smoking amp on standby

[jim]

Had a "Spinal Tap" moment last Saturday night.  We finished Set 1.  I flicked my Deluxe Reverb on standby and went to the bar for a beer.  A stranger walked up and said
"Dude, your amp is on fire!"   I said "Thanks, man"   "No, its REALLY on fire"  I turn to see smoke billowing out of the amp.  I ran over, unplugged the amp and stuck my nose into the smoke.   I was relieved that it was not the acrid smell of burning electronics but electrolytic gel sizzling over hot tubes.   

I open the amp later to find a split electrolytic on the totem pole.  The caps are five years old but are "off brand" So question is--Is it better just to turn off the amp between sets?
Also for lack of anything else on hand I had used 220mf 350V caps in series with balancing resistors.  Is this too much capacitance for the rectifier tube?  Or was it simply time for something to happen?  Jim

[pompeiisneaks]

As far as I understand it the only thing standby does is kills rectifiers, but it shouldn't hurt your caps.  They sometimes just go.  BUT there may have been something else that cooked that cap as well.   Since you don't mention what kind of amp or more detail, it's kinda hard to know for sure. 

There's a great article by the valve wizard on standby and why it's pointless: http://www.valvewizard.co.uk/standby.html

If you need to quiet the amp, use the guitar volume, volume pedal or just turn it off.

~Phil

[shooter]

I had used 220mf 350V caps in series with balancing resistors.  Is this too much capacitance for the rectifier tube?

I'm a SS rec builder, but the data sheets seem to suggest something around 50uf or less depending on rec tube if it's not choke based at 1st node.

[sluckey]

I had used 220mf 350V caps in series with balancing resistors.  Is this too much capacitance for the rectifier tube?

Yes. A 5AR4/GZ34 would be much happier if you use two series connected 100µF/350V caps.

Those caps remain connected to the rectifier even when the amp in in standby mode. Is your Deluxe Reverb a real old Fender, a Fender Reissue, or a homebrew clone?

[PRR]

If it was too much for the rectifier tube, the tube wudda split and leaked.

It failed on Standby because the running B+ is lower than the cap voltage in standby.

Caps fail. Fact o life. Favor "good" caps.

As I doubt you had over 250V average on each cap, it maybe "should not" have failed. But stuff happens.

Replace both caps, and any others from that batch, and the equalizing resistors because one may be over-stressed from the failure.

Agree that unless you need instant-on, OFF kills all stress and heat, and may be better for the guts.

[pompeiisneaks]

I flicked my Deluxe Reverb on standby...

Gee you did say what kind of amp, ignore me, I think I'm losing it 

Edit: spelling losin git is a bit different from losing it lol

[jim]

It was a DR reissue--I replaced the boards with Hoffman. The transformer is Hammond 290cx for the Vibrolux but it drops right into the the DRRI chassis cutout. Using a copper cap--not sure if cap limits apply to that.  Also using a Bassman output transformer at 4 ohms. So not really a DR.   I repaired it and it sounds even better but I haven't played out yet.  Jim

[sluckey]

Using a copper cap--not sure if cap limits apply to that.

The limit is associated with a tube. It's not a factor for the copper cap SS rectifier.

[jim]

also using 6L6's now, of course.  I think it would be safe to assume that a cap simply failed.  In the future I will turn the power off for breaks instead of using standby.

[Ritchie200]

Naw, just make it part of the show!

Jim

[tubenit]

 

Using a copper cap

--

It was probably10 yrs ago but I had two copper caps fail on me. Something inside shorted. I've never used one since.

With respect, Tubenit

[jim]

This copper cap has been used for about 15-20 gigs or so with no failure so far.  If I go to a tube I think I'll need to go to 100mf caps in series on the standby  switch.  I think I should check out the sound with just solid state rectification and ditch the copper cap.   I replaced all the e-caps including the 220 mf pair and so far it sounds great. Jim

[whoops]

he caps are five years old but are "off brand"

What does "off brand"  means?

So question is--Is it better just to turn off the amp between sets?

Well the Standby switch it's sure something that the circuit doesn't need but it's also not what lights amps on fire.

You have to address the problem, and the reason for the Fire to have happened.
Too much filtering for the rectifier tube?
Low quality electrolytic caps? Or not with the specs needed for your mixed circuit amplifier?

I not turn the amp off during sets,
I would just turn the volume pot on the guitar all the way down, or release the input jack on the amplifier to shut the sound and leave the amp On during the Break.

[jim]

There was no arcing or burnt insulation smell--just boiling electrolytic ooze from a split cap.  The electrolytics actually had no name printed on them just values and polarity.  I attribute their failure to time.  The amp is working fine now--I replaced all the caps with "Sprague" and I think I will simply turn the volume down at breaks instead of  using standby.