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Tube amps and Standby Switches. we have apparently been living a lie! :)


kidblast

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Ok so like many here, I have tube amps (3 to be exact).

 

a Fenderd HR Deville 4x10, a Marshall JTM60, and a Goldtone GA30RVS.

 

I stumbled on a few interesting articles.

 

Evidently the practice of using our standby switches to let the valves warm up, and then when powering off "cool" down before hitting to off switch... isn't really necessary and, if you read some of these stuff, might possibly do more harm then good.

 

have I been following the defacto rule all the years for nothing? hmmm..

 

take a look and your then reply with your thoughts.

 

[1] http://www.wiredguitarist.com/2016/11/13/tube-amp-destruction/

[2] http://www.wamplerpedals.com/news/blog/talking-about-gear/should-i-put-my-amp-on-standby

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I cant' say I've religiously done it every time, but 98% of the time, I do use standby.

 

My Marshall is 20+ years old now. been re-tubed twice. my Goldtone was bought in 02?.. I re-tubed it last year, but only because the volume would drop after about 30 minutes after powering it up. (hasn't done it since so I guess it was time) My deville is 19 yeas old,.. re-tubed once....

 

 

Anyways,, I'm not sure it matters one way or another.

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Anyways,, I'm not sure it matters one way or another.

 

Minutiae matters on an academic level only. Practically speaking, it is proven every weekend that it doesn't matter, but that won't ever stop internet geniuses from telling you how wrong you are and how much you have de-valued your vintage amp by not following standby switch protocols.

 

rct

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Guest Farnsbarns

I use my standby switch to prevent the amp hissing and humming with no guitar attached, to prevent pops and bangs when disconnecting a guitar and pops when powering down.

 

There's no doubt in my mind that valve amps sound better after a few minutes (or more) of use so preventing the no-guitar-attached hum during a warm up period seems reasonable.

 

There is also the unknown fluctuations in the circuit as all the other components come up to heat with temp affecting resistivity of most substances.

 

I think I'll keep using standby switchest but it's interesting that part of the reason they exist may be driven by myth. Interesting but not surprising.

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ONE SIMPLE RULE:

 

LEAVE THE STANDBY SWITCH ALWAYS TURNED ON if your power amp is either cathode biased or controls grid bias through it.

 

The first applies to next to every common Vox amp until today.

The latter is valid for early Marshall 50W amps. It simply is a faulty design they corrected on later models.

 

Most other amps can be operated as you like without running the risk of serious or immediate damage.

 

For those who are interested, here's why.

 

Long before I started playing guitar and even longer before I owned my first valve/tube amp, I had been servicing the Vox AC30TB and Marshall 50W halfstack of my bandmates. I was the only one who had some basic knowledge, and we all had no money, so I simply did it. I made my observations of amp use, and I later had some views to the circuits quite clearly arranged then in point-to-point wiring.

 

During the first months of my first band the Marshall top needed a major repair in mid-1979, and the Vox wore out power amp valves/tubes very fast. In fact, I found out soon that either can be avoided by following the rules I stated above.

 

This is the situation explained: Some early Marshall amps controlled their grid bias circuit with the standby switch. This is very bad because the power amp valves/tubes run shortage current when turning from standby to on. The grid bias voltage takes a few seconds until it will be built up at the filter capacitors being initially uncharged. The plate voltage, however, is even higher when turning on since the power supply has been without load to that very moment but with capacitors fully charged.

 

One of the Marshall's power amp valve/tube sockets - they had a ceramic base - had gone bad due to arcing right after turning the standby switch on, instantly obvious through extremely loud hum and buzz from the speakers. I replaced the sockets - sadly I only got plastic-based ones - and I REWIRED THE GRID BIAS CIRCUIT TO THE HOT SIDE OF THE STANDBY SWITCH. Years later I read just this recommendation named "Marshall Tube Saver Mod" in Aspen Pittman's "Tube Amp Book" Vol. 3.

 

However, the problem can't be solved with amps using cathode-biased power amp circuits like Vox AC15, Vox AC30, Vox AC30TB or the like. The cathode capacitor must be charged through plate current, and the valves/tubes will have to be operated far beyond their permitted operational limits for this period every time you turn the Standby switch on with power on and the valves/tubes heated.

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I like this bit from the Wampler article -

 

"....Cathode poisoning was such a problem that they would have to put a new set of valves in the Juke Box every thirty-forty years!”

 

Got me thinking.....I've never changed the valves in my Park MV100. OTOH my old Vox regularly burns components out.

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I like this bit from the Wampler article -

 

"....Cathode poisoning was such a problem that they would have to put a new set of valves in the Juke Box every thirty-forty years!”

 

Got me thinking.....I've never changed the valves in my Park MV100. OTOH my old Vox regularly burns components out.

Leave the Standby switch of your Vox permanently on. Please refer to my post right above yours.

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Leave the Standby switch of your Vox permanently on. Please refer to my post right above yours.

Cap this is an old AC10 - no standby switch!

The original Vox valve amps always do this, it is a shortcoming in the design.

This is on good authority from David Petersen, a valve amp expert who really knows his stuff - he wrote an excellent book on Vox amps.

...and my Twin Reverb II can blow fuses just like bbp says above!

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I looked at this Twin Reverb that blew fuses if you turned both switches on at the same time when the amp was hot. So there! [flapper]

This is NEVER a good idea. The situation created is similar to that with old 50W Marshalls. After having turned the amp off, leave it at least one minute off before switching on again. This will cool down the valves/tubes just as much as to avoid shortage current through operation without correct bias.

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Cap this is an old AC10 - no standby switch!

The original Vox valve amps always do this, it is a shortcoming in the design.

This is on good authority from David Petersen, a valve amp expert who really knows his stuff - he wrote an excellent book on Vox amps.

...and my Twin Reverb II can blow fuses just like bbp says above!

Sorry that I couldn't help. :( Although this is not a real comfort, a Standby switch would be of no use in this case but make it all worse instead. <_<

 

Most Vox amps run their valves/tubes very close to their permitted dissipation ratings, regardless if with or without signal. :unsure:

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I looked at this Twin Reverb that blew fuses if you turned both switches on at the same time when the amp was hot. So there! [flapper]

 

That was what lead to the invention of the tin foil around match fuse.

 

rct

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Well I guess I have been livin the lie but I can't say it's caused me any problems that I know of.

Have only once had a tube go bad on me a very long time ago.

And any other swaps I did were out of curiosity so I'm good with my lying demon b!tches.

I shall go on fooling myself.

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This is NEVER a good idea. The situation created is similar to that with old 50W Marshalls. After having turned the amp off, leave it at least one minute off before switching on again. This will cool down the valves/tubes just as much as to avoid shortage current through operation without correct bias.

Yeah - Or use the standby switch the way it's supposed to be used - like the instructions say. That way you don't have to be Leo Fender to turn on your amp.

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