Univalve Issues

[mike shaw]

First let me say that I did post some of this at the Univalve bbs but I didn't really receive much valuable info.

OK - I have a Univalve that unfortunately was christened by my wifes cat. By the time I realized it the urine was dry and had corroded some parts. I cleaned it all up with contact cleaner, scraping etc. Fired it up and blew the HT fuse. More cleaning etc, finally got the thing to idle without blowing the fuse (NO tubes in amp).
Good. I then noticed a bit of a 'glow' under the preamp board (no tubes in amp). Turned board over and cleaned with contact cleaner / alcohol. Glowing stopped. HT fuse did not blow during this. No obvious burned components etc.
Next, there was a faint smell coming out from under the power supply board. No smoke, no blowing of any fuses. I'm thinking it could be some cleaner residue burning off a filter cap (maybe). Still no tubes in amp
I will likely start up again by using a current limiter but am wondering what may be happening.
If I do have some kind of short or blown resistor etc. shouldn't one of the fuses blow?
Anyone have any suggestions on my next step?
This thing has really got me wondering if there really is a problem or just a bit of crud someplace.
Thanks!!! Mike

[mike shaw]

I plugged it in again. Attenuator off. No tubes in amp. LoV setting. Speaker cab connected. No input - no guitar cable plugged in
Under power, standby on - no problems
Flipped standby to play, saw a whiff of smoke coming from big power resistor.
Back to standby, no smoke
Thinking that it might be cleaner residue on power resistor flipped from standby to play and back to standby a few times to try to burn off any cleaner. When flipped to play, smoke would start after about 5 seconds.
After a few standby to play toggles, I noticed the power resistor was stating to glow slightly like it was overheating.
That's where I stopped.
Any ideas? Thanks!! Mike

[hasserl]

It's hard to guess what may be going on. I'm not really familiar with that amp, or what the power resistor is used for. It could be in the power supply or it could be a cathode resistor as that is a cathode biased amp, right? But if you've got the tubes removed there should be no current flowing so a one should not have enough current flowing to get hot. So it would seem that you've got current flowing somewhere, which means something is still shorted out. That's the best I can do without having more info, but my post will bump this back up to the top and maybe someone else will have a better insight for you.

[mike shaw]

Thanks for the info and bump. I think the power resistor is for the attenuator. Nonetheless, this little dude definately needs so TLC. Thanks again! Mike

[SatelliteAmps]

A few things. You shouldn't be using a cleaner that is leaving residue to just massively clean an amp. Without knowing which cleaner it is, it is hard to say if it would be an issue. Probably not something that is getting burned off. Filter caps should never get hot enough to burn any kind of residue off. Smoke is always bad. If it is some sort of residue, it is usually just a weird smell, not actual smoke.

Power resistor could be in a few places. Could be in the attenuator, power supply, or even the bias (I believe the amp is a cathode biased amp, but I don't have the schematic in front of me). Trying to figure out what is wrong, really depends on which one it is, and where in the circuit. My guess is that it is on the first filter, in the power supply section. Filter cap could be bad. If it was in the attenuator, I don't think you'd be having this issue. To far along the circuit.

The HT fuse is usually a bad tube, or an arc'd socket. If the socket is arc'd (or cat damaged) it could be conducting current, possibly high voltage to ground, causing the fuse to pop, weird glows, and smoking resistors. It might not be something you can see.

Cycling the amp won't fix the problem, but running it in this condition could cause more damage, making it harder to find the cause. Getting resistors hot enough to glow orange, repeatedly is not going to help figure it out. If it is a high voltage issue, there is risk of electrocution as well. There are some things that should be checked before turning the amp on again.

Without knowing what is actually happening and being able to test the amp, it is difficult to say exactly what is going on. But my first thoughts are an arc'd socket (cat damage), filter cap, or an arc'd transformer.

[mike shaw]

Hi Adam! Thanks for the reply. At this point I think I'm going to admit that this is something that is beyond my scope and send her back to THD for a little luvvin'. Thnaks again! Mike

[Ed DeGenaro]

I e'd you.

[mike shaw]

Hi Ed! Got it. Thanks again!
Mike

[hasserl]

Hi Adam! Thanks for the reply. At this point I think I'm going to admit that this is something that is beyond my scope and send her back to THD for a little luvvin'. Thnaks again! Mike

Probably a wise choice. Hope it all works out for the best. Darn cats.

[mike shaw]

I think so - I feel most comfortable sending her home to visit the folks! LOL!
In fairness to the cat - she was old and near the end of her life. She was a good cat for almost all of her life. Who knows, maybe when I get really old I'll be peein' on my amps too! Had a grandfather who used to pee in empty pickle jars ....