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Hoffman Amps Forum image Author Topic: Ampeg SB-12 inspired amp  (Read 233 times)

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Offline Banjan73

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Ampeg SB-12 inspired amp
« on: April 30, 2026, 12:57:34 am »
Hello!
I`ve just tested my new home grown amp. The quest this time was to build a bass amp for my son. I googled a little bit, and the Ampeg SB-12 stood out as a nice candidate for beeing a base/idea to my build. My approach for new builds is to be inspired by classic amps, get the schematics and draw them all over again the way I want them to be.
So this amp is inspired by the 6L6 version of the SB-12. I have (as always) used SS rectifier for HV and the filament is also rectified. The tonestack (James/Baxandall) is almost identical, with minor modifications. Power transformer is from a Tandberg Huldra 4 radio, and output tranny is a Hammond 1650H.
Well. The first test is performed with a band. I tested it with my Les Paul, and the bass player tested it with a double bass and an electric bass. I must honestly say that I liked the bass sound better than plugging in a guitar to this one. But thats the point with this one, to be a bass amp, hehe.
I need to do some minor mods/measurements to this one, and I need to build a enclosure for it. I didn`t have two ECC83 tubes, so the second one right now is a ECC81. But tubes are ordered. I suspect the sound to be a little different with a ECC83 in the second position.
Anyway, are there any recommendations for a loudspeaker for this one? I am looking for a speaker with high sensitivity. My first chioice right now is a Mojotone greyhound 12" (101db/W), but I don`t know that speaker. Any other suggestions?
Heres some pictures and schematics:

Offline Banjan73

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Re: Ampeg SB-12 inspired amp
« Reply #1 on: April 30, 2026, 01:19:32 am »
Ouch!
I just spotted a minor, but important error on hte schematics. B+ is connected earlier in the filter chain.
Heres updated schematics:

Offline Banjan73

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Re: Ampeg SB-12 inspired amp
« Reply #2 on: May 01, 2026, 06:37:05 pm »
No speaker thoughts here? Jensen C12N is supposed to be the original, but 97-98db...
Anything els than mojotone greyhound that I should consider?

 


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