I want to idiot-proof my system. I have an Aikido preamp using 6SN7's, which feeds a solid-state power-amp.
Right now, I am using an Amperite 30S delay tube to pre-warm the filaments. before B+. Then I switch-on the power-amp. I shut things down in reverse, with the power-amp first, followed by the preamp. I can switch both off at the same time without any thumps, but if I turn on both at the same time, I get a very audible thump when the B+ switches on.
I just ordered a Belkin PF60 power conditioner, which can switch on different banks of plugs with a delay of up to 15S. Hence the following question:
QUESTION: If I replace my Amperite 30S delay with an Amperite 10S delay, then my 6SN7's will only get 10S of filament warm-up before the B+ switches on. Will this be detrimental to the tubes?
I vagualy remember reading that as little as 5S heating is sufficient (maybe this was in the Morgan Jones book).
Thanks,
Charlie
Right now, I am using an Amperite 30S delay tube to pre-warm the filaments. before B+. Then I switch-on the power-amp. I shut things down in reverse, with the power-amp first, followed by the preamp. I can switch both off at the same time without any thumps, but if I turn on both at the same time, I get a very audible thump when the B+ switches on.
I just ordered a Belkin PF60 power conditioner, which can switch on different banks of plugs with a delay of up to 15S. Hence the following question:
QUESTION: If I replace my Amperite 30S delay with an Amperite 10S delay, then my 6SN7's will only get 10S of filament warm-up before the B+ switches on. Will this be detrimental to the tubes?
I vagualy remember reading that as little as 5S heating is sufficient (maybe this was in the Morgan Jones book).
Thanks,
Charlie
I know that the 6SN7-GTB had a controlled heater warm-up time specified at 10.5 seconds. But this had more to do with heater current settling down than it did with cathode temperature and emission. Still, I'll bet that any version of 6SN7 will work fine with 10 seconds of delay between heater power and B+.
Brian,
That was my guess. I suppose that the only risk is cathode-stripping and as far as I can tell, this is only a real issue at very high voltages, while I am only running mine at 280VDC (less per cathode).
In fact, when trying to trace hum, Bruce Anderson had the preamp running without any heater on at all (using cheap tubes of course).
Regards,
Charlie
That was my guess. I suppose that the only risk is cathode-stripping and as far as I can tell, this is only a real issue at very high voltages, while I am only running mine at 280VDC (less per cathode).
In fact, when trying to trace hum, Bruce Anderson had the preamp running without any heater on at all (using cheap tubes of course).
Regards,
Charlie
You'll be fine. The other risk is running the heater for long periods of time without B+, where cathode interface or poisoning can occur.
This is only a tangentially related question, so excuse my thread jacking and also my ignorance:
Lots of guitar amps have a standby switch, which I've gleamed to serve the same function as this delay of which you speak. So why don't more hifi amps just use a standby switch?
Lots of guitar amps have a standby switch, which I've gleamed to serve the same function as this delay of which you speak. So why don't more hifi amps just use a standby switch?
El Zombre,
Good question. I expect that in tubed guitar amps, the standby switch serves to switch-off the B+ voltage, while keeping the heaters running at either 100% or lower. There have been threads on this.
It certainly makes sense with guitar amps, where a guitarist may play for while then take a break. However, I guess that most guitarists would fully power-down the amp for longer periods.
For audio use, I would hazard a guess that the tubed amp is either left on for a couple of hours playing or is fully switched-off. Considering that some of the popular tubes such as 6SN7's are getting expensive, fully switching off could extend tube-life.
In other words, I don't know what the answer is, and I am just guessing (or BS'ing).
Charlie
Good question. I expect that in tubed guitar amps, the standby switch serves to switch-off the B+ voltage, while keeping the heaters running at either 100% or lower. There have been threads on this.
It certainly makes sense with guitar amps, where a guitarist may play for while then take a break. However, I guess that most guitarists would fully power-down the amp for longer periods.
For audio use, I would hazard a guess that the tubed amp is either left on for a couple of hours playing or is fully switched-off. Considering that some of the popular tubes such as 6SN7's are getting expensive, fully switching off could extend tube-life.
In other words, I don't know what the answer is, and I am just guessing (or BS'ing).
