Power Tube Question

[4406cuda]

I already posted this on the main forum, but my main question was not answered.


I want to replace my KT 88 tubes with either Gold Lion KT 88 tubes or stick with Svetlana's.

In either case, is a Bias needed? I would like to just buy a matched pair and pop them in.

I don't bias my own amps.

 

[Alex_S]

Yes, most probably it is needed. That is not depending on the brand of the tubes but on the tubes values. So even if you would replace with the same brand you'd need to check and probably adapt the bias.

 

[Alex_S]

To be complete: if you don't check/adapt the bias you either have a bad sound or damage the tubes or both. So bring it to a tech if you can't do it by your own...

 

[LunatiBSW]

Bogner suggests getting it biased by a tech or oscilloscope for optimum results.
Think about it, you run optimum current by biasing fresh tubes for best operation.
It's like running premium 93 octane gas when it's recommended, do it and everything will run smooth, don't and it will usually have issues sometimes small sometimes larger

 

[4406cuda]

Thanks everyone, I suspected that would be needed.

 

[WormHoles]

Thanks everyone, I suspected that would be needed.

Always check the bias when replacing power tubes in any tube guitar amp.

It's simple: Pop the new tubes in, have a DMM that is capable of reading mA.

Tube Type Dissipation in Watts:
(1)6V6 (2)6L6GC (3)EL34 (4)E34L (5)KT77 (6)6CA7 (7)KT66 (8)6550 (9)KT88
(1)14 Watts (2)25 Watts (3)25 Watts (4)25 Watts (5)25 Watts (6)25 Watts (7)25 Watts (8)35 Watts (9)35 Watts

Ex: calculation - (Tube W)/(Plate Current) = Amps (100%)

ex: for KT88 (35W) & Plate Current (450) -> 35W/450DCV = 0.078A = 78mA
At 70% dissipation in Watts (78mA)x(0.7) = 54mA per tube - to be safe against low main voltage and out of crossover distortion.