From KT90 to KT88

[ManUtd]

Can i just swap them?
My amp uses 4 peaces KT90 and i want to change to KT88.
Do i have to put in one by one adjusting bias seperately?
What`s the difference in bias on these tubes?

Regards,
ManUtd

[rknize]

They should swap fine. What amp is this? The KT88 does have slighly lower plate dissipation, so you may want to turn the bias down a bit before putting them in. Do them in pairs or all at once, not one at a time.

[ManUtd]

Originally Posted by rknize

They should swap fine. What amp is this? The KT88 does have slighly lower plate dissipation, so you may want to turn the bias down a bit before putting them in. Do them in pairs or all at once, not one at a time.

Thanks for Your reply.
It is a chinese amp. Push Pull design.
Ming Da MC368-B90

[rknize]

Sounds like that amp will bias for EL34s as well.

[ManUtd]

Originally Posted by rknize

Sounds like that amp will bias for EL34s as well.

Here is scematic with KT90.
Is it 33k at V1 and V2 ? for Bias adjustment?

What will readings be with KT88 ?

[rknize]

Correct.

[ManUtd]

Originally Posted by rknize

Correct.

Thanks,

And those measurement should be similar, no difference in measurement?

[richwalters]

220K grid leaks must be a record value with fixed bias around 500V B+. Pray it doesn't get flogged.

[ManUtd]

Originally Posted by richwalters

220K grid leaks must be a record value with fixed bias around 500V B+. Pray it doesn't get flogged.

I`ll check with my amp inside.
Found this schematic on net.

[rknize]

The amp may have been designed with EL34s in mind. If the coupling caps are 0.47uF per the schematic, you should be able to use 100k gird leaks without losing LF response.