The Steel Guitar Forum

Bob, It is possible that the author of the article predicated his conclusion on the feeling that it is better to leave the tube heaters hot rather than turn them on and off several times during the day.
There is some validity in that.
The constant heating and cooling of the tube will increase metal fatigue and that is thought by some to decrease the life of the tube.
After all, the heater of the tube is very much like an incandescent light bulb.
I don't think the difference is significant.
During the day I turn my amps On and Off as needed. If I will only be away from the amp for less than an hour, I leave it On.
I worked in Broadcasting for many years. The tube equipment was on for 24 hours a day and the tubes, including the power output tubes sometimes lasted for years.
Of course, we didn't drive them to the limits as is done in a Guitar Amp.
If I am doing a gig, I use the standby switch between sets....it keeps the amp quiet and if anyone walks by and brushes the strings there is no sound.

Blake

Do pre-amp tubes need to be replaced more often than power tubes? In relation to average playing out, say 2 nights a week, how often (generally speaking) does tube replacement come around?

<SMALL>Do pre-amp tubes need to be replaced more often than power tubes? </SMALL>

No,in general,I wouldn't change a tube out just because it has a little time on it. If it is noise,gassy,or obviously exhibiting a low gain problem,then one,of course,would replace it.

Someone stated above about the blue glow in the power tubes. At a high plate voltage this is completly normal. Now, a red plate element IS NOT NORMAL.

I,like Mr.Stoner,grew up on tube stuff and today,I find many mis-beliefs by the younger generation about tube circuits. Many techs now-a-days haven't even had any training in tubes. There is a reason tube amps sound better than SS amps. While I won't go into this area,the techs that understand tubes,know where I'm comming from.

Replaceing tubes just because (bla,bla).......is a myth. Most of you don't remember when RCA, G.E. and other brand tubes were abound. they were good tubes,made here in the U.S.A. The crap we are forced to purchase from overseas today,is floor-sweepings.

Please send me all your tubes you have changes out for new ones !!!

Rule of thumb.....
Unless the amp is giving you a problem.... leave the tubes along !!

Bill Buntin: The pre amp tubes usually last longer than the power tubes because they are not stressed as much.
What Bill Crook said is correct. We come from the same era of tube equipment.
Blake

When I worked for Little Roy, we made a lot of money from people that would bring their tube amp in and want it "retubed". It didn't do any good to try and reason with most of them. "The customer is right" so I'd do it. Even retubed Ralph Mooney's Twin Reverb one time.

I had a good stock of used tubes for quite a while.

Well I guess Gen LeMay and SAC were wrong ie: bla bla too. They had an SOP that all tubes would be replaced with certified and tested replacements at regular intervals. Seems they couldn't tolerate a failure in the middle of a song either.

Maybe it's a cost factor that is most influential in the matter and while I don't change strings like this I have seen bands that restring before each show. That would be cost prohibitive for me but on the other hand I don't wait for one to fail either. There has to be some middle ground in both matters and background and the situation have a lot to do with it.

If you are just practicing at home is one thing but playing a show for a top name act is something else. You act accordingly.

Regards, Paul

I had a similar problem with my peavy tube amp, in regards to the tubes glowing red and the 60 cycle hum thing,is it possible that the power tubes are still ok and filter caps is all that needs replacing( I shut the amp down just as soon as I heard the hum )there doesnt seem to be anything melted inside the tube or is this condition a "death sentence" for the tubes?

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sho-bud,session 500,american standard strat,shecter tele,peavy classic 50

Blake,
That Is pretty much what he was saying. But as I stated the first time, he said a tube slowly burns Itself up. If not kept on, the deposits would build up on the tube, instead of falling to the bottom, making the amp sound like It was frying bacon.

Don't claim to be a tube amp expert, but I've always been able to keep my own working,
and what he said makes sense to me.

When you said the tubes In your power amps at the station would last for years, isn't that telling us something.

