I was looking at some old 813 tubes that were once commonly used for Amateur radio transmitters, as the final output tube. While the common audio output tubes like 6L6 and 807 can produce about 25 to 30 watts audio output (per tube), running around 300 to 450 volts plate voltage, this 813 tube is rated at 250 to 300 watts output RF (per tube), but running at around 700 to 750 volts on the plate.
I'm not planning to do this, but if this 813 tube was used in an audio amplifier, and using 700 +/- plate voltage, would this tube be able to put out around 250 to 300 watts audio power (per tube)? Yea, I know it would require a custom audio output transformer.
Froim the data sheeds the 813 is only good for around 350 watts of audio power with 2 of them in push pull with 2500 volts on the plates. Around
260 watts with 1500 watts on the plates for 2 of them.
I doubt they would make much power at all if only 700 volts were used on the plates. The tubes are designed for over 1000 volts.
If running in anything resembling linear operation (RF or AF) that is about all that can be gotten out of them and have them last. Running class C at RF (audio would be very distorted) you can get more out of them, but not 250 watts per tube with 700 volts on the plates.
Yes, but the 'Amateur radio transmitters' he's talking about are from the '40s and '50s, which were shipped with the original metal 6L6, not the later glass versions. A lot of them were built with W.W. II surplus tubes, of which the 6L6 was readily available as surplus into the '70s.
We aren't talking about stereos or guitar amps. The were audio outputs for radios, or modulators for medium power AM transmitters designed for Amateur radio service. I was servicing these radios back in the '70s. That is four decades ago.
--
Never piss off an Engineer!
They don't get mad.
They don't get even.
They go for over unity! ;-)
I was looking at some old 813 tubes that were once commonly used for Amateur radio transmitters, as the final output tube. While the common audio output tubes like 6L6 and 807 can produce about 25 to 30 watts audio output (per tube), running around 300 to 450 volts plate voltage,
UNQUOTE:
--
Never piss off an Engineer!
They don't get mad.
They don't get even.
They go for over unity! ;-)
So you agree, OP was not asking about transmitters? He also wasn't asking about 6L6's of either type! (though his reference to 30W/tube says he meant 6L6GC).
He was asking about 813 (transmitting) tubes in an audio amp.
Phil was right. Now can we please end this pissing match?
** I only wanted to point out that regular 6L6 type tubes, as sold in the last 40 years, can output 100W per pair under the right supply conditions - something the data books do not mention.
It all about raising up the plate supply voltage while keeping the screen supply under 400V - plus matching the load correctly.
The 813 has fairly similar restrictions on the screen supply voltage.
Seems to me to would have to load is pretty heavily, not just to get the power, but also to try to keep the plate volage down. If you go to 2X 700 volts, it might not be a matter of the tubes, it might be the tubes sockets.
What does limiting the G2 do ? Keep it from arcing to the suppressor grid ? I have wondered before about why the hell doesn't all this shit just arc and weld itself together. Well, OK I know it has to do with the vacuum, but still.
However wiki reports that permissivity of air at STP is only something like 1.000 point whatever, with 1 being the standard.
I just referred to the common audio output tubes. Wondering if a transmitter tube (like an 813) is capable of audio output power in the same wattage as that same tube would put out as a transmitter (asuming the plate voltage, biasing, and signal input to the tube was about the same.
From this thead, I did learn that these tubes need a lot higher plate voltages than I thought (like 1500 to 2500 volts).
I also learned (after doing some research on the web), that the original metal 6L6 tubes, did not have the same power output as the glass version. I thought they were the same tube in a different container.
*** And this explains something that occurred 40 some years ago. When I was running my tube power amps for my stereo, (four 6L6GC tubes Push-Pull Parallel, in each mono block amp), one of the tubes went bad. I went to my box of used tubes and found a 6L6 metal case, and used that for a temporary replacement. Although that tube tested GOOD, the amp just did not sound or perform properly. It did work, but lacked a lot of the "punch" it had before. A few days later I bought a new 6L6GC, and the amp worked great once again.
Now, 40 some years later, I learned why that metal 6L6 did not work properly !!!!
