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In Reply to: RE: What can you build with a 50mA 5k SE output transformer? posted by vbenonisen on February 15, 2017 at 06:54:57
I use a Lundahl LL1663 for my 50 monoblocks.... If you want to dive into the world of valves on the rare side...I've picked up 5 RCA balloon 50s over the last decade to support...If I had it to do again, I would have gone with the 2a3...the sound is glorious though...
Stuben
Follow Ups:
The 50 would have been something yes. But oh so expensive and difficult to get hold of. How many watts do you get out of it?
I'm running them as delicate as reasonable ...about 4-5 watts of very big sound. I have had difficulty driving them. I have a prototype EL84 line stage that is getting the job done finally. The monos are IT coupled 417a-50 output.
I was working out of town years ago and had some spare cash...now I'm very happy with the results less the expense.
Stuben
I'd suggest using a 4P1L. Just 2 stages - no preamp needed with 2v in and sensitive speakers. Mu of 4P1L is around 11. Much more than 45. Also filament bias is an advantage - no cathode bypass caps.
The 01A Gen 2 preamp design is the best sound I've built or heard for an input stage. Good combination.
Yes, 4P1L is a great alternative, but isn't one tube per channel too little to drive a normal loudspeaker (Let's say a Audio Note AN-J for the sake of argument).
I use a pair, which is the equivalent to a 2a3, with a 70mA OPT. A single is equivalent to a 45. You can use three in parallel - just wire the filaments in series, then in parallel between the tubes. For 3 you really need a 100mA OPT.But if you want some volume at 50mA, you need a higher plate voltage. 4P1L is rated 250v a-k though you could probably push it a little.
Edits: 02/15/17
Apply Paul Joppa's 102 dB. rule to the claimed 93 dB. sensitivity and you get 8 W.
A look at a chart of 300B operating conditions
http://tdsl.duncanamps.com/dcigna/tubes/sheets/misc/4300b-2h.gif
suggests that 450 V. on the plate and -103 V. on the grid will work with your "iron". Don't expect lengthy service life under that sort of regime.
Eli D.
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