PLEXI GAIN-20

[TIMBO]

Hi guys, i liked this from Tone Junkie http://www.el34world.com/Forum/index.php?topic=11645.0 and have parts from previous Titanics (maybe one day they might float  )

The basics are there so by putting the different known circuits together hopefully it might generate a sound.
The title is what it is.The fairly standard Plexi circuit with an extra gain stage that can be added.
The original circuit had a spare triode that i thought might be handy up front (Mark Huss 18w lite 11b and Tone Junkies possible future mod)
The power amp of EL84/6V6GT that can be used (separate only)I did this because the amps are getting more and the room is getting less 
I've added DC to V1 and V3 just to see if this makes any difference to noise as this is another hi gain build that is bound to have noise problems.
Transformers:- PT Magnetic Components 290-0-290 @120mA
                     OT Magnetic Components 18w Marshall
Some Questions:-

Is the PT rated high enough to service this circuit? (as per the cheat sheet i think it is ok)
Is turning off a pair of power tubes safely done by disconnecting the cathode Cap/Resistor from ground?
The Cap/Resistor Combo on the power tubes seem to be the norm, i was hoping to push the EL84 tubes to possibly get 20w but i am thinking that this can only be done with a fixed bias, am i right?
I was thinking that the NFB might be cool if some fixed values were able to be dial in or would it be just as easy to have a pot as a veriable resistor? (any thoughts on values)

Thats all for now. Thanks

[Tone Junkie]

When you build it if in the high gain mode the bass is to muddy you might have to drop the first cathode cap down from 47uf down to lowest probably 2.2 uf but somewhere in between.
Bill

[TIMBO]

Thanks Tone, i think this one will have a few tweaks done to it.

[Tone Junkie]

Im still tweaking mine . when Im done I will send it to you for referance. but this thing rocks
Bill

[TIMBO]

Hi guy's, a couple of questions,

The PT is wired up and when turned on i am getting 317vac on the two secondary wires,but after rectification its only 287vdc (unloaded). Is this enough to power the EL84/6V6s, I was hoping it would be a lot higher (317x 1.4=440v)

The PT has secondary taps of 0v,5v & 6vac which i am using the 5v rectified for future relays, it is showing 6.4vdc unloaded and the 6v i am using for V1 & V3 DC heaters and it is showing 8.4vdc unloaded.Will the 8.4v drop enough when loaded or will the 12ax7 heater handle this voltage or should i just use the 5v rectified? Thanks

[tubenit]

i am getting 317vac on the two secondary wires,but after rectification its only 287vdc (unloaded).

You're saying the voltage has DECREASED after rectification without tube in??????

That doesn't sound right ???   Make sure your voltmeter is set properly and with good batteries in it. Can you remeasure the voltage again & repost, please.

With respect, Tubenit

[Tone Junkie]

Yes my friend something doesnt sound right you definatly dont want 8.4 on the heaters.
Bill

[EL34]

The voltages should not drop without a load.

If you have a voltage drop without tubes, you need to look for a short to ground somewhere.

[PRR]

> 317vac on the two secondary wires,but after rectification its only 287vdc

With or without filter-cap??

With cap should of course be Peak: 317*1.414 or 448V minus load-losses.

WithOUT cap you will get AVERAGE: 317*0.9 or 285V.

[TIMBO]

Sorry guys sent you on a goose chase,PRR got it right. I have set up the PT and was just checking that the rectifier and the heater/relay rectifiers were working. I haven't done much more than just wire the PT to the mains and the four diodes (on cap).

I am wanting to use DC for the relay and v1,3 heaters so i got a 6.2v zenner and 5.1v zenner can i replace the 1n4007 diodes with these to correct the voltages?

My other question is it ok the to disconnect the EL84/6V6 cathodes to "switch off" the tubes not being used.

Thanks Again