6CG7s in the 007t

[sschell]

Until now, I've been using the included GE 8CG7s in my 007t. Today, however, I received a set of Japanese-made B&K 6CG7s and swapped those in place of the GEs. I then went through the re-biasing procedures (akin to trying to enter a revolving door in the middle of a tornado). Now for the problem...

With the pot turned all the way up, I'm barely getting any volume. This is compared to the ear splitting volumes the 86G7s put out at about 9 o'clock. Are the tubes bad, or did I not bias them properly?

[kevin gilmore]

First time i've even heard of 8cg7's in an 007t. if the unit really was set up for the 8cg7's then the filaments of 6cg7 would

be way high. In any case unless the tubes are competely toast, if they bias right, then they pretty much have to work.

In fact if the tubes are toast, they would not bias correctly.

offset to make the difference between the tubes zero

bias to make the difference between each tube and ground zero.

[sschell]

I guess that really depends on what you define as "right". I was able to bias the tubes' filaments dead on 0 for TVR 3 and 4 on both channels. TVR 1 and 2 are probably within 1.5V of 0, but I wasn't able to get them to settle. I had about the same result with the 8GC7s, which I settled on as "good enough", so I figure the same would be true of the 6 volt version.

[kevin gilmore]

+/- 10 volts in any direction is just fine. You can get it to zero but it won't stay there due to the unregulated power supply.

Has to work.

[luvdunhill]

86G7? wtf? did you try the old tubes, does the amp/headphone still work with those?

[Dusty Chalk]

I think that was a typo, I think he meant 8cg7 (which he says earlier in the post).

[sschell]

Chalk it up to user error. The new (and old) tubes are fine. I accidentally plugged my iPod into the Tape input, instead of the regular input. My dad hit the input switch and just about blew out my eardrums.

All is well.

[Dusty Chalk]

Doh!

Hey, I'm just glad the fix was easy (albeit painful).

[spritzer]

First time i've even heard of 8cg7's in an 007t

Only some of the II/A units have them. Rumor has it that Stax found a large stash of 8CG7's for virtually nothing...

[sschell]

I should note that I bought my 007t (and O2s) used on eBay, I'm assuming from Yama's (seller was from the same town in CA). So my tube compliment may have differed from what was originally shipped from Stax.

[spritzer]

I've never seen one of the 8CG7 amps but it would be mighty reckless of Stax not to mark them in some way. I'm sure they know the bias procedure for these amps is well known and people are replacing the tubes. Perhaps why Stax is moving to the ECC99 since it is only new stock and the only upgrade would be to the gold pin version.