whats the difference between an el 84 and ul 84

[lespaulblues]

I was wondering if i could use a pair of ul 84 mullards instead of el 84.
Whats the difference and can you do it.
Has anyone used them.
Thanks.

[zaphod_phil]

They need a 45V heater supply - see http://tdsl.duncanamps.com/show.php?des=UL84

There's also PL84s that take a 15V heater supply, and 10BQ5s that take 10V. So if you can find a suitable voltage heater transformer, you can use some great bargain NOS tubes.

[WaZaK]

UL84's need a 45V heater supply

That's interesting: @ only 100mA Ih.
Is there an equivalent (45Vh) 12AX7 that you are aware of?

[olddawg]

Couldn't you just use a separate heater supply transformer? It wouldn't be very big physically. You could also regulate a 12v transformer for a 10v filament. Sounds like lots of possibilities. If the rest of the pinout is the same you could even build switchable filament voltages to accomodate different tubes.

[klingo]

UL/PL84 have an amplification factor µg2g1=8
EL84/10BQ5 ........... µg2g1=19

anyway, from the datasheet you can get 18w out of them with 230v/plates, 200v/screens, 130R shared cathode resistor into a 4K OT.
http://www.mif.pg.gda.pl/homepages/fran ... p/PL84.pdf

however, a typical 18w preamp might not be the best choice under these kind of low voltages.(assuming the preamp is sharing the same HV supply than the power tubes.)

[zaphod_phil]

Surely, you could still run UL84s or PL84s at normal 18W type voltages and load impedances? When did guitar amp designers really care that much about maximum voltages shown in data sheets? Anyway, if those two have less gain, 10BQ5s may still be a good cheaper alternative for EL84/6BQ5s.