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There needs to be a ground reference for the filament supply, the older transformers had a center tap that was grounded to the chassis like the red/yellow is. Without it the amp will hum like crazy until you teach it the words.

In the late '60s Fender went to using two 100 ohm, 1/2 watt resistors to create a virtual center tap. So you need to wire one from each of the two green filament wires going to ground. Fender usually did this at the pilot lamp socket.

An alternative would be to add a hum balance control that you can adjust to set the filament ground for the least amount of hum. This would require a 100 ohm, 5 watt pot that would replace the two resistors.

Keep the red/yellow lead connected to the chassis.

Mr. Bill wrote:So you need to wire one from each of the two green filament wires going to ground. Fender usually did this at the pilot lamp socket.

To clarify, are you saying I need to run a ground wire from one of the lug terminals on the pilot light housing to the chassis where the two green wires from the transformer connects?

You can directly tie one side of the 6 volt winding to ground like a Champ if you want, but for best hum reduction you should choose one of the other methods.

If you go with the two 100 ohm resistors, mount a ring terminal on the transformer mounting bolt that is right next to the pilot lamp socket as your ground point. Then connect a 100 ohm resistor from each of the two sides of the filament winding that connects to the pilot socket down to the new ground point. This way each side of the winding is grounded through a 100 ohm resistor to the chassis.

I will try and find photos of this for you.

Here's one from BillM's site.
http://billmaudio.com/wp/wp-content/uploads/2011/03/IMAG0133.jpg

Whew! Thanks for catching that and pointing it out. Does this look right? I'll solder them to the terminals when I do the filament heater wires. They are piggy backed onto the ground wire off the rectifier board. I didn't have 1/2 watt 100 ohm so I went with 1 watt.

Dub, that's perfect! As always.

Well, today I finished up all the wiring and the anxiety, rapid heart rate and shallow breathing set in. I hooked it up to my Bandmaster speaker cabinet, held my breath and flip the power switch. So far so good, so I flipped the standby off and it came to life pretty as you please. I thought sure something would smoke, pop, crackle or do something but it just set there idling until I hooked up and guitar and was blown away at how cool this thing sounds.

Mr. Bill, the schematics show a plate voltage of 430v and this is running 473v. Any ideas or recommendations?

That's great! Congratulations. The brownface amps have their own vibe that's different than tweeds or blackface - almost a best of both worlds. Now you need to build yourself a Showman!

Amazing job there Dub. Congrats on a great build.

Modern voltages tend to be higher than the voltages that are listed on the schematics. Your plate voltage is less than 10% high. If you measure the ac wall voltage does it come in at 120vac? Your filter caps are rated for 500vdc so there are no problems there. And as long as the output tubes bias up ok they should handle the voltage ok as well.

If you really want to reduce the voltage you can add a Zener diode to the center tap of the high voltage winding.

Thanks, Mr. Bill! I've been playing it for a while now and if there are no dangers with that volatge, I'll just let it be.

MWaldorf wrote:Now you need to build yourself a Showman!

Never thought of it before but that Bassman 100 that I've been so unhappy with would certainly make a good platform for a Showman. Wheels are turning! Showman makes a great bass amp too don't they?

dubtrub wrote:Thanks, Mr. Bill! I've been playing it for a while now and if there are no dangers with that volatge, I'll just let it be.

MWaldorf wrote:Now you need to build yourself a Showman!

Never thought of it before but that Bassman 100 that I've been so unhappy with would certainly make a good platform for a Showman. Wheels are turning! Showman makes a great bass amp too don't they?

Yes, they do. If you're going to build one, I'd go for the 6G14-A brownface circuit with the harmonic vibrato and presense control. I love mine.