5F6A combined 5E3 circuit idea

[aronaut]

here's a link to a schematic im working on, like a 5E3 but becomes 5F6A from inverter onward http://www.zeromassstudio.com/images/5f6amod.jpg
will this work? will It need 270k into the inverter? Also what are thoughts on using the other half of the 12AX7 for a gain boost?
Any help is greatly appreciated
thanks!

[Bruce / Mission Amps]

here's a link to a schematic im working on, like a 5E3 but becomes 5F6A from inverter onward http://www.zeromassstudio.com/images/5f6amod.jpg
will this work? will It need 270k into the inverter? Also what are thoughts on using the other half of the 12AX7 for a gain boost?
Any help is greatly appreciated
thanks!

You can't use your boost switch like that... with the switch open the grid of the B triode has no bias and no grid load on it. It will draw max idle current and maybe blow out.

[aronaut]

Ah, I see, then the switch could go after C5? I'm trying to find things to do with that B triode. Also, is it possible to go straight into the phase inverter after the volume or does it need another triode there? my understanding is it is only preparing the signal for the tone circuit, which I don't want anyway.

[Bruce / Mission Amps]

Ah, I see, then the switch could go after C5? I'm trying to find things to do with that B triode.

No. Besides that, on a quick glance, I couldn't even find C5.
If you really have to have that second triode as another "channel" or "boost"... split the two cathodes of V1 (a and b) with two 1500 ohm resistors and two different cathode bypass caps.
Put your "boost" triode's cathode (V1b) biasing resistor on top of a 100K resistor, which your boost switch will short across.
With the switch is open, the triode will not really amplify much of anything but with the switch closed, it will conduct and add a bunch of signal to your parallel volume pots.
If you setup the two triodes with different frequency pass bands, (I call this stagger tuning)... it will have much more effect on over all tone rather then just rippin' woofy gain.
As an example on V1b, try a 2k2 to 2k7 cathode resistor with a .68uF to 1uF cap across it and make C3 .022uF.

I'm trying to find things to do with that B triode. Also, is it possible to go straight into the phase inverter after the volume or does it need another triode there? my understanding is it is only preparing the signal for the tone circuit, which I don't want anyway.

It might not need much of another gain stage, but I think yes, you might need some kind of gain after the parallel volume pots.
Is this a working and proven amp design put out by WeberVST?
Maybe with two 12AX7s it will work OK. Not sure.

You might find making it a one channel amp and using V1b for the volume pot recovery stage, will be the best use of it.
Stock, the volume control recovery/amplifier stage is running fairly flat out and has gain of around +35 to 40 or so. It is actually the gain stage in a tweed amp that is what creates the voltage swing needed to drive the power tubes to full power... the next stage in a tweed Deluxe is a zero gain, cathodyne driver phase inverter and it really just follows the voltage swing of the voltage gain stage prior to it.
The LTP phase inverter you drew on the other hand has some gain.
Enough? I don't think so but I'm not sure.

I'd just use V1b as the triode in front of the LTP and alter both stages with a little tweaking to make them both a little less gainy.
As far as the LTP PI goes, with the use of V1b as a gain stage, R34 as a 1200-1500 ohm resistor might make the amp sound a little better and making R36 a lot bigger, like 39K to 56K will help too.
I guess the main thing is to fool around with it and use your own judgment.

[aronaut]

Bruce, thanks so much for your info and replies. your probably right to ditch the boost idea and use the B triode for the volume recovery, I've also read this stage gives some nice compression characteristics, is this true?. I'm now thinking about 2x6V6's LTPPI a 5E3 type pre and 25w OT, I think 40w 6L6 might be overkill for my needs (my band has no drummer and I want to downsize from my MM HD150 rig). here are 2 versions of a schematic, I have not changed the resistors in the PI yet, but this is the basic idea:
1. http://www.zeromassstudio.com/images/mod6v62.jpg
2. http://www.zeromassstudio.com/images/mod6v63.jpg

I'm not sure how much difference those two pre's will make and I suspect i'll need to fiddle with the cap before the PI

thanks!

[Bruce / Mission Amps]

DOH!!
The more I think about this why not try and build a 5G9 type Tremolux (without the trem) out of these parts?
Two 12AX7 in that amp with an LTP phase inverter works great.

[aronaut]

oh yeah, I'm looking at the 5G9 now, like my original idea without the volume recovery stage. with a 25w OT how much clean headroom do you think this would have before breakup?