substance into the air that is also supposed to be bad to breathe.

This may been it. The amp started cooking when it t went idle for about ten minutes, I had just finished a movie and getting ready to watch another one.

Ol' Fashioned Girl · Jun 28, 2011

Arcturus said:
Mods, could you move this to Tech Help please? Better suited for that forum.

Sorry we missed this... if you ever need to draw a mod's attention again, you might just click on the little 'report post' icon at the lower left, under the person's avatar, etc. That'll send a message to us.

I'll move this now, even though it's late, 'cause there just might be someone lurking in Tech Help who can, you know, help.

Any Electronic Gurus out there? Really need some help.

Arcturus

Arcturus

whacko

Keeping up with the class

Arcturus

benbradley

It's a doggy dog world

Arcturus

Ol' Fashioned Girl

Hand? What hand?