Charlie
That’s a good question, for which I have no crisp answer. Of course, it will depend on the tube type, and on the frequency and duration of “abuse”. All oxide-coated cathodes will eventually develop some interface; it’s part of aging – like wrinkles. But I think you can hasten this aspect of aging by frequently holding the heaters on without B+. I would guess (only a guess) that keeping the heaters on for a minute or two without B+, if done every day for months, might degrade the tube faster in the “out years” than if it had gotten B+ after 10 seconds or so each time. Perhaps someone can cite a study on this. BTW, computer triodes were designed to be switched “high” (no current) for long periods of time with heaters cooking. They used special cathode materials to reduce interface formation.
Perhaps this is one reason that many people like the sound of computer tubes like the 7044, 7119, 6350, 5963, 5965, etc. I know I do. The 5687, especially the 5687WA, is spec’d as an amplifier but some of the data sheets comment on its special design for low interface formation, too.
Perhaps this is one reason that many people like the sound of computer tubes like the 7044, 7119, 6350, 5963, 5965, etc. I know I do. The 5687, especially the 5687WA, is spec’d as an amplifier but some of the data sheets comment on its special design for low interface formation, too.
I have built one Aikido with 12AU7 and 5687 as buffer.
As 5687 takes large amount of filament current, it takes sometimes for the amplifier to stabilise.
I would suggest you could measure the anode voltage of the two 6SN7's at the bottom to see how long it takes to stable. Then, you can add some more margin to it for the B+ delay circuit.
Johnny
As 5687 takes large amount of filament current, it takes sometimes for the amplifier to stabilise.
I would suggest you could measure the anode voltage of the two 6SN7's at the bottom to see how long it takes to stable. Then, you can add some more margin to it for the B+ delay circuit.
Johnny
Well, Brian, I think you argue for the way I do it, just switch on everything at the same time. The voltages in small-signal service are way below anything that will strip the cathodes so I think that those fears are groundless- I think we could both name lots of pieces of classic equipment where the B+ was switched on at turn-on yet tube life was normal-to-outstanding.
Cathode poisoning is a hazard with a lot more solid data behind it.
Cathode poisoning is a hazard with a lot more solid data behind it.
I've built them both ways, both immediate SS B+ turn-on and also delayed. I haven't noticed a problem with stripping either way. Maybe I haven't lived long enough to see it. As you say, most audio voltages aren't high enough to cause any major stripping problem anyway. Still, where feasible, I like things to come on g r a d u a l l y.
What an interesting discussion. My Belkin PF60 arrived. I haven't yet plugged the unit in. I was wondering how a device that Belkin list at $699 can retail for the $150 that I paid. Well, I think I discovered one reason. The units are listed as having either a silver or black chassis. Mine has a silver faceplate, but the rest of the unit is black. It has also crossed my mind that my unit could be a clever counterfeit, although I wouldn't expect it to be very profitable to manufacture a unit that likely has a very small marketplace.
Anyway, I have to wait for my 10S tube delay to arrive. I am quite excited, as I'll be able to switch on the Belkin, it'll switch on the preamp, after 10S, the Amperite will switch on B+, then after another 5S, the Blekin will switch-on the rest of the system.
You can really tell that I am a nerd at heart, just don't get me talking about the evolution of rare cacti - I won't be able to stop.
Regards,
Charlie
Anyway, I have to wait for my 10S tube delay to arrive. I am quite excited, as I'll be able to switch on the Belkin, it'll switch on the preamp, after 10S, the Amperite will switch on B+, then after another 5S, the Blekin will switch-on the rest of the system.
You can really tell that I am a nerd at heart, just don't get me talking about the evolution of rare cacti - I won't be able to stop.
Regards,
Charlie
Regardless of the minimum warm-up time needed....why not just play it safe and be conservative...give it 30 seconds for example....you can't go wrong with more warm-up time...unless 30 seconds is too long for an impatient audiophile to listen to music...
Guitar amps do have a standy-by switch for the B+ ...but it must be used properly since it is not idiot proof.... For example I installed 4 NOS EL34 Mulllards in a 100W Marshall and biased it up... I then lectured the customer like a Drill Instructor about proper warm-up use of the Stand-By switch.....
The idiot stripped the cathodes within 2 weeks and the tubes were noisey as heck.... due to improper use of the standy-by switch...you can't turn on the ON switch and the B+ switch at the same time.....
