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#1 A2 Driver

Posted: Mon Apr 24, 2017 6:51 pm
by ACPEN
Hello! Its been sometime since I've posted here, but thought someone may find this useful - I've built several Amps using TZ40, 811A, 812A etc in class A2 - usually with a triode strapped pentode as driver - I've also tried several true triodes (usually of the B9A base variety) but not found anything exceptional - until, the P61 came to my notice - I won't go into detail (you can look it up) but its a very cheap, very suitable triode as an A2 driver. There is also a P41 (4v htrs) version. Only slight drawback is the British Octal (Mazda) base - readily available thouh, so no real problem. If you haven't tried the P61 its worth a go!

Regards,

David.

P.S - Its entirely possible that you all know about these anyway - if so, well done!

#2 Re: A2 Driver

Posted: Mon Apr 24, 2017 7:11 pm
by pre65
Hi David, nice to hear from you again. :)

I'm due to re-visit 811a in A2 in the future, so I'd be interested to see the circuit you used.

#3 Re: A2 Driver

Posted: Mon Apr 24, 2017 10:12 pm
by pre65
There is an 811a thread in "projects".

http://www.audio-talk.co.uk/phpBB3/view ... =11&t=3696

#4 Re: A2 Driver

Posted: Tue Apr 25, 2017 6:51 am
by steve s
Those Mazda valves are good, but still not quite up to the early large anode equiverlants, early ml4 and the like take some beating, but the Mazda does beat most 50's valves
They are on the lines of an early L63
I have to be careful what I say after a few years of using a 1930's cosser triode at the wigwam show the prices have more than tripled on ebay

I have a nice collection of early acpen valves now with a view to building something with them after your comments on them