Changing the pinout on a preamp tube.

[fretknot]

Has anyone made this modification? I'm considering changing the pinout on an amp that uses a 6EU7 to accommodate the 12AX7 and other iterations of the 12A*7/5751 variety. I think it will offer more flexibility, and the 12AX7/ECC83 is a common tube and the 6EU7s are going for higher prices.

 

[corliss1]

You definitely wouldn't be the first or last.

 

[Peegoo]

You bet.

You're not really changing the pinouts on the tube; you're modifying the circuit to accommodate a different tube topology. Quite common, actually.

 

[fretknot]

You bet.

You're not really changing the pinouts on the tube; you're modifying the circuit to accommodate a different tube topology. Quite common, actually.

I guess I didn't phrase that question properly...anyway I'm trying to get this Skylark up and running. It may require re-populating the resistors and some of the smaller capacitors. I think the circuit has some heat damage.

 

[Swirling Snow]

That is what you have to be careful of. Changing parts so the tube works is fairly straight forward. Accommodating increased current draw, heat dissipation, etc. is the challenge. Still, I think it's a worthwhile swap, for reasons you mentioned.

 

[uriah1]

I remember an old gibby amp my amp tech was going to do that to.
He decided not to

 

[fretknot]

I went ahead and modified the circuit to accommodate the 12AX7. The amp is up and running now, with a JJECC83S in V1. It was touch and go with some other repairs for awhile, but it's going well and the amp sounds pretty good.

 

[CoolBlueGlow]

Yup, I've done this - recently in fact. Got rid of the 12AX7 in a circa 1977 five tube Princeton and went with a 6DJ8 at V1...just for grins.

Works great. 6DJ8 is a frame grid dual triode. Mighty quiet and non-microphonic.

 

[Powdog]

Why? A 6EU7 is a great preamp tube, and there are plenty NOS around for less than a NOS 12AX7 (crazy prices). Time and effort could be better spent on different parts of a Crestline circuit. Just my useless 2 cents.