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Old 27th August 2006, 01:16 PM   #1
glennb is offline glennb  Australia
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Default Anyone used PT15 / VT104 ?

Hi. Has anyone used the PT15 / VT104 directly heated pentode (Pa=30W) ? Basic specs and a photo are at http://www.tubecollector.org/pt15.htm

I've only found one design on the 'net at http://www.vt52.com/diy/diypage/corne/pt15_amp.htm

There's a box of 10 sitting on my shelf, and despite the weird 5 pin base, I'd like to do a simple P-P Triode-strapped Class A power amp.
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Old 27th August 2006, 05:34 PM   #2
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I have a pair that I played with briefly on the breadboard. My testing was class A1 triode connected SE.

It worked OK, but wasn't excellent. I did not put a lot of time into it, though.

I think this tube begs to be driven in A2. I haven't tried it yet, but it looks like it could be a really good performer if you drive the grid to peaks of +10 or +20V. It's on my list of things to try...

There's a couple of Japanese SE designs posted here:

http://www2u.biglobe.ne.jp/~tossie/F_PT15-E.html
http://www2u.biglobe.ne.jp/~tossie/PT15-E.010106.html

The PT15 is "unobtainium" in the US - I got the pair I have from Belgium. Lovely tube, as you say despite the weird (for us!) base. Are there some available in Australia?

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Old 28th August 2006, 08:09 AM   #3
glennb is offline glennb  Australia
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Quote:
Originally posted by pmillett
I have a pair that I played with briefly on the breadboard. My testing was class A1 triode connected SE.

It worked OK, but wasn't excellent. I did not put a lot of time into it, though.

I think this tube begs to be driven in A2. I haven't tried it yet, but it looks like it could be a really good performer if you drive the grid to peaks of +10 or +20V. It's on my list of things to try...
Yeah, the plate characteristic graphs shows G1 driven at up to +60V and 60ma, but thats for peaks only, its way above the Pa=30W curve.

Thanks. SE Triode-strapped Class A1 is only good for about 2 - 3 W. PP Class A2 will do much better than that.

Quote:
The PT15 is "unobtainium" in the US - I got the pair I have from Belgium. Lovely tube, as you say despite the weird (for us!) base. Are there some available in Australia?
A pair were used by the RAF in airborne transmitter T1145 on the famous Lancaster bomber during WW2. I got mine as a single lot at auction. I doubt if more are available.

A bit of casting around shows they go for about GBP 15 used, and GBP 100 new.

I found another Japanese reference at
http://translate.google.com/translat...um=2&ct=result
"Direct thermal 5 polar transmitting tube by low pressure heavy-current. Bass of force!"
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