Simul/EQ C+ owners using STR-447's in Class-A?

[JOEY B.]

If you fit into this category, try a little experiment for me please. I have 2 sets of the MESA EL-34 STR-447's (one green pair and one grey pair). Both of them exhibit a very slight orange glow in the middle of the tube (the early look of a redplate condition) when I play my amp at these settings in Class-A mode. I just had an inner 6L6 STR-440 blow out and take a screen grid resistor with it :shock: . All the voltages in my amp test good when it is at an idle state, I am just wondering about the "under load" state. If you meet this criteria, set your amp like this, cut the lights down low and give it hell (low note power chording) for about 2 minutes while watching the tubes and report back. I am looking for some peace of mind, as my #6 GT6L6-GE's do not do this when put into the same sockets. I am hoping it is just the tubes, not the early stages of a bias supply capacitor issue.

1000 thanks to all that can help,
(Paranoid, does not want to see another smoking C+) Joey

Class-A
Presence-3
Pull these knobs: Treble, Master 1, Lead Drive, Lead Master

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[JOEY B.]

Both of them exhibit a very slight orange glow in the middle of the tube (the early look of a redplate condition) when I play my amp at these settings in Class-A mode.

Joey,
Not sure what you are looking for.
Do you want to know if others EL34's exhibit the same orange glow under the settings you state?

I am only looking for the STR-447 owners (hopefully the green or grey color codes). Other brands may or may not exhibit the same symptoms. Give it a try though, if you want. If other brands did the same thing, I would feel much better 8) .

 

[Octavarius]

Strange, man. :shock:

I do use both STR-447 EL34's and STR-440 6L6's in mine (all grey), and the 447's glow like they normally should. I actually use nearly the same settings as you do, exept having the masters cranked up that high, but as I said, all tubes glow normally. Even in Class A.

I did have a red plating issue a while ago where the right 447 would constantly short, even after I changed the tube out. But it hasn't been doing that in a while now... They were probably running to hot with the export bias, so I'll be ordering some cooler EL34's next time.

I'm not at home right now, so I can't try anything out, but as soon as I get the chance I'll check it out. But I don't know if it'll be the same since mine's an export where the bias voltages are different.

 

[JOEY B.]

Strange, man. :shock:

I do use both STR-447 EL34's and STR-440 6L6's in mine (all grey), and the 447's glow like they normally should. I actually use nearly the same settings as you do, exept having the masters cranked up that high, but as I said, all tubes glow normally.

If the master volumes are reduced from these settings, there are no issues with tube color on the EL-34's. But at these settings my GT 6L6's look fine :? .The export bias may make a difference. Let me know what happens.

 

[JOEY B.]

Redneck Update!!!

The very slight orange glow in the extreme center of the STR-447's must be something inherent to this particular brand/type of tube played at these settings in Class-A mode. I transplanted the tubes from my C+ head into my C+ combo (which had a complete checkup with Mike B. on 3/6/06) and had the exact same tube color situation at these same settings. It does not happen in Simul-class mode. The amp sounds fine, but after my 6L6/smoked resistor issue, I became very aware of the tubes while playing. A very special thanks to Ed (Boogiebabies) for helping to calm my nerves and verify the integrity of the circuits in question .

 

[JOEY B.]

I picked up some brand new STR-442's (dusty box) from my local Boogie dealer. I let them burn in for about 2 hours. When I get the chance to crank it loud, I will make some observations and report back to the board.

 

[Boogiebabies]

I think the gray is a bit too hot and Class A just pushes them over the edge. It may just be a situation where the voltage spikes up 10V which draws more plate current, then puching the master volume makes the draw even higher. At idle it may sit fine, but under a good load it has to be drawing much more bias than you can imagine. Sometimes they may swing another 15-20ma more under load. I don't trust the Sovtek EL-34 over 465V's or a much cooler grade in 485V Simuls. Those NOS Svetlana 442's are a bit tougher. Even with a gray, you should not have a problem. I have a duet of STR-447's in gray, but you have me too skeert to see what they draw.

 

[JOEY B.]

I don't trust the Sovtek EL-34 over 465V's or a much cooler grade in 485V Simuls. Those NOS Svetlana 442's are a bit tougher. Even with a gray, you should not have a problem. I have a duet of STR-447's in gray, but you have me too skeert to see what they draw.

