what about pt15?

[dsdn.]

Hi
I'm new, in this forum. I'm french, and my english is not fluent any more, because I didn't practise ennought since i was at school. I saw few thread were some people talk about pt15. I have a quad, and I would like to use them for making a push pull in triode connection. I'm not so experiment to create all the staff, and I have never seen a push pull with tese tubes on the web. Is someone, have seen something like that, or have an idea?
I have already made three amplifiers: a pp of 845, an SE of 845 driven by an r120, and a se of 6b4G.
Thank you.

DAvid

[James D]

David,

Welcome to the forum! And your english is miles better than my written french which is horrible

I have built a PT15 PP amp. Circuit is below. I used a Aikido front end and a parafeed IT phase splitter to drive the push-pull output stage. The output stage has the WE harmonic equaliser and by adjusting the pot a 20dB or so reduction in third harmonic distortion can be acheived.

ciao

James

[dsdn.]

ok thank you, it will help me, I do not found the way to calculate the final transformer impedance. I don't tink I will use a transformer between the final stage and the driver. But it's a good begining for me. I don't think the pt 15 needs a really "strong" driver.

DAvid

[James D]

PT15 Ra is about 2.6K so Ra-a should be between 5-10K... 10K works very well.

The Aikido driver is a superbly neutral and open driver but Iagree its not necessary to have such 'drive' for the PT15. IT phase splitting is the only way for me. I really don't like the sound of other methods but everyone has their own opinion on this

Please keep us informed of your designs and building progess

ciao

James

[dsdn.]

Well, I will have two transformer 8K left. These J L Chrétien's Construction, so could it be abavailable for the project?
How much watts offers your schema?

DAvid

[James D]

8K is fine, each side will see a 4K load in Class A which is fine. WIth Ia=60mA through each PT15 and Va=400V you should get an honest 10-12Watts from the amplifer.

[dsdn.]

it would be ok for a test but what abot an impedance for a pp in ab 1with much more "watts" (sorry my english) and mush more "watts", and also the way of the amplifier would go througt? (if I explain myself well, I hope so! but the time could have during a bit so ...)

DAvid

[James D]

There has been much debate about that - basically its a transistion state where the laoding changes with signal level. The two end conditions are clearly defined - in Class A where both valves are conducting all the time each valve sees an impedance of Ra-a/2 nad in Class B where only one valve is conducting at a time each valve sees an impedance of Ra-a/4 so half the Class A load. Class AB1 and AB2 are transistion states wher the load the valve sees depends on the conduction state of the other valve and that depends on signal level and mode of bias, etc.etc.

THe PT15 is suited to Class A in triode and to Class B in pentode - its not really designed for AB1 or AB2 and you don't get a lot more power out of it in AB1 or AB2. Pentode Class B is nice and would double the power output - and funnily enough again an Ra-a=8-10K works well... Class B in this case would require fixed bias applied to the G1 with the cathodes of the two valves connected to ground.

In their original application as the transmitter valves in 2nd World War bombers they where used in Pentode Class B with a crystal microphone connected directly to G3 (not G1).

[Corne]

According to the data sheet the PT15 was designed to run class2, the graphs go to +80V on g1.
The datasheet can be found at: http://www.mif.pg.gda.pl/homepages/f...139/p/PT15.pdf

However to run these tubes A2, AB2 triode with low distortion is quite difficult. It requires a complex driver circuit that has low output impedance and is able to supply tens of mA current without distorting the signal.

Corne

[James D]

They were indeed designed to run Pentode Class B2 i.e with G1 positive and grid current following - easily acheived in the aircraft by running from a battery/accumulator system on G1. They also often ran with G3 positive by up to +40Volts as well for a bit of extra linearity and gain. But they can only run AB2 or B2 as they run out of power dissapation very quickly when operated like this...

In triode mode they are an A1 or B2 proposition again due to power dissapation limits.

James