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Post subject: Anyone have any info on Gebs Amp?
Posted: Thu Feb 23, 2017 9:55 pm
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I bought a little tube amp off of offerup for $15. The guy said he got it at an estate sale with a little lap steel guitar, but sold the guitar awhile ago and is now selling the amp. It's in rough shape, but the price was right. Ones I found similar look to all be from the 40's. Guy says it works but needs a new cord. I wouldn't plug it in the way it is, cord is falling apart, and a few other wires inside have breaks.

Looks like it's been modded a little. I'll maybe take it apart tomorrow and look at the inside. Looks like someone added an extra knob, and changed the speaker, but looks like there's part of the old speaker still in there? Small transformer and stuff. Here's some pics of the outside, and I'll post pics of the inside later. Let me know if it's worth doing anything to, or should I use it for decor.

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The last pic is just a pic I found on google that shows what I think the original speaker was like


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Post subject: Re: Anyone have any info on Gebs Amp?
Posted: Fri Feb 24, 2017 12:32 am
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Interesting! Looks like 1940s era stuff. Found this via Google.

http://www.antiqueradios.com/forums/vie ... 6&t=196953


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Post subject: Re: Anyone have any info on Gebs Amp?
Posted: Fri Feb 24, 2017 1:54 am
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BMW2002Ti wrote:
Interesting! Looks like 1940s era stuff. Found this via Google.

http://www.antiqueradios.com/forums/vie ... 6&t=196953


Offhand I'd say that the amp under discussion there is identical to the specimen Jason posted here. The field-coil Lansing speaker is particularly noteworthy and probably dates back to the era when James B. Lansing and Altec-Lansing were one and the same company.

Arjay

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Post subject: Re: Anyone have any info on Gebs Amp?
Posted: Fri Feb 24, 2017 9:32 am
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Cool little amplifier; what is the tube compliment?
How about a pic under the hood if you have one.


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Post subject: Re: Anyone have any info on Gebs Amp?
Posted: Fri Feb 24, 2017 9:53 am
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sfceric64 wrote:
Cool little amplifier; what is the tube compliment?
How about a pic under the hood if you have one.


Check out the off-site link that Steve posted -- some great photos there.

Arjay

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Post subject: Re: Anyone have any info on Gebs Amp?
Posted: Fri Feb 24, 2017 7:26 pm
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Here's some pics of the inside. It was held into the cabinet with just one screw and a square nut.

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Post subject: Re: Anyone have any info on Gebs Amp?
Posted: Fri Feb 24, 2017 7:32 pm
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Oh and the tubes are 6V6GT, 5Y3GT, and 6N7.


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Post subject: Re: Anyone have any info on Gebs Amp?
Posted: Fri Feb 24, 2017 8:03 pm
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Kind of has an early K&F feel to it, although not built quite as well with the exception of the Tranny which looked pretty stoudt.

Interesting for sure.

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Post subject: Re: Anyone have any info on Gebs Amp?
Posted: Sat Feb 25, 2017 2:18 am
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T2Stratman wrote:
Kind of has an early K&F feel to it, although not built quite as well with the exception of the Tranny which looked pretty stoudt.


+1

There is a passing resemblance to the early K&F efforts. I surmise that such construction was state-of-the-art in the mid/late '40s.

Arjay

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Post subject: Re: Anyone have any info on Gebs Amp?
Posted: Sun Feb 26, 2017 11:07 pm
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I haven't come across anything, but the pictures sure help identify a few unsafe/weak areas.
Death Cap
2-Prong power cord
Lack of suitable FUSE
Extension cord used for speaker connection? maybe not but hard to say for sure

plenty of room to work w/ and an easy enough reference given only three tube topology
I'd use the Champ schematics as a guide, since there are no other real comparable models out there and the likely slim chance of finding the original schematic.
It should be a relatively easy fix to get it safe and running again.


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Post subject: Re: Anyone have any info on Gebs Amp?
Posted: Tue Feb 28, 2017 12:50 am
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My silly guess is its from the 18th week of 1944 or shortly there after.
Heres a link to some pre-war amplifiers, mystery amp #1 has some similar components to your amp but I believe that its from a company called something like the Western music manufacturing company(also a smallish LA maker).
http://prewaramps.org/index.htm
I think its probably safe to say that, Leo most likely put this company out of the amplifier business by the late 40's or very early 50's. Along with the war of course and National-Dobro probably helped them out of the lap steel business. Not to many mom/pop survivors in the musical instrument manufacturing industry in the LA-area.

