Play old tape on scope, does it look like Kansas City Standard?
Or alternating clock and data pulses (Trash-80) ??? You might
could still load the sound file into MESS...
http://www.trs-80.com/
Or alternating clock and data pulses (Trash-80) ??? You might
could still load the sound file into MESS...
http://www.trs-80.com/
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Hello,
About B+ on a cold tube, Sy thanks for bringing it up. One of my first tube projects in the last 10 years (I took a break) was a knock off of a EAR from MapleTree Audio. The output tubes were NOS RCA 12B4A’s. At cold start one of the tubes would always have lightning in a bottle with large sounds from the $1.00 test head phones for a couple of seconds. I replaced the offending tube with a used Ebay GE tube. There was no more lighting. There was only 330 or so cold volts on the tube. I used the same offending tube where it did not see cold volts at startup and it worked fine. Now that tube is lurking unidentified in the junk bin.
At the time I was plexed between “bad tube” and the stuff I had read about “cold starts” being hard on good tubes. That was the only tube I ever had a cold start problem with.
DT
All Just for fun!
About B+ on a cold tube, Sy thanks for bringing it up. One of my first tube projects in the last 10 years (I took a break) was a knock off of a EAR from MapleTree Audio. The output tubes were NOS RCA 12B4A’s. At cold start one of the tubes would always have lightning in a bottle with large sounds from the $1.00 test head phones for a couple of seconds. I replaced the offending tube with a used Ebay GE tube. There was no more lighting. There was only 330 or so cold volts on the tube. I used the same offending tube where it did not see cold volts at startup and it worked fine. Now that tube is lurking unidentified in the junk bin.
At the time I was plexed between “bad tube” and the stuff I had read about “cold starts” being hard on good tubes. That was the only tube I ever had a cold start problem with.
DT
All Just for fun!
The 5U4 was the standard equipment rectifier in the post war years; worse was to come when evil smelling selenium rectifiers were used. The metal rectifier was the norm in lower voltage TV sets.
Nearly all the tube amps of the late 60's started to use sil rects. Did the instantaneous Bmax destroy tubes ? Nup. No evidence of stripping at anything used in consumer equipment.
Enclosed, anything cheap to save was the norm. One of those nasty rabid cap-input filter circuits. ca 1967. The description mentions KT88's should ahve a life of 10,000 hrs....
richy
Attachments
I don't have his book with me, but if these cites were related to the Scrapbox Challenge, then one must absolutely let a 6528 or similar tube heat for >30s. Has nothing to do with cathode stripping, it's gettering. Mercury tubes also need a preheat.
But the longevity of tubes in old Audio Research amps, Dyna SCA35s, Berning amps and preamps, and classic Marantz gear (e.g., 9, 8b) are certainly data points in favor of the "it's irrelevant" point of view for normal tubes operated at normal voltages.
But the longevity of tubes in old Audio Research amps, Dyna SCA35s, Berning amps and preamps, and classic Marantz gear (e.g., 9, 8b) are certainly data points in favor of the "it's irrelevant" point of view for normal tubes operated at normal voltages.
The reason I delay B+ voltage in my circuits is in order to avoid overvolting the power supply capacitors. One of my longstanding fave caps only comes up to 400V rating, and two others to 450V, and this is not enough for an open circuit with, say, a 325Vac transformer secondary. Now that I think of it, I'll probably lose the second switch on the Mœbius, since I'm now using a voltage doubler supply at 150Vdc or less final. It has been conclusively shown, as far as I am concerned, that there is no damage to the cathode of the tube by applying B+ before it's warmed to emitting temperature. I'll be reviewing the voltage possibilities of the Machine circuit as well, since why complicate things when it's not necessary?
Aloha,
Poinz
AudioTropic
Aloha,
Poinz
AudioTropic
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Having read a LOT of original material about the life of valves, I have only come across two references to standby / warm-up switches. One is in Tomer's book, and rather dubious. The second is from "Valve Reliability in Calculating machines" by L. Knight. Electronic Engineering, Jan 1954.
"Another unconfirmed supposition is that it may be mildly injurious to the cathode to apply any anode or screen potentials before the heater has fully warmed up. Thus it may be beneficial to arrange for a delay of about two minutes on the HT supplies."
Note the use of the words unconfirmed, supposition, may be and mildly. In other words, there is no evidence for it at all!
(And two minutes? Heck, why not make it two days...)
"Another unconfirmed supposition is that it may be mildly injurious to the cathode to apply any anode or screen potentials before the heater has fully warmed up. Thus it may be beneficial to arrange for a delay of about two minutes on the HT supplies."
Note the use of the words unconfirmed, supposition, may be and mildly. In other words, there is no evidence for it at all!
(And two minutes? Heck, why not make it two days...)
No, it is not unproved possibility.
It is superstition generated by ignorant people who generalize without knowledge. High current density on surface of filaments, high voltages in huge big generator tubes cause a phenomena that does not exist in smaller indirectly heated tubes with huge in respect to current and voltage cathode areas.
Joshua; you either know, or repeat speculations without understanding. However, it does not exclude that you may know something (well, there are not yet any evidence, however it's unproved yet possibility).
No, I have no direct knowledge about that phenomenon, or its' actual possibility. I only see HT delay used by some respected tube designers, which makes me wonder.
That may well be so – and it may not, I don't have any evidence either way.
I just purchased quad NOS Telefunken EL156 which cost me a fortune. Once the first of that quad will meet its' maker, I will not have the money to purchase another one and I'll have to switch to other tubes, not as good as Telefunken EL156.
Thus, my instinct says to apply HT delay – better be safe than sorry.
My instincts say you may damage them by abrupt B+ application that causes direct current spikes through control grids that cause high current spikes through saturated output transformer. This instincts are based on knowledge, unlike instincts about black cat that can cause misfortune, but can not, I don't have any evidence either way.
Good luck Joshua!
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Thank you.
Your black cat reminds me of Schroedinger.
My plan is to delay the filament voltage of the HT rectifier.
Yeah, like to shoot a corpse. By the way, what do you think happens to a rectifier tube when high voltage is applied when it has cold cathode?
Schrodinger was particularly right, particularly wrong: he did not understand that all free oscillations in Nature tend to be coherent. Nothing is random except results of observations by statisticians who has no deep knowledge about driving torses of what they observe.
Here is a recent article from FoxNews: FOXNews.com - Scientists Decode the Song of the Sun
I did not ask about a price; I've asked about what happens to it.
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Hello Sy and All,
I looked back at post #1. Directly Heated cathodes were excluded from the clarification of B+ and cold starts.
I suppose that other exclusions should also exist. For example, the cold B+ should be below the design center listed value for maximum plate voltage.
I know many of us hot rod our tubes beyond the maximum listed plate voltage that may be a good reason for a delay. As mentioned previously, respecting the maximum power supply capacitor voltage is also a good idea.
DT
All just for fun!
I looked back at post #1. Directly Heated cathodes were excluded from the clarification of B+ and cold starts.
I suppose that other exclusions should also exist. For example, the cold B+ should be below the design center listed value for maximum plate voltage.
I know many of us hot rod our tubes beyond the maximum listed plate voltage that may be a good reason for a delay. As mentioned previously, respecting the maximum power supply capacitor voltage is also a good idea.
DT
All just for fun!
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