Glancing at the datasheet of S11E12, inner mu is 5.5, which is probably too low for Andy's application.
The very low filament voltage DH Tetrodes look interesting to me, YL1000, YL1130, YL1190 (they also have US designations). YL1000 is available and cheap at about £5 each but mu is only around 7-8. YL1130 has about twice the mu, so may work well and can be had for around £10; PSE with series heaters may be an option. YL1190 is harder to find and the filament is current hungry; I have some of those and they measure nice in triode, I had thought of running them from NiMh batteries.
The very low filament voltage DH Tetrodes look interesting to me, YL1000, YL1130, YL1190 (they also have US designations). YL1000 is available and cheap at about £5 each but mu is only around 7-8. YL1130 has about twice the mu, so may work well and can be had for around £10; PSE with series heaters may be an option. YL1190 is harder to find and the filament is current hungry; I have some of those and they measure nice in triode, I had thought of running them from NiMh batteries.
Lots of interesting ideas here. I'm also considering something simple like PSE EL84 or 6V6. Not sure which would sound better - they both have their fans. 6V6 could open the door to 6W6, but unfortunately these are harder to find in the UK.
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I still think that you should try the F2a. It's a 10 000 hour tube with a mu of 17 and rp of 1 KOhm. If you run it conservatively it will last a lifetime. It is a very good sounding tube. If i’m not mistaken you have a pair?
You're right, it's been a while since I last looked into this type and I hadn't realized that the original NOS tubes were this expensive. There are however current production Shuguang tubes that go for about $250 a pair on Aliexpress.
EL3010 is another interesting valve - keep them coming! Not for me this time, rare and expensive in the UK.
I've been horny for those for years now but the price is prohibitive. They would be the ultimate cathode follower drivers in my class A2 amps... 😎
Andy, you mentioned low mu drivers in the first post. How low, or to put it differently: how many volts of drive signal is available for the output stage?
Cathode biased using 400 ohm cathode resistor with 31.7 volts across it.
If I used a 3.5k primary instead of 5k primary the drive requirement would be lower
Steve
I use a variety of drivers in separate chassis from the output chassis. I have 6C4C, 26 and 10Y for the DHTs and 27, 37, 56, 76 for the indirectly heated drivers. I like them all. I tend to use 56 and 27, mu of 13.8 and 9, since they're simpler and in a smaller chassis, and I have plenty of them. 56 is punchy and 27 mesh is more subtle.
Those number are not horribly low, assuming a normal line output level from the source and that the input tubes have plate loads that doesn't load them down. Should be enough to push a trioded EL34 or similar into clipping. KT66 perhaps?
56 and 27 work fine into trioded EL6, EL12 types I normally use, and I have a good sounding amp that uses 5881WXT+ but that's a 5K OPT. The EL34s I have just didn't sound that great in triode.
I never use gyrators, just resistor loads for the drivers.
I never use gyrators, just resistor loads for the drivers.
A bit more info about the opt would help, EL3010 or E130L could be an option in either triode or as pentode with a-g1 fb.
If interested in any of those tubes, make me a offer, i have some i could let go for a decent price (mind you, the EL3010 costed once the equivalent to a month salary, 1400,00DM a pcs, so even on ebay they are dirt cheap today)
EL34 in triode is also a good option, (but may actually be more expensive per hour than a E130L) a bit higher than 3.5k load would be better, but hey, triode isn exactly picky about that
If interested in any of those tubes, make me a offer, i have some i could let go for a decent price (mind you, the EL3010 costed once the equivalent to a month salary, 1400,00DM a pcs, so even on ebay they are dirt cheap today)
EL34 in triode is also a good option, (but may actually be more expensive per hour than a E130L) a bit higher than 3.5k load would be better, but hey, triode isn exactly picky about that
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