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I need recommendations for an output tube that works well with up to 50mA with 5K single ended output transformers. The 45 and the EL84 is an obvious choice but what else? Is there something exotic, strange or unusual that would work well with these parameters?
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6CK4 is an IDHT, simple to implement an will net you ~2 watts. Triode strapped 6L6s (6bg6g, 807, 6V6s, 6ar6s...) will work within that range.
50s are not that expensive when compared to their sound quality.
Given their low bias rating I'll guess that they are smallish xfmrs; making the 6ck4 or 6v6 the best bet.
6CK4 and its cousin 6AH4 should be on the list for sure. Y'all can go out an hoard all you want, I have a decent stash of each already...heh-heh-heh.
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
and get a tetrode like the 4-65 and use its g2 as anode. Check it for dissipation ratings, but IIRC it is 10 or 15W. The larger 4-125 is sporting a 20W g2...LOL
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
300B at between 300 - 350 Volts plate to cathode (running at 50mA).
91.
"Confusion of goals and perfection of means seems to characterise our age." Albert Einstein
I have a pair of old 300B tubes. Maybe that's an idea. I've read that 300B tubes doesn't sound good with low current and low voltage but who knows. Anyway how many watts can you expect with 50mA?
+1
That operating point/range sounds good to me, albeit at lower power. The 300B would last longer too..
Type 2E24 will work with this load. As Andy suggests, run filament bias. Schade plate-to-grid with a pentode driver.
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
6JT8 😀. JH
nt.
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
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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