I also learned in recent times that for best performance, a pair or quad of output tubes should be MATCHED. Back then, I never knew anything about matching. If it was the proper numbered tube, and a tube that tested good, I'd just plug it in and GO....
The short answer is that most of the tubes will put out the same power at audio as they will at RF. Not counting some specific tubes such as the microwave tubes. Tubes start loosing efficency as the frequency goes higher into the RF ranges. The common 6146 tube might put out about 50 watts up to about 50 MHz but will work to 150 MHz but only put out 30 watts and stay within the ratings.
There is one other thing to look at. That is the class of service. Running class C will put out the most power but can only be used for certain types of RF signals due ot the distortion. It can not be used at all for normal audio amplifiers.
As with the 813 tube, most tubes rated for much over 50 watts output will often have a plate voltage of over 1000 volts,many like to have
2000 volts or more.
For the best sound the tubes should be matched. They are operated in what is called a push-pull circuit. Often close to class B. That is when one tube is putting out power,the other tube isn't during a cycle. It is at the crossover point that if they are not well matched you get most of the distortion. Many audio amps often operate more like AB class to help eliminate that problem. It is not much of a problem at RF due to the way the output circuit works.
I can relate to using ceramic sockets, because the standard ones would likely burn up from such high voltages.
What are the standard sockets made out of anyhow????
Considering the closeness of the tube socket pins, I could see where there could be arcing between pins at voltages that are or exceed 1000V. Plate caps eliminate that problem. However, I would assume that the wire going to those plate caps would need to have insulation capable of the voltage, and where they go thru the chassis, would need grommets that can handle the voltage too. Not to mention the connections below the chassis such as terminal strips.
I have not worked with any voltages exceeding 1000V (except the HV in the old tv sets). But since I am on a farm, I know what an electric fencer can do. If a fence wire gets too close to a tree (for example), it will snap and shoot a spark a half inch long, or longer. Most of those fencers are around 5000 V. Those fence wires are all run on porcelin insultors. (although there are now plastic ones that work as well).
I have felt them fences far too many times too..... I have been literally knocked down from them more than once, if I was well grounded.... NOT FUN. :(
Fortunately those fencers do not kill a person or animal (or we would not use them, since livestock are expensive and dead people are not a good thing). The voltage is high, but the current is low. (and it pulses).
Anyhow, while I have not done it, I am sure building transmitters (or anything else) using those high voltages, require special components and wiring, which in itself requires special knowledge.
I have 2 amplifiers for my ham radios. Both have about 2700 volts on the plates of the tubes. The current drawn by the tubes is almost one amp. I have worked on them several times. To do that I make sure the capacitors have fully discharged by watching the voltmeter on the amps go near zero. When I take the cover off, vurey carefully, I then short the capacitors to ground to make sure the volt meter is not giving a false reading. The voltage and current is not like a fence charger. It will dump a lot of current into you and often kill. Fence chargers are more like a static electricity shock, lots of voltage,but little current. They are made to shock and not to kill.
It does take some special insulated wire for the amps and other high voltage items. Most common wires are insulated for around 600 volts or even 300 volts. That 2700 volts will often burn through wire insulated like that . Only 'good' thing about it,is that it will not jump much of an air gap. However with RF applied the operaing voltages inside the amp is somewhat greater and can arc a short distance.
Most of the tubes operate with less than 500 volts on the pins with the higher voltage going to the cap on the plates. Ceramic is often used because of the heat on the pins of the tubes. The filiments get hot and direct transfer heat, and the heat of the plate is radiated to some extent. Afer all, if an amp is putting out 1000 watts it is using close to 1500 to 2000 watts to do it. That is almost as much as some of the smaller 'bathroom' portable electric heaters put out.
Double voltage into double load = double the power. "
I think you got this f***ed up somehow. When the load impedance is halved then the power is doubled. I'll put it down as a typing error unless you argue the point.
What's more, double the voltage into the same load if four times the power, not two.
Perhaps you are older and thus have more knowledge then I on some of this. From what I understood from the old days, tubes (valves) generally break down due to the cathode nit being able to put out current, and that is where all the current comes from.
However of course there can be other failure modes. Are you saying that some sort of arc or leakage is damaging the valve ? If so I would like your explanation of this failure mode.
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