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T1509 18th February 2012 09:34 PM

Building a VT46/PT25H PP amp
Hi All,

Looking to build a decent stereo amp based on the VT46/PT25H Pentode.

Just trying to find output transformers for these bottles.

I'm firmly from the "if I cant measure it, it isn't happening" brigade, so oxygen free cryo treated solid silver type stuff isn't for me - I want to build a decent amp at an affordable price, that performs and reproduces as faithfully as possible whatever I feed into the input.

Any suggestions would be much appreciated.


T1509 19th February 2012 07:00 PM

There seems to be a lack of data for these tubes in PP, am I right in thinking that the quoted 5K anode load in Vade Mecum will mean that I need a 5K centre tapped transformer for the output (looking at the amp from a pair of class A amps bolted together point of view)?

That being the case, I see that both VVT and Hammond list transformers that will do the job.

Thinking on drivers, and phase splitters - I have a good stock of 6SN7s, and L63/6J5 types, or should I stick with 4v heaters throughout?

nafunga 13th December 2012 11:20 AM

I've recently completed a VT46 SE Amp which is really very good. I appreciate that you want a PP design but note you are enquiring about suitable drivers. In my SE amp. I've used the high mu triode 6SQ7GT (mu 100) which drives the VT46 very well. I should mention that despite their 30W rating (VT46), I am only running them at 30mA with an HT of 250v. Anode load is 3.5K. The PSU is LCLC smoothing. I'm interested to know how you get on.



T1509 13th December 2012 05:58 PM

Hi David,

Progress has been about nil - I've got conflicting info on the heater requirements for the VT46, ive seen both 4v and 5v quoted....

Ive got a pair of transformers, and have got most of the metalwork, just need to finalise the PSU, and commence building.

6SQ7GT - double diode triode.... Well, they are certainly cheap and available!


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