Grrr. Lost a GE 6L6GC yesterday.

[efhjr]

:cry:

One of the GE 6L6GCs I had in one of my McIntosh MC30s died on me yesterday night, right as I was powering up the system for the weekend. It was one of four GE 6L6GCs I have. It was popping and scratching loudly when I powered up the system for the previous few days, and then last night I realized its plates were glowing. So I powered down the system, yanked that sucker out, and popped in some 6L6s I had as backups -- two RCA black cans and two generic-looking tubes (Sovteks, I think).

Well, at least I think it died. The popping stopped when I pulled it, and those glowing plates were scary.

I was surprised at how the highs became muddier but the bass louder when I replaced the GEs, but I prefer the GEs. They're just magical.

Guess it's time to find one or two more GEs.

Anyway, thanks for letting me spill my guts. That GE was one helluva tube and it'll be missed.

[Steve Hoffman]

They are everywhere. Get another one (or three). Make sure they are from the same era though. I only use GE's in my Mac 30's. Every other tube just doesn't make it (in the qualities that I like, namely Midrange Magic).

[indy mike]

Say Boss, what do other makes from the NOS world do to the sound? Do some do a number on the bass as mentioned in the initial post (which in my case might not be a bad thing, if I had a pair of neat-o Macs, that is)...

[Steve Hoffman]

Originally posted by indy mike
Say Boss, what do other makes from the NOS world do to the sound? Do some do a number on the bass as mentioned in the initial post (which in my case might not be a bad thing, if I had a pair of neat-o Macs, that is)...

Well, RCA's are brighter than the GE's. KT-66's like Genelex and Gold Lions sound like your "loudness" button has been pushed; top and bottom but the mids suffer.

The GE's have a "rightness" that I've never found with other (and usually more expensive tubes).

[audio]

Don't know if you want it, Gene, but I've got a NOS Genelex KT 66 in original box. If this floats yer boat, send me a PM and we'll take it over to the classifieds.

[Gary]

Huh. Starting to feel guilty about my spare GE's. Efhgr, if you want, send me a PM.

[electrode10101]

I would definitely check the 12AX7 driver tube, and the voltages around the 6L6's to make sure everything is operating properly. Tubes usually glow red when there's either a short, or a lack of bias voltage, causing excessive current draw. Use the voltage tables in the operating manual as a guide.

McIntosh amps are pretty gentle on output tubes, so something like this could mean a problem underneath.

If you don't do the work yourself, seek out a good tech.


John Diamantis

[Ronflugelguy]

A driver tube on my 240 was causing my output tubes to glow red.

[efhjr]

Originally posted by electrode10101
I would definitely check the 12AX7 driver tube, and the voltages around the 6L6's to make sure everything is operating properly.


Thanks for this info, John. I currently have a black RCA in the spot where the GE was glowing, so I can't tell if the RCA is misbehaving or not.

OK, a couple of questions:

Could the glowing be caused by not having the gain control set properly?

Does the 12AX7 drive both 6L6s, or should I consider rolling another one of the 12* tubes?

[Steve Hoffman]

In a McIntosh 30, if you look at the amp from the front, the four input tubes are the following. left to right:

12AX7: The driver tube (most important of the 4).
12AU7: Phase splitter.
12BH7: Differential driver.
12AX7: Cathode follower (lowers impedance).

These tubes should be checked on a good tube tester to get the most out of your amp...

[efhjr]

Thanks for the help, Steve and everyone else.

I replaced the two 12AX7s, and now the power tube closest to the front of the amp is glowing, and the one behind it isn't glowing at all. The amp is making music, but I am concerned.

Suggestions, anyone?

[Tullman]

I have read the Groove tubes is now making GE 6l6's. They are using the original machinery and schematics.

[electrode10101]

If you still have an output tube that is glowing, something is "broke".

The "gain" control will not effect the tube operation.

If you have still another 12AX7, try it in the "cathode follower" position. If this doesn't solve it, you have a problem with the bias circuitry. (could be a bad resistor (usually is) or cap.)

Swap the output tubes. See what happens. If the same tube glows red in the other socket, maybe it's bad.

Take the output tubes from the other (good) amp, and plug them in to the one giving you trouble. If the tubes glow red on the superstructure (big grey part in the middle), turn off the amp, and bring it to a tech for service. Make sure they understand tube equipment, of course. :rolleyes:


John Diamantis

[NOSValves]

Sounds to me like that amp is in need of a checkup for sure !! I would take it out of service pronto.

Craig

[efhjr]

Swap the output tubes. See what happens. If the same tube glows red in the other socket, maybe it's bad.

Thanks for the insight, John.

I replaced both 12AX7s with newer Ratheons (the old ones were Telefunkens). I also rolled the 6L6s. Now there's no popping, no glowing plates, no nothing, just happy music.

I *believe* I may actually have had two bad 6L6s (I had a Sovtek that wouldn't glow in either socket), and a flaky 12AX7 may have been complicating things.

I believe I will call around my home town to find someone to check out the resistors, caps, and voltages in the amp to make sure it's running up to spec.

[NOSValves]

efhjr,

Be very careful and keep a close eye on the plates with the room dark there should be absolutely no glow to the main plate structures with the room dark! It may have indeed just been tubes but this is not something to play with. A output transformer is a terrible thing to waste.

Craig