6EY6 & Cathode bias

[6267]

I am redesigning an output section to be happier with 6ey6 rather than the 6v6gt's it originally used. B+ is 350, screen voltage around 320-340, cathode bias resistor (shared) is 250 ohms. Seems a bit hard on the 6v6s, anyway. Got some Tung-Sol 6ey6, black plates, heavy anode dissipation ridges, altogether a much stronger looking tube than the RCA 6v6 I was using. I measure -22.5v across the 250 ohm resistor, giving about 45 mA per tube with the 6ey6s in. The problem is that the sound is grainy and harsh, as though bias were too cold. I'm going to ignore the published 11w anode dissipation, since that was with big multi-kilovolt spikes coming through etc in television service. The plate structure looks like it can take a beating. I find it hard to believe this tube can not dissipate as much as for instance an EL84. I am wondering if anyone had a good bias resistor recomendation for this operating point, or if they had experience with the tube regarding plate dissipation in musical service. I feel like I should decrease the cathode resistor a bit, maybe 25-75 ohms and run the current a bit higher. PT is the biggest damn thing I've ever seen, so I'm not worried about current overstressing anything except maybe the OT. Or can the harsh, grainy, buzzy sound come from too much current?!? I would expect "soupy" 2nd harmonic and easy overdrive from too little bias...any help?

[6267]

I'm not sure if they burned in, or some solder fluff somewhere stopped doing something bad, but I plugged them in again today and the sound was pretty good actually. I'm still working on the preamp(s) for this multi-output beast, so it's more than possible that a preamp problem was giving the grainy sound. I think 250 ohm are ok for 350v B+, plus they'll work ok with 6L6 and 6CA7. Of course the OT will need to be replaced with something a little beefier & lower Z for those, or the speaker mismatched.

p.s...6sn7 both halves, shared 300 ohm cathode resistor, ground one grid, drive the other off a voltage divider from OPT secondary, 8-10k a-a load on the two anodes driving the standard low-z reverb tank sounds really, really good...if only the recovery stage was working out so well!

[Bruce / Mission Amps]

I'm not sure if they burned in, or some solder fluff somewhere stopped doing something bad, but I plugged them in again today and the sound was pretty good actually. I'm still working on the preamp(s) for this multi-output beast, so it's more than possible that a preamp problem was giving the grainy sound. I think 250 ohm are ok for 350v B+, plus they'll work ok with 6L6 and 6CA7. Of course the OT will need to be replaced with something a little beefier & lower Z for those, or the speaker mismatched.

p.s...6sn7 both halves, shared 300 ohm cathode resistor, ground one grid, drive the other off a voltage divider from OPT secondary, 8-10k a-a load on the two anodes driving the standard low-z reverb tank sounds really, really good...if only the recovery stage was working out so well!

I've run lots of them with good results at 10-12 watts each in push pull 6V6 style amps using cathode bias and with 6k5 to 8k primary impedance OTs.
I think they are pretty tough at audio freqs.

[6267]

The envelopes aren't even warm at 15w (minus a little for screen disp.) and the plates look fine...can't see the screen (no alignment holes) so I guess I'll just have to hope they're not glowing cherry red . Nice little tube, although with the filament power I have available I could've gotten away with damn near anything save the OPT impedance. Little different tone than a 6v6, but it sounds good. Thanks!