dBX 376 and 586

[cvalona]

Hello, can somebody tell me if it's acceptable / OK, to swap the 12AU7 out for a 12AT7 tube.
I read some where that in some cases introducing a tube of a higher Gain rating could possibly
damage the rest of the unit's circuitry ? Is this true ? Would I be actually gaining, no pun intended
anything by making such a swap ? Maybe I'd be better off just up-grading to a better quality 12AU7.

Thanks for the help, clv

 

[ranjam]

I only have the 386, so I may be 100% off base. I really doubt you'll 'hurt' anything by swapping tubes. I also doubt the tube is doing much anyway, regardless of what dbx propaganda says.
Anyway, the 12AU7 has less gain that a 12AT7, so you'd have less gain overall if the tube did anything. It's too bad dbx are such @$$holes about releasing any service literature. Hell, I couldn't get parts when I needed them. So I'll never know what the tube does. What I should do, and you can do it as well, is this; take a signal generator with a measured 250mVAC or 500mVAC signal at say 1KHz or 500Hz, or whatever. Now set the drive to '0' or 'high noon', and see what you read on the LEDs. Say it's '0' or '+4' on the Analog Level scale. That's with a 12AT7. Now with a 12AU7 I'd expect '-8' or '-4' with the lower gain tube. Now, if the tube is there for decoration, or it's a cathode-follower circuit, the gain reading won't change. You won't know if the tube is doing anything (since it could be a cathode-follower circuit), but you'll know you aren't damaging anything. You could measure the Plate voltages, and if it's +200VDC with a 12AT7 and +180VDC or whatever with a 12AU7 you may be damaging something, and I wouldn't use a 12AU7. But experimenting is the only way to tell, and a great way to spend a Sunday afternoon.