Weird problem with input jack of a tube amp.

[toneless]

I have a Fender Deville with a weird problem...
When I play with the clean channel the amp has a dedicated volume control.
When I push the "drive" switch and play in "gain mode" the amp has another "volume" pot and one "gain" pot.

The problem now... when I unplug the jack and plug it again, the gain is less and  both volume pots work!
Is it a jack problem? A relay problem?

[Paul Marossy]

A few questions:

1. With the amp at a very low volume, can you hear the relay clicking when you unplug/plug the cord in?
2. Is your footswitch connected to the amp when this happens?
3. Is it a Blues DeVille or a Hot Rod DeVille?

Looking at the Hot Rod DeVille schematic, I don't see how it could be the input jack(s)...

[toneless]

A few questions:

1. With the amp at a very low volume, can you hear the relay clicking when you unplug/plug the cord in?
2. Is your footswitch connected to the amp when this happens?
3. Is it a Blues DeVille or a Hot Rod DeVille?

Looking at the Hot Rod DeVille schematic, I don't see how it could be the input jack(s)...

1. No. I can't hear anything. I think it's the most possible that it may has a mulfunction.
2. No.
3. Blues Deville.

Thanks for the reply...

[Paul Marossy]

It sounds like the relay is stuck in both positions, but that does not seem very likely to me because of how they are normally built. But, I have seen relays do some weird things, too. It would also explain with you have sound from both "channels" with a lower output. Sometimes I hate those darn pseudo-two-channel amps...

[toneless]

It sounds like the relay is stuck in both positions, but that does not seem very likely to me because of how they are normally built. But, I have seen relays do some weird things, too. It would also explain with you have sound from both "channels" with a lower output. Sometimes I hate those darn pseudo-two-channel amps...

The sound is οκ untill you unplug the jack and plug it again...
"Gain mode" works fine but when you plug the jack again  the gain is lost... the sound is still very loud but without any gain. The gain "led" still glows...!

[Paul Marossy]

Hmm... that is weird. I am suspicious of the preamp tube that is on the input - maybe it has an internal short or something. I would try a different tube in there and see what happens.

[toneless]

You believe that one of the 12ax7a's has a problem? 
Anyway I supose I have to change the relay.
Thanks for the help.

[Paul Marossy]

You believe that one of the 12ax7a's has a problem?

Possibly. A 12AX7 is a dual triode. Looking at the schematic, if there was an internal short inside the tube, then it would mess with the relay as it is inserted between the two triodes. My guess is that when you plug a cord into the input jack, it changes something and you get the weirdness that you are currently experiencing. What brought this on? Did you change preamp tubes recently? Try the tube first before you go thru all the trouble of changing the relay!