5150 III 6L6 heather voltage change?

[Emetal]

Hi, this amp has factory set 5,9 VAC as heather voltage for PI 12ax7 and two 6L6 tubes. After the research engineers at EVH "concluded that, this change is crucial to getting the famous brown sound" It also causes "cathode stripping" and shorts the life span of tubes. Is there any way I could get the voltage to proper 6,3 VAC ?? Probably not since transformer is wound that way? Any ideas?

[The Dude]

IMO, 5.9V rather than the usual 6.3V - a difference of only .4V is not going to cause any substantial damage to tubes or shorten their lifespan by any noticeable amount. This is just more internet lore.

[Emetal]

Yeah, probably not, but I am not a fan of a brown sound and would love to hear that amp's sound with proper heater voltage..

[Chuck H]

I'm no scholar on the matter but discussions here have indicated that concern about cathode stripping in guitar amps circuits is almost to be ignored. Some amps put some pressure on the tubes (mostly power tubes relative to the matter) but this is NOTHING at all like the stress put on tubes used for transmitters. Tubes put to that sort of service with exceedingly high voltages are the rare cases when cathode stripping needs to be considered. WRT guitar amps it's even been mentioned (and practiced) here that for amps running moderate voltages a standby switch isn't even necessary. How does this relate to low-ish cathode voltage? Well, the biggest cause of cathode stripping is a tube that still has cold filaments when HV is applied. Ergo the implementation of the standby switch. But we're talking pretty damn cold and with plate voltages that are pretty damn high.

5.9V would be about 7% low. That's not even breaking the ten percent tolerance for filaments. In fact there was another discussion here that demonstrated that within a few percentage points (still in the tolerance) that a high filament voltage is more detrimental than a low one. And, furthermore, a small low measure at the filament could actually extend tube life.

Peavey is a clever and smart company. I don't think they would sell a product with a design parameter that causes premature failure under any circumstances. They might have gone as low as they learned they could get away with. Otherwise I agree with His Dudeness. Any direct info about the 5150 series amps on line is suspect of being lore or lies perpetuated by individuals that not ignorant of circuits, but also aren't at all technicians or engineers.

[Emetal]

Unfortunately everything I mentioned in post was information from amp designer himself
https://m.youtube.com/watch?v=CrVRW-cS69g

[g1]

As far as I know, cathode stripping is a concern for monstrous tranmitter tubes, not small audio stuff. And within reasonable limits, slightly low heater voltage is more likely to extend tube life than reduce it. Especially if compared to higher than spec heater voltage.

The 5.9VAC heaters in this amp is set by the power transformer. To run higher heater voltage would require installing a separate, dedicated heater transformer.
I will ask if you have measured the actual heater voltage in your amp while running. It will vary depending on line voltage and you would need to know what line voltage Peavey specifies for their measurements/design specs.

[mozz]

What about rectifying it and then regulating it. Actually you will never see cathode stripping in your lifetime. The seller or designer is full of it. Maybe these Chinese tubes are garbage and are prone. How about using a Variac and run about 130-135v, that will cure it.

[Helmholtz]

What about rectifying it and then regulating it.

Don't think that would work with power tube heaters.

How about using a Variac and run about 130-135v, that will cure it.

Mains voltage should be 220V in Serbia.

Increasing input voltage will also increase B+, which might actually lower tube life.

[Helmholtz]

See paragraph about dropping heater voltage here: http://valvewizard.co.uk/heater.html

[mozz]

I'm just being sarcastic about the heater voltage, yeah i know B+ will rise if you boost the primary voltage. Whether there would be a actual change in sound going from 5.9v to 6.3v, i vote no.

[Helmholtz]

Whether there would be a actual change in sound going from 5.9v to 6.3v, i vote no.

Agree.

[Chuck H]

FWIW the discussion of filament voltage starts at about 14:00 on that linked video. In case that helps.

[Chuck H]

I'm sorry (and perfectly willing to be corrected) but I think this guy is smart enough, and good enough to tweak amps. But without more logic behind his statement about cathode stripping I feel like it's just a regurgitation of what has gone around the web previously on the matter before it was ACTUALLY addressed. Further, he states that the filament voltage is more responsible for the "brown sound" than other voltage reductions. This is not my own experience and it seems that other posts here would be in agreement with that. Fact is that Eddie was a guitar player. This guy is an engineer that may or may not have the full picture on esoteric matters. But here on the forum where it HAS been examined from multiple members (of exceedingly high regard) and angles I'm inclined to disregard the comments on filament voltage as it relates to the EVH amp tone.

JM2C

[The Dude]

......Further, he states that the filament voltage is more responsible for the "brown sound" than other voltage reductions. This is not my own experience......

^^^^^^That! A 7% difference in heater voltage is not going to make that much difference, tonally. I'd say "at all", but a nitpicker may notice. I'm betting, in a blind test, you couldn't say which amp had lower heater voltage. Lowering B+ would make more difference tonally and biasing tubes to the point of destruction would, also. "It sounded great until it smoked". Cathode stripping is more of a thing at RF frequencies and, even if it were a significant issue in the audio range, 5.9V is still within the 5-10% tolerance of most tube manufacturers.

[loudthud]

Back in the bad old days, Tektronix made a curve-tracer for tubes called the 570. It had limitations like the screen supply was only 300V max, but it could be used to display the characteristic curves of most tubes like those you see in a tube manual. To setup for a certain tube, you obtained a tube socket mounted to a small rectangle of sheet metal with banana sockets of each socket pin, then ran short banana to banana jumpers to the instrument to complete the test circuit. A large switch selected the heater Voltage, but the first thing you did when you started testing a tube was adjust a small variac to adjust the heater Voltage on a large meter on the front of the scope. Once the curves were displayed, you could adjust the heater Voltage to observe the effect on the curves.

From my recollection, the effect on a 12AX7 of 7% change in heater Voltage would be on the order of what you might see between two 12AX7s from different manufacturers.