Will this work?

[cobalt]

Just trying to use some of the bone pile......

Wondering what I missed, seems to neat and easy.

Thanks in advance for any tips or advice on the design. Basically an Eagle with an added pre-amp.

weirddave

[Invertiguy]

You might want to add mixing resistors after each volume pot before the output tube grid to prevent crosstalk between channels, but other than that, try it and see if any issues arise. Might need another gain stage before the output tube as well, tone stacks are a heavy load and lose a lot of signal, but it all depends on what you're end goal is sound-wise.

[cobalt]

It's got a tone stack by-pass switch(like the eagle super), so by-passed the pre-amp should deliver about the same voltage as the other pre-amp.
Kinda voxy/champ

Have another tranny set.....planning same pre-amps, 6V6 power out. Looking like point-to-point.

Thanks for responding! I have a couple more ideas, but better to build, THEN tweak!

I gotta point out I am concerned about current(B+), and heater hum. Any ideas?

weirddave

[d95err]

You need to improve the power supply filtering. Supplying the preamp tubes from the same node as the screen supply is bound to cause a lot of noise and possibly oscillations.

A grid stopper for the power tube is probably a good idea too.

[cobalt]

So I should make another PS node and move the pre-amps to that node?

A power tube grid stopper? Like a 68K to ground at the socket?

Let's see if my math is right for current:
The power tranny is rated for 250VCT at .13A with FWB should be around 310V at .08A. Power tube plate should draw a max of .033A at 310V(10W), screens a max of .01A at about 290V, 12AX7 a max of .004A at 250V, and EF86 about .005 at about 220V. So, about .052A? From .08A reserve of 22MA? Heaters add up to .95A+/- 10% plus plenty of reserve for power-up.

Looking for more ideas.....do you think different values in parts of the circuit would be more toneful? Trying for a clean to dirty in ax7 channel, and grunt to chime in the ef86 channel.

Also, is 130ohm enough cathode bias or should I plan on 150ohm?

Thanks again everyone!

weirddave

[tictac]

I'd try feeding all preamp tubes from the 15K node before attempting futher modifications; if it works your good to go...

TT

[Phil_S]

A power tube grid stopper? Like a 68K to ground at the socket?

No, just put a small value resistor on the grid pin and attach the other end to the input wire. Anything from 470 Ohm to 5K Ohm might be appropriate. Common choices are 1K or 1.5K.

[tubeswell]

+! about the mixing resistors going into the second 1/2 12AX7. Without them the AC load on either V1 stage is higher (and anything you can do to reduce the AC load on an EF86 is good, because they have a high output impedance)

[cobalt]

So, what kind of value for mix resistors? Two of the same value one from each pre-amp?

Thanks again!

weirddave

[tubeswell]

220k to 470k, try it and see.

[cobalt]

A while from trying.......at design stage.

To be a little more clear, some parts are from the bone pile, some are new.
New: PT, resistors, pots, some caps(all Ecaps), switches, jacks chassis and rectos.
Used: OT, tubes, sockets, and one of four 5ohm speakers.

At this point trying to make a viable schem, them noodle layout, and then drill chassis.

Thanks for the advice, and please keep it coming.

weirddave