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    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Need help with PP pentode design

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Fuling

Fuling

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Joined 2001
#1
Good afternoon.

To make a long story short:
I need 100+ watts of tube power for bass guitar use, and I´m a bit short on money.
My best idea this far seems to be 6 x PL504 (only because that´s what I have in the junkbox) in PP pentode mode.

I´m a complete newbie to pentode PP amps so I need help to design the output stage.
What plate load and plate/screen voltage would give maximum output power with these tubes?
(And remember, I´m aiming for raw power, not hifi)

I´m planning to wind the OPT myself, so a bit of guidance would be nice since I´ve never made a PP OPT before.
I have some 150 and 300VA transformer cores that should be fine, and the frequency response isn´t that critical.
40Hz to 10-12kHz is enough.

Any help would be very appreciated!

Cheers
/Daniel
 
#4
Fuling said:
Well I have two pairs of Svetlana EL34 and a suitable power transformer, so that could be an alternative.
Any ideas of suitable voltages and impedances?
Click to expand...

Hi Fulling !
You need 800V at 200mA to do that.

I hope you know this may kill you !

The load impedance is around 10K for a pair.

Gimme the size of your avilaible iron, I'll try to compute for winding !

Cheers, Yves.
 
#5
For voltages, I assume you are refering to plate voltage, Refer to the data sheets, and look for the settings that will get you what you want

http://tdsl.duncanamps.com/tubesearch.php

If memory serves they can take up to 800V on the plate and around 500 on the screen. Remember to tie G3 to the cathode.

In my bass amp (ampeg v4) I had it wired for 6CA7 (same thing as EL34's) for a while. Sounded real good. I switched to the JJ 6L6's. Reason- Long story, best for a new thread.

For info on PP topology refer to

http://www.diyaudio.com/forums/showthread.php?s=&threadid=38278

I think you will be very happy with EL34's. Nice and deep.

Unless you wanted to go for some 6550's

Good Luck
Matt Newkirk
 
#6
Oh, 800V is a bit too sweaty for me, and the power transformer I have "only" gives 500V after recification.

Well, before I decide for anything I´ll have a chat with a friend who has tons of tube related junk, maybe he has something that can be of use here.
I think he once mentioned that he has a big OPT suitable for 6 x 6L6 or something laying around... That would´ve been perfect.

I´ll be back when I have talked to my friend, making an OPT from scratch seems unnecessary if he has one for sale.
Thanks anyway!
 
#10
Fuling said:
Well well well, look what a little googling can do!

http://www.onestone.de.tt/

The site is in German (which I don´t understand much of), but the schematics speaks for themselves!

Amps with 4x PL504 and 6xPL504!!
Simple topologys and mains transformers on the outputs!!
Whoaah!
Click to expand...
Be interesting to see how this works out for you. Have fun and enjoy. This is my sort of fun project, cheap and built from stuff laying around and/or free.

I hope you want this just for home, as it gets real old real fast humping heavy high power tube amps around, and ~100W won't be enough in a lot of situations. I'm going to build some of Bill Fitzmaurice's designs so I can have lighter cabs and need a lot less power than my JBL based rig. Contemplated a small-ish tube amp, which I have plenty of parts for laying about, but may go with a small digital module to power it just for the weight.
 
#11
Hi

I´ve been talking to some people today and I´ve been offered an old AGA cinema amp that seems suitable for heavy modifications. Lots of heavy ironware in a cool chassis, what else could I ask for😀
Some 500V B+ delivered through dual 5AR4´s, thats what I´d call a power supply...

Will probably end up with a quad of EL34´s or 807´s, depending on the OPT. (The original OPT is useless, but the guy had one that seemed quite OK for the job)
 
#12
Originally posted by: newkirklabs
If memory serves they can take up to 800V on the plate and around 500 on the screen. Remember to tie G3 to the cathode.
Click to expand...

There were some "good" NOS 6CA7's that could handle 800V on the plates, but as far as an EL34 being able to WITHSTAND 800V without melting down, dunno! There were very few made that could come even close! They're not exactly the same really, technically/structurally. Even the JJ's are rated only for up to 600V safely and dependably.
A quad EL34 would probably be the way to go! 😉

Wayne 🙂
 
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