can i remove the vibrato circuit??

[liwei]

i'm beginner.
i want to built a fender bf bandmaster AB763 without vibrato,only keep normal channel. Can i just cut the vibrato circuit off (refer to the attach drawing)?will it change the sound?
thanks!!

[txstrat]

Yes, you can leave the vibrato channel out and I don't think it will alter the sound that much (except of having no vibrato) . Have a look at the voltages.
Very important thing is to change the value of the cathode resistor (second half of the preamp tubes). There is a shared resistor for two triodes in the original schematic. If you cut one triode out you need to double the value of the resistor as it is now only for one triode. Use a 1.5k resistor just like in the other triode of the preamp.

AND BE VERY CAREFUL AND THOROUGHLY IN WHAT YOU ARE DOING - TUBE AMPS CAN BE LETHAL

Matt

[liwei]

Yes, you can leave the vibrato channel out and I don't think it will alter the sound that much (except of having no vibrato) . Have a look at the voltages.
Very important thing is to change the value of the cathode resistor (second half of the preamp tubes). There is a shared resistor for two triodes in the original schematic. If you cut one triode out you need to double the value of the resistor as it is now only for one triode. Use a 1.5k resistor just like in the other triode of the preamp.

AND BE VERY CAREFUL AND THOROUGHLY IN WHAT YOU ARE DOING - TUBE AMPS CAN BE LETHAL

Matt

ok,change the 820ohm to 1.5K.
Thank you Matt,very helpful!


actually,i don't quite understand what i'm doing......but wish me luck....

[txstrat]

actually,i don't quite understand what i'm doing......but wish me luck....

I do.
What about starting with a KIT as a first try? Don't know if there's a KIT for a Bandmaster, though.

If you don't like that I would recommend to have a look not only at the schematic but at the layout plan for your desired amp too. If you set everything like in the layout plan of a Fender amp you might have less problems.

Matt

[pvsage]

You can leave out the vibrato power supply as well. Where the vibrato circuit connects to the two 220K resistors in the power amp, just connect the resistors to ground.

Minor variations of the AA763 and AB763 with just the "normal" channel are fairly common in the boutique market, so if you build it right, you'll probably be happy with the results.

http://schematicheaven.com/fenderamp...b763_schem.pdf
Take a look at the pdf for this Bandmaster on Schematic Heaven. Do you see the 12AT7, 12AX7, and two 7025's in the layout page? Simply crop out the 12AX7 and the 7025 beside it, along with the related circuitry on the board and panel - this should get you 95% of the way there.

By the way, you can also leave out the 220K mixing resistor after the Normal channel - with just one channel, you can go straight to the phase inverter.

[Albert Kreuzer]

You can leave out the vibrato power supply as well. Where the vibrato circuit connects to the two 220K resistors in the power amp, just connect the resistors to ground.

Are you sure? The "vibrato power supply" is the bias supply, you wouldn't want your power tubes to run without bias

Cheers,
Albert

[pvsage]

D'oh!

You're right, Albert. I missed that because I'm almost exclusively a cathode bias guy.