Hoffman Amplifiers Tube Amplifier Forum
Other Stuff => Solid State => Topic started by: DummyLoad on January 05, 2021, 01:23:42 am
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positively THE best sounding SS guitar amp i have played to date. no kidding. no clue what's behind the goop that inspired the H.A. Dumble secret squirrel crap, but it has magic. (assume that it's preamp ckts., 'mkay?). :icon_biggrin:
for testing i'm playing into an open-back cabinet with a JBL MI50 and it sounds glorious. very "warm" sounding for a SS amp. the tremelo is fantastic, goes from a light wave to hard whomp-whump. the speed is lacking in the upper end, but is still pleasant overall.
some background: this came to me via an old roommate. it has had a rough life and the mating speaker cabinet with the JBL D130 is long gone! :sad2: hopefully now has better days to come. obviously stored in a damp, hot, and dusty, environment - all the chrome is pitted, the tolex is dried out, moldy, and peeling away from inside of the cabinet, and the aluminum faceplate has come corrosion. the good is that the lettering is still intact. the controls work and only the volume on one channel and the trem intensity pots needed a good dose of deoxit. now in retrospect i was in the shed looking for aprilia M/C parts, and had to move it out the way yet again - being in a foul mood, that's IT this thing has to go! so it was headed to the $#!t for sale heap. i had second thoughts, thinking, ya kno', i bet that damn thing still works - so glad i didn't sell it as-is now.
the securing scheme for the main PS filters and PT CT ground was an issue. consisted of a ground lug attached on TOP of 2 plastic cable clamps that were used to secure the caps. the plastic of the cable clamps literally crumbled away leaving the "ground lug" floating. bob crooks, surely you knew better than that? shame! at the very LEAST, bob could have put the ground lug next to the chassis with it's own jam-nut, and not on top of the heap of plastic that was sure to expand/contract and loosen over time. see pics in link for clarification. needed caps! it had 1000uF 25V and all i had on-hand were 2200uF 50V that fit with leads extended (see pics). i plan to order some cable clamps that fit to secure the caps. the small 2200uF does not need clamping. will drill another hole for the cap clamps. the ground lug stays put.
this unit has a quasi-complementary AB output stage with a bipolar 25V power supply. has delco brand transistors for the output stage: 2 x 100W DTG-110 TO-3 output transistors. i believe that the phase inverter is transformer. haven't traced the circuits, because most of the preamp circuits are formed in epoxy modules. it appears the the power amp driver is the 2N663 TO-3 package next to the audio transformer. all the transistors and date marked components have dates that correlate to mfg. date of april 1965, so i do believe that i am the first person to take an iron to it.
https://www.dropbox.com/sh/celi0j694i4xrdx/AACJDuJyk0YC_2DY1Sqd1BK4a?dl=0
--pete
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obviously stored in a damp, hot, and dusty, environment
maybe your squirrel magic? :icon_biggrin:
I like the GM PA!
picture a skinny clueless 19yr old, being handed a PACE work station, with the words, "now Son, all you have to do is clean out all that goo, don't destroy anything, the whole Ship depends on you fixing that module" :w2:
glad you took the time to bring back a dinosaur from the way back days! :occasion14: