Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: john59 on November 12, 2012, 02:36:35 pm

Title: Correct primary impedance for a GA-20 OT
Post by: john59 on November 12, 2012, 02:36:35 pm

Does anyone know the correct primary impedance for an early 1950's Gibson GA-20?

Title: Re: Correct primary impedance for a GA-20 OT
Post by: Geezer on November 12, 2012, 03:36:18 pm

Knowing Gibson, they probably used several different output transformers for that amp designation over the years.

Tweed deluxes from that time used an 8k output. I suspect the Gibson used very close to the same value. 6.6k came later in the black face deluxes.

$0.02

G

Title: Re: Correct primary impedance for a GA-20 OT
Post by: john59 on November 13, 2012, 11:36:19 am

Yes. I figured it might be around 8K-8 ohms. That seems about right. The ToneClone (Mercury Magnetics) guy says that one of his is 9K-4 ohms! But they are a little coy about there spec details.
I was hoping that if someone out there has an orig GA-20 they might say. John.

Title: Re: Correct primary impedance for a GA-20 OT
Post by: jazbo8 on January 11, 2014, 12:11:29 am

Bump.

So any 6.6k-9k OPT should work? How about the wattage? The stock one looks quite small and is said to be the key to get the distortion in the amp. Anyone tried to clone the amp, if so, please share your experience.