The Steel Guitar Forum

I have a Bandmaster Reverb that's one of my favorite amps ever for standard guitar. The compression and sag make it breakup ever so slightly almost like a Vox amp. If someone was to use it with a PSG, you'd want to use a big efficient speaker and not crank it too loud.

Matthew Dawson wrote:...
Also, the bias supply is weird on the Silverface Bandmaster Reverbs. It allows you to balance the bias between the two tubes but gives a lot less control over the overall bias. Changing the bias supply to the standard Blackface style makes it a lot easier to bias the tubes to get the amp sounding good.

I always like to convert my Fender amps to the Blackface adjustable bias voltage control and ditch the "balance" thing. Just buy matched power tubes so balancing isn't an issue.

B

It's easy enough to add a trimpot for the main bias, then you have bias and balance. Being able to unbalance the finals can give you more even harmonics, useful for guitar (not so much for steel). Also gives more flexibility in dialing out crossover distortion... note the 100K/82K PI plate resistors on some Fender amps. Sometimes perfect final balance is not what you want!

Can the PT support a heftier tube? Like a KT-66? Or is that silly?

Two KT66 require 4.4A heater current (including 6 preamp tubes), compared to 3.6A for 6L6gc. If the Hammond 290DX specs are accurate, the PT only provides 4A heater current. It is likely the PT will run very hot and possibly self destruct - I wouldn't try it.

Steven

7581A output tubes will work fine. Preferably military spec.

Jay Ganz wrote:7581A output tubes will work fine. Preferably military spec.

Those are rare and expensive, and would be a waste in that amp in its current config... it wants NOS GE. It's never going to be a loud pedal steel amp unless the OT and PT are changed... then youll have a hacked-upTwin.

Actually the 7581A's I have ARE in my old '65 Twin.

I have a pair of 7581's in a BF Bassman... that thing will split your ears. I got them from Lord Valve back when they weren't that expensive, maybe 40$ a pop. They're well over double that now. Put a set in a buddy's evil twin and had to disconnect the bias ground resistor... They needed every bit of -50v to bias without red-plating.

Wow I didn't realize they were that much $ these days! I got a set of 4 some years ago for about $80
and a bunch of Tung-Sol 5881's as well.

Here they are for $135/pop:

http://www.tejastubes.com/7581a-philips-ecg-sylvania/

... I hear Tung-Sol is making new ones... probably re-badged 6L6. The real thing is very expensive.