Help diagnosing Tube Amp PLEASE

[Cqwet Dbdfte]

Maxing out on plate voltage spec, atypical in the 6V6, may not be conducive to max lifespan.

 

[FunkyTek]

yeah, but it screams nicely on the way out

 

[CJ]

I have seen a few amps where the screen voltage is actually higher than the plate voltage, a filter choke is usually about 100 ohms and screens might have 5 ma running through them so v drop through choke might be a paltry 1 volt at idle , if the dcr of the opt is a couple hundreds ohms then the v drop might be 30 ma x 200 = 6 volts so the screens will be 5 volts higher. But thus has been posted upstream so I be redundant. Not all amps use screen resistors BTW.

I use to pay $3.50 a piece for black plate RCA 6L6GC but not any more.

So changing tubes was no big deal back in the day. At today's prices of 50 bucks for a soviet piece of junk it is no wonder that people only replace them when they fail. But we get 50 bucks plus parts for a typical service job so it is wiser to change tubes when you notice the tone slipping a bit.

You will have to change a JJ 6L6 about tens times quicker than a NOS GE or RCA black plate and your tone will also suck with the JJ tubes but people don't realize this unless they have used NO'S tubes in their amps.

All the rock stars used up all the good stuff, replacing tubes after every show with Mullard metal base EL34's, shame on you ZZ Top Led Zeppelin and Van Halen, Iommj gets a free pass just because,

 

[soapfoot]

Even that may be changing somewhat, in my experience

For some tube types the NOS stock has become so picked-over that they are no longer a reliable bet to offer substantially-better performance or longevity compared to the best new production.

The RCA 6L6GC is my favorite all-time, but for a truly nice NOS pair you’ll pay almost as much as you’d pay for an entire affordable tube amp

Otherwise you’re buying used or untested or eBay stock and at this point I’d rather a nice selected matched pair of something new-production

 

[CJ]

If you read the Tube Dumpster articles by Eric Barbour in VTV then you mind find an escape route.

He had an article on the 6386, saying that they will be going up quick, sure enough all the 670 guys snapped then all up at 5 bucks a pop, dang dang dang if I had only read the article earlier. There are some Soviet tubes from the 60's that do work for git amps but you need to know how to cross ref them and also which brands are the best. Good way to support Ukraine right now.

 

[Cqwet Dbdfte]

Stop using tubes, use those class-D amps!
Sooo much better!

 

[CJ]

Poor Fender just spent a ton on their new pedalboard, 1600 bucks, amp modeling, effects data base, nice user interface but they run it through a class D speaker cabinet, oh well I guest you could plug it into a real amp.

https://www.sweetwater.com/c633--Mu...Zo4TvPQfXgGuszxVonYaAouIEALw_wcB&gclsrc=aw.ds

 

[Cqwet Dbdfte]

Even the very high end audiophools are getting into Class-D amps. I suppose you could design it like an offline converter with a "small" HF transformer on the output, outputting a couple of KW, and generate the "tone" in that stomp box to the input.
Probably already been done.

 

[soapfoot]

…outputting a couple of KW, and generate the "tone" in that stomp box to the input.
Probably already been done.

sort of

Something like this has been SOTA for quite a few years, but instead of a stomp box it’s a convolution amp emulator

The Kemper Profiling Amp uses a Class D power amp, for instance. I think the Fender Tone Master series might also?

It can work okay

I’ve been stuck using one of the Tone Master twin reverbs for the last 6 weeks on a situation where I didn’t get to spec the backline

I was the most militant tube amp purist for my whole life but you know what? It sounds fine

Maybe not quite as great as the very best vintage twin I’ve ever played but easily light years better than the worst vintage twin I’ve played!

 

[Cqwet Dbdfte]

Class D can output lots of power with small thermal loss, and be made clean, BUT there is no graceful overload. Clipping must not happen, some input compression, or AGC,/ALC would be needed. Maybe that amp emulator includes feedback of some kind from the PA to keep it from clipping.
This guy Berning makes expensive switch mode tube amps for sound reproduction. Interesting and unusual.

 

[sonolink]

Thanks for your input Funkytek

 

[rmburrow]

If both 6V6's failed from mechanical shock at the same time, the amp may have been dropped.
Shock protection is a possibility, vibration maybe not so much of an issue, tubes were used in WW2 aircraft. Good easy to grip handles on equipment could help.
What brand tubes failed?

With all the environmental BS affecting manufacturing of any sort (especially in the US), quality and reliability is out the window. I suggest going to Ebay and getting ruggedized tubes such as JAN (Joint Army Navy) 6V6's built to a mil spec, 5751's in lieu of 12AX7's, etc. You are out of luck with EL34's. The only suggestion I have is to operate those vertical only. Some AM broadcast transmitters in the 1 to 5 kw range used EL34's as drivers for high power tetrodes (i.e. 4-400A, 4-1000A etc.); the EL34's would short due to sagging screens, etc. with the tubes operated horizontally. Since there was space available to use a socket adapter and operate the tubes vertically, the tube life increased substantially. This may also work with other power tubes in particular.

 

[rmburrow]

I have seen a few amps where the screen voltage is actually higher than the plate voltage, a filter choke is usually about 100 ohms and screens might have 5 ma running through them so v drop through choke might be a paltry 1 volt at idle , if the dcr of the opt is a couple hundreds ohms then the v drop might be 30 ma x 200 = 6 volts so the screens will be 5 volts higher. But thus has been posted upstream so I be redundant. Not all amps use screen resistors BTW.

I use to pay $3.50 a piece for black plate RCA 6L6GC but not any more.

So changing tubes was no big deal back in the day. At today's prices of 50 bucks for a soviet piece of junk it is no wonder that people only replace them when they fail. But we get 50 bucks plus parts for a typical service job so it is wiser to change tubes when you notice the tone slipping a bit.

You will have to change a JJ 6L6 about tens times quicker than a NOS GE or RCA black plate and your tone will also suck with the JJ tubes but people don't realize this unless they have used NO'S tubes in their amps.

All the rock stars used up all the good stuff, replacing tubes after every show with Mullard metal base EL34's, shame on you ZZ Top Led Zeppelin and Van Halen, Iommj gets a free pass just because,

CJ...even the Mullards shorted out prematurely, especially if horizontally mounted in an amp. You are right about the NOS GE or RCA black plate 6L6GC's. I like the old JAN tubes myself....

 

[ubxf]

I'm using a tube preamp into a class d amp and like the result

 

[pucho812]

Stop using tubes, use those class-D amps!
Sooo much better!

Are they? Or as I like to say they are different. I have great sounding examples of both with tubes and with class D.
Have you heard the quilter amps? No tubes and are quite impressive.

 

[Cqwet Dbdfte]

Tubes advantage is their utter circuit simplicity, (and potential for cheap generation of microwave power for cooking, extremely high RF power in broadcasting, and high noiseless gain in TWTs.

Disadvantages are many.
Scarcity, price, fragility, variability between samples and mfgs, aging,
very high voltages, size, heat generation, microphonics, inevitable use of expensive signal transformers.