band master

[rockingrandy]

i have just bought a 68 band master. im in the proccess of looking at my tune up options . im new to this cool forum so be gentle .
problem 1: vibro channel is much lowwer in volume to the normal
vibro works but lowwer volume .

Q: how can i determine output power

Q: how loud should i exspect this amp to be.

Q: looking at buying a tube testers what is a good one

problem 2 i want to check my tube bias on new tubes installed by previos ownwer.
Thanks in advance

randy

[TD_Madden]

I also have a '68...and the "vibrato" channel also has a lower volume.....so does my late 70's Vibrolux Reverb....maybe just a design "feature"?

No idea why...sorry!

[Regis]

problem 1: vibro channel is much lowwer in volume to the normal
vibro works but lowwer volume . Preamp Tube? Swap the 1st and 2nd 12AX7's and see what happens.

Q: how can i determine output power - It's a 40 watt amp.

Q: how loud should i exspect this amp to be. That's a relative term, no way to say without knowing what you've heard before, or what speakers you are using.

Q: looking at buying a tube testers what is a good one Go Here.

problem 2 i want to check my tube bias on new tubes installed by previos ownwer. Go Here.
Thanks in advance

[Bruce / Mission Amps]

I also have a '68...and the "vibrato" channel also has a lower volume.....so does my late 70's Vibrolux Reverb....maybe just a design "feature"?

No idea why...sorry!

The 50K intensity pot on the Vibrato channel loads the Vibrato section's preamp down a little no matter where the pot is turned.
The other channel is not exposed to the pot in the same way so there is a little more signal available from it.

That's why some tweakers like to use a 50K pot with an on-off feature... the switch lifts the 50K load from ground and there is a significant increase in signal strength delivered to the phase inverter tube.
It slightly effects the Vibrato intensity but you could use a 100K pot and always have more gain...
A "tweak to taste" trick I've done for many years on some SF or BF Fender amps was to lift the intensity pot's grounded lug with a 27K to 68K resistor... (bypassed switched in and out with the stock bright switch, if there).... I'd bypass the volume pot with a 47pF cap all the time and use the bright switch so you'll still have some Vibrato when switched one way and the amp is more gainy, but throw the modified bright switch to shunt the resistor to ground on both ends and... bingo, stock amp again.

[Alex R]

You can measure output power rough-and-readily thus: feed the output into a dummy load same value as the speaker impedance. Have both a true RMS voltmeter and a scope hooked up across the dummy load. Put a clean sine wave signal from a signal generator into the input, then with the signal generator output and amp controls find the maximum amplitude clean output waveform on the scope before clipping sets in. Read off the AC voltage, square it and divide by the resistance of the dummy load. This will give the RMS wattage of the output.

Customers like to know this, so long as it exceeds what they thought of as the amp's wattage, which with EL34s it generally does. My personal best was 144 watts out of a TSL100. Frightening when you look at the tiny little OT.

[Regis]

Bruce is right about the tremolo bypass, I should have mentioned that. I did it to my Bandmaster and you get a noticeable bump in gain when you switch the trem out.

[TD_Madden]

on my '68 Bandmaster I use the old disconnected ground switch to "turn-off" the tremolo since I didn't have an extra switched pot.

I did replace the pot in my Vibrolux, though....just didn't think to compare the two channel volumes with the tremolo bypassed.....

I have both wired to provide tremolo on both channels (also reverb in the case of the Vibrolux).