The STR-442's that I found are the "green" color code, which may be a slight bit cooler than the "gray" Sovtek. You may have hit the nail on the head concerning current draw under load. I have one pair of green 447's and one pair of gray 447's. They both exhibit the same condition. I hope to have the chance tomorrow night to put the Svetlanas to the test.

 

[JOEY B.]

One more blue flaming STR-440 6L6, and one more blown screen grid resistor. This time it was the other socket and resistor. The amp is back up and running with ALL svetlana tubes and another new fuse and resistor. Wish me luck, dammit. :evil: I'm about to request a quad of STR-415's from MESA if these Svets do not do the trick.

 

[Octavarius]

Yeah, Mesa told me to run Red or Yellow on both pairs too. They said "especially in the 6L6 positions".

 

[Boogiebabies]

One more blue flaming STR-440 6L6, and one more blown screen grid resistor. This time it was the other socket and resistor. The amp is back up and running with ALL svetlana tubes and another new fuse and resistor. Wish me luck, dammit. :evil: I'm about to request a quad of STR-415's from MESA if these Svets do not do the trick.

Sweet baby Jesus !!!

At this point, I would say you have bum STR-440 tubes. I would also look at carbon build up or really dirty tube sockets.

 

[JOEY B.]

Sweet baby Jesus !!!

At this point, I would say you have bum STR-440 tubes. I would also look at carbon build up or really dirty tube sockets.

I have had a total of four "suspect" STR-440 tubes, each coming from a different pair. One blue, one gray, and two green. I ended up using the better looking tube from two pairs of "green" 440's in the inner positions on my combo with no issues (yet). The tubes that have a faint blue glow at idle (which is normally no big deal) have been the ones to give a problem under a a heavy load in either amp. I saw the last one fail. It went from a faint pusling blue glow to a white/blue haze over the entire tube. Then a spark came from the center near the grid, and that's all she wrote :evil: . I will be calling Mike today to get his take on all this, his opinion on the color code/position of the 6L6's and EL-34's, optimum current draw and what not, in a Simul C+.

 

[Octavarius]

Yeah, Mesa told me to run Red or Yellow on both pairs too. They said "especially in the 6L6 positions".

What does that mean? Especially when using 6L6's in the outer two sockets (make sure they are red or yellow too)? Or especially when running El34's and the amp is switched to Simul, meaning the inner two 6L6's are engaged?

Sorry Joey don't mean to hijack.
I hope BB is right and it's bad tubes. While they can handle hegher voltages it'd be a bummer to see this happen to some NOS 415's. Yikes!!!

He meant the inner 6L6 pair. He said it in this way; "You should shy away from using Blue, Grey or Green colored tubes, especially in the 6L6 positions"

Sweet baby Jesus !!!

At this point, I would say you have bum STR-440 tubes. I would also look at carbon build up or really dirty tube sockets.

I have had a total of four "suspect" STR-440 tubes, each coming from a different pair. One blue, one gray, and two green. I ended up using the better looking tube from two pairs of "green" 440's in the inner positions on my combo with no issues (yet). The tubes that have a faint blue glow at idle (which is normally no big deal) have been the ones to give a problem under a a heavy load in either amp. I saw the last one fail. It went from a faint pusling blue glow to a white/blue haze over the entire tube. Then a spark came from the center near the grid, and that's all she wrote :evil: . I will be calling Mike today to get his take on all this, his opinion on the color code/position of the 6L6's and EL-34's, optimum current draw and what not, in a Simul C+.

Same thing happened with one of my grey EL34's. Only it didn't die. And that was in Class A with Master 1 at 3-4 and LD Master at 3. It happened when I switched back to Simul-Class, so it was probably the pulse from the switch that made it knock over.

