Loss of volume in bandmaster reverb

[pine]

I have noticed a drop in volume on my amp; I always play through the channel that has reverb. Then I found that if I turn up the volume on the other channel, the one without the effects, I get the volume back, along with some noise. Is this normal, and if not what is the problem?

Additionally, the plate voltage is only about 406V; does this mean I have to bias my 6L6s at 50mA?

[MWJB]

Even in a tolex 2 channel Fender there is still a little interplay between the channels, however this is usually quite subtle, often only tangible with the channel you are not using's volume & tone controls flat out.

By turning the unused channel's volume and/or tone controls up you will introduce additional noise from the unused side. This should only be the regular mild hiss, or "blow" that is typical of wide open amps. If it's so loud that it interferes with playing, recording or micing up you may have a problem, try a quieter preamp tube for starters.

You're not bridging the 2 channels with a patchcord are you? The reverb and non-reverb sides are out of phase with each other, bridging will cause a drop in output.

If you have noticed a volume drop in the reverb channel, irrespective of the position of the unused channel's controls you probably have a malfunction...if retubing doesn't help see a tech for a fuller investigation/service.

Your amp should sound fine, or at least as Fender intended, with 30-35mA of plate current at 406v. If you bias to 50mA your plate voltage will drop still further (already sounds a bit low to begin with?). If you try 50mA and like it, with 20W plate dissipation you will need to use a genuine 30W NOS 6L6GC, or the JJ (not all current production 6L6s will like this much current). However, the bandmaster (Pro/Vibrolux/Tremolux) OT AFAIK is a little smaller than some 2x6L6 Fenders, so I'd be wary of running it at such high currents.

There's no exact, correct bias setting, as long as you have enough current to limit crossover distortion (unless you like it?) and not so much as to damage tubes & transformers (let's say 25-40mA), whatever sounds best to you is correct.

[pine]

Even in a tolex 2 channel Fender there is still a little interplay between the channels, however this is usually quite subtle, often only tangible with the channel you are not using's volume & tone controls flat out.

By turning the unused channel's volume and/or tone controls up you will introduce additional noise from the unused side. This should only be the regular mild hiss, or "blow" that is typical of wide open amps. If it's so loud that it interferes with playing, recording or micing up you may have a problem, try a quieter preamp tube for starters.

You're not bridging the 2 channels with a patchcord are you? The reverb and non-reverb sides are out of phase with each other, bridging will cause a drop in output.

If you have noticed a volume drop in the reverb channel, irrespective of the position of the unused channel's controls you probably have a malfunction...if retubing doesn't help see a tech for a fuller investigation/service.

Your amp should sound fine, or at least as Fender intended, with 30-35mA of plate current at 406v. If you bias to 50mA your plate voltage will drop still further (already sounds a bit low to begin with?). If you try 50mA and like it, with 20W plate dissipation you will need to use a genuine 30W NOS 6L6GC, or the JJ (not all current production 6L6s will like this much current). However, the bandmaster (Pro/Vibrolux/Tremolux) OT AFAIK is a little smaller than some 2x6L6 Fenders, so I'd be wary of running it at such high currents.

There's no exact, correct bias setting, as long as you have enough current to limit crossover distortion (unless you like it?) and not so much as to damage tubes & transformers (let's say 25-40mA), whatever sounds best to you is correct.

I'm not bridging channels, and I do have RCA Blackplates . The amp has been blackfaced, and I put a Mercury Magnetics Super Reverb OT in there (running a 4X10 cab). I was trying to make a Super out of the Bandmaster. Do you still think 50 mA is OK?

[MWJB]

The amp is going to get much hotter running at 50mA (especially if you're using a seperate speaker cab with a Bandmaster head), don't forget that that's 50mA at idle and will go up as you play. Is it too much? The OT should take it (ask MM if you have doubts?).

With your tubes drawing that much current your B+ voltage is being pulled down, you might get better dynamics & more apparent headroom by backing off the current?

When it was blackfaced did the amp get new electrolytics, including those in the preamp & bias supply?

[pine]

The amp is going to get much hotter running at 50mA (especially if you're using a seperate speaker cab with a Bandmaster head), don't forget that that's 50mA at idle and will go up as you play. Is it too much? The OT should take it (ask MM if you have doubts?).

With your tubes drawing that much current your B+ voltage is being pulled down, you might get better dynamics & more apparent headroom by backing off the current?

When it was blackfaced did the amp get new electrolytics, including those in the preamp & bias supply?

No, it has the original caps; I was actually looking for less clean headroom, I want it to break up a little. Now it doesn't break up until volume is at 7

[MWJB]

"Now it doesn't break up until volume is at 7", that doesn't sound normal.

OK, first stop is a cap job - all electrolytics in the power supply, bias circuit & preamp cathode bypass. Then a voltage check.

A quick & easy way to get the amp to break up & reduce headroom would be to replace the 12AT7 phase inverter tube with a 12AX7 and/or remove the preamp valve for the channel you are NOT using (rebiases the remaining valve).