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Hello, and I'm a brand new addition to this forum (you guys sure have a fun place here). Anyways....

I've been reading everyone's commentary on the different tubes that may be installed in this preamp section - and I've come up with a question. Now - I'm not saying I actually want to do this, but - could I put a complete set of 12AT7s in the preamp (all 4 tubes)? What about 12AU7s? Can I swap them around in any combination I can think of?

I'm interested in any "tone-related" words anyone might have, but I'm really wondering about the amplifier's tolerance for this kind of experimentation (will I stress or damage it?). This has been my main (and usually only) gigging amp for about 35+ years, and I don't think I could live with myself if I accidentally killed it.

<Hylight 4 input, bought new in about 1973, with one internal mod - that I do not plan to undo (hence this opening question)>

Thanks all!

"Toto, I don't think we're in Kansas anymore"

Hi and Welcome to the Vintage Hiwatt Forum!

I may get overruled by the technical experts, but I don't think you would be placing your amp in danger by experimenting with 12AX7, 5751 or 12AT7 tubes in various locations. The 12AU7 gain is much lower than the above and I don't think you'd like the results.

To my untechnical way of thinking, it's kind of like squeezing a balloon. The pressure you place (or relieve) in one place is transferred to another. In other words, it's a balancing act.

Also note that V2 and, especially V3, have less impact on tone. I typically run a modern production tube in V3, because that position hasn't warranted vintage NOS stuff.

Let us know your results,
Dave

P.S. I deleted your duplicate post .

Dave,

First off - thank you sir for cleaning up after me. I'll try not to be so messy next time.

As near as I can see, everything you've said is pretty consistent with what I've read thus far. I will do a little experimentation based on what you've offered here. What happened was that I double checked the identity of all the tubes while considering a complete retube (and recap) of the amp (I've just put in my 4th set of output tubes... =C=s this time). I found that the 12AT7 was in the wrong position - V3 insted of V4. I know it's been this way for 20 years at least (the tubes all got replaced in it while it was on loan to someone else for about a year - and i imagine that's when it happened). The AT7 is the only Mullard in the set, so I figure they couldn't find a replacement for it... and then they put it back in the wrong place.

I expect you know how it is: You spend half your life with an amplifier and you get so used to it's peculiar quirks that you can't make friends with any other amps. They are just too unlike your bread and butter favorite (at least that's how it is with me). I'm afraid to rearrange it for fear of how it might change - but I would like to correct that mistake. It's been gnawing at me ever since I discovered it.

I'm thinking I'll pick up a quality 12AX7 for V1 and a 12AT7 for V4 - and that way I'll have a diverse enough set of tubes in my hand that I can meaningfully try some combinations. I've been haunted by the feeling that this amplifier could perform better, and maybe the misplaced AT7 has a detrimental effect (though, my particular mod might like some slightly lower gain stuff anyways - and I think the AT7 is a little less gainy than the AX7?)

Thank you for responding to my question, Sir. I've certainly got the wheels in my head turning now.

-Bob M-

bmellott wrote:
I expect you know how it is: You spend half your life with an amplifier and you get so used to it's peculiar quirks that you can't make friends with any other amps.

You're preaching to the choir, my friend! I lugged the same Twin Reverb thousands of miles, for nearly a couple of decades before being brave enough to try something else as my bread and butter amp. Now, I'm glad I "took the risk" on Hiwatt .

One of the heads I purchased came with a 12AT7 in V1. Didn't sound quite right to me until I switched the tubes around. Only way to find out with your own amp is to experiment.

Dave

Yes, any tubes with that pinout will work, sort of, and won't hurt anything. 12AX7, 12AT7, 12AU7, 12AY7, ...

I really like a 12AX7/ECC83 in V1, but feel free to experiment.

--mark