Mind asking Mike about a Simul export model as well while you're at it? Please?
And let us know what he says, 'cause I'm really interested in this issue as well. :shock:

 

[Boogiebabies]

When you look at the export transformer, it is basically from the IIB era and only puts 450-460 volts to the plates. The negative voltage is higher as the plate voltage is much lower than the 105. The lower plate voltage, the higher the negative voltage appears to bias the tube to the same level. Under load, the X-101 may only put 430-440 volts to the plates. Even if it had a stout tybe with a strong natural current draw, red plating an STR-447 may have more to do with it's design and internal shorts. The 105 is just a headroom beast and under a 35ma load still hold 483 volts to the plates.
In audible terms, the X-101 would provide a different harmonic spread than the 105 due to the lower plate voltage. The 105, however has superb attack, headroom and may be deemed less forgiving as it does not blur notes like lower voltage power sections. Now, since all of my Euro friends seem to have a monopoly on the export model, especiialy Swedes, Norwegians and cheeky Brits, I will have to be really nice to you guys and hope one is bequeathed to me in on of your wills. Octavarius's superb example has cost me a few nights of sleep.

 

[Octavarius]

When you look at the export transformer, it is basically from the IIB era and only puts 450-460 volts to the plates. The negative voltage is higher as the plate voltage is much lower than the 105. The lower plate voltage, the higher the negative voltage appears to bias the tube to the same level. Under load, the X-101 may only put 430-440 volts to the plates. Even if it had a stout tybe with a strong natural current draw, red plating an STR-447 may have more to do with it's design and internal shorts. The 105 is just a headroom beast and under a 35ma load still hold 483 volts to the plates.

Hmm. That's interesting. Well, I'll try cooler rated tubes, and we'll see what happens. I'm really interested in hearing what Mike B has to say about this all. :shock:

In audible terms, the X-101 would provide a different harmonic spread than the 105 due to the lower plate voltage. The 105, however has superb attack, headroom and may be deemed less forgiving as it does not blur notes like lower voltage power sections.

I really feel the urge to try a 105 next to my X-101 right now. I guess you do too.

 

[JOEY B.]

No word yet from Mike, but the slight redplating does not happen when the amp is in Simul mode, only in Class-A. And only with the EL-34 type tubes. I tried a quad of #6 GT6L6GE 6L6's in this amp with no redplating or blue flaming in Class-A or Simul modes. I also played my combo today that has STR-440 6L6's. "Red" outer pair and "Green" inner pair. No issues whatsoever. The 6L6 failures must have been somewhat faulty tubes pushed to their limits by the monster 105 trans. The redplating may be my EL-34's being too hot of a tube for these amps' voltage/current in Class-A mode cranked up. I just talked to Groove tubes, and they said the GT6CA7GE's will be available in about 4-5 weeks. I guess I'll just keep the amp in Simul mode until then, or keep the volume down when in Class-A.

 

[JOEY B.]

How did the 442's handle it? I know they were Greens but I'm under the impression the 442's would/ can handle the voltages better.

About the same as the 447's as far as plate color. Neither of them have an issue until you get to extreme volumes in Class-A mode, though. I like the clean tones better out of the 442's so that is what will stay in the amp for now.

 

[JOEY B.]

The tubes that have a faint blue glow at idle (which is normally no big deal) have been the ones to give a problem under a a heavy load in either amp. I saw the last one fail. It went from a faint pusling blue glow to a white/blue haze over the entire tube. Then a spark came from the center near the grid, and that's all she wrote :evil: .

The last tube failure must have been a brief internal short, brought on by extreme current. The tube is back in the amp and idles fine. I won't dare put any signal thru it, for sure.

 

[JOEY B.]

I just got off the phone with Mike. He suggested grounding pin #1 on the outer sockets (by attaching it to pin #8 ) to help with the redplating of the EL-34's. He said that ONLY "red" color code MESA 6L6's should be used in the outer sockets of the Simul C+. If MESA EL-34's were used in the outer sockets, he recommended "red or yellow" color codes. The 105 trans made these selections even more important. Ideally the current draw (mA) at idle would be mid 30's for the inner 6L6, (it probably won't get much better than) mid 50's for outer 6L6 with the 105 trans, and mid 30's for outer sockets with EL-34's. There are still some STR-415's at Petaluma for $75 each that fall between what is now known as the "green and gray" color codes. 8) Time to warm up the soldering iron.

 

[Octavarius]

Great. You didn't ask about the X101 tranny, then? Well, let's hope BB is right about it biasing the tube to the same level. :shock: Good info!