All you really need to do is research the early resistor markings and convert them to a more modern type.
From what I remember its something like, the base color is the 1st digit then dot colors are the 2nd digit
and the end color represents the multiplier. Google for sure will yield results as well as indicators of what the wattage is.
Verify the PT output voltages
Update the power supply electrolytics, possibly add dropping resistors
Sort out the OT/electromagnetic speaker
Install an appropriate fuse and power cord
Replace the bypass capacitors/electrolytics
Add some grid stop/input impedance resistors
Or
Keep it in original condition, although its already been modified w/ a tone pot and maybe a speaker swap.


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Post subject: Re: Anyone have any info on Gebs Amp?
Posted: Tue Feb 28, 2017 4:55 am
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sfceric64 wrote:
I think its probably safe to say that, Leo most likely put this company out of the amplifier business by the late 40's or very early 50's.


Leo kept many of the larger companies behind the eight ball as well until they eventually folded their tents in the '60s. I'm thinking of Standel, Rickenbacker, Guild, a few others. Some of these companies built pretty good amps but they just could not compete with Fender's superior marketing, distribution, and servicing networks.

Arjay

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Post subject: Re: Anyone have any info on Gebs Amp?
Posted: Tue Feb 28, 2017 8:54 pm
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Thanks for the link to the pre war stuff. First thing I guess I'll do is put a new temporary power cord on it and see if it powers up and see what the mod does. The cord now is made up of three cords, about a foot of the original cord that's falling apart, about 6 ft of what looks like an extension cord, and about another 6 ft of another cord with the plug on it.

I understand using the output transformer from the original speaker, but do I need the magnetic part of the original speaker too?


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Post subject: Re: Anyone have any info on Gebs Amp?
Posted: Tue Feb 28, 2017 10:04 pm
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At this point, I'm assuming you are comfortable working inside the chassis and are aware of the hazards?
Also my advice should be considered novice, I am a beginner. The others that have posted in this thread have light years of practical experience and there input is the best you can get anywhere for free.

I would verify ground continuity throughout the amp. Visually inspect all the tube pins and sockets for arc burns, etc. Lightly pull on all connections to make sure nothing is loose. Un-tape and view splice connections.
Measure all resistors and replace as necessary.

If I were going to fire it up in its present state; I would run it unloaded 1st (no tubes) just to check Vac components of the power transformer & line voltages at switch. It shouldn't be run to long; under a few minutes just to verify the PT is functioning as expected. Get/verify the secondary voltage(somewhere about 250-300) at the rectifier tube, the 5.0 filament line voltages at the rectifier tube and the 6.3 voltages going to the 6n7 and the 6v6. Verify the line input voltage @ the on/off switch. Check everywhere else to ensure there is NO Vac.

If they all check out, the next step would be to rebuild the power rail (capacitors, dropping resistors) and replace the electrolytic used for the 6n7 bypass. I wouldn't risk any tubes in the amp or the rest of the components w/o rebuilding the power supply section and replacing the bypass electrolytic.
After a good power supply is in place and the bypass electrolytic changed, you should start adding 1 tube at a time starting w/ the rectifier and verifying its B+ voltage (it may be slightly high w/o the full tube load) and other tube supply voltages. Then the output tube (verifying the plate/screen/cathode/bias voltages). As long as everything checks out(resistors, capacitors, OT, etc.) add the preamp tube and verify all the voltages.

The speaker, OT and EM impedance device could/should be checked w/o any power and out of circuit. Of course never run an amp w/ tubes installed w/o a proper connected load.

Its best to have a spare good set of tubes available for testing as well.

If you plan on testing w/ the current tone/coupling capacitors, measure for DC voltage leaks. Any DC voltage on the edit: meant to say GRID not platesplates of tubes will affect the signal/tone and result in wearing out the tube at a higher rate than normal operating parameters.

Any critical failure(PT, OT, EM coil, Speaker, Tube) will slow you down considerably while trying to find suitable replacements and be fairly expensive to replace.

That's about all the wisdom I can muster off hand for now.


Last edited by sfceric64 on Wed Mar 01, 2017 2:19 pm, edited 1 time in total.

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Post subject: Re: Anyone have any info on Gebs Amp?
Posted: Tue Feb 28, 2017 11:31 pm
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http://i.imgur.com/NHUuPo6.jpg

Wow! Vintage solid carbon resistors. Those can have very nice tonal qualities. Hope they are all in spec (think 10% tolerance is about the best you can expect).


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