Dynaco Mark II's, 6550 tubes possible?

Archived from groups: rec.audio.tech (More info?)

In article <1123120644.116675.78680@o13g2000cwo.googlegroups.com>,
tomrp@juno.com wrote:

> Is it possible to use 6550 tubes in Dynaco Mark II amps? These were
> originally made for EL 34 tubes, but someone told me that if the bias
> was changed to 1.92 mv, 6550 tubes work fine.
>
>
> ????????
>
> Tom
>

You can use 6550 tubes. The bias voltage can even stay the same, 1.56
Volts (not mv), the tubes will run cooler and last longer, maybe even
sound better. Dyna ran the 6550 tubes pretty hot in the Mark III, they
did not have a real long life. In the Mark III, I run the tubes at 1.25
Volts, which is about the same heat as 1.56 Volts in the Mark II.