Planning a Model 26 build

[ArcticWhite]

I'm planning on building a Model 26 Woody using transformers and field coil speaker from a 1946 Philco Record Player Radio console.
Any mods I should consider off the bat? I know that the tone control isn't safe as is, it puts 375 volts across the pot, and thus, needs a cap across the naked side, and both caps should be rated at 600v or so.
I guess I should add 1500 ohm grid stoppers before the power tubes.
Anything else?
My Philco field coil speaker is a 12" instead of the ten inch original. I'm on the fence about building with a different set of iron altogether and using a ten inch, but I've never built a field coil amp, so I'm kinda excited about that aspect.

Also gotta figure out how I'm going to cut this chassis down a bit, to make it work in a combo cabinet in some way...
Time to get out the grinder.

 

[David Barnett]

There's an awful lot of Vox amps out there with the same tone control, and no apparent problems from it.

 

[ArcticWhite]

There's an awful lot of Vox amps out there with the same tone control, and no apparent problems from it.

I'm just going by what robrob says about it.

Note that the pot has approximately 375v DC on it because it is connected between the power tube plates. This is not a safe design. A second cap needs to be added to the Tone pot #1 terminal (brown wire) to keep DC out of the pot. A 0.1uf 600v cap would be adequate and I also recommend upping the Tone cap to 600v.

 

[2L man]

I think there does not come any danger for amp user when tone pot is connected to power tube anode. There is mains transformer which make amp electrically safe isolating calvanic connection. But longevity of that potentiometer might come shorter? There are potentiometers which are rated for higher voltage. Install a fuse to DC HV just after rectifier tube. There is also primary fuse and finally mains board fuse to protect.

 

[isaacteller]

Uncle Doug to the rescue!
The modified schematic is in the link in the video.

 

[printer2]

Doug never cranks an amp, which is a shame.

I think there does not come any danger for amp user when tone pot is connected to power tube anode. There is mains transformer which make amp electrically safe isolating calvanic connection. But longevity of that potentiometer might come shorter? There are potentiometers which are rated for higher voltage. Install a fuse to DC HV just after rectifier tube. There is also primary fuse and finally mains board fuse to protect.

A 2W full size pot has a much bigger voltage rating than the little pots used on guitars. A non-metal knob would alleviate some worries. The idea that the pot is grounded on the chassis also should take care of most of the concern.

 

[ArcticWhite]

Doug never cranks an amp, which is a shame...

Not really. He's kind of a crappy guitarist. Great guy, great resource but he should really have a buddy demo his stuff.
Ulp.
Am I going to hell, or what?

 

[printer2]

Not really. He's kind of a crappy guitarist. Great guy, great resource but he should really have a buddy demo his stuff.
Ulp.
Am I going to hell, or what?

Massive distortion covers many sins.

 

[tele_savales]

I've mentioned via YT to Doug that all the Fender amp demo's he does sound identical with the volume on "2". He told me how deafeningly loud they were, which I replied "Isn't that the point?"
I guess he prefers massive engine noise over his own guitar playing.
He's also admitted his hands are too wrecked/arthritic to play anymore, as half the members here have posted as well.

 

[ArcticWhite]

Uncle Doug to the rescue!
The modified schematic is in the link in the video.

I noticed that Uncle Doug moved his tone control from after the power tubes, to the more traditional location conjoined with volume.
Seems almost blasphemous.
But easy to try it both ways.

 

[wangdaning]

Massive distortion covers many sins.

That is what reverb is for