50/50 - Anyone tried 5751's?

Triaxis, Quad Preamp, Stereo Power series, Recto Preamp

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Pyramid Head
Bottle Rocket
Posts: 18
Joined: Sun Apr 08, 2018 12:58 pm

50/50 - Anyone tried 5751's?

Post by Pyramid Head » Wed May 09, 2018 4:21 am

Hello everyone!

I've got a TriAxis going through a 50/50 (NOT a Stereo 2:50), with two 1x12" Recto cabs (skipping irrelevant gear).

I've had great success running those tubes in the 50/50:
-> 3x JJ ECC83S (Matched & Balanced)
-> 2x Mesa STR 420
-> 2x SED Winged =C= 6L6GC
(The 2 pairs of 6L6 complemented each other very well.)

But now it's time for a full retube and I've got a few options on which I'd like your advice.

I'll be running Ruby 6L6GCMSTR/Mesa STR 440.

For the Driver and the 2 Phase Inverters I've got the following Matched & Balanced tubes (3-4 of each):
-> JJ ECC83S
-> Sovtek 12AX7LPS (115/115 Gain... on the high side)
-> Ruby 12AX7AC5 HG+ (110/110 Gain... Strong too)

And to my surprise I found an old JAN GE 5751 that I never used and forgot I had. Not only is it Matched & Balanced, but it has a Gain of 90/90, so it's not so much a huge drop in gain as a different tone from a 12AX7.

I was wondering if any of you tried 5751's in their 50/50, and what did it change? Feel, Headroom, Volume, Tone...?

Since I only got one 5751, I was thinking I might try it in the Driver position, and use a pair of MPI from what I have & listed earlier.


Mark II
Posts: 93
Joined: Tue Aug 01, 2006 5:31 pm

Re: 50/50 - Anyone tried 5751's?

Post by joey_truelove » Tue May 29, 2018 7:46 pm

In the power-amp the lower gain level is basically going to make the outputs harder to push and would likely only make it quiteter. Couldn't say this would be a desirable trait.

Gain experiments in the pre-amp of an amp makes more sense, since you still would have plenty of opportunity to reach good signal level before the signal reaches the outputs.

'But aren't the input twin tetrodes bit a pre-amp per se?' you might ask. Well, these work more like attenuators to allow you to lower the signal going into the outputs. At full tilt they basically just pass the signal unaltered.

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