Do shunt tubes exibit different behaviour in reverse polarity? - Page 1
Forum section: electronics / projects

author: Deactivated-1
author_rank: Frequent Contributor
timestamp: October 10, 2023, 09:46:33 am
content: Does the cathode have some exiting doping on it to promote a lower striking voltage? If not, is there any difference in running them in reverse polarity?Inspecting an 0B2 shunt tube, the anode actually is the inside tube. That which would be the cathode in normal vacuum tubes.Could that mean that running it in reverse polarity could allow for higher dissipation because the anode in that case would be the outside and have higher surface area to dissipate heat?Then why not make them like that to begin with?Would the cathode actually cool when current is passed trough it? Is that then the reason for putting it on the outside to absorb more radiant heat?

author: jonpaul
author_rank: Super Contributor
timestamp: October 10, 2023, 10:55:06 am
content: OA2, 0B2, are designed for a regulation via glow discharge.As current varies the area of the glow increases.The cathode is the rod in the center, (-) has low e material and points to start the glow.The large cylinder is the anode (+)The rated voltage regulation applies only in the rated polarity.See glow discharge text by J J Thompson, Ellenbas, etc.Also notes from SignaliteJon

author: CaptDon
author_rank: Super Contributor
timestamp: October 10, 2023, 01:12:47 pm
content: As stated, the anode is NOT the rod in the center. The anode is the outer cylinder and like any other normal vacuum tube is designed to radiate accumulated electron strike energy. Sadly the initial ionization voltage can be 1.5 times the regulation voltage and that is a critical factor if these glow regulators are used as screen voltage regulators if plate voltage is present or simultaneous with screen 'overvoltage'. One upside is the glow regulators can handle the weird 'reverse' screen current seen in some R.F. amplifier tetrodes.

author: CaptDon
author_rank: Super Contributor
timestamp: October 10, 2023, 01:22:00 pm
content: I do remember years ago playing around with some glow discharge regulators in reverse polarity to see what would happen. They were useless in that mode. Unpredictable and excessive ionization voltage and very poor regulation with current change. Kind of like trying to use a normal diode at its reverse breakdown as a zener. Wish I still had that old Dressen Barnes 300A (?) 0-300vdc with -0 to -150 also and a heavy 6.3vac with center tap on the front panel. It had a little 7 pin glow regulator inside and it was the perfect bench power supply for vacuum tube experimenting.

author: Wolfram
author_rank: Frequent Contributor
timestamp: October 10, 2023, 03:17:54 pm
content: These are gas tubes, so the cathode gets bombarded with heavy ions and the anode gets bombarded with electrons, and both heat up. A bulk of the dissipation happens in the anode, see for example the very asymmetric electrode sizing in high pressure xenon arc lamps. I am not 100 % confident, but I believe the same also applies at the pressures and current densities used in regulator tubes. There's also the issue of sputtering, which happens to a much larger degree for the cathode due to the mass of gas ions compared to electrons.What I suspect is the main reason for the electrode sizing is that the tubes operate in the "normal glow" region of the discharge volt-amp characteristic, where voltage drop is practically constant and the discharge surface area changes with current. This basically gives a minimum cathode area per current in order to have tight regulation, and the voltage regulation gets much worse once this current is exceeded.If you run the tubes in reverse, voltage regulation will be much worse on account of going into the "abnormal glow" region of the V-I characteristic at much lower currents, and not having an emissive coating on the now-cathode doesn't help either.Some references:https://ntrs.nasa.gov/api/citations/19650009902/downloads/19650009902.pdfhttps://core.ac.uk/download/pdf/85235388.pdfhttp://www.introni.it/pdf/Philips%20-%20Cold%20Cathode%20Tubes%201957.pdfhttps://static1.squarespace.com/static/5f0983034219c6086e8100ac/t/5f457ab38fad354580679f87/1598388917389/Chapter+15+THE+GLOW+DISCHARGE+AND+COLD-CATHODE+TUBES.pdfhttps://patentimages.storage.googleapis.com/8a/68/3a/a520ce05c4520d/US1878341.pdfhttps://ieeexplore.ieee.org/document/6432379