Newcomb Mobile PA amp E-10M project

[zenit55]

Just acquired this rather interesting amplifier.

It appears to be vintage Newcomb E-10M PA amp that's designed to run from 110 AC, as well as 6V DC through battery clamp terminals using a vibrator power supply.
First of all, what are these 6V batteries? It is clearly not something that's being sold now. Was that some kind of a car battery?

It also appears very much modded. Somebody added a bunch of jacks all over the place, and a relay. There is also an outside box with a transformer inside that plugs into that 4 pin jack on top with a VU meter attached to the front. Not really sure what the purpose would be (maybe an input transformer for a mic). It is also too bad about the faceplate - somebody added a tone knob in the middle.

I want to get it up and running again, but should I preserve the 6V running ability? This might interfere with being able to run a 3 prong cord, because amplifier uses a jones plug with 2 cords (one for 6V, another for 110V). Is it even possible to get these 6V batteries these days?

[Stevem]

Yes, Cars and trucks up to even the mid 1950s with some where a 6 volt system, not 12 volts.

I can't fathom any use for keeping that amps ability to run on 6 volts!

[Phil_S]

Nice platform to build a guitar amp. Given its age, I'd strip it and then figure out what to do with it. Maybe a tweed deluxe (if that is your thing) or a Princeton, Marshall 18W, or Vox AC15. It's got octal sockets. I'd stick with 6V6's.

LOL on the 6v thing. I think Steve is on to something there. You could hook this up to your car or truck for mobile use. I wonder though, I had a friend who owned a 1951 Ford F1 (flathead 6) that had a 6.3v positive ground electrical system. I wonder if this thing would have worked with that truck?

[Stevem]

I think I would convert the metal case single triode 6SF5 tube over to a 6SL7 since they pull the same heater current and then you have a added gain stage to play around with.

[zenit55]

I think I would convert the metal case single triode 6SF5 tube over to a 6SL7 since they pull the same heater current and then you have a added gain stage to play around with.

I was actually thinking about doing that. right now its set up kind of weird. signal goes through first triode of 6sc7 into 6sf5 then back to 2nd triode of 6sc7 (paraphase phase inverter). The other thought was to make a pentode (something like a 6sj7) input stage on that 6sf5 socket. Definitely don't want to make a 5e3 clone out of it (been there done that). But first I think I will just return it to stock and freshen up all the caps, because its such a mess right now.

[Phil_S]

Like I said, strip the chassis. Here are octal preamp ideas that should work with a pair of 6V6:
5F2 Princeton V1-6SL7, V2-6SN7 concertina only uses half.
Marshall 18W V1 and V2 6SL7
Vox AC15, V1-6SJ7 will need tweaking, V2 6SL7 - obviously only one channel no trem
TW Blues Express, V1 and V2 6SL7, tight fit with all the pots, can't say this is a good fit
Gibson GA-20, one channel only V1-6SJ7 (needs tweaks) and V2 6SL7. If interested I can post my tweaked schematic. Lotsa grit in this one at a manageable volume.

There are lots of possibilities.

[zenit55]

That ga-20 sounds interesting. I would appreciate it if you posted your schematic.

Like I said, strip the chassis. Here are octal preamp ideas that should work with a pair of 6V6:
5F2 Princeton V1-6SL7, V2-6SN7 concertina only uses half.
Marshall 18W V1 and V2 6SL7
Vox AC15, V1-6SJ7 will need tweaking, V2 6SL7 - obviously only one channel no trem
TW Blues Express, V1 and V2 6SL7, tight fit with all the pots, can't say this is a good fit
Gibson GA-20, one channel only V1-6SJ7 (needs tweaks) and V2 6SL7. If interested I can post my tweaked schematic. Lotsa grit in this one at a manageable volume.

There are lots of possibilities.

[Stevem]

You can find the schematic at the schematic heaven site.

They list a ga20 ga20t which with Tremolo.

The ga20 RTV is a fully different amp.

[Phil_S]

Here's the schematic of what I built. This has what I ended up with by trial and error for the 6SJ7. I didn't like at all what Gibson did with it. The file dates from 2009, so there is more that I forget than remember. This is what Aaron (xtian) calls a beaks and feet project. Most parts came from the bone pile. Ignore the PCB material on the inside; that was used to patch holes in the chassis. I believe this will fit in your chassis nicely.