Bob Carlson.
<FONT SIZE=1 COLOR="#8e236b"><p align=CENTER>[This message was edited by Bob Carlson on 11 November 2001 at 08:04 PM.]</p></FONT>

Replacing all the tubes with new ones is not a 100% guarantee. I've replaced a lot of "warranty" tubes for customers, and returned them to the electronics distributer for replacements. Both when I did amp repair and earlier when I worked for a Motorola 2-way radio dealer.

I was in the AF at the time LeMay was the SAC chief. The only thing I'll say is I'm glad I was never in SAC. NASA had much more stringent requirements/regulations on equipment (more stringent than "mil spec") and they never required periodic replacement of tubes.

Gary:
If your tubes were OK before and your filter caps did a meltdown - it's not a "death sentence" for the tubes. You shut the amp down, like I did when the caps failed on the Twin Reverb. Well, I had two of the caps (yes - just two and not all five) replaced. It seems that three out of five were the original Astron's! At any rate, it cost about $60. in parts and labor and everything is jake. I didn't need to re-tube and you might not have to, either. Next time I need tubes I'm going to try Svetlana's.

Rob Yale

Bob, I like the comment about the flakes from the cathode falling to the bottom of the tube.

Have you looked at the way the tubes are mounted in your Fender Twin? They are upside down. If the flakes fall from the cathode..they fall to the top of the tube, and can collect on the mica insulating washers around the plate and grid structure...maybe causing some popping and noise...maybe not.
Most tube guitar amps have the tubes upside down.
Over the life of a tube certainly part of the cathode may become "dead" and in some cases flake off. Unless you are into rejuvenating tubes (a whole subject in itself) it is better to just replace the tube.
Paul, There is no rational accounting for the way the military does things. Like Jack, I've found factory fresh tubes that were bad. There is no absolutely accurate way to predict when a tube will go on on you. Back in the days of analog, tube type television, we kept accurate records of our tubes parameters, measureing the camera tubes once a month and replacing any that had started to weaken. However, we never replaced all at once, because there is drift and aging to be accounted for and a completely retubed camera would be unstable for several days and require constant adjustment.
I agree, when you are with a Major Act you want to be in the best shape. I was never in that league, but when I played for money, I always carried a spare set of tubes for the amp, just as I carried spare patch cords.
You probably had one or more complete amps as back up.
In tube techonlogy, it is fun to discuss things like this...but there are no absolutes. Too many variables in the tubes themselves, in the equipment and in the way the equipment is used.
Bob, I'm not sure what you ment by your last comment?
Blake
<FONT SIZE=1 COLOR="#8e236b"><p align=CENTER>[This message was edited by Blake Hawkins on 12 November 2001 at 06:35 AM.]</p></FONT>

Paul, After looking over my long winded reply above, I feel I should say a little more about the Military Electronics Maintenance.
The data which results in the Periodic Replacement of components such as tubes is based upon engineering predictions of MTBF, Mean Time Between Failure.
Frequently this data is supplied by the equipment manufacturer and is based upon calculated rather than emperical information.
Naturally, everybody is into the CYA mode, so they come up with some very conservative proceedures designed to protect everybody.
When I was in the military, one of our maintenance sheets called for inspecting the knobs every day. We always filled it out and sent it in...the knobs were solid aluminum...never even scratched one.
Blake

Blake; First let me say it is a pleasure talking with you and Jack and all the others who have joined this Topic. It is a very broad subject and will endure many opinions.

I recall walking from WRAL studio engineering to the studio, very carefully carrying a Vidicon tube to be replaced in a camera. Those you replaced based on degradation of any gun and not on a routine basis. Redundancy of cameras was our CYA.

You also reminded me of something from my military past. We used to have to fill out EFRs (Electronic Failure Reports.) and your spare replenishmnet program was based on your failure trends. I never made out an EFR on a fuse because I felt that when it blew, it didn't fail; IT WORKED ! That was what it was supposed to do. If it didn't blow and the circuits following it were destroyed; then it FAILED !

When I ran out of fuses I called for bench stock and was refused. You show no consumption. And like so many others I learned the hard way; You don't mess with the system or you loose. It isn't nice to fool with Father USAF !!

