For those of you who may someday be called upon to work on one of these as I was the other day please note this about the commonly found schematic for this amp.
V1 is indeed a 12AX7 as the tube lay out shows and as the pins are numbered on the schematic, but the schematic has V1 labeled as a 6EU7 which IT IS NOT!
The labeling of the tubes on the schematic would have you believe that the amp uses three 6EU7s and it only uses two.
Eipiphone EA-33RTV
Moderators: pompeiisneaks, Colossal
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Stevem
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Eipiphone EA-33RTV
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Eipiphone EA-33RTV
It might have been an undocumented mid production change. I've seen several amps that used 6eu7's changed to 12ax7's.
Tube junkie that aspires to become a tri-state bidirectional buss driver.
Re: Eipiphone EA-33RTV
Nothing about the Gibson/Epiphone amps from the 1960's should surprise anyone. I agree, it is rather unusual to see the schematic with the 12AX7 pin numbers and 6EU7 in the tube chart. This was Gibson's way of delivering a transitional model?
To put a finer point on this, as an example, I own a GA20-RVT. It has a factory schematic glued into the cab. The schematic is 100% accurate to the amp that is in the cab. Yet, there are two other known versions of this amp for which you can find schematics on the internet, but mine is no where to be found. It's not that mine is so different from the other two -- differences are insignificant -- just that until I saw mine, it appears no one was aware of a 3rd version. I was brand new to tube amps when I bought this amp. When I posted on line for help (in the dark ages when a forum was text only) no one wanted accept there was a 3rd version.
I was unsuccessful in separating the schematic from the cab. I tried and decided to stop before I damaged it beyond recognition. I wanted to be able to scan it so I could attach it to an email. (I was working at an art college and could get access to a scanner. Digital cameras existed. They were large and clunky, and either low res or very expensive and landline phone didn't take pictures.) I ended up drawing a copy by hand. So, thanks for the stroll down memory lane.
Gibson was well known for making the amp du jour -- using whatever was on the shelf that was close enough. And mine is wired for 6EU7's.
To put a finer point on this, as an example, I own a GA20-RVT. It has a factory schematic glued into the cab. The schematic is 100% accurate to the amp that is in the cab. Yet, there are two other known versions of this amp for which you can find schematics on the internet, but mine is no where to be found. It's not that mine is so different from the other two -- differences are insignificant -- just that until I saw mine, it appears no one was aware of a 3rd version. I was brand new to tube amps when I bought this amp. When I posted on line for help (in the dark ages when a forum was text only) no one wanted accept there was a 3rd version.
I was unsuccessful in separating the schematic from the cab. I tried and decided to stop before I damaged it beyond recognition. I wanted to be able to scan it so I could attach it to an email. (I was working at an art college and could get access to a scanner. Digital cameras existed. They were large and clunky, and either low res or very expensive and landline phone didn't take pictures.) I ended up drawing a copy by hand. So, thanks for the stroll down memory lane.
Gibson was well known for making the amp du jour -- using whatever was on the shelf that was close enough. And mine is wired for 6EU7's.
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Stevem
- Posts: 5144
- Joined: Fri Jan 24, 2014 3:01 pm
- Location: 1/3rd the way out one of the arms of the Milkyway.
Re: Eipiphone EA-33RTV
Yup, I know the Gibson strangeness very well.
For example my 1954 Gibson GA77 with a recording jack and two 12AX7 preamp tubes, yet a octal 6J5 for a splitter took me near 2 years of looking to find a schematic that matched it!
This model Gibson May be one of the first guitar amps to use a duel triode 9 pin tube outside of the Hi Fi world of amps.
For example my 1954 Gibson GA77 with a recording jack and two 12AX7 preamp tubes, yet a octal 6J5 for a splitter took me near 2 years of looking to find a schematic that matched it!
This model Gibson May be one of the first guitar amps to use a duel triode 9 pin tube outside of the Hi Fi world of amps.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!