Emission Lab contact

About the Emission Labs tubes and how to use them.
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Joined: Sat Aug 04, 2018 7:15 am

Emission Lab contact

Post by archeus68 »

I've been trying unsuccessfully to email or contact the Emission Lab guys.
Anyone have regular channel way to ask the a question?

I'm look for a schematic of their 300B with the center tap in a push pull circuit.
Also what a Parallel Push pull schematic would look like?
So something like a Williamson circuit going to four 300B's with the center tap. Would love to see what this circuit may look like?
I have a 300B amp that has the capability to use the Octal 300B.
Here is a link to a youtube video of the Amplifier in use after it was completed.


Youtube link http://bit.ly/2O7tbPi
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pam29 - Copy.png (144.2 KiB) Viewed 13754 times

J. Leven
Posts: 191
Joined: Fri Jan 13, 2012 12:27 pm

Re: Emission Lab contact

Post by J. Leven »

I would never build a pp amp as in the schematic, but only with separate heating and cathodes in autobias, adjustable,
the operating point stability is quite important at pp.
As it is drawn, 2A3 pp it can run, this is not optimal,
to your question, until now I have not used center tab 300B,
If you need more power I would prefer a KT150 in pp

Greetings from Germany

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Re: Emission Lab contact

Post by Admin19 »

At Emission Labs we build tubes, and we have no service for schematics, of the kind you are asking for. The problem with "schematics service" if you know how to do it yourself, you would not need help, and if you do not know how to do it yourself, it becomes difficult. So you can use excisting schematics as an inspiration, but there is a lot of fake schematics around, which are never tested, and are just junk for that reason.

I much recommend you to use the schematics of Mr. Leven, who does this excellent work here, and the personal support along with it.

For myself, I think you can actually make PP designs, but this is more difficult by itself, and more difficult for DHT tubes too, as you can damage them by trial and error experiments in class AB. So class A Push Pull is safer. Like this you get more efficiency still, and most of all: A lot less distortion at high power. Using the center tapped versions of the 300B-XLS or even 520B-V3 is a very good idea for PP. There is nothing special to know about using the center tapped tubes, just regard them the same as a INDIRECTLY heated tubes, so connect the bias resistor to the center tap, and you're done. Then same as with INDIRECTLY heated tubes, connect the heater voltage to where it says "heater" on the data sheet. The difference is only, the heater voltage with center tapped tubes must be floating. So if AC heated (which may hum slightly, but it works) EACH tube needs it's own, floating AC heater. Same with DC. It needs a floating DC supply for each tube.


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