5751's instead of 12ax7's?

[docmh]

My Vibro-King has 12ax7 preamp tubes. I was thinking of trying a Jan 5751
in the gain stage slot. I read this could improve clean headroom. Since it's 70% output of a 12ax7, what would the difference be if I used one in the phase inverter slot? How about in the reverb slots? Any harm to the amp?

Appreciate any input.

[trey85stang]

they are a drop in replacement for 12ax7's they pull the same current and it is a safe swap.

[skylabfilmpop]

Try it in the first (v1) position, sounds great there in my bassman, deluxe reverb, tweed deluxe and /13 cj11 and jmp Marshall!

[Blue Strat]

You can use them anywhere a 12AX7 is used. Don't use them in a reverb driver circuit designed for 12AT7s...you'll kill the tube even if slowly.

Try all sockets, one at a time, and see what you think. No one can describe what you'll hear better than hearing for yourself.

[Ace_F4i]

I just tried rolling one of those into my 5150 to try to get a little better clean tone. Honestly i didn't think it was really worth it. There was a noticeable drop in gain and an increase in clarity/punch when i tried it in the V2 (i have a NOS in v1 already) and thinner sounding gain in V3. I didn't try it in the phase inverter but i got a 12ax7a w/ matched sections for that.

Overall it definitely gave the amp a more rock crunch characteristic and made my clean tone better but it appeared to decrease my sustain (a LOT of the gain is bled to ground in a 5150) and definitely neutered my lead channel. My final conviction: this tube would be good in a V2 position if you have an overdrive pedal to make up for what is lost.

[Blue Strat]

I just tried rolling one of those into my 5150 to try to get a little better clean tone. Honestly i didn't think it was really worth it. There was a noticeable drop in gain and an increase in clarity/punch when i tried it in the V2 (i have a NOS in v1 already) and thinner sounding gain in V3. I didn't try it in the phase inverter but i got a 12ax7a w/ matched sections for that.

Overall it definitely gave the amp a more rock crunch characteristic and made my clean tone better but it appeared to decrease my sustain (a LOT of the gain is bled to ground in a 5150) and definitely neutered my lead channel. My final conviction: this tube would be good in a V2 position if you have an overdrive pedal to make up for what is lost.

Different amps, different sockets, different players, different opinions.

[GearHeadFred]

Different amps, different sockets, different players, different opinions.

+1 on this. I find Fender AB763 circuits very sensitive to preamp tube TYPE swaps in V1/V2 as well as V6 (PI), mostly in the clean headroom department.

[59Vampire]

I use on in v2 of my 5e3 in lace of the ax7 and it really tames the wooliness

[Gris]

MAY increase headroom in V1, V2 (will be cleaner further up the dial but less volume at same point on dial...). Likely decrease headroom in PI. Reverb is a taste thing, but usually less gain-y tubes work better there.

[elkym]

SRV like the 5751, In your phase inverter, esp. if it's a matched triode, it will improve headroom, if only just a touch. In your Preamp I'm not sure what it should do...

SRV used them in all of his preamp stages if I recall... not sure on that, though.

Try it out! Let your ears do the judging!

[cochese]

I would have to ask how loud are you running the Vibro King and what type of guitar, pickups, efx? That's a pretty loud amp to begin with.

As for the 5751 I have heard all the SRV stories but when ever I try the 5751 I put the 12ax7 back. Your results may vary. I would probably try a 12AT7 in the PI slot before the 5751.

[docmh]

I appreciate all the input. I'll take it to rehearsal tomorrow and try different tubes. I'm playing A Heritage Roy Clark semi-hollow guitar
with Tom Holmes pickups. I can't get the amp past 4 even at gigs. I like playing clean but this amp breaks up past 3 with the humbuckers. I really don't like pedals but if I use one it's a DOD preamp 250 with just a little edge or an RC booster, if I play at lower volumes.
The one thing I do know, is I like SED Wing C power tubes the best in this amp. I love the sound of this amp with the volume up to 3. After that it
breaks up a little too soon for me, so I'm trying to improve the headroom. I tried the TIm C mod I saw on some sites but really didn't like it. Didn't sound like a VK to me anymore so I put it back to stock.

[Ace_F4i]

Different amps, different sockets, different players, different opinions.

exactly. i was just stating what happened in my case. Generally the amp will distort less and you can expect this tube to have a nicely detailed harmonic content (more than any of the new production tubes i've tried) in an initial or tone stack socket.



If you want more volume/headroom before your power section starts to break up i'd recommend a boost pedal. Some of them are designed specifically for this purpose and are designed to be transparent. I recommend the Xotic RC booster- it's very transparent but has overdrive too. The keeley katana is nice too and can get a lot more bang out of single coils. If you want volume check out super chili picoso.. 30db clean uncolored boost. They're all actually relatively inexpensive compared to other boutique level pedals... i think around $150-$200.

[cochese]

Are you using the second input. This is usually padded down in most Fender amps and should give you more clean headroom. You will lose a little high end but can make it up with the tone controls. As that is a non master volume amp you are probably hitting the output stage hard with the humbuckers. I would try the 5751 or 12at7 in the PI slot. A 5751 in the preamp will work but might be too dark with the humbuckers. Just experiment. The other thing to try as I recall with that amp there is a loop. I believe the the guitar hits the reverb circuit first. You could try just patching into the efx return and see if you get more clean headroom. It might be that 6v6 needs replacement.

[espinete]

i love 5751's tubes as a main tube for v1 and v2 specially for cleans.sweeter tone for sure but still with balls for me.increases headroom..,etc.,.
but it depends of the amp.get some cheap 5751 tube from a friend and try it by your own in different positions

[slegros]

I wasn't a big fan of using a 5751 in V1 in either my Bluesbreaker or my Ampeg. It does give a bit more headroom, but to me it was very different tonally to a 12ax7. Its definitely a different sound to a 12ax7. Whether that sound is for you or not depends....