Voltage increase when standby off?

[soma_hero]

I replaced the PT in my champ the other day, and just got around to playing it. Measured the B+ in standby and it was 307. Fired it up and started playing, sounded great. Then my 6V6 red plated without me realizing and burned out. I thought was a bad tube and replaced it, then saw the second tube red plating and cut power. Measured the B+ and it somehow fires up to 400V when the amp is taken out of standby. How can it jump 100V like this?

Any ideas?

[jjman]

Different people use the word “standby” differently. It’s better to use “play mode” and “silent mode” to avoid confusion regarding standby issues.

It’s completely normal for the B+ voltage to increase when in silent mode, assuming you are not switching the CT of the HV winding. The only new risk here is that the filter cap will see this higher voltage when in silent mode. If it’s a 450v cap you should be ok on that.

The red plating is likely related to something else like a shorted cathode cap on the 6v6 or a bad resistor their. What is the cathode voltage when on? What is the resistance to ground on the cathode when off? Why was the PT replaced? Was the HV winding shot? Are you using the recommended fuse rating?

I don’t think there is any reason to have a standby switch on a Champ type amp. I know some famous gurus have said otherwise.

[soma_hero]

Yeah my situation is a little different. In silent mode the voltage is around 307. Then flip it to play mode and the voltage goes up to 460V. This is with a 6V6 in or out.

I replaced the PT because it was huge and I wanted to use it in another build. It was like a 400ma transformer for a champ... replaced it with a more reasonable 100ma hammond.

I'll do some more poking around at the parts in there, but it doesn't make any sense that the voltage could shoot up over 150V going from silent to play. I would imagine the exact opposite when it gets loaded down more...

[Merlinb]

If the switch is before the reservoir cap then you're probably trying to measure pulsating DC during silent mode, which you DMM will read as low. When you throw the switch that all gets smoothed out by the cap, to something the DMM can read properly.

[soma_hero]

Hmm... thats very interesting Merlin. All caps are after the switch...

[Kregg]

Different people use the word “standby” differently. It’s better to use “play mode” and “silent mode” to avoid confusion regarding standby issues.

I wasn't aware that "standby" had an alternative meaning that would confuse folks when discussing the standby switch on amplifiers. Please enlighten us further.

[Structo]

I've just always thought when an amp is in standby there is no high voltage to the tubes. Thus no sound.

When off standby or in the play mode the high voltage is supplied and you can play.

I prefer the panel is labeled with Standby and Play.

[jjman]

Different people use the word “standby” differently. It’s better to use “play mode” and “silent mode” to avoid confusion regarding standby issues.

I wasn't aware that "standby" had an alternative meaning that would confuse folks when discussing the standby switch on amplifiers. Please enlighten us further.

Many people say things like "..when I turn the standby switch on.." Some people use that to mean one thing and some the other. This poster says they have higher B+ when "out" of standby. Something sounds to be backwards in the amp. Using "play" and "silent" cannot be misused or misinterpreted by anyone. In this case removing any ambiguity regarding the mode was a good starting point towards focusing on what’s really happening.

[soma_hero]

The word 'standby' is pretty explanatory. 'Standby' meaning literally 'standing by' as in ready to act when called upon but not acting yet... So in standby = no HT voltage. Out of standby = play mode = acting.

I'll get around to playing with this amp more later.

[Kregg]

So what we have is a case of poor semantics; like when someone says, "I couldn't care less", or "unthawed"? As I've always maintained "we" cannot educate a "public."

[jjman]

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