I recently bought three 829 tubes off thEbay, and when they arrived I found that they were in worse condition than indicated by the seller. The seller refunded my money so I have no beef with them.
However, I am perplexed with the tube behavior.
All three are USN 829 tubes (not B version).
All three have good filaments.
All three get warm when the filaments are driven.
All three show no getter flash.
I expected the tubes to be gassy. However, they don't draw excessive current.
I biased them with a 470 Ohm cathode resistor, Zener regulated 180V on the screens, and 100K grid to ground resistors.
My NOS versions come up at 30mA cathode current for a bias voltage of 14.2V. Close to what I expected.
However all three tubes I received have zero emission! Nothing! Va = 300V, VG2=180V, the voltage across the cathode resistor is below 20mV which indicates less than 42uA current through the two sections combined.
Can anyone explain this to me?
However, I am perplexed with the tube behavior.
All three are USN 829 tubes (not B version).
All three have good filaments.
All three get warm when the filaments are driven.
All three show no getter flash.
I expected the tubes to be gassy. However, they don't draw excessive current.
I biased them with a 470 Ohm cathode resistor, Zener regulated 180V on the screens, and 100K grid to ground resistors.
My NOS versions come up at 30mA cathode current for a bias voltage of 14.2V. Close to what I expected.
However all three tubes I received have zero emission! Nothing! Va = 300V, VG2=180V, the voltage across the cathode resistor is below 20mV which indicates less than 42uA current through the two sections combined.
Can anyone explain this to me?
This is very Cool !!
I just got a couple of those this last winterToo !!! ............. from a local seller !! 😀
I also got quite a few other tubes to mess with as well, But sadly one of the 829's is broke but one is still intact and appears to be New NOS.
I am very interested in seeing what you can do with these, and maybe I will get mine running as well, else I just have to leave them sitting displayed on my desk. 🙂
Cheers !!!
jer 🙂
I just got a couple of those this last winterToo !!! ............. from a local seller !! 😀
I also got quite a few other tubes to mess with as well, But sadly one of the 829's is broke but one is still intact and appears to be New NOS.
I am very interested in seeing what you can do with these, and maybe I will get mine running as well, else I just have to leave them sitting displayed on my desk. 🙂
Cheers !!!
jer 🙂
If full of air I would expect the filaments to go up literally in smoke or burn out with some drama.
Perhaps the cathodes are poisoned or they were run so hard they are out of emission?
Lack of getter is a likely indication that they have high hours. I don't recall NOS ones I had as having a lot of getter relative to their size. I also had several that went out with a bright flash of light at first power, and few others that ran away (red plated). I ended up with the Russian equivalent which was reliable.
Perhaps the cathodes are poisoned or they were run so hard they are out of emission?
Lack of getter is a likely indication that they have high hours. I don't recall NOS ones I had as having a lot of getter relative to their size. I also had several that went out with a bright flash of light at first power, and few others that ran away (red plated). I ended up with the Russian equivalent which was reliable.
Ive seen this on a batch of 6BQ5, dozen of tubes with less than 1mA emission. I still have a bag of those to play around with somewhere.
Try overvoltage on the heaters of 50-60% to see if you can re-form the cathode.
Try overvoltage on the heaters of 50-60% to see if you can re-form the cathode.
The filaments have burned out on two of the three after about an hour of run time each. I will test the third one again and see how long the filament lasts. I suspect gassy enough to prevent any emission, but not enough to cause the filament to flash but still burn out slowly.
With the right amount of gas funny things happen.
I had a GU 50 which did not light up the filament at nom 12V, although heater current was flowing and the tube did get warm. No emission either, I first thought. But then I wound up the heater voltage gradually until it glowed like a good one - at no less than 25 volts ... and now there was plate current, too, almost normal, below 200V. Any higher triggered a beautiful gas discharge.
Obviously a rather small amount of gas caused enough convection cooling of the filament to suppress glow and emission.
If you try this, make shure you have a current limiting resistor in place. If the gas discharge fires up the internal resistance of the tube drops to near zero ...
I had a GU 50 which did not light up the filament at nom 12V, although heater current was flowing and the tube did get warm. No emission either, I first thought. But then I wound up the heater voltage gradually until it glowed like a good one - at no less than 25 volts ... and now there was plate current, too, almost normal, below 200V. Any higher triggered a beautiful gas discharge.
Obviously a rather small amount of gas caused enough convection cooling of the filament to suppress glow and emission.
