No Heater Voltage Bassman Head

[7string]

Hi. I have heater voltage problems with my BF Bassman head. 0 volts. No orange glow on the tubes. It is built like a Model 2204 50W Marshall. It has been running great for a few years now. It has the stock type Fender/Schumacher transformers and 6L6GC's. It has the 100ohm artificial center tap resistors and the CT wire taped up and tucked away. They are only 1 watt resistors but look good and all the wiring looks good, none of it seems to have been hot. I don't measure a short on the sockets. The tubes also tested to not be shorted.

The problem has been intermittent. The first time it happened at rehearsal I was able to bring it back by wiggling the pilot lamp tabs. Lasted the rest of the night and the following week. Next time it happened  I changed the pilot lamp holder. Tubes lit up for a few minutes, then petered out. With no tubes and no bulb I can get the 3v on each side. I put in a different set of 6L6's and back down to 0v. A couple of times I measured 6v on one side and 0v on the other.

Do you guys think its the PT? I do have another used one of unknown condition. Thanks for any advice you might have.

[LooseChange]

Lift the two heater wires from the circuit and check for voltage... If okay, check the rest of the circuit for a bad connection.

[John]

If it were me, I'd try to get a look at the filament wires right where they come out of the transformer. Almost sounds like you have a broken wire that makes contact sometimes, and of course the break won't conduct much current. Dunno much about trannies, but it seems like you'd have a burnt smell if the 6v winding had given out. HTH!

*edit* Do what LC says first, he's way more experienced than me!

[stratele52]

+1 john

Most of the BF bassman;

Transformer heater wire go to pilot lam socket AND from there they go to the tubes heater pins

if your pilot lamp do not light properly And tube's heater no light ,the problem is a bad wire or solder AT transformer heater wires.

Check connexions at pilot lamp socket , problem must be there, or very very close

[stratele52]

These test are good if only the heater voltage is missing and B+ ( high voltage) is ok


If no B+ and no heater voltage , check power transformer primary connexions or fuse or fuse socket

[Ed_Chambley]

Check across the heater wires, not one to ground.  See if you get over 6.3vdc.  If so, you have a bad wire connection.

Which Bassman?

[TubeGeek]

Check across the heater wires, not one to ground.  See if you get over 6.3vdc.  If so, you have a bad wire connection.

Which Bassman?

Ed probably meant 6.3 VAC

[stratele52]

 +1 TubeGeek

Sure Ed mean AC volts

[7string]

Thank you for the suggestions. I'll be home from work soon to give them a try.

I did make sure my meter was set to AC.   

The light turned on every time. Even if the tubes didn't.

It is a scratch build from old Bassman parts. Two good friends gave me what was in their amp boneyards.

[7string]

Solved (I hope). Resoldered all of the connections on the tube pins. There was one on the first output tube that looked a little suspect.

Thanks again for the help.

[plexi50]

Take high res pics of your suspect areas. They stand right out on a computer screen and are sometimes hard to see with the naked eye. The tube sockets are where i have found many heater voltage problems as well as the dreaded hum pot

[Ed_Chambley]

Yes AC.  I have had dc heaters on my mind.