Did I lose a tube? Part 2

randog · « **on:** 20 Dec 2003, 04:58 pm »

I need your opinions!

The matched pair of Sylvania GB 5751's that I bought for my Norh CD-1 were gold pins. One blew.

The guy who sold me them has located another that tests within 10% of my good one, but it doesn't have gold pins.

Should I take it or wait until I can find another with gold pins to match? In other words, do you think the sonic differences will be discernible?

Also, is 10% an acceptable range for matching?

Thanks,
Randog

markC · « **Reply #1 on:** 20 Dec 2003, 11:57 pm »

IMHO 10% is acceptable, but if it ain't a gold pin, it aint the same tube.

randog · « **Reply #2 on:** 22 Dec 2003, 10:49 pm »

I was afraid of that.

Can I get another tubophile to concur with Mark?

Same tube but steel pins in one and gold in the other = no-no.

Thanks,
Randog

Wheezer · « **Reply #3 on:** 23 Dec 2003, 05:42 am »

Quote from: randog

Same tube but steel pins in one and gold in the other = no-no.

I'm coming at this from a hobby-radio perspective, so I'm sorry if this is apropos of nearly nothing, but I wouldn't rule out a replacement based on gold-plated pins versus unplated. If one is merely talking about a "ruggedized" (versus non) tube, it should in fact be "the same." (I don't mean to pooh-pooh the matching of tubes.) I guess I'm confused about that "10%" figure (10% of what?). Plate current?

randog · « **Reply #4 on:** 23 Dec 2003, 01:33 pm »

It just means they test within 10% of each other on a tube tester.

Randog

Wheezer · « **Reply #5 on:** 24 Dec 2003, 01:59 am »

Quote from: randog

It just means they test within 10% of each other on a tube tester.

Not knowing the kind of tester, I'd guess the metric is plate current. The effect of gold plating on the pins I would think to be negligible in comparison with +/-10% current. If the replacement is being offered gratis for the failed tube, I wouldn't sweat it--the 5751 apparently has slightly lower gain compared with a generic 12AX7, but one could always view the situation as an opportunity for blind A/B listening.

In any event, you might want to keep an eye on the Glowbugs mailing list; "www.tubeman.com" also claims matched GE 5751 pairs for about $50 (no affiliation on my part, nor have I done business with them).

I'm probably out of my depth here, though, so I'll just wish you good luck.