Phonoland

I know the 6sk7 is the compensation control tube, my question is what is the difference between a 6sk7 & 6sk7gt tube?
Yes I know the GT is a "Glass Tube" version of the 6sk7, but is there any benefits or draw backs for using either version?

Ron,
In "general"--if the tube is called out with only "numbers", it is the first "version" of that tube, in which case, the later version(s), can be safely used. If however it is called out with a suffix, it is not always safe to use an older version( this would depend on circuit design).
Ron Rich

Ron & Ron In this circuit glass vs metal makes no difference.

Two things to look out for:

1) Hum due to heater-cathode leakage. This shows up when gain reduction, thus tube conduction, is highest. You'll hear it coming out of squelch and after a loud record ends...if the dade isn't long enough.

2) "Phony" SK7 In 1993 I bought some from ICC and they were unusable due to having a sharp cutoff instead of the long "remote" cutoff of a real SK7. I curved them and they looked like 6SJ7. Someone must have figured "what the hell -they look the same".

FWIW: I have glass Hickok SK7's in my V-VL location machines. They have been in there for 20+ years and still operate properly.

Rob

Hi Rob,
I don't know who/what "ICC" is--but if it's "International", I have heard "rumors" that they purchase tubes from "all over", "scrub"off all markings, and re-mark them ? I am pretty sure this has gone on, for years, by other companies, also---
Ron Rich

Yep, International. I only bought about 5, but being "frugal" myself, I decided not to waste them and designed a simple circuit to have them trigger an SCR to replace 2050 in stepper and trip service. Three of them died in less than two months, two lasted several years. Great quality control. I used a 'real" GE sk7 in the same circuit and it lasted 7+ years and was still good when I changed the design.

Rob