Driven pentode preamp ideas

[chopstuck]

I'm looking for a hot sparkly driven pentode sound and I was wondering about using a Fender Princeton first stage with tone controls to drive a signal pentode.

After the tone stack will the signal level need attenuation ?

Will I then treat the pentode differently to decrease the gain with the hotter input signal ?

Do I change the plate, screen and cathode resistors from the established classic vox format ?

I have tried Merlins suggestions and had lost those vox clean highs.

I'm looking for more gain without turning to mud and still having some bottom. I have tried the rotary tone switch - couple of good values in there. Tried the Zodiac tone control too. - only works well while clean- in my experience.
I suppose I can try the Clubman pre but I had a real one in the 90's and hated it - Way too loud !

Maybe a small bottle Clubman would work ?

Plan is to go into a typical Vox PI and el84 power section.

Can anyone point me in the right direction.

I have built 6 pentode preamps and I'm still lookin'

[LeftyStrat]

I've actually started working on something similar. I'm using a 12ax7 with the classic TMB Fender tone stack between the two halves, then running this into an EF86, but using more conservative values ala Merlin (100k plate, 680R cathode) along with his "Mighty Merlin Morph Control (tm)"

I'm still laying out boards right now, so I'm not sure how much I will need to attenuate before hitting the pentode. For inspiration, look in the Dumble Discussion section for the EF86 special, which is a similar topology, and uses the Dumble-style Drive and Ratio before and after the EF86. It also has a one knob tone control after the pentode.

I actually have two power amps set up to run this preamp into. One is the AC10. The other is a ltp pi into cathode biased 6V6.

[chopstuck]

I just tried the morph control and I found it just took away all the pentode character and killed the tone. My normal channel is a single triode that sounded much fuller than the neutered pentode.

I'm still ax-sperimentin'

[LeftyStrat]

I just tried the morph control and I found it just took away all the pentode character and killed the tone. My normal channel is a single triode that sounded much fuller than the neutered pentode.

I'm still ax-sperimentin'

Was this a first stage pentode or was it driven by prior stages?

[Reeltarded]

You really need to hear a Selmer Zodiac up close. That is a smashing amp. It rips!

[chopstuck]

That morph control was on a regular vox pentode channel.
I didn't care for it in that application.

[10thTx]

Have you looked at the HoSo56? It uises a 5879 in V1.

http://www.el34world.com/Forum/index.php?topic=6176.0

With respect, 10thtx

[chopstuck]

Yes, I built that amp. One of my favorites. I learned a lot about reverb with that exercise.
Still it uses the pentode as the first stage and I'm looking at a pentode in the second stage. I guess because of Merlins comments on getting hot pentode tone without the headaches of microphonics and such.

[Reeltarded]

It seems that part of the trick would be big bypass on the somewhat neutral first stage so the ef can do it's thing. My recent Marshall rebuild was going to have one as a second stage, but having only one EF86 on hand might have been the reason I was unsuccessful in making that circuit work. I think this tube might just be awful.

I still really like the idea.

[10thTx]

OK, then how about this as an idea. I built this for my son.

The V1-b 68k grid to ground resistor would have been better off as a 100k pot.

With respect, 10thtx

[gingertube]

You really need to hear a Selmer Zodiac up close. That is a smashing amp. It rips!

Would that be the "Twin 30"? It is the only Selmer schematic I've seen with a pentode. Did you note the extremely agressive bottom end roll off (18dB/octave) after the pentode stage, there to stop some high gain "mud"?

Cheers,
Ian

[Reeltarded]

Yes, Zodiac Twin 30.

It is very sedate and even kind of dulled or relaxed until you bang the volume and then it turns into a snarling animal, much like an older AC30-TB. Same kind of thing with the cabinet as an AC30 too. Whatever the circuit does plays VERY well with the cabinet. I would never try to copy one exactly like I would with certain Marshalls, I would just start around that ballpark.

Thing is awesome..

[jazbo8]

Yes, Zodiac Twin 30.

It is very sedate and even kind of dulled or relaxed until you bang the volume and then it turns into a snarling animal, much like an older AC30-TB. Same kind of thing with the cabinet as an AC30 too. Whatever the circuit does plays VERY well with the cabinet. I would never try to copy one exactly like I would with certain Marshalls, I would just start around that ballpark.

Thing is awesome..

Which channel? The parts values are quite different between them... Channel 2 has 6.8M screen resistor, so the voltage must be super low.

Jaz