7199 to 12ax7 swap; is this possible?

[pete kanaras]

amp is an ampeg reverbrocket2. ampeg used a 7199(which is a pentode/triode)as the phase inverter in this amp. stock it's way clean sounding and a bit anemic so i would like to hit the power section with a stronger signal. i'd like to know if i could pop in a 12ax7 or 12at7 in it's place w/o harming anything. does the socket need to be rewired? any guidance would much appreciated

[Wakarusa]

For starts, you can't substitute a 12A_7 for a 7199 without a serious rewire of the socket and surrounding circuit. Second, a direct substitution probably wouldn't get you what you want.

The triode section of the 7199 has performance similar to a 12AU7. Not much gain you say, but it doesn't matter since it's set up as a split-load (cathodyne) phase inverter. This style of phase inverter has unity gain, so a higher gain triode won't hit the power section any harder. The pentode section of the 7199 is capable of a lot more clean gain than one of the triode sections of a 12AX7.

All of that said, a Reverberocket 2 from the 60's shouldn't be anemic at all. Turned up it should scream :) (nice reverb too). I'd make sure it's operating correctly before looking for mods.

[pete kanaras]

cool todd, thanks for the informative response. i'm going by the shop tonight and we will give this puppy the thorough going over.

All of that said, a Reverberocket 2 from the 60's shouldn't be anemic at all. Turned up it should scream :) (nice reverb too).

something is definitely amiss then. a full cap job and such should bring it back up to snuff. the reverb pan will be replaced 'cause it isn't nearly as glorious sounding as ampeg capacitor 'verb is supposed to be. it's very trashy sounding, like a cheap digital approximation of spring reverb. however, the trem in that amp is to die for. jeez louise!

thanks much again,
pete

[Wakarusa]

Before trashing the pan see if the 'verb driver tube (and associated circuit) is in good shape. Second, take a peak in the pan -- sometimes they'll get jostled around and stuff will break/come loose. Occasionally you can fix it (though a broken spring is usually a death sentence for a pan. I've never figured out how to fix one so it'll work again).

[pete kanaras]

ok, will do. i'm heading over now and will let you know what we come up with. fingers crossed

[G.R.Amps]

you can substitute a 6GH8A for the 7199 with a couple of pinout changes. This is what the Dynaco guys do. Google for schematic. I've done it on my Gemini II with good results. AES has the tubes cheap.

[pete kanaras]

update

replaced the pan and 6u10 and the 'verb now sounds wonderful. the fresh tube also bumped the overall gain and grunt up noticeably as well, nice. i also popped in an emi cannabis rex that i'm very pleasantly surprised with; it is a really great match for this amp. been gigging with it and enjoying the break from the usual amps i use. i plan on getting a barber barq eq soon for some added versatility; this amp with it's flat (at noon) tone stack is a perfect candidate it seems. a very hip amp indeed, and thanks all for the suggestions!