Initial voltage at tp1 and tp2?

[garyb]

Hi, I'm about to fire up a pair of eiclones, if you'll excuse my newbie question, what should the initial bias voltage be on tp1 and tp2 for 6550s?
Thanks
Gary

[TomMcNally]

Hi Gary -

With tubes in the sockets, inputs shorted, and a load
on the speaker terminals (speakers are fine)
adjust for 550 mv to start. I think Shannon would
push 6550's as hard as 650 mv (55 ma or 65 ma respectively)
If the plates get red, turn 'em down a little !

Good luck with the amp - share some pictures if you can.

... tom

[garyb]

Thanks for the quick reply. So -50v at tp1, tp2 is ok without tubes? The reason I ask is I built a pair of posideons with El34s and then replaced them with kt90s without turning down the bias pots, (that mistake won't be repeated).
Gary

[TomMcNally]

Yep ... -50 v with no tubes is the place to start.
When the tubes are in, check everything quickly
and adjust as necessary.

It's all in the manual - take a look at the first message in the
Eiclone forum.

... tom

[garyb]

Thanks for your help. Fired up one eiclone and it sounds great. Even after reading the documentation numerous times before my first post I guess a little paranoia set in. The bias voltage went to over .9v before bringing it down to .65v and all is well.
Many thanks
Gary

[Shannon Parks]

Good to hear you are firing up some Ikes. I might start at 50 or 55mV, and then take a plate voltage reading. Let's say you adjust it to 55mv and then read 480V at the plate. That means we are dissipating 480v * .055A or 26.4W on your 6550, which has a max dissipation of around 48W. I might shoot for 70% of max dissipation which is 33.6W as a goal. So then I'd adjust in 5mA (ie 5mV) increments upwards until I got close to 33.6W at idle. You have to carefully measure your plate voltage, too, to see how lossy your power transformer is. But you only need to do this during the first tune up.

[garyb]

Thanks for the additional advice, I'll adjust them. All the parts are off of the rev A BOM. No photos, but they look just like Toms' amps.
Gary