To stand-by, or to not stand-by?

[MWJB]

If guitar amps were built with filter caps beyond what the tube rectifier could stand, then they would all fail under warranty. As I said in the post you quoted, most guitar amps are designed not to overstress their rectifiers. Few mass produced amps have more than 50uf at the first filter, neither this, nor 100uf, falls in to the realms of a dangerous capacitance for the common rectifiers quoted. I did provide context.

I'd love to see one of these mythical "popular guitar amps that adheres religiously to data sheet specs"...I won't hold my breath ;-). Data sheet ratings are often conservative...as I suspect that you are aware.

[Gtr_tech]

For example, my Peavey tube amps kill their screen voltage to go on standby, leaving B+ "hot" IIRC. I think Hartley Peavey addressed that in one of his writings but I can't remember.

That approach to the stby sw is kinda novel. It solves the problem of cathode damage due to long periods on stby by killing the screen voltage, but not the plate v. That way, the output tubes will pass a *small* amt of current when in stby and cathode poisioning won't occur due to excess space charge.

[ThermionicScott]

I like the approach on Merlin's page about wiring a high-value resistor across the standby switch. That way, there's a trickle of current flowing in standby, but not enough to do any damage when the amp is switched on.

- Scott

[kg]

If guitar amps were built with filter caps beyond what the tube rectifier could stand, then they would all fail under warranty.

are tubes warranty items in the first place?

As I said in the post you quoted, most guitar amps are designed not to overstress their rectifiers. Few mass produced amps have more than 50uf at the first filter, neither this, nor 100uf, falls in to the realms of a dangerous capacitance for the common rectifiers quoted. I did provide context.

context or no context, i'm pretty sure a 100uF input cap on a 5y3 falls out of the design max values.

rca data sheet, 5y3:

typical cap input filter component operating points:

filter input capacitor 10uF

TEN microfarads. not fifty, not one hundred.

I'd love to see one of these mythical "popular guitar amps that adheres religiously to data sheet specs"...I won't hold my breath ;-). Data sheet ratings are often conservative...as I suspect that you are aware.

data sheet ratings WERE conservative. what is the quality of vaccum tubes available these days?

eleven years ago someone else asked about putting large value input caps after a tube rectifier:

Max Rectifier Capacitance - AMPAGE Archive

the FACT of the matter is that if you want your tube rectifiers to last, you adhere to guidelines for max input capacitance. as always, max input capacitance is a rule of thumb that is partially offset by the transformer secondary impedance: a high impedance winding will allow one to push the value, because it inherently limits current. max input C is also affected by total b+ rail current draw: the "hot" amp cannot stand as large an input capacitance as does a cooler one. as a result many rectifier data sheets do not have a hard value per se. that does not mean that larger input caps do not negatively affect rectifier life.

remember it is not about the capacitance value per se, but the conduction angle and total peak current draw during that time. pull too much current too quickly, expend the space charge that exists around the cathode, and tube life gets shorter. that is just the way it works, whether or not "experts" making current production musical instrument amps are aware.

[MWJB]

Nobody makes, or has made a 5Y3 rectified amp with a 10uf input cap (unless part of a Pi input filter) for what...55yrs?

Ref. the recent Silverface Champ Cap Job and Replacement Cap Can thread in "Vintage Amps" section of the forum.

Data sheets also suggest voltages way under 415vdc for a 6V6 GT, and under 470vdc, or 495vdc for a 5881...I guess all those BF Deluxe/Princeton & 5F6A Bassman & Brown Concert/Pro/Bandmaster owners had better just send their amps to me & I'll be sure to "dispose of them", I don't care if they are reliable & sound great...they don't conform to data sheets so are obviously travesties of nature and must be burned at the stake!;-)

What a relief that my 5R4 in my old bandmaster couldn't read data sheets, otherwise I feel sure that it would have gone on strike...rather than deliver years of reliable service with 50uf at the first filter ;-)

Data sheets are written by tube manufacturers, amps are built & designed by amp manufacturers, they have different goals & different agendas.

Suggesting that a 5Y3 equipped amp can't run with more than 10uf at the first filter is irresponsible scaremongering.

KG also wrote: "data sheet ratings WERE conservative. what is the quality of vaccum tubes available these days?" Well, as regards the 5Y3...it's the same as it always was, the only current production "5Y3" I'm aware of is the Reflector tube, which although delivers more B+ (thus not recommended for designs that already push the B+ for a given tube, or cap rating), is pretty bullet proof & has a nice slow start. Otherwise guys using 5Y3 are using the NOS tubes to which the data sheets refer. 5Y3 is typically much more susceptible to failure due to excessive current draw or voltage. As for other tubes, well you can't tar them all with the same brush, but there are tubes made today of excellent quality with regards to reliability.

