GMI-30 looks a lot like one of the tubes you have been playing with.
VT127-A have uranium lead ins, harmless stuff but still cool.
Elton Britt - Uranium Fever - YouTube
VT127-A have uranium lead ins, harmless stuff but still cool.
Elton Britt - Uranium Fever - YouTube
I have been collecting HK54 / 35T / 35TG for a design. They are uncommon, so I've bought a few a untested at low prices. Success rate for the untested tubes is low as you might expect.
Would it be accurate to say that tubes that have a healthy filament and are slightly gassy are worth holding onto for the sake of baking, whereas those with an unhealthy filament are not?
Here is one HK54 in my tracer, filament looks good but there is slight gas, I think it might be salvageable. This is a pulse tracer, so it will not activate the getter.
Here is another with a dim filament as an example, I assume these are not worth trying to save.
Would it be accurate to say that tubes that have a healthy filament and are slightly gassy are worth holding onto for the sake of baking, whereas those with an unhealthy filament are not?
Here is one HK54 in my tracer, filament looks good but there is slight gas, I think it might be salvageable. This is a pulse tracer, so it will not activate the getter.
Here is another with a dim filament as an example, I assume these are not worth trying to save.
Post #50 would suggest that you can, my experience has been tubes with a dim filament are gassy, the glass gets scorching hot as heat is transferred in the poor vacuum. Voltage for the rated current is low relative to the datasheet. It is a 5V / 5A filament, only dropping 2.5V at 5A. Probably obvious that the tube cannot be saved, just need confirmation before I throw away three or four of these with dim filaments, my inner hoarder is crying.
I've not had any with dim filaments. Some of my 826s had smoke come off the filament as soon as I powered the filament, meaning that there was a total loss of vacuum in that tube. Those can't be salvaged.
I'd go by the curves (as long as your tracer has some sort of current limit protection). That should tell the story of the tube's performance.
I made a variable DC supply that goes up to 1000V with a variac, transformer, and bridge rectifier/cap. Then I got some big power resistors for current limiting.
I bring the voltage up slowly with an appropriate voltage on the grid (0V for a lot of tubes) and see if current seems right. With tubes that are slightly gassy, the gas will ionize at some point and the tube current will suddenly increase a lot. Plate voltage will drop when this happens if you have current limiting resistors.
The slightly gassy tubes that I have successfully rescued had a blue gas cloud and then cleaned up within 10 minutes. The gas ionized at less than 100V. The ones that never got better after 20+ hours of baking glowed more of a purple color and ionized closer to 400V. After all that baking, there was actually some black material that left the anode and is loose in the bulb.
I'd go by the curves (as long as your tracer has some sort of current limit protection). That should tell the story of the tube's performance.
I made a variable DC supply that goes up to 1000V with a variac, transformer, and bridge rectifier/cap. Then I got some big power resistors for current limiting.
I bring the voltage up slowly with an appropriate voltage on the grid (0V for a lot of tubes) and see if current seems right. With tubes that are slightly gassy, the gas will ionize at some point and the tube current will suddenly increase a lot. Plate voltage will drop when this happens if you have current limiting resistors.
The slightly gassy tubes that I have successfully rescued had a blue gas cloud and then cleaned up within 10 minutes. The gas ionized at less than 100V. The ones that never got better after 20+ hours of baking glowed more of a purple color and ionized closer to 400V. After all that baking, there was actually some black material that left the anode and is loose in the bulb.
Point taken Jan, thanks.
I had something similar happen to one of the dim HK54, filament smoked, flashed, and was pulverized. I think the dim filament phenomenon is a loss of vacuum, the tubes do not conduct at all, I'll just toss them. I'll try baking those with a bright filament that are slightly gassy, thanks.
I just happened to have an Edcor power transformer laying around and then I built a doubler so I could get up to 1000V or so. Needless to say, I don't touch anything while it is running except the Variac knob. All probes are set up before I power up and I keep my hands well away from everything. Same goes for my transmitter tube amp prototype.