It pays to read the manual!!

Thread Starter

MaxHeadRoom

Joined Jul 18, 2013
28,619
I don't see how there's any room for confusion. Warm up the tubes with the audio off, then turn on the audio. Seems intuitive to me, as MrChips noted in #17.
This is not in dispute, it is the fact of the Standby switch labeled STANDBY ON when in fact it is audio pwer ON.
And standby at 0 (OFF) IS STANDBY on.
Max.
 

MikeML

Joined Oct 2, 2009
5,444
It seems that the underlying issue is that there is some OLD WIVES TALE out there that indirectly-heated tube cathodes must be preheated before the B+ is switched on (regardless of how the switches are labeled).

I have asked for a basis for this; so far no one has supplied any science-based evidence that it is really required.
 
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strantor

Joined Oct 3, 2010
6,782
It seems to me that the problem is that MaxHeadRoom, his son, and all his son's friends are bunch of morons. It is obvious to everybody else what the switches mean.
[/sarcasm]
 

wayneh

Joined Sep 9, 2010
17,496
My bass player - who happened to be an electrical engineer - told me it was more about protecting the speaker from a pop or surge than about the amp itself. But that was a long time ago, so my recollection could be fuzzy. Ahh, good times.
 

Thread Starter

MaxHeadRoom

Joined Jul 18, 2013
28,619
It seems to me that the problem is that MaxHeadRoom, his son, and all his son's friends are bunch of morons. It is obvious to everybody else what the switches mean.
[/sarcasm]
Thank you very much, definitely shows a sign of maturity.:rolleyes:

To bad, I thought this was a civilized forum, according to forum rules, "Ad hominem tactics and directed abuse are always "off-topic". :(
I guess I thought wrong.
 
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wayneh

Joined Sep 9, 2010
17,496
This is not in dispute, it is the fact of the Standby switch labeled STANDBY ON when in fact it is audio pwer ON.
And standby at 0 (OFF) IS STANDBY on.
Max.
Yes, a better label would remove ambiguity, like MUTE and PLAY. I can recall not really reading the label (almost impossible on stage) but instead relying on what I could hear. If I ever heard anything while it was warming up, I knew the standby switch had been toggled to the wrong position.
 

strantor

Joined Oct 3, 2010
6,782
Thank you very much, definitely shows a sign of maturity.:rolleyes:

To bad, I thought this was a civilized forum, according to forum rules, "Ad hominem tactics and directed abuse are always "off-topic". :(
I guess I thought wrong.
It was a little immature, but it was not aimed at you. Rather, at the detractors who repeatedly seem to be insinuating what I said in sarcasm font.
I apologize if I offended you.
 

nsaspook

Joined Aug 27, 2009
13,087
It seems that the underlying issue is that there is some OLD WIVES TALE out there that indirectly-heated tube cathodes must be preheated before the B+ is switched on (regardless of how the switches are labeled).

I have asked for a basis for this; so far no one has supplied any science-based evidence that it is really required.
It's not a wives tale. You want the plate current from uniform thermionic emission not from field emission (resulting in ion flow) surrounding a hot spot. As the cathode is heated there is a point where the atoms (before complete electron thermionic emission) in the presence of a field gradient (from plate voltage) on the cathode from the edge to center will migrate to neutralize the charge on the cathode to a surface non-uniformity creating a hot spot. This hot spot will stay formed as the cathode is heated as the current density at that point is in equilibrium with the energy flowing from the cathode as a whole. This process might last only a few seconds the first time but if continued it could cause permanent damage on a power tube.
 

MikeML

Joined Oct 2, 2009
5,444
It's not a wives tail. ...
I have several tube manuals around here, including the RCA Radiotron manual, and there is no mention of this. Billions of consumer products were made and sold, and tubes seemed to have a reasonable MTBF without any provision for this. I personally owned and used lots of tube-based products which had no delayed B+ turn-on. Why is it that this topic comes up only with audiophiles???
 
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nsaspook

Joined Aug 27, 2009
13,087
I have several tube manuals around here, including the RCA Radiotron manual, and there is no mention of this. Billions of consumer products were made and sold, and tubes seemed to have a reasonable MTBF without any provision for this. I personally owned and used lots of tube-based products which had no delayed B+ turn-on. Why is it that this topic comes up only with audiophiles???
It's something you might see with higher power beam electrode tubes (like 6L6, 807 types) where there is focusing to increase current density and secondary electron emission suppression. I've had long meetings on indirectly heated cathode failures at work for plasma sources with 1kW+ cathode heaters to improve source life from 80 to several hundred hours to at least a week. It's not quite the same as audio output tubes but the basic physics for thermionic emission instabilities are the same.
 
