6550C v. KT88

[mr2racer]

Hey All,

I am curious to know impressions of these two tubes for sonic qualities? I converted my Dynaco Mark VI's to KT88's to get away from the hard to find 8417. But I'm not happy with the sound and wonder if 6550's would have been a better choice?

[Zero Cool]

or KT-120's

[the_manta]

Transconductance is a problem here:
8417: gm=23mA/V
KT88: gm=11.5mA/V

Why not use the EL509-2 made by SVETLANA ?
gm=18mA/V
Seems like a good choice and is available from new production.
http://www.jogis-roehrenbude.de/Roeh...L509-02_SV.pdf
Be aware of 300V max. screen voltage.

[ChrisA]

Originally Posted by mr2racer

Hey All,

I am curious to know impressions of these two tubes for sonic qualities? I converted my Dynaco Mark VI's to KT88's to get away from the hard to find 8417. But I'm not happy with the sound and wonder if 6550's would have been a better choice?

So you made two changes at once, new tubes AND some "conversion". It is hard to know if the tubes really do sound different or if it is something else you changed. Maybe tell us what you did.

I agree it is better to have an amp that can use new production tubes

[mr2racer]

I also replaced the front end with a 12AU7-12AU7 LTP. I think this is more likely the problem. I've rebuilt the original Dynaco boards and found a matched pair of 7199's so that will be the next modification. I used Mundorff silver in oil coupling caps.

Another possibility is EL34. I recently built an 8b copy and really loved that midrange.