Gibson not sure of model - schematic

[pontiacpete]

Yes

[Tom Phillips]

It would be interesting to see an autopsy of the "electrolytics in a box" caps.

[mozz]

So I’m not getting any signs of DC anywhere. There’s 120vac on the rectifiers but nothing on their cathodes. With no way of testing the 25z5s and none in my tube stock, I think I should just pass on this one.

Is this a repair or something you picked up?

[pontiacpete]

It’s a repair

[Justin Thomas]

Tom Phillips I've taken a few of those apart just out of curiosity. Nothing remarkable; mostly full of hard yellow or red wax that makes an absolute mess of everything it touches. I didn't really go farther than that.

Jusrin

[pontiacpete]

It would be interesting to see an autopsy of the "electrolytics in a box" caps.

here are a couple of pictures

[mozz]

Wondering if the caps shorted and took out all the rectifiers. 106v string run on 125v would be a bit hot. You can ask on the antique radio forum if anybody has a set for cheap. Etsy has 5 for $23.

[pontiacpete]

That’s reasonable enough to give them a try. I’ll be back when I get them in.

[mozz]

I think it's well worth ($$$$) trying to restore as long as the output transformer and chokes are ok. And field coil and speaker, they can be rebuilt.


Found some info.

EH-160 AC/DC
Some sections of urban America still relied on direct current in the ’30s, and in rural areas DC generators were the only supply of electricity. Gibson tried to accommodate those unfortunate few electric guitarists from these districts (and foreign markets) by offering a “universal-type” power transformerless amp capable of running just about anywhere, sometimes referred to in catalogs as the EH-160.

These were offered during the entire run of the 150, but the varieties are beyond the scope of this article. Mention should be made, however, of one that appears in The Tube Amp Book by Aspen Pitman. The 11-tube amp (page 47, Volume 3) is mistakenly noted as using a “…duet of 6L6s” when the four tubes in the back right corner should all be 25B6 power amplifier pentodes. There is a good chance this amp says EH-150 on the control panel (which matches the 150’s panel to a T), but a schematic for what appears to be this exact model, officially labeled EH-160, shows up in an old Gibson amplifier service book.

On the far left, in front of a transformer -like device (probably the power supply choke) are four 25Z5 rectifiers. Across the front right are three metal-cased 6C5 triodes, with one driving the phase inverting transformer, a second for the microphone input and a third for the two instrument inputs. The idea of universal-type AC/DC amps had been used previously for radios and would be exploited on student models by numerous guitar companies after WWII. Usually, this type of amp’s heaters are run in series, with their total adding up to approximately 110 volts. Since Gibson wanted the amp to compare favorably to its standard model, they ran a series that included the four 25Z5 rectifiers and one of the 6C5s (106 volts total) in parallel with the four 25B6 power tubes and remaining 6C6s (112 volts – note; the first number in a tube’s designation relates the heater voltage, e.g. 5Y3 uses a five-volt supply, 6L6 uses six-volt, etc.). As to how much current the amp drew or the amount of power it could produce, we’ll have to wait until one turns up in working order.


Also, slightly better schematic
https://jt30.com/gibson/index.html