New build ideas/recommendations

[davidwpack]

Oi! I'm starting my preliminary ideas and rough draft drawerings fer my next build. As some may have read in a previous post I made about restoring a couple of Ampeg B25-Bs I am more than thoroughly impressed with these amps for guitar. I've bounced around a couple of ideas but I keep coming back to the Ampeg in at least as far as the preamp goes. The hang-up is that these amps had a 7199 preamp tube which was replaced with a 6U8A and adapter.  I'm wondering on how integral these tubes were in the sound of the preamp. I don't particularly want to use either tube but I don't want to make a change that is fundamental in the sound of this amp. Anyways, I was just wondering if anyone had any ideas or recommendations on a suitable replacement that is tonally and functionally similar and that is currently in production. Any ideas or suggestions would be cooooooool!

[PRR]

You want a pentode and a triode, loaded and biased very-nearly the way Ampeg ran the 7199.

It does not have to be a dual-tube, if you are scratch building. I'd be inclined to try 6AU6, a once VERY common pentode, plus half a 12AU7 (which is what the T side of 7199 is). 6AU6 is $8-$10 at TheTubeStore, and may turn up cheaper at other places, cheap enough to buy a bunch and sort them for sonic quality (mostly good but a few hissers or clankers). Save the best to stay with the amp and dump the others on eBay.

[davidwpack]

That sounds very interesting. I'll have to figure how to incorporate this into a design. Maybe not as complicated as it sounds. I'm pretty sure that I bought a few 6AU6 a while back for a Silvertone Twin Twelve (1474) I've got. I'm gonna dig that amp out of the closet and try to figure out what they designed around that tube. Thank you for your response!

[sluckey]

6AN8 is a very similar tube with a different pin-out. Sunn used these for a pentode gain stage and triode cathodyne phase splitter. The Sunn circuit is very similar to the Ampeg circuit. I would expect they both sound about the same. Hoffman has several in his yard sale...

     http://hoffmanamps.com/MyStore/catalog/yardsale.htm

[davidwpack]

Hey thanks. I'm looking at the 6AN8 right now. It seems like there was/is a viable market for these triode-pentodes. I wonder why there aren't any in production or if there will be a future production of these tube types.

[Sonny ReVerb]

I've been researching this as well, since I fell down the Ampeg rabbit hole [thanks for the push, Steve ;)]. There is some good info on this page, though it's a bit hi-fi oriented. They are more concerned with distortion reduction than guitar amp aficionados.

[davidwpack]

Ha. I just bookmarked that page minutes before you posted that. Yeah that is some great info.

[sluckey]

6GH8 is another option. Cheap too! Check out the first three items on this page...

https://www.tubesandmore.com/search/node/6GH8A

[davidwpack]

Ohhhh wow that is incredibly cheap. Thank you! In your opinion, do you think it would be safe to build an amp with a tube that's no longer in production? I guess at that price there can't be an incredible shortage of them huh? By the way Sluckey, I'm thinking I'll probably model a couple of your amps as far as switching channels rather than having the 4 inputs. Also having one of the stacked pots for the ultra hi switch. I'm not crazy about the ultra lo switch. I don't use it. It sounds more like a high cut switch rather than a low boost as there is an audible, noticable volume drop when engaged. Might be better suited for bass guitar but for guitar I don't like it at all. But yeah, I'm gonna look at that tube and maybe scoop up a bunch of those. Thanks again!

[davidwpack]

Hey, just ordered a small batch of the 6GH8 tubes. Have any of you guys done much with this type? I'm wondering what values I'd have to alter to use 6V6 or EL84 rather than the 7027A type that's in the Ampeg B25-B.

[sluckey]

I'm wondering what values I'd have to alter to use 6V6 or EL84 rather than the 7027A type that's in the Ampeg B25-B.

I would use 6L6. No changes required other than maybe socket pin numbers.

[davidwpack]

I was thinking about the 6L6. I was thinking too that it'd be cool to get that preamp in a lower power version. I'm still working out some of the design ideas. I've got a few swimming around.

[PRR]

7027 is 6L6GC with a funny pinout. I think at some point it was a penny less (perhaps because the pinout locked-in replacement sales).

6V6 and EL84 are distinctly smaller tubes, you are getting away from the theme. But they are no harder to drive and I would make no change.

[davidwpack]

Good deal. Thanks. I wasn't quite sure.