M90, possible to change KT88 for 6550 with just bias adjust?

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RG955TT

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I really like my M90 but would like to move it a bit more to the organic side and get rid of some of the metalic top end that KT88's are known for. Anyone experiment with a change to 6550's? Is this possible with just the bias trim pot in the amp? Thanks
 
Hi RG955TT.

Yes you can change the kt 88's to 6550's.
The bias trimmer's range will be enough for biasing different grades of 6550's.


Jan
Elmwood Amps
 
Thank you, in your opinion would this give me a little less metalic top end on the more gainy sounds? Again, I love the map I just want to move it a bit towards more organic, smoother top end. I think perhaps I should have purchased the M60 with EL34's for that but would appreciate any insight you can give me. Thanks

Bob
 
Hi Bob

The 6550's and KT88's are both beam tetrodes.
They do differ in sound and response.
There are big differences between brands and grades even within the same type.

EL 34's, pentode, will work in the M90 too due to the fact that the screengrids have a separate lower voltage winding, you might have to change resistor R 066 to a higher value to obtain the right bias for EL 34's.

Jan
Elmwood Amps
 
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