66 Ampeg Gemini from 6V6 back to 7591...

[echodeluxe]

so i have a 1966 Gemini 1 and i love it. someone changed the 7591's to 6V6's at some point and althought the amp sounds good, id like to convert it back to 7591.

i already rewired the PI slot to accept 6GH8's because the 7199 tubes either gone or way too expensive.

i found this on google from the vintage archives: Ampeg 7591 to 6v6 - AMPAGE Archive

anyone ever done this? any insight? thanks guys.

[Chuck H]

Why not check values and rewire it as per the original schematic rather than attempting to reverse engineer a modification? You can't really know what's happened to the amp otherwise anyway and any amp that age should have the resistors checked for drift too.

Ampeg made a lot of different Gemini's (or would the plural of Gemini just be Gemini?). Can you give specifics on the model and features?

[Enzo]

Gemini is already plural, it is Latin for "twins". The singular is "geminus."

[Chuck H]

I guess I knew that if I had thought longer on it! Still... When discussing persons that are astrologically Gemini or amplifiers named as such, might the moniker become a singular?!? Then requiring repluralization!?! (Ha! And I got to make up another word too!)

[Enzo]

And I could throw in "pluperfect" too.


When you start to using constructions like "Geminis are always reading their horoscopes," you are bastardizing the language. Yes of course we do it all the time. But that obviates the -i versus -us question of Latin form. But yes, if we have taken a good Latin word, and turned it into a proper noun, then our own pluralization rules would take over. And in that case it would be Gemini and Geminis.



Now next time someone brings in an old amp, you look at it closely, ponder a moment "Hmmm..." and tell them, "I think this amp needs repluralization."

[Chuck H]

Trimming the Oxy use I see!

[Jazz P Bass]

Astrology?

I have always thought the amp lineup was actually named after rocket designs of the period.

[g1]

Astrology?
I have always thought the amp lineup was actually named after rocket designs of the period.

Agreed, it was Fender who had the Zodiac line of SS amps, but we're getting OT on the OT here .

[echodeluxe]

Why not check values and rewire it as per the original schematic rather than attempting to reverse engineer a modification? You can't really know what's happened to the amp otherwise anyway and any amp that age should have the resistors checked for drift too.

Ampeg made a lot of different Gemini's (or would the plural of Gemini just be Gemini?). Can you give specifics on the model and features?

that was my original idea, but then i kinda figured i would have to trace the whole circuit since i cant be sure exactly what was changed without doing so.

as far as checking resistors for drift, thats kind of a fools errand. the components that should really be checked would be the electrolytics, but those should just be replaced in an amp this age anyway.

as far as features and model, from 64 till 67 the Gemini 1 was largely unchanged. are you asking me on specifics of my amp or are you curious as to that amp model in the first place?

its about 25 watts, 12ax7 and 6gc7 preamp tubes (6gc7 reverb driver) with a 7199 phase inverter and originally 7591 power tubes. solid state rectified. cathode biased.
reverb on channel one, tremolo single 12" speaker (Jensen P12R)

mine is a 66, and some amps in that year had the factory option to have a reverb pot installed on the rear of the chassis to ass reverb to channel two. mine has that mod, but i dont use it. it does work.

i rewired the phase inverter slot for 6gh8's instead of the rare and expensive (and usually microphonic) 7199. i also beefed up the cathode and plate resistors to 100k on the PI. celestion vintage 30 for now, since the original speaker is blown, and way underpowered for this amp anyway.

[Chuck H]

It sounds like you know what you need to do. But why does the need to replace the power supply filters negate checking resistor values?

I was asking after the model to be sure I was searching for the exact right schematic.

I still think a full go through and back to stock effort is ideal for that amp. Most of what is original wiring should be obvious and much of what was changed may be, That should speed the effort.

[Enzo]

The Gemini space capsules were so named because they carried two astronauts - "twins". So mythology or space rockets, the name Gemini is from the same place either way.