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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
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13th Mar 2019, 3:25 pm | #21 |
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Re: Valve warm up times
They have filaments, not heaters. The filament starts emitting electrons immediately it gets hot, which takes well under a second. An indirectly heated valve which can be heated by AC has a separate heating element and cathode, and the cathode will only start emitting electrons once the heater has warmed it up sufficiently, which will take at least tens of seconds.
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13th Mar 2019, 4:26 pm | #22 |
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Re: Valve warm up times
Something like this? https://uk.farnell.com/schrack-te-co...tht/dp/2975029
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13th Mar 2019, 5:21 pm | #23 |
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Re: Valve warm up times
Some mobile two way radio sets had directly headed cathodes in the RF output stage that could warm up so quickly that the press of the button on the microphone and talking delay wasn't noticed.
The big CATs (cooled anode triodes) in the old BBC transmitters where warmed up over a period of minutes to lengthen life. The answer is less than a short bit of a second to minutes, take your pick! |
13th Mar 2019, 6:33 pm | #24 |
Nonode
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Re: Valve warm up times
And the vast numbers of ordinary sized valves used in the code breaking computer at Bletchley were also warmed up gradually in order to reduce failure rates.
AFAIK they used standard heater transformers but with a large variac controlling the mains into these. The minute chance of failure when switching on was acceptable in normal equipment, but became a problem with thousands of valves used. Consider a one in ten thousand chance of heater failure when turning on. For a radio set turned on twice a day, it could be decades before a valve failed. For a valve based computer, it was likely that at least valve would fail during each turn on. |
13th Mar 2019, 7:20 pm | #25 | |
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Re: Valve warm up times
Quote:
These were using the little B7G battery-filament valves. In the 1950s/1960s loads of two-way VHF PMR radios used "Quick-heat" PA valves: given the feeble output of typical motorcycle/car generators and batteries of the era everything-possible was done to conserve power when on receive - such as not heating the transmit-valve filaments unless they were actually needed to provide RF: they generally had low-voltage/high-current filaments that were powered via a current-limit resistor from the TX/RX relay. The QQZ06/40 is a good example. http://www.r-type.org/exhib/aad0308.htm Press-to-transmit. Filament heating fast enough to produce 60 Watts of VHF/UHF output within half a second from cold.... |
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14th Mar 2019, 9:32 am | #26 |
Heptode
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Re: Valve warm up times
In some of my projects i use a PY81 as a delay. The heating-up time can be about 50 seconds.
Three pages from "Data and Circuits of Television Receiving Valves" (Book IIIc , Electronic Valves, Philips 1953): |
14th Mar 2019, 11:17 pm | #27 |
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Re: Valve warm up times
I've ordered 2 relays. 60v coil DPDT. Will fit the 470 ohm 10 watt resistors and the relay will short them out under normal operation. If the EB91 circuit fails, the relay will drop out putting the 470 ohm resistors in circuit. I may even connect red LEDs in the circuit to indicate the failure of the bias. Any thoughts please.
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15th Mar 2019, 11:13 am | #28 |
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Re: Valve warm up times
LEDs across the cathode resistors (with series resistor)?
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15th Mar 2019, 2:13 pm | #29 |
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Re: Valve warm up times
Yes that set-up should be pretty good and bomb-proof!
You can easily change from fixed bias to cathode bias just by pulling out the EB91. If you ever wanted to of course... |
15th Mar 2019, 3:09 pm | #30 |
Hexode
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Re: Valve warm up times
Yes. That looks good.
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21st Mar 2019, 4:29 pm | #31 |
Hexode
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Re: Valve warm up times
One last question, if I may. I have a spare 6.3v winding on the power TX which I intend to use on the EB91 heater and two 100 ohm fusible resistors between the 60v taps and the EB91 cathodes. I read on the net that the most common faults with the EB91 is heater / cathode shorts. Should that be enough with the relay as a safety net?
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21st Mar 2019, 6:24 pm | #32 |
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Re: Valve warm up times
Probably will be.
I take it you are using the 60V taps to the EB91 cathodes, so the negative supply appears at the anodes (commoned together)? A more elegant solution would be an isolated 60-0-60 winding, with 60V taken to anodes, common the cathodes and heater together and take this to 0V so the 60-0-60 centre tap is the negative bias rail. But only applicable if you have the luxury of this winding, or a separate transformer! |
21st Mar 2019, 9:17 pm | #33 | |
Hexode
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Re: Valve warm up times
Quote:
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21st Mar 2019, 9:55 pm | #34 |
Hexode
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Re: Valve warm up times
If I can find a small transformer 230v in - 60 - 0 - 60 out.
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22nd Mar 2019, 2:58 am | #35 |
Heptode
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Re: Valve warm up times
I would add that if you are dealing with new mercury vapor rectifiers, like an 872, etc. The initial warmup time is 30 minutes before B+ is to be applied.
After that it's 15 minutes. Per Thermatron/Faratron/Solidyne company installation instructions. I used to work on vinyl welders, and the failure to give appropriate warm up time was a total cash cow for me, since they used from 4 to 6 rectifiers in a single unit $$$$$$. I could mark on the calendar the weeks I would need to replace them. |
22nd Mar 2019, 10:42 am | #36 | ||
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Re: Valve warm up times
Quote:
Peter |
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22nd Mar 2019, 12:42 pm | #37 |
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Re: Valve warm up times
What's the reason for the super-long warm-up time? I can understand the need for the cathode to get right up to emitting temperature, so there is adequate space charge to prevent cathode bombardment by mercury ions. But this is achieved in a couple of minutes at most. And I would have thought that this sort of time would be enough to vapourise any mercury droplets which happened to have formed where we don't want them - on supports between anode and cathode.
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22nd Mar 2019, 12:57 pm | #38 |
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Re: Valve warm up times
That is a long time- perhaps to let the bulb get good and hot on just heater power and vapourise much of the fine grey globule mist on the glass for good vapour pressure?
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22nd Mar 2019, 1:10 pm | #39 |
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Re: Valve warm up times
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22nd Mar 2019, 3:06 pm | #40 |
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Re: Valve warm up times
I would have thought a time delay circuit is much less expensive than one rectifier let alone four to six of them.
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