i was looking at a push pull OTL amp that uses 4 36kd6 tubes.
two of those tubes have no heater connections.
Can someone please explain why this could be?
two of those tubes have no heater connections.
Can someone please explain why this could be?
Looking at the tube datasheet these have 36V heaters, so if you're looking at a schematic, then it's drawn in error. A heater is pretty much intrinsic to a valve.
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I think he means the other tubes in the amp.
Hot cathode - Wikipedia, the free encyclopedia
"Hot cathodes may be either directly heated, where the filament itself is the source of electrons, or indirectly heated, where the filament is electrically insulated from the cathode; this configuration minimizes the introduction of hum when the filament is energized with alternating current. The filament is most often made of tungsten. With indirectly heated cathodes, the filament is usually called the heater instead. The cathode for indirect heating is usually realized as a nickel tube which surrounds the heater."
Hot cathode - Wikipedia, the free encyclopedia
"Hot cathodes may be either directly heated, where the filament itself is the source of electrons, or indirectly heated, where the filament is electrically insulated from the cathode; this configuration minimizes the introduction of hum when the filament is energized with alternating current. The filament is most often made of tungsten. With indirectly heated cathodes, the filament is usually called the heater instead. The cathode for indirect heating is usually realized as a nickel tube which surrounds the heater."
Theoretically, it is possible to make a cathode as a pipe that goes through top and bottom of the tube, and heat it externally, for example by a candle flame.
Still, anode power source is needed.
I remember such devices that were placed on top of kerosene lamps that generated enough of DC voltage to run battery powered vacuum tube receivers.
So, it is possible to make such vacuum tubes that require heat only to perform.
Still, anode power source is needed.
I remember such devices that were placed on top of kerosene lamps that generated enough of DC voltage to run battery powered vacuum tube receivers.
So, it is possible to make such vacuum tubes that require heat only to perform.
An externally hosted image should be here but it was not working when we last tested it.
i am looking at the amp itself. Or i would be if i was home.
When i first powered up the amps they were not working and i thought that was why.
Two tubes had heaters worked and two did not, ergo bad heater in two tubes. Swapped the tubes out and around. No heater glow with a tube in sockets 1 and 4.
Looked at the board and i cannot see the heaters connected to anything for those two sockets.
When i first powered up the amps they were not working and i thought that was why.
Two tubes had heaters worked and two did not, ergo bad heater in two tubes. Swapped the tubes out and around. No heater glow with a tube in sockets 1 and 4.
Looked at the board and i cannot see the heaters connected to anything for those two sockets.
Did you get it with power cord snipped off? Somebody probably selected the 36V heaters so 4 in series could be run from 120VAC line voltage unisolated.
OK so you have an amp where 2 of the heaters are not wired and the amp does not work. What else would you except?
When I read the first post I thought you have a working amp and were wondering how it could still function with two dead tubes. I had several ideas (1) maybe the tubes are parallel and now one is taking the load, or (2) maybe it was push-pull with only the push side working and it might work but sound bad.
So now I have to ask: Did this amp ever work? If not then it is simply built wrong
I used to have this old 125 watt solid state PA amp that was transformer coupled to the speaker. There was a 12AX7 tube wired but without heater connections. The socket pins were shiny and untouched by solder and the amp worked just fine. Still not sure why the tube was there 😕
Perhaps the 9-pin socket was intended for some other purpose, a plug in matching transformer perhaps. SOmeone comes along later and sees the empty socket and sticks a tube in it. Amp continues to function as it did without the tube.
This is not as silly as it may sound. I have serviced/restored juke boxes for decades, and in older tube models, it was not unusual to see cable connections between subassemblies made with octal connectors. And I can count on finding the occasional juke wherein someone has plugged a tube into a cable socket and vice versa. (Usually accompanied by a denial that ANYONE had been inside the unit.)
This is not as silly as it may sound. I have serviced/restored juke boxes for decades, and in older tube models, it was not unusual to see cable connections between subassemblies made with octal connectors. And I can count on finding the occasional juke wherein someone has plugged a tube into a cable socket and vice versa. (Usually accompanied by a denial that ANYONE had been inside the unit.)
There are devices that function without a heater (called cold cathode) but that doesn't seem to be the likely answer here.
The above pictured device is a thermoelectric generator and has absolutely nothing to do with thermionic emission used in vacuum tubes.
Besides the odd cold-cathode device, there are gas tubes which have a traditional oxide type cathode heated by ion bombardment. 0Z4 is an example. These start by conducting bidirectionally (much like a neon lamp), which heats up the cathode. As it gets hotter, emission produces space charge and reverse conduction goes away. In operation, electrons go to the plate, carrying load current, while ions go to the cathode, keeping it hot. As you might guess, these tubes are only useful in a narrow range of plate currents, otherwise the cathode is too cool (resulting in reverse breakdown and excessive ripple) or too hot (resulting in damage).
I don't know of any amplifier tubes operated in this way. There are gas triodes and tetrodes, but as far as I know, they are all thyratrons, not useful for amplification (at least in any immediately obvious way 😉 ).
Tim
Besides the odd cold-cathode device, there are gas tubes which have a traditional oxide type cathode heated by ion bombardment. 0Z4 is an example. These start by conducting bidirectionally (much like a neon lamp), which heats up the cathode. As it gets hotter, emission produces space charge and reverse conduction goes away. In operation, electrons go to the plate, carrying load current, while ions go to the cathode, keeping it hot. As you might guess, these tubes are only useful in a narrow range of plate currents, otherwise the cathode is too cool (resulting in reverse breakdown and excessive ripple) or too hot (resulting in damage).
I don't know of any amplifier tubes operated in this way. There are gas triodes and tetrodes, but as far as I know, they are all thyratrons, not useful for amplification (at least in any immediately obvious way 😉 ).
Tim
It is rumoured that some circuits include a non-functional valve simply as a cynical marketing ploy. People fall for it!
In some cases it may be worse than that - the valve may reduce the sound quality because people who do this trick don't always know what they are doing.
In some cases it may be worse than that - the valve may reduce the sound quality because people who do this trick don't always know what they are doing.
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