Fender Bandmaster not working

[Howie]

Hi Folks, i've recently bought a non working Bandmaster, the choke has been replaced in the past with a non original looking one and some wax has dripped into the bottom of the cabinet.

What i'm asking is could this just be the problem? how do i test for a faulty choke?

The amp is powering up but with a very distant hum, the tubes all work fine in my other amps and i dont think it's the output transformer.

I'd love some help before i blow dough..

Howie

[JD0x0]

pop the amp open and check for faulty wiring blown caps etc. If everything looks okay check the choke with a multimeter.

[Howie]

Thanks, i'll have a dig around, what should the choke read??

[JD0x0]

Thanks, i'll have a dig around, what should the choke read??

Im not exactly sure because im not sure what choke it is. If you can find specs online they should read close to that. If you get some rediculous readings somethings probably wrong

[jjman]

Choke should be about 100ohms. If it's open there's no DC on the plates of any preamp tubes nor PI.

[rfgordon]

Check all the voltages against the schematic values or common sense values for plates, cathodes and bias. Bad voltages usually tell the story.

[Howie]

Checked board for obvious looking faults, next checked the filter caps only to find two of the three 20uf caps had blown apart, they looked to be the original brown paper ones so i guess they just failed with age.

Thanks for all the replies so far, anyone know of any good mods that can be done to increase the gain a little? maybe the pre-amp cathode stage? i've heard of a mod on the driver section?

Howie

[JD0x0]

Checked board for obvious looking faults, next checked the filter caps only to find two of the three 20uf caps had blown apart, they looked to be the original brown paper ones so i guess they just failed with age.

Thanks for all the replies so far, anyone know of any good mods that can be done to increase the gain a little? maybe the pre-amp cathode stage? i've heard of a mod on the driver section?

Howie

increasing the mid resistor will give you more mids and a pretty nice gain boost, you could also bridge the two channels so the normal channel runs into the vibrato channel

[aclempoppi]

The pre amp cathodes can be seperated, giving you the ability to adjust the caps and resistors to your preference. The negative feedback resistor can also be bumped up to give a more raw sound. I also like a 1mfd cap across the 100ohm resistor connected to the feedback resistor to provide presence. My amp is the'67 Band Master(AB763). ART

[Howie]

Yeah i'm thinking along similar lines, i've kept the Vib channel pretty much stock, i've changed the feedback resistor to a 4.7k, i've changed the first channel cathode to 2.7k and .68mf, i've also serviced the entire amp with new resistors and caps wherever, oh i have changed the mid resistors to a fat 22k on the normal channel and an 8k on the Vib channel.

The normal channel sounds pretty much like a good JTM45 or something, and the Vib channel still has a classic Blackface tone with slightly less scoop in the mids.

I'll try the prescence tweak this afternoon.

Howie