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previous: Troy I've got a friend's GA-5T right now... -- 9/15/1999 5:11 PM

Re: GA-5T Different Tubes

9/17/1999 3:42 PM
Carl B.	Re: GA-5T Different Tubes That's exactly the amp I have. And Bruce's comments is right on the money: It's Completely Hip. Four things I've done to mine: 1) Filter cap job. 2) Change the wiring on the 6EU7 to accept 12AX7 variants. Much more choice on tube manufacture with the 12AX7. 3) A wire jumper on one pin of the 6C4 socket across to the another pin (sorry, forgot which ones) that allows for using a 6AB4 in that socket. The 6C4 is one half of a 12AU7, the 6AB4 is one-half of a 12AT7. So you can guess what that just did. El-Rip-ero! Check Duncan's site on for wiring of those two tubes, you'll get the mod as soon as you see the pin-outs. The jumper-wire doesn't preclude still using 6C4s in there, but you won't want to. 4) Put a killer speaker in there. Takes this amp into the "sublime" realm. I found an ancient PM10H Jensen (yes, "PM" this thing has a coffee-can full of alnico for a magnet and must be from the early 50s). I'd suggest getting one of Ted Weber's ring-alnicoed 10" variants (Blue Pup?) to turn your friend's amp into magic. The only thing is, when you do all this, you'll kick yourself. It's your friend's and you will absolutely have to have it. Better to buy it now from him on the cheap, then fix it up for yourself, or you'll be the "Good Martyred Samaritan." Best believe me on this!

9/17/1999 3:42 PM

Carl B.

Re: GA-5T Different Tubes

That's exactly the amp I have. And Bruce's comments is right on the money: It's Completely Hip.

Four things I've done to mine:

1) Filter cap job.

2) Change the wiring on the 6EU7 to accept 12AX7 variants. Much more choice on tube manufacture with the 12AX7.

3) A wire jumper on one pin of the 6C4 socket across to the another pin (sorry, forgot which ones) that allows for using a 6AB4 in that socket. The 6C4 is one half of a 12AU7, the 6AB4 is one-half of a 12AT7. So you can guess what that just did. El-Rip-ero! Check Duncan's site on for wiring of those two tubes, you'll get the mod as soon as you see the pin-outs. The jumper-wire doesn't preclude still using 6C4s in there, but you won't want to.

4) Put a killer speaker in there. Takes this amp into the "sublime" realm. I found an ancient PM10H Jensen (yes, "PM" this thing has a coffee-can full of alnico for a magnet and must be from the early 50s). I'd suggest getting one of Ted Weber's ring-alnicoed 10" variants (Blue Pup?) to turn your friend's amp into magic.

The only thing is, when you do all this, you'll kick yourself. It's your friend's and you will absolutely have to have it.

Better to buy it now from him on the cheap, then fix it up for yourself, or you'll be the "Good Martyred Samaritan."

Best believe me on this!