6550 / KT88 with lowest heater draw?

[BassmanPaul]

Originally Posted by B-string

7027A's had higher design voltage ratings but were/are essentially a 6L6GC with an external suppressor grid connection.

Not quite Mr. B.

the 7027 is still a beam tetrode just like the 'GC. Pin one is a second connection to the screen grid. Very often pin one is grounded or used as a tie point. Dropping a 7027 into a 6L6GC socket will kill the screen supply. It does more damage if sub'ed for an EL34.

[dunwichamps]

True on the point about them handling a bit more plate and screen RCA datasheet say 600V plate 500V screen, better than a 6L6

[beans-on-toast]

Fortunately on most Ampeg amps, including the VT-22, pin-1 of the power tubes is left unused. Always good to check first because you never know if someone modded the amp and decided to use that pin.

[christw]

Originally Posted by beans-on-toast

Fortunately on most Ampeg amps, including the VT-22, pin-1 of the power tubes is left unused. Always good to check first because you never know if someone modded the amp and decided to use that pin.

Like my B-12XTC? Nothing like some B+ to wake you up.

From what I've read on other sites, before I try 6550 I might want to change the screen resistors from 470 ohm 1w to 1k 5w and change R50 to 82k. Seeing as how I'm not a total noob to circuit boards and soldering, I might consider doing this one on my own. It wouldn't be totally out of my league but it would definitely be a learning experience. I know enough to be safe and pass it off to a tech if I get in over my head. That's pretty important IMO. Thoughts?

[B-string]

Originally Posted by BassmanPaul

Not quite Mr. B.

the 7027 is still a beam tetrode just like the 'GC. Pin one is a second connection to the screen grid. Very often pin one is grounded or used as a tie point. Dropping a 7027 into a 6L6GC socket will kill the screen supply. It does more damage if sub'ed for an EL34.

Thanks for the correction Paul. I was going from memory, not the best idea these days. I was in a bit of a rush.

[beans-on-toast]

Originally Posted by christw

Seeing as how I'm not a total noob to circuit boards and soldering, I might consider doing this one on my own. It wouldn't be totally out of my league but it would definitely be a learning experience. I know enough to be safe and pass it off to a tech if I get in over my head. That's pretty important IMO. Thoughts?

It's the best way to learn. It isn't always easy going but you figure out what to do. Just try not to do more harm than good. It helps to have some descent tools.