Thanks for the memories !! Paul

The fact is: the standby switch is there to prevent "cathode stripping", which is caused by high voltage being applied to the tubes before the filament has heated the electron-emmiting coating of the cathode to the proper operating temperature. The tube life will be shortened if not given enough time to heat the cathode before applying the high voltage. 45-60 seconds is the recommended time to allow sufficient warmup.
This is realy necessary, especially in Fender amps some of which are designed to apply voltages to tubes which are above the maximum ratings of the tube.You can take it to the bank!

Bob Farlow, What you say is true about not applying the HV to the tube before it is at operating temperature.
So, a Fender Twin should be powered up by first turning on the Standby Switch, then the Main Power switch.
That's a good practice...but the operator has to be trained to do it.
Most of the time when we use the standby switch, the amp is already hot.
Perhaps we will never know who put the first standby switch on an amp or his reasons.
There are standby switches on solid state amps as well as tube types.
I agree that the Fender Twin..really stresses the tubes. They are operated at or above their maximum ratings.
In looking at the phlosophy of their design, I don't think the engineers were concerned about tube life.
They were squeezing every bit of power and performance possible from the amp.
If they were worried about the voltages at initial turn on, there are many "tried and true" ways they could have used to hold the HV off until the tubes were at operating temperature.
Given all the discussion in this thread, The Fender Twin, has been an exceptionally popular and well regarded amplifier. Certainly among the best guitar amps ever made. No matter how you treat them, the tubes seem to give a fairly long life and good service.
Blake
<FONT SIZE=1 COLOR="#8e236b"><p align=CENTER>[This message was edited by Blake Hawkins on 12 November 2001 at 09:49 AM.]</p></FONT>

<SMALL>There are standby switches on solid state amps as well as tube types.</SMALL>

Why, and on what transistor amps?

Blake Hawkins,
you say you like my comment about the flakes from the cathode falling to the bottom of the tube.

And have I looked at the way the tubes are mounted in my Fender Twin? They are upside down!

When a light bulb is screwed in, is it upside down? Wouldn't that be the ideal place (it can't get to the top) for the flakes to fall?

Same ideal place for them to fall with a tube.

What I meant by the last part was, the power amps at the station were on 24 hours a day and you said the tubes lasted for years, isn't that tellig us something?.

Enough said from me, i got better things to do.

Bob Carlson.
<FONT SIZE=1 COLOR="#8e236b"><p align=CENTER>[This message was edited by Bob Carlson on 13 November 2001 at 02:54 PM.]</p></FONT>

Bob Carlson,
I'm sorry, I didn't realize that you were unfamiliar with the differences between the construction of a light bulb and a vacuum tube.
In a light bulb the filament is located in the center of the bulb...there is nothing above or below it so if something falls and goes to the top or bottom it makes no difference.
A vacuum tube has many more elements;heater, cathode, grid or grids and plate or plates.
These are all mounted vertically on a support structure. At the bottom, the elements are supported by the glass seal or in come cases a reinforcing bead. At the top there is a support insulating element which holds the elements apart and adding strength. This is usually a mica washer.
If the tube is burned base down and something flakes off...it will fall into the base and probably cause no more trouble as long as the tube is not moved.
If the tube is burned upside down with the base up, then a piece falling material could be stoped by the mica washer and vibration and such cause a short or a degradation of the performance.
Also, a guitar amp is a special case in that it is moved frequently, tumbled, and bounced around. Anything that is loose will wind up causing trouble.
My point was not to attack you, but to point out, that whoever originally made that statement did not understand vacuum tubes nor their special use in guitar amplifiers.
Sorry if I am wasting your time...just trying to bring some understanding to an otherwise arcane subject.
Blake

Still makes interesting reading, Blake. And a refresher course is always good for the memory factory. I'd say you are right on !!

Regards, Paul

Thanks Paul!
I have a question for you....Did you ever work with Curley Williams or Paul Howard?
I am originally from Georgia and was a fan of Slim Idaho. Did you know him?
Doug Seymore and I have been trying to pinpoint which year Slim had his fatal traffic accident. Do you by any chance remember?
Thanx
Blake