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-   -   From KT90 to KT88 (http://www.diyaudio.com/forums/tubes-valves/182619-kt90-kt88.html)

ManUtd 6th February 2011 04:51 PM

From KT90 to KT88
 
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 6th February 2011 05:09 PM

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 6th February 2011 06:22 PM

Quote:

Originally Posted by rknize (Post 2459665)
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 6th February 2011 06:39 PM

Sounds like that amp will bias for EL34s as well.

ManUtd 6th February 2011 08:01 PM

Scematic
 
1 Attachment(s)
Quote:

Originally Posted by rknize (Post 2459759)
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 6th February 2011 10:54 PM

Correct.

ManUtd 7th February 2011 09:26 AM

Quote:

Originally Posted by rknize (Post 2460030)
Correct.

Thanks,

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

richwalters 7th February 2011 02:58 PM

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

ManUtd 7th February 2011 03:22 PM

Quote:

Originally Posted by richwalters (Post 2460505)
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.:mad:

rknize 7th February 2011 04:44 PM

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.


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