If you try this, make shure you have a current limiting resistor in place. If the gas discharge fires up the internal resistance of the tube drops to near zero ...
I bought a box full of identical good looking TV sweep tubes at a hamfest for $1 each several years ago. All had shiny getters and showed no outward signs of use, much less, abuse. I don't remember the number, but they were big compactrons worth far more than $1 each.
I was surprised to find zero current flow at all on all of them. I mean tie all grids + plate together and feed them several hundreds of volts positive, yet the current meter needle doesn't move kinda dead.
The usual cause of death here is that the little steel jumper that connects the cathode itself to the base pin is blown like a fuse, but that wasn't the case here.
A hammer time autopsy did not reveal any obvious failure either.
I suspect that your 829's were full of air. A fully coated heater may not draw excessive current, but will die a fairly quick death in air.....there is usually some smoke inside the tube though.
I was surprised to find zero current flow at all on all of them. I mean tie all grids + plate together and feed them several hundreds of volts positive, yet the current meter needle doesn't move kinda dead.
The usual cause of death here is that the little steel jumper that connects the cathode itself to the base pin is blown like a fuse, but that wasn't the case here.
A hammer time autopsy did not reveal any obvious failure either.
I suspect that your 829's were full of air. A fully coated heater may not draw excessive current, but will die a fairly quick death in air.....there is usually some smoke inside the tube though.
If you go back to ebay try and find ones which you can clearly see the silver getter at the base of the tube. Avoid the transparent ones.
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i had a once NOS box with russian gu32 (circa 1965) (similar design to 829). Of all them (approx. 20 pieces), only a third were usable. bad ones didn't have a glossy getter coating ... I don't use them...think that with those upper anode outlets over time they lose their "tightness".
I am surprised that more people don't build amps with this tube. It is specified as a an AF Power Amplifier & Modulator in AB1 (40W), and RF output device in AB2 with up to 90W out if forced air cooled and 70W out with natural air cooling.
I expect one could run AB2 and get more than 40W out.
I thought about building a 50W linear for 2M with one, but lack the RF experience.
I expect one could run AB2 and get more than 40W out.
I thought about building a 50W linear for 2M with one, but lack the RF experience.
I built an amp with them, but the tolerance is trash, and they want 13k5 plate to plate or something if you built the datasheet spec amplifier. Not a common transformer. I found paralleling both halves and using four tubes in an amp worked alright using 5k loading and 400V B+ 200V screen.
I used GU29. All have getter flash but one had only one getter flash out of the two like the second one didn't get fired. The only tubes I will use without a visible flash are those newer Soviet ones like 6D22 where the getter is modern and doesn't make a flash.
I used GU29. All have getter flash but one had only one getter flash out of the two like the second one didn't get fired. The only tubes I will use without a visible flash are those newer Soviet ones like 6D22 where the getter is modern and doesn't make a flash.
I had a bunch of these, some 832's, and some larger Amperex tubes whose number I don't remember that fit the same sockets. As others have found many of the 8XX tubes were bad or gassy enough the cause bias drift. The taller Amperex tubes seemed to work OK, but I only had a few.
I gave them all among with my 4CX250B's and chimneys to a ham who wanted to build RF amps.
My 2 meter RF amp was made with sand, MRF150's. I got a bunch of them by buying dead MRI amp boards for like $20 each. Usually only one of the dozen or so transistors was dead.
I have four that test new, and three that are moderately to well used to play with.
I am thinking of using a combination of cathode bias plus a small amount of positive fixed bias to adjust the lower current section to match the higher current one. Maybe a resistor from the screen supply to a pot in parallel with a pair of diodes to set a 1.4V adjustment range.
A bias point of 350V and 50mA looks like a 10Kp-p transformer might work. Output will be below 20W. Screen supply will be a zener ref to a pass FET.
I am thinking of using a combination of cathode bias plus a small amount of positive fixed bias to adjust the lower current section to match the higher current one. Maybe a resistor from the screen supply to a pot in parallel with a pair of diodes to set a 1.4V adjustment range.
A bias point of 350V and 50mA looks like a 10Kp-p transformer might work. Output will be below 20W. Screen supply will be a zener ref to a pass FET.
That's it. One tube 6600 ohm load well over 50 watts out. I still gave them all away. It's just easier to feed an SSE board with a phase splitter and get 75 watts with the same set of transformers and a pair of KT88's.