For Hi-Fi equipment I prefer to make a soft-start circuit....you adjust the time until the B+ turns ON.....after you hit the ON switch, the heaters are ON for a designated amount of time...use 30 seconds...then the B+ kicks in....when using a relay you will get a audible "pop" or "clunk" unless you place the filter caps after the relay ...another method is to go to the Power Supply regulator circuit and pull down the reference and slowly ramp up the reference... This brings the B+ up smoothly....
Chris
Guitar amps do have a standy-by switch for the B+ ...but it must be used properly since it is not idiot proof.... For example I installed 4 NOS EL34 Mulllards in a 100W Marshall and biased it up... I then lectured the customer like a Drill Instructor about proper warm-up use of the Stand-By switch.....
The idiot stripped the cathodes within 2 weeks and the tubes were noisey as heck.... due to improper use of the standy-by switch...you can't turn on the ON switch and the B+ switch at the same time.....
For Hi-Fi equipment I prefer to make a soft-start circuit....you adjust the time until the B+ turns ON.....after you hit the ON switch, the heaters are ON for a designated amount of time...use 30 seconds...then the B+ kicks in....when using a relay you will get a audible "pop" or "clunk" unless you place the filter caps after the relay ...another method is to go to the Power Supply regulator circuit and pull down the reference and slowly ramp up the reference... This brings the B+ up smoothly....
Chris
Can you turn on the B+ smoothly while heating the filamen by changing the rectifier tube to let say 5AR4 or GZ32?
Old fashioned
Hi guys
I wired a switch between the centre tap of my psu so when i turn on the r red switch it starts up the filaments and cooling fan and then after many minutes i flip the toggle switch to activate b+ no thumps and then on power down i turn off toggle (b+) then the red switch (which controls everything.. you cant turn on b+ without the heaters on)
speaking of preserving tubes i run the sn7's at 6V with no sound difference to 6.3V but with a greatly increased tube life. I use dc but have organised wiring to be mirror image from left to right so i swap tubes over to other side to prevent the dreaded dc build up.
Hope this helps
Nick
Hi guys
I wired a switch between the centre tap of my psu so when i turn on the r red switch it starts up the filaments and cooling fan and then after many minutes i flip the toggle switch to activate b+ no thumps and then on power down i turn off toggle (b+) then the red switch (which controls everything.. you cant turn on b+ without the heaters on)
speaking of preserving tubes i run the sn7's at 6V with no sound difference to 6.3V but with a greatly increased tube life. I use dc but have organised wiring to be mirror image from left to right so i swap tubes over to other side to prevent the dreaded dc build up.
Hope this helps
Nick
Well, I can't remember where I read it, but for lower voltages such as those used in most amps (200-350VDC), it seems that cathode stripping is really not too much of an issue. In fact, I vaguely remember someone suggesting that only in cases where B+ is over 1kV is there a problem.
Furthermore, isn't it possible that waiting too long before flipping on the B+ can cause tube degradation?
Anyhow, my 10 seconds before B+ works fine, as my power-console delays main amp switch-on by 15 seconds which gives a solid 5 seconds for all bumps and thumps to leave the system!
Charlie
Furthermore, isn't it possible that waiting too long before flipping on the B+ can cause tube degradation?
Anyhow, my 10 seconds before B+ works fine, as my power-console delays main amp switch-on by 15 seconds which gives a solid 5 seconds for all bumps and thumps to leave the system!
Charlie
Just for the record....
There was a well known pre-amp that uses 6922 pre-amp tubes..
The pre kept eating up tubes..... The tubes would last not more than a week , regardless of brand , quality...ect....
The tubes would become extremely noisy and crackling and basically useless .... The problem was "WARM-UP-TIME" was too short before the B+ was applied.... I over increased the warm up time to like 45 seconds....and the problem was gone...
I never heard any problem with keeping the heaters on without B+ ..... Nothing documented with actual data...just the usual arm waving BS....
Chris
There was a well known pre-amp that uses 6922 pre-amp tubes..
The pre kept eating up tubes..... The tubes would last not more than a week , regardless of brand , quality...ect....
The tubes would become extremely noisy and crackling and basically useless .... The problem was "WARM-UP-TIME" was too short before the B+ was applied.... I over increased the warm up time to like 45 seconds....and the problem was gone...
I never heard any problem with keeping the heaters on without B+ ..... Nothing documented with actual data...just the usual arm waving BS....
Chris
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