EL34 to KT90

HI,

I have an integrated tube amp rated 50watts per channel and its using 4 EL34. I'm thinking to replace the tube with KT90 will this have any bad effect on my amp ?

I have run the amp with KT90 for 2 hours and everything is ok. Will it blow the output transformer ?

Aki,

R u sure kt90 is a direct replacement to el34? I did replaced 6550 tube with kt90 in my Cj premier 11a. My amp don't like the tube, after few months the kt90 tube died。

For El34 tube replacement u may try EH 6ca7, this is a direct replacement.

its not a direct replacement, i just want to know will it damage my amplifier if i keep using KT90 in long run.

Kt90 ? At most according tube guitar kakis said KT77 is closest to EL34 besides 6CA7. KT90 is kinda of a long shot don't ya think ??

yah i know, will it damage my amplifier ?

Last time Ella power amp sold by diyhifisupply.com can interchange between el34/KT88/KT90 just by adjusting the bias. If your amp is fixed or auto bias, damage might be imminent.

Assuming yours is manual bias, the voltage/mA rating for biasing the KT90's are still unknown for your amp.

mine is auto bias, i think i should stick with EL34 to avoid damaging my amp.

Anyone should be fully aware, read, diagnose and analyse the operating parameters of the amp circuitry and architecture in question before popping in other kinds of tubes, you've no idea what may happen next. Trial n error in this case may result in either way and surely banking on your own luck nothing bad happens. This isn't a good approach.
1. Is the heater supply and B+ current capacity sufficient to cater for bigger valves than EL34 or its suggested alternatives?
2. Is the output transformer size capable of sufficient anode current for KT90 or 6550 types?
3. Does the output transformer anode to anode (push pull) resistance within other tube operating specs?
4. Is the power tube location to each other have enough breathing space so there's no overheating? (power tubes need at least 1" or more apart for better ventilation)
5. Tube circuitry have dangerous and fatal voltages inside. Know exactly what you're doing!
The above are some due consideration in circuit analysis before doing anything outside manufacturer recommendations on alternatives. As far as I know, best and safe to stick to designed tubes or recognized alternatives, not bigger variants that may not even perform to its actual potential as they're designed with entirely different operating perimeters.
My 2 sen.

P.S. If you like KT tetrode tube, KT77 maybe a direct swap for EL34.

Yes, if I were u , I will stick back to el34 to aviod any damage to your amp. What make u change your el34 to kt90? U don't like the sound of your amp? What it is lacking?

Lack of power

Lack of power may be due to many reasons of which:

1. The design of the amplifier itself, from input sensitivity to circuit design operating parameters and likely output transformer limitations if any.
2. Speaker inefficiency that may require more amplification power.

Swapping for bigger tubes doesn't equate to getting more power out of it. The circuit design determine optimal power output with least distortion decided by manufacturer. For example, Quad II uses KT66, only 15W tube power, but in a Mullard design can be at least 35W peak power using the same tubes.
Manufacturers design a amplifier circuit based on a given tube's operating parameters, NOT the other way round.