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killivolt

Joined Jan 10, 2010
835
After all this talk; I don't think I want a tube amp anymore. I think I'll remove my blues pickups and re-install the ones originally fitted at the factory.

I have a friend who has a small amp that can mimic several tube amps of old. I was impressed with the sound.

kv
 

nsaspook

Joined Aug 27, 2009
13,087
After all this talk; I don't think I want a tube amp anymore. I think I'll remove my blues pickups and re-install the ones originally fitted at the factory.

I have a friend who has a small amp that can mimic several tube amps of old. I was impressed with the sound.

kv
But does it have blue leds to mimic that warm tube glow when played loud? :D
 

alfacliff

Joined Dec 13, 2013
2,458
the standby switch is to kill hum when you arent using the amp, without having to warm up the tubes again. no b+. no noise from speakers.
 

ian field

Joined Oct 27, 2012
6,536
A while ago my son, who plays in a band, acquired a quality second hand British made tube amp.
He seemed to be going through power tubes, a matched set of four replaced at a time.
The amp has two ON switches, Power on 1 or 0, and a stand by SW. 1 or 0.
Now intuitively, to me, you would put the Stand by switch on, wait a couple of minutes and then the main power on.
After getting me to look at it after the last failure, I downloaded the manual.
Evidently he (and I) had it backwards.
The main power is switched ON followed by the standby ON after 2 minutes.!
Power down in reverse.
Hopefully this cures his expensive replacements.:(
Max.
When I can get hold of a suitable test subject/victim - I plan to experiment with solid state replacements for valves.

What I had in mind, was either a Darlington or Sziklai hybrid with JFET input followed by a bipolar for a good current rating - put that in cascode with a high voltage power MOSFET and you're in business.

Probably need a pretty chunky heatsink though!
 

ian field

Joined Oct 27, 2012
6,536
It will. Hitting a cold power tube with B+ poisons the cathode.
IME: cathode poisoning is most often caused by undervolted heaters or standing around for long periods with too little anode current - apparently the normal electron flow sweeps up positive ions that bombard and contaminate the cathode coating.

Sometime in the 90s; some 'genius' at Philips circulated a memo stating that the high stability of modern SMPSUs meant that CRT heaters could be run at 6.15V instead of 6.3V - at the time I was servicing monitors for a living, and had a solid stream of units coming in with virtually no emission. In the vast majority, the heater was somewhere close to the 6.15 mentioned in *THAT* memo.

Some engineers were risking excessive X-ray emission by simply turning the wick up on the SMPSU till the heater voltage came right - my solution was to upgrade the heater circuit with a Shottky-barrier rectifier, usually the SMPSU was flyback, so the SB rectifier needed a snubber to be added, the SB rectifier also has higher junction capacitance, so in each case the heater reservoir electrolytic had to be beefed up.

The low beam current cathode poisoning came to light with some types of screen saver. I remember a long past version of AVG antivirus that incorporated a screensaver that worked very well - it practically wiped out the contrast without affecting the total brightness. There was no burning impressed on the phosphor, but it kept enough beam current to send the ions packing.
 

nsaspook

Joined Aug 27, 2009
13,087
I think the 'wifes tales' part about tubes comes from people taking information about the types of tubes sensitive to the effects like tube transmitters that needed several minutes to warm (much longer to condition a new tube) and making a blanket statement about all tubes. Most plain Jane receiver tubes run at power levels too low to be affected but large beam power tube cathodes should be at normal operation temperatures so there is an excess of easily accelerated electrons on the active surfaces for uniform current flow before full b+. Most of the old tube amps used tube rectifiers so there was a built in b+ delay (30 seconds for some rectifiers tubes designed for cold slow startup) for the amp stages. With a solid state b+ supply you would be full voltage as soon as the switch is on unless there was a timer or b+ standby switch.
 

Thread Starter

MaxHeadRoom

Joined Jul 18, 2013
28,619
It was a little immature, but it was not aimed at you. Rather, at the detractors who repeatedly seem to be insinuating what I said in sarcasm font.
I apologize if I offended you.
Apology accepted.
I will assume at this point it was a misunderstanding all around. :cool:
Max.
 

debe

Joined Sep 21, 2010
1,389
Where you have the powersupply using tube rectifiers it probably doesn't matter. But if the power supply uses solid state devices then there is HV before the cathode is fully heated. In marine radars they have a built in timer so the Magnetron is fully heated before the HV is applied. And the radar power switch has a standby position that keeps the magnetron heated if you dont want to wait for the warmup period.
 
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