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Old 18th February 2012, 09:34 PM   #1
T1509 is offline T1509  United Kingdom
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Join Date: Feb 2012
Location: UK - South
Default 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.

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Old 19th February 2012, 07:00 PM   #2
T1509 is offline T1509  United Kingdom
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Join Date: Feb 2012
Location: UK - South
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?
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Old 13th December 2012, 11:20 AM   #3
nafunga is offline nafunga  United Kingdom
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Join Date: Jul 2005
Location: Whitstable , Kent. UK
Default VT46 AMP

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.


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Old 13th December 2012, 05:58 PM   #4
T1509 is offline T1509  United Kingdom
diyAudio Member
Join Date: Feb 2012
Location: UK - South
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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