I've tried shining on it with a flashlight, UV-light and putting it in the freezer, but to no avail.
It seems to be a Mullard tube, and the last (?) digit is 1.
Rather tall loctal, taller than ECH21 and the likes. Makes me think it's a power tube, but I'm no pro.
I've attached a few pics; tell me if you need others and I'll happily upload 🙂
It seems to be a Mullard tube, and the last (?) digit is 1.
Rather tall loctal, taller than ECH21 and the likes. Makes me think it's a power tube, but I'm no pro.
I've attached a few pics; tell me if you need others and I'll happily upload 🙂
Attachments
Thank you! EBL21 and UBL21 seem to have the exact same pinouts and specs according to the valve museum (EBL21 @ The Valve Museum, UBL21 @ The Valve Museum). However, they are not listed as interchangeable. What's the difference between them?
Is there a 'code' pressed into the metal base? Or painted between the valve pins?
K7* = EBL21 (6.3 volt @ 0.8A heaters)
NP* = UBL21 (55 volt @ 0.1A heaters)
No not interchangeable. Put 6 volts across the heater pins and measure the current perhaps.
K7* = EBL21 (6.3 volt @ 0.8A heaters)
NP* = UBL21 (55 volt @ 0.1A heaters)
No not interchangeable. Put 6 volts across the heater pins and measure the current perhaps.
Last edited:
Yes, it says
YH
K7F
So EBL21, then. Thanks a lot!! How do you know all this stuff? 😵
I guess the page at the valve museum is in error. I should make it a habit to always check more than one source..
EBL21 or UBL21 are one of the great forgotten fantastic linear pentodes; not to put too fine a point on it, if you run a matched quad of them they are BETTER than a pair of EL34 with lower distortion and without the massive g2 melting emissions of that.
sshh!
The snag with the UBL21 is the heater. In theory 4 could be run from an isolation transformer for 230V, with a small drop. How do people solve that? I also have a lot of UCL11 that I'd like to take advantage of.
The snag with the UBL21 is the heater. In theory 4 could be run from an isolation transformer for 230V, with a small drop. How do people solve that? I also have a lot of UCL11 that I'd like to take advantage of.
Last edited:
The heater of the UBL21 is 55 V./100 mA. A "universal" Triad N-68X will easily feed a pair of 2 tube series heater strings. Insert a 150 Ω/5 W. resistor in each string, to guarantee tube survival, even if the AC mains voltage is high.
The UCL11 is 60 V./100 mA. So, only 5 V. need be dropped per tube pair, when fed by a N-68X. Therefore, a 50 Ω/2 W. dropping resistor in each 2 tube heater string is appropriate.
Triad do 230-230V toroid isolation transformers dirt cheap.
You would use 8 off of the UBL21. (2 quads).