i want to build 3D21WB tube PP amp

[lieukiem]

Dear all,
I have 10 tubes 3d21wb, pls help me find some Circuit to buld pp AMP?
http://www.classiccmp.org/rtellason/tubedata/3D21WB.pdf
tks

[tubelab.com]

There is a very long thread that dealt with the development of a driver circuit for use with 6L6GC's. During the course of that development I tested the circuit with several different tube types. The 3D21WB was included. I could get 75 watts from a pair in triode mode. This is discussed starting around post #331. The last driver schematic is in post #277. It works good and was not changed since then. The power supply was not completed for this amp, and I have not had time to work on it in a while. I will return to it, but I can't say when.

I have a totally new driver circuit (similar design but uses pentodes) to try that isn't done yet. I want to test both with the 3D21WB's and several other tubes when I get time.

6L6GC AB2 Amp

[TheGimp]

Check out what Tubelab did with his Octal Driver Board. Scroll down near the bottom. Looks like they can perform similar to KT-88s and a pair may be capible of near 100W in PP.

Octal Driver

Dang, George beat me to It. I spent too much time googling I guess....

[tubelab.com]

Dang, George beat me to It.

And I am usually the slow one.

I complained that I went through all of 2008 without building a single amplifier. I vowed that I wouldn't let 2009 go by without building at least one amplifier. Well as of Dec. 31 I didn't have any amplifiers that I had built in 2008 or 2009. I realized that I had built a Simple P-P in Nov. but I took it all apart so I could rebuild it while taking pictures for the assembly manual, so I guess that I did build one amplifier in 2009. After I put it back together, and build at least 2 more Simple P-P's, I plan to go back to the higher powered P-P stuff.

The Octal Driver board that is mentioned here is a good start for building several high powered P-P amps using conventional audio tubes (6L6GC, EL34, KT88). It also works well with sweep tubes, and other unusual tubes like the 3D21WB and 7403. I also plan to test it on some bigger tubes like the 813, and do some more screen drive experiments.

About two years ago I breadboarded a little 10 watt P-P amp using all pentodes. It used 6AU6's and 6AQ5's because I have hundreds of them. Local (Schade) feedback and direct coupling was used. It worked very well, but wound up on the shelf forgotten.

Recently Pete Millett designed the "Engineers Amp" using a similar all pentode with local feedback (but not direct coupled) circuit. I bought a board (I refer to it as the "red board") and built it. It works very well and I have already hot rodded it to 125 WPC. It also reminded me about the 6AQ5 amp. A search of my hard drive revealed a nearly complete PC board layout for that amp. I am thinking that it would make a good driver board too.

I still have the Universal Driver board too, so it will be time to see what they will all do when connected up to all sorts of different tubes. I bought 5 more of the 7403's (like a 3D21WB) so I expect that they will be part of the test.

[TheGimp]

Any chance you will try 6146s with the driver board?

[lieukiem]

tks tubelab.com,
this schematic resemble your idea,


and driver Schematic here:http://www.pmillett.com/images/UNIAMP.PDF,

is it ok, with KT88 opt : 6,6K->8Ohm, with 3D21WB, OPT=?

Ps: sorry, my English is not good.

[tubelab.com]

Any chance you will try 6146s with the driver board?

That question was asked back in the 6L6GC in AB2 thread. Along with this one:

I was curious if 6146 tubes could take the challenge. Do you have any ?......What about pentode with local feedback?

My answers in posts # 339 and #341. Were pretty much focused on making a big amp using a triode wired pentode tube, without any feedback. The discovery of the 3D21 / 7403 with its 850 volt screen grid rating seems to be the enabler for this idea and the initial experiments proved that it would work.

Since then I have spent some time cranking some stupid amounts of clean good sounding power out of the Red Board, I may abandon the "triode only" requirement. I set up a breadboard for testing all sorts of different octal tubes with the Octal Driver board last year. I have not powered it up yet. Once the Simple P-P stuff is out of the way, I hope to explore the upper limits of a bunch of different tubes.

The 6146 got a bad name in the audio world (post #339 again) back in the late 60's and has been pretty much shunned ever since. I gave all of my 6146's and 6159's to a friend who wanted to build a broadband distributed RF amplifier several years ago. I know that there is at least a dozen sitting in a box somewhere from a military surplus pulse generator that I parted out a year or so ago. If I can find them, I can crank them up. They should do OK in pentode mode.

lieukiem, I think that the driver board shown will work. It uses a transformer for the phase splitter, which I prefer to avoid. Transformers that work good are not cheap, and Sowters are not common in the US. If you chose to use this board, I would look for a quality transformer.

Anytime you chose an uncommon tube you must be prepared to experiment since there aren't many examples available to copy. I still haven't had the time to fully investigate the 3D21WB tube, and it may be a while before I have the time to do so. Most of my experiments were done with a 3300 ohm load. This was obtained by using a 6600 ohm transformer with the 8 ohm load on the 16 ohm tap. That worked good in triode mode. My output transformers don't have a UL tap, so that was not tested. you will need to adjust the values of the cathode bias resistors for proper current depending on the choice of tubes and power transformer.

[TheGimp]

From what I've read, the RCA 6146B introduced in 1964 was a problem for transmitters as well. It was supposed to be a drop in replacement for the 6146/6146A with higher plate dissipation rating. However, it had a nasty habit of parasitic oscillations in transmitters and often resulted in burnt circuits. I think there were some Collins Motorola and Heath Kit transmitters. I got my tubes from my dad who used to have a Collins (what model I don't know).

It seems the biasing requirement for the 6146B is different than the bias for the 6146/6146A.

All my tubes are 6146Bs except one 6146.

[AirPower]

this is my 3D21WB shematic, you can do the same