5751s in a vox AC15C1


trying some things to clean up my AC15C1 a little bit. currently it sounds kinda grainy and noisy and i'm hoping some fresh tubes will help. i know voxes seldom get truly *clean* and i'm fine with that, but what i'm getting out of it now is not what i would consider chime.

as it needs new tubes anyway, i'm curious to hear from folks who have tried 5751s in their preamps. do you like them? did you go back to 12AX7s? which brand did you use? my budget is not large, but i see reasonably priced options from JJ (which i would prefer to avoid), Tung Sol, TAD . . . anything else of which i should be aware? thanks.

edit: i suppose i could consider 12AY7s or 12AT7, too.


I haven't tried the 5751's but of the few preamp tubes I have tried I like the Tung Sol 12ax7's best. They seem to be lasting well past others and they sound great to me.
They're easy to find too. I have been using the JJ EL84's for power tubes and I think the are very good.

I'll be interested to hear from anyone that can speak to the gain differences of the 5751's vs the 12ax7's? I wouldn't mind more headroom. I have read that the 5751's are 'brighter' but that was not from an authoritative source. If true, it would not be more desirable for me. They are 'mil spec' so they may last longer?

Interested is what others have found.

Clyde Billt

Gold Supporting Member
I had a Phillips 5751 in my AC15C1 for quite a while.
I liked it but it didn't give me as much clean headroom as I was expecting. Which was the reason I tried it.
But it didn't have as much mushy gain when everything was dimed. I liked that.

It was nice when slightly overdriven with a pedal (Eternity Burst), and with the volume back a bit it was very clear and articulate.
I have read that the 5751's are 'brighter'
Not noticeably brighter per se but more defined. To my ears anyway. I think the cele blue helped in that respect as well though.

I did go back to ECC83's (12AX7). Now I use an old Telefunken in V1. Cleans are lovely and the overdrive is really smooth.


I tried both a TS 12AT7 and a JJ 5751 in V3 of an AC30C2. I preferred the 12AT7 but I'm still giving the 5751 another chance. You may want to try the V2 position for type experimenting, that may have the most impact on the gain. In V1, it may change the amp too drastically. Try Tungsol.

Timbre Wolf

Hyperspatial Gravity Surfer
Platinum Supporting Member
I've used a plain ol' common '60s GE 2-mica gray-plate 5751 in V1 of my AC30CC1, and was surprised at how much I liked it there. I've never found another amp where I like that tube (and have preferred other black-plate 5751 in other amps). The V1 tube governs the "Normal" channel initial input and provides an extra gain stage for top boost channel. It gave me a little more sweep on the volume settings, and rounded the treble edge down a bit. Of course, it did not displace my late-'50s long-plate Mullard ECC83, for my favorite sound, but I've kept the 5751 in place there for general use.

- Thom


a Blackburn Mullard in V1 will clean up a lot of the harsher top end that comes with cheap Chinese (modern production) tubes.

it's worth springing for an ANOS one if you can.
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