Jolida 1000p 6550 model - EL34 substitution

Hello all. I recently purchased a Jolida 1000p amp, brand new. The amp normally comes with EL34 tubes, but 6550/KT88 tubes are offered as an "upgrade." The listing said the amp would be the EL34 version, but I got the 6550 version. Since the amp is advertised as being able to use one tube or the other, would I be able to substitute EL34 tubes after a bias adjustment? If I understand correctly, one cannot put a 6550 tube in an EL34 amp, but perhaps you could do it the other way around, since the EL34 has lower plate voltages.

I already know of the inherent voltage incompatibility of the two tubes. I am asking about this amp, in this instance. Thank you.

 

JD 1000 P | Jolida

The EZ-Biasing system make the operation and the maintenance of the JD 1000 BRC a simple matter.

sez their web page, but it would be worth contacting them to verify their bias system.

 

What does the manual say? Since biasing is automatic (as best I can tell), there's either going to be a switch somewhere or else plug and play.

 

The manual operates under the assumption that you chose the EL34 model. It makes no mention of substituting tubes or 6550 tubes at all.

Biasing is done with tiny knobs next to the tubes.

 

Does anyone else have any input about this substitution?

 

Jolida
21310 Ridgecroft Drive
Brookeville, MD 20833
(301) 953-2014
[email protected]

 

I emailed them a week ago, but these guys are painfully slow about replying to me. Maybe I ought to give them a call...

 

Maybe your dealer/person you bought it from might know?

 

You should. Most amps built for the 6550 will be able to handle either. If it was set-up for EL34 though, it might not have the bias range to go up to where a 6550 is normally operated. The LED readings will also be off when you use a different tube, so you'll have to ignore those and use a meter. But to optimize the circuit for either, it really should be modified a bit to suit your favorite. In short, it's best to find an amp that you like the sound of and stick with its intended tube complement.
-Bill

 

You can substitute an EL34 for a 6550 or KT88, if it will correctly bias the EL34.

Where you have to be concerned, is where you have 6550/KT88 power amps that are designed to push the tubes hard to get the maximum power.

Amps like these have high plate voltages and the output tubes are run hard.

EL34's will have shorter lives in these applications due to the wear. They are smaller bottle design than the 6550/KT88 and they don't dissipate heat as efficiently as the larger bottle 6550/KT88's do.

 

I received an email back from Jolida last week, and they confirmed that either model will accept either tube type. The only caveat is that the EZ bias system is effectively worthless if you put the other tube type in its irrespective model, since the EL34 model wants 400 milliamps, and the 6550 model wants 500. I biased mine manually to 420 milliamps.

Running the 6550 model with EL34 tubes creates an interesting effect when listening to music, as the increased voltage during loud volumes will cause the bias LEDs to light up during the peaks!