7199 phase inverter tubes

[blownaparte]

Am I the only one who thinks the Sovtek 7199 gives the 40-watt Sunns a torn speaker sound? I just re-tubed my Sentura I and I've tried everything to get the smooth even distortion I used to get from that amp. I had it re-capped, I replaced the pre-amp tubes, the power tubes, biased the power tubes (twice) and still the thing breaks up way too early and doesn't break up like it's supposed to.

I've just ordered a NOS 7199 and I'm hoping it will give me the sound I'm looking for. I know this amp can do this. It did when I bought it. I don't remember what the original phase inverter was, (for some reason I'm thinking it was a Sylvania), but it was SMOOTH.

What I'm wondering is whether all Sovteks sound like this or whether I should be hoarding NOS 7199. Is anyone else making new 7199s?

[JoeArthur]

Never having played through a torn speaker myself, I'm not really qualified to answer the question. So this is just some rambling.

In general, I've found Sovtek tubes to vary greatly in quality. I divide tubes into two groups first - separating the microphonic ones from the non-microphonic ones.  If I need to I will use a microphonic one in a non-signal position, like a tremolo oscillator.  Otherwise, it hits the trash.  I find the sound from a microphonic tube to be very non-musical and "metallic" sounding and I just don't like it.  Doing this with a batch of 10 new Sovtek 12AX7's, I found 3 of them to be extremely microphonic and only suitable for the trash.  4 were good enough for non-signal use, leaving only 3 that I would use in an amp's signal chain.

If it is non-microphonic, then the tube will more than likely sound just like any other tube clean.  When pushed, some are more graceful than others as they start distorting.

Tap the 7199 lightly with your fingernail.  If you hear a metallic ringing sound through the speaker, then it is probably trash material.  Some of the worst you can hold next to your ear and shake it and they positively rattle.

[Isaac]

I'm confused. The pre-Model T Sunn amps used a 6AN8 for the phase inverter, and a quick check shows that the pinout on the 7199 is different. Is my information wrong, has your been modified to use a 7199, or could that be your problem?

[blownaparte]

You're right and you're wrong Isaac. The 60-watt Sunns (Sceptre, Sentura II, etc.) use a 6an8 for the phase inverter, but the 40-watt heads (the El-34 heads) use a 7199.

I'm afraid the phase inverter is going to be a problem for all of us who love the pre Model-T amps because while NOS 6an8's are still available. I don't believe anyone is making new ones. The again, if someone does begin making a new 6an8, there's no guarantee they'll be any better than the Sovtek 7199's.

-Blownaparte

[Soundmasterg]

You can easily rewire the circuit in your amp to use the 6AN8. It is more readily available NOS, and is much cheaper than 7199's NOS. No one is making one now but there isn't really a danger of running out of NOS 6AN8's any time soon. Sovtek makes a 7199, and I think EI might also...I forget. None of the current ones are as good as NOS though. Personally I like the sound of the 6AN8 better than the 7199 anyway. There are some other NOS tubes that are similar to the 7199 and the 6AN8 that can be used also, but they would require rewiring the socket.  Your closest RCA tube manual and Vacuum Tube Valley magazine/website should have some info on subs.

[loudthud]

I've found that 7199's and 6AN8's don't always bias properly in Sunn amps. The circuit Ampeg used in the B25 (and others) is less sensitive. Check that the plate and screen resistors have not drifted in value and the cap on the screen is not leaking. Install a pot in place of the pentode's 680 ohm cathode resistor and adjust until you get 80V on the cathode of the triode. I haven't tried the Sovtek 7199 but have seen the problem with NOS 6AN8's.

[Isaac]

I have a dead Sceptre that I'm thinking of putting the split-T configuration in. Someday, maybe...