By the way, I can read plain text perfectly well...no need for the bold text.

[Steve Conner]

Are you guys still debating this?

It's a perfect example of de facto vs. de jure standards.

The de jure standard for a 5Y3 is 20uF, or whatever it says in the datasheet. At that capacitance, the NOS rectifier would meet or exceed its rated hours of life, or I guess the manufacturer would replace it under warranty. So due to the economics of that, it was probably worth while overbuilding them such that most (but not all) samples would take a lot more.

The de facto standard is that it has to survive in an amp with 100uF of first filter capacitance, for long enough not to piss off the customers. So I imagine that's how they are made nowadays.

Back in the old days, transformers were made with a HT winding of thinner wire than necessary to make it fit. The extra resistance helped widen the conduction angle and lower the peak current, and you could use more filter capacitance than the datasheet headline figure. The Mullard GZ34 datasheet has a chart that shows you exactly how much. I have no idea if this is still done.

Same story with screen ratings in EL34s. The de jure standard is 300V or whatever, the de facto standard is that it has to survive one set in a plexi cranked up full. Svetlana used to make EL34s with thick copper screen supports and oversized cooling fins, for this very reason. But they still called it an EL34. Any EL34 you can buy now probably has a higher screen rating than a NOS one.

[kg]

well i guess the answer is:

if you build something, and it works, your design is a "good idea" and should be immediately considered best practice.

to hell with the substantial body of research that suggests tradeoffs of longevity have been made!

[MWJB]

It is the "substantial body of research" and common amp building practice for the last 50 odd years, that leads me (& many other amp manufacturers, builders & customisers) to this conclusion. I'm not talking about one man's experience with one amp...I am talking about thousands, if not tens of thousands of amps.

Perhaps you would like to list commercially available 6V6 amps with 315vdc on the plate and a 10uf input filter after the 5Y3 to back up your assertions? I won't hold my breath...then again, it's likely to be a very short list indeed, so maybe I will! ;-)

[hasserl]

Perhaps you would like to list amps with 5Y3 rectifiers w/ greater than 50uf input capacitance.

[MWJB]

Why suddenly greater than 50uf, KG is confident that 10uf is design max? There are plenty between 10uf & 50uf, like Fender 5F1, 5E3, 5F2A, 6G2, BF/SF Champ, Ampeg R12/R12A/R12R, Gibson GA15, Gibson GA16T, Gibson GA19RVT (& lots of other Gibsons) Mesa LSS, just off the top of my head....I'm sure that I can expand this list substantially. I have used 100uf with 5Y3/5AR4 for years, I also know a high profile boutique builders (selling hundreds of amps a year) who do too. It's not for me to name them & involuntarily include them in some witchhunt.

[kg]

i didn't say 10uf was the max, i said it was a typical cap input value. you know, from a datasheet. those little numbers and symbols and things on them actually mean something.

to me, at least.

now, if you're too stubborn to think that input capacitance doesn't have a DIRECT EFFECT on tube rectifier life, be my guest. just don't spread your bullshit and we'll be fine.

[MWJB]

"Bullshit"? How very reasonable of you...I expect to see empirical data to support that assertion? 10uf being a typical input cap value in a real world 5Y3 amp...now that really is bullshit, but I guess your bullshit trumps my bullshit for some bullshit reason (ooh this is fun, if only saying "bullshit" a lot was informative, or made you right). I can also read lower case quite comfortably, upper case is not necessary. I am neither hard of seeing, nor hard of thinking.

I'm sure there are filter cap values that will kill a 5Y3, just not values that we typically see in tube rectified amps. There's that awkward little thorn in your side called "context" again.

At least we agree that the data sheets are wrong...now we're just debating by how much more than a factor of 100% they are wrong by. A data sheet is a bit of paper, useful to a degree, but musicians don't play bits of paper on stage, crowds don't "ooh & aaah" at the sound of RCA data sheets, they go to hear music, played by musicians, on amps that exist in the real world, usually post 1940 whatever...Jeez if the modern practice of big filter caps freaks you out, what are you going to do when you see a jet plane or an I-Phone?

Your positive contributions to this thread are only noticable by their absence, it appears that you have only rolled up for some sort of conflict. If that's what you enjoy then far be it from me to disappoint you...