Oahu Alamo Model 12 restoration opinion?

D-Lab

Member
Messages
16
Hello all,
I went to a Ham radio swap meet today and picked up a rough Alamo model 12 combo amp. The back is missing. Original speaker missing. Cabinet is rough, missing veneer. Missing tubes. Filter cap blasted.
Put it on the bench. Replaced the tubes/speaker/output transformer and installed new filter cap. Plays now and sounds good, however lacks gain due to the stock 6SJ7 tube. So, the question is, do I update the preamp with a 6SL7, to obtain the gain, or do I leave it stock, so not to offend the collectors? The amp is far from stock now with my repairs. I plan to make a new rear panel. The original was nothing more than 1/2 plywood. Oh yes, I also found that this amp was not wired correct as per the Riders schematic. Screen was circuit mis-wired, although I saw no evidence that the amp had past maintenance? I plan to make a schematic, in case you guys need it.
Heres a few pics of the project.
TD


 

joelster

Silver Supporting Member
Messages
3,370
I'd keep that one as stock as possible. I guess the mod you're talking about could be reversible...

You might find that you get more gain out of it if you replace the old coupling caps.
 

Sweetfinger

Silver Supporting Member
Messages
12,969
Not all amps match a published schematic. A 6SJ7 should have plenty of gain and would be my choice over a dual triode. You can experiment with different preamp resistor/cap values.
You can reference a 5C1 Champ, Silvertone 1331, Gibson Les Paul Jr.,
and various old Valco amps. My 1331 is such a sweet sounding little amp...

http://myfenderchamp.files.wordpress.com/2010/03/champ_5c1.png

http://s286.photobucket.com/user/cerrem/media-full//1331_schematic.jpg.html

http://prowessamplifiers.com/schematics/thumbs/GibsonLes_Paul_Jr.gif

http://schematicheaven.net/bargainbin/dickerson_mots_1946.pdf
 

D-Lab

Member
Messages
16
Very good Sir, I appreciate the input.
Will stick with the 6SJ7.
Will swap out the coupling caps tonight and see if it perks up
 

Baxtercat

Silver Supporting Member
Messages
12,701
I've had several of the pink caps blow on old finds like this.

FoMoCo brand tube...6V6s [lower current draw] for car radios. :)

 






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