12bh7 Carmen Ghia

[murraym3]

Hey. I have been checking this forum for a while and finally decided to get on it and this is my first post.

For music I do local gigs a couple of times a week and some small studio work but my job is audio. Plus I have a humble but useful project studio at home.

My Electronics background is I have helped recap an old Quad eight console and installed a Euphonix CS 3200 plus a few other things here and there. In my own time I tinker with electronics, finally bought an Oscope, and am just past the point of being too dangerous to dig into something with more voltage and bigger filter caps. I've modded my Epi Valve Jr and my amp tech has done some work on my Marshall and Fender but he has also shared much knowledge with me.

I have recently purchased a Dr. Z Carmen Ghia and I'm sure most here have heard what a good amp it is. I love it and am not planning to do any mods to it but I do want to try different tubes. I love the harmonic structure of this amp but am curious if I change tubes for a little more headroom will it have a negative affect on the tone? I guess I should know better but I can't seem to keep my mits out of the chassis and I could use a heads up before I spend the $$$.

Any thoughts, mostly concerning using a 12bh7 or 7025 in either V1 or V2. I think the pinout is the same.

...sorry this post is so long. Thanks.

[rockon1]

Those two tubes mentioned are pretty far apart from each other in terms of gain. The 12BH7 is somewhat the equivelent of a 12AU7 gain-wise around 20mu(compared to a 12AX7 100mu) I believe but draws more current than a 12AU7 so its important to know if the amps up to the task first. The 7025 is a low noise 12AX7. In fact most 7025 versions of the 12AX7 are identical in appearance. Bob

[murraym3]

I agree, the 12bh7 may have too little gain for this amp though I was thinking it may give more headroom, possibly at the expense of loosing the other qualities of the amp.

I would hate to take something and make it less fun to listen to just so I can make it do something it wasn't designed for but I want to try.

Either way, I think a good 7025 would improve fidelity over a 12ax7, yet it could be a case of apples and oranges.

Thanks for the reply and the reminder about finding the requirements for current draw.

[rockon1]

You might want to try a 12AY7(45 mu) or a couple 5751's(70 mu). I recently put a Tung Sol 12AY7 in the V2 of my V32 with good results. Bear in mind its a "real" Tung Sol not one of those name only new production ones.

I want overboard a couple of years ago and bought over 1000 old stock (used) 12AX7's,12AT7,'s 5751's,12AY7's etc.... so I have a vast number to choose from. Differences in gain, tone and break up characteristics(distortion) can range from subtle to big. Bob

[mjones99]

Originally Posted by murraym3

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Any thoughts, mostly concerning using a 12bh7 or 7025 in either V1 or V2. I think the pinout is the same.

...sorry this post is so long. Thanks.

A great little known tube to use for V1 in this or any head is the 12BZ7 which is a low noise, lower impedance version of a 12AX7, actually if you look this tube up each of its two halves are about like a paralleled 12AX7. You can usually get them NOS at Antique Electronic Supply, Antique Electronic Supply for around 7 bucks each. Same exact pinout as a 12AX7. Warning this tube has slightly higher gain than a 12AX7, it is more like 110-120 per half instead of 100 per half, plus the lower plate impedance makes the stock 100K plate loads more like 150Ks on a 12AX7. So you can get some serious grit if you want. My 2 cents, otherwise, 7025s, 12AY7s, or 5751s are sweet in this amp. You should go to Duncan's Amp Pages Software and download the tube data program and you can search tube data by pinout, designator, etc. like you could look up a 12AX7 and then hit a button and see all the tubes with the same pinout in a list.

David Jones (Dr. Distortion) A.A.S., B.S.S., MSCP, CCNA
Designer of the Octal Fatness, Octal One, OctaLuxe, and the .32 Special
Trust me, I'm a Doctor...

[Guitarist]

Get yourself a small collection of tubes and swap them in to taste.