This GA20 'Crest' currently listed on eBay. It's a rare model where, in Gibson-speak, rare doesn't necessarily translate into 'spensive. Preamp is 3 X (not sure, seller doesn't say, see below), twin 6V6s, with a 5Y3 rectifier. This is a transition model ... more Gibson-code for 'didn't stay in the product line very long'. It is not listed in the Gibson Master Service Manual; no public domain schematic. Seller originally mis-ID'd the date ... it's late 50s and probably has a speaker-mounted field coil / output transformer (note little silver corner below the tube cover). The auction amp:
Another GA20 'Crest' from an earlier auction. Preamp tubes unknown, with Weber speaker - note wiring strip highlighted by magenta box:
Older model GA20s with three 6SJ7s in the preamp and twin 6V6s/5Y3; note the use of field coil speakers and the wiring strip:
(edited in, previously overlooked) Mid-50s GA20T
(edited in, previously omitted) later-50s GA20T
Gibson remodeled the GA20 'Crest' into the poor man's GA40LP ... the GA20T Ranger (earlier version). Note that the model now has a circuit board instead of wiring strips. Originally fitted with a standard Jensen P12R and conventional output transformer. The preamp in this model is 12AY7 / 5879 / 6SQ7 / 12AX7 ... like a GA40 except that the GA40 has another 5879 in channel 1 instead of a 12AY7 continuing Seth Lover's interest in using pentodes for preamp gain stages and bringing the GA40s R/C filter into channel 2 (this is my amp).
The last version of the GA20T; 3 X 6EU7 and a 5879 in channel 2, circuit board and, the power tubes and rectifier moved from the left to the right. Originally sold with either a ceramic speaker or Jensen P12S ... both having a shallower profile than a P12R. In the pic below; the speaker magnet only lines up with the opening between the preamp and power tubes because the baffle has been re-cut to allow the speaker to be mounted a little further to the right (this is default's amp):
So .... the auction amp could have 6SJ7s, 12AX7s, or 6EU7s in it's preamp.
Finally, there's an interesting (version 2) Gibson GA2RVT 'Maestro' on ebay Here. It has one more preamp tube than the tweed and 'crest' model Gibson GA19RVT Falcons and it also has the R/C filter inherited from the GA40LP. This amp is in the Gibson MSM at page 71; appeared first in the vinyl tweed, this is the last version. 12" speaker, monitor out ... I think it's going to go in the higher 3 figures:
Another GA20 'Crest' from an earlier auction. Preamp tubes unknown, with Weber speaker - note wiring strip highlighted by magenta box:
Older model GA20s with three 6SJ7s in the preamp and twin 6V6s/5Y3; note the use of field coil speakers and the wiring strip:
(edited in, previously overlooked) Mid-50s GA20T
(edited in, previously omitted) later-50s GA20T
Gibson remodeled the GA20 'Crest' into the poor man's GA40LP ... the GA20T Ranger (earlier version). Note that the model now has a circuit board instead of wiring strips. Originally fitted with a standard Jensen P12R and conventional output transformer. The preamp in this model is 12AY7 / 5879 / 6SQ7 / 12AX7 ... like a GA40 except that the GA40 has another 5879 in channel 1 instead of a 12AY7 continuing Seth Lover's interest in using pentodes for preamp gain stages and bringing the GA40s R/C filter into channel 2 (this is my amp).
The last version of the GA20T; 3 X 6EU7 and a 5879 in channel 2, circuit board and, the power tubes and rectifier moved from the left to the right. Originally sold with either a ceramic speaker or Jensen P12S ... both having a shallower profile than a P12R. In the pic below; the speaker magnet only lines up with the opening between the preamp and power tubes because the baffle has been re-cut to allow the speaker to be mounted a little further to the right (this is default's amp):
So .... the auction amp could have 6SJ7s, 12AX7s, or 6EU7s in it's preamp.
Finally, there's an interesting (version 2) Gibson GA2RVT 'Maestro' on ebay Here. It has one more preamp tube than the tweed and 'crest' model Gibson GA19RVT Falcons and it also has the R/C filter inherited from the GA40LP. This amp is in the Gibson MSM at page 71; appeared first in the vinyl tweed, this is the last version. 12" speaker, monitor out ... I think it's going to go in the higher 3 figures:
J