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The Johnson Viking II 5R4 rectifiers are a little critical. When unkeyed the huge 10HY choke can produce a large back EMF. Newer 5R4GYB can arc at the plate to filament. This will eventually ruin the tube. Only use 5R4 rectifiers with a wire spring support on the filament at top. This increases the filament to plate spacing and does not arc. The GE 5R4GA brown base are built with the spring wire filament and all 'potato masher' tubes with the large base extending up the side are good. (Note, the 'potato masher' needs base ground down on one side about 1/8" each tube to fit). Potato masher picture below:

Good reason to solid state! My Viking 1 has been SS'ed for 53 years!

If going SS, build your own. Commercial Solid-state 5R4s are only rated 3KV PIV. With the massive 10HY choke EMF, I would use 5KV PIV.

If you’re that worried, why not just hang a diode across the choke, like we do relay coils?  1N4007, backwards. 1N5408 if you’re conservative. Diode and a resistor equal to the choke’s DCR if you’re really conservative. The back EMF current can’t exceed what was flowing, so well under an amp, the reverse voltage on the diode is the HV, so well under a kV. For AC coils, use a RC snubber. Back EMF has been a necessary electrical engineering calculation for decades, nothing new here.

Ed

The reason I am worried is newer 5R4GB arc at the filament to plate on top mica at times in the Viking II. The 5R4 style with the filament spring wire on filament at top do not arc as the filament is farther away from the plate.

The PIV must only withstand the normal B+. The back EMF is conducted by the diode in its forward direction.  PIV doesn’t apply when conducting in the forward direction.  The forward conducting diode plus the choke DCR is the low R path that dissipates the stored energy.

Ed

The 5R4's have a PIV rating of 3100V, so I don't see a problem.

My Viking II CDC does not have enough tube socket spacing for the potato masher types, whereas my Apache TX-1 does.

My Viking arced with as stated with the newer tube style. I used the potato masher and did grind down the base on each tube to fit. I forgot to mention the base mod and kind of a pain for some. Just buy the GE 5R4GA brown base- fits perfect. (I will edit my post).  The tubes did not arc with the filament center spring type design vs newer filament on mica top that is closer to the plate. GE 5R4GA brown base is using the spring filament that has the greater spacing and a normal size base unlike the 'potato masher'.

On the 5R4 topic... I have an RCA SSB-1 marine radio that uses a power supply similar to the Viking, 1800 volt full wave, choke input, pair of 5R4s.  On occasion, a spark will jump from one of the 5R4 pins to the chassis, with a loud "pop".  What could cause this?  Dirt?  Thanks for the help.
Oh yes, the tubes are the "masher" type.
73,
Fox   

Replace the tube sockets with a HV type. See pix:

Whether it’s by the normal load, arc, designed/added suppression, or corona discharge, the energy stored in the choke has to go somewhere.  In n8fvj’s case, he sees arcing in some versions of the tube and recommends tubes with greater insulation. In your case, it then arcs from the pins.  Others let it dissipate another way, but it still goes somewhere.  This is only an issue with a choke input.  A CLC filter, it dumps back into the first capacitor, reducing the spike to where it isn’t high enough to arc.

If the spike is a problem, or a concern, whether founded or unfounded, suppress it with a few uF, a reverse biased diode, a spark gap. But don’t anyone think that a better tube makes that energy go away…it just directs it to the next lowest insulation.  In your case, it’s the tube socket.

New 5R4s are easier and cheaper than chokes these days…maybe let the damned thing arc if you don’t want to modify it.

Ed




U = 1/2*L*i^2 where L is in Henries, i is in amperes, and U is in Joules.

Since the tube and wiring are a capacitor when reverse biased, if you know that capacitance you can calculate the spike voltage because
U = 1/2*C*V^2 where C is in Farads and V is in volts, and energy is conserved. When the spike voltage exceeds the breakdown voltage of some element, it breaks down… in fact that’s the point of a spark gap, it provides a breakdown point below that of the choke or rectifier’s breakdown voltage, so that’s where the arc happens, by design.
 
You could also choose a spike voltage and calculate how big of an input C you’d need to accept the energy.

Back EMF is not some phenomenon. It’s physics, and well-understood physics at that.

I am not clear as to where this supposed arcing is occurring. Are you referring to the top support pins protruding through the mica insulators at the top?


Maybe I am 'curiouser' so I did some measuring on a 5R4GYB “Brown-Base” and 5R4WGB “potato masher (JAN-CTL-5R4WGB) TUNG-SOL” pulled from stock.

Both have 2” long plates, are 0.125” thick, and 0.5625” wide. The 5R4WGB “potato masher' has larger filament/mica support wires of 0.0625” whereas the 5R4GYB “Brown-Base” has 0.03124” support wires. The 5R4WGB “potato masher“ has a larger diameter bulb and base of course.

The 5R4WGB “potato masher” tubes have a “U” loop supporting the filament wires, whereas the 5R4GYB “Brown-Base” has only a straight wire supporting the filament. Both tubes have filament wires that rise 0.125” above the mica insulators.

The 5R4WGB “potato masher” tubes have a larger filament wire distance between the filament wires and the plate (0.250”) at the top, whereas the 5R4GYB “Brown-Base” has a shorter separation distance (0.125”) between the filament wires and the plate at the top.

So the  5R4WGB “potato masher” tubes should have a lower arc tendency than the 5R4GYB “Brown-Base” tube.

Salt spray and water deposits can settle on the sockets causing resistive traces.

With HV rectifier tubes, I always use ceramic octal sockets.

I have the GE 5R4GA brown base and Heintz Kaufman 5R4WGB potato masher tubes in front of me. Both have about 1/8" filament spacing from filament to plate. DMOD, what potato masher are you measuring?

I was asking you to answer the first question-- where is this arcing occurring? "I am not clear as to where this supposed arcing is occurring. Are you referring to the top support pins protruding through the mica insulators at the top?"

I identified the tubes in reply #11 as such: "I did some measuring on a 5R4GYB “Brown-Base” and 5R4WGB “potato masher" (JAN-CTL-5R4WGB) TUNG-SOL pulled from stock."

I have other WGB “potato masher" rectifiers with the same exact measurements.

Both tubes have 0.125" (1/8") plate spacings.

Again: "The 5R4WGB “potato masher” tubes have a larger filament wire distance between the filament wires and the plate (0.250”) at the top, whereas the 5R4GYB “Brown-Base” has a shorter separation distance (0.125”) between the filament wires and the plate at the top."

I stated in my original post arc from filament to plate. It is at top mica.

My Heintz Kaufman 5R4WGB had 1/8", not 1/4" spacing from filament to plate at top. In fact you are stating very potato masher tube has 1/4" spacing, That means the plate is over 1/2" wide- not.

Remeasuring, both tube's plates are 'rectangular' tube structures each having 2” long (high) plates, are 0.125” (2/16") thick, and are 0.59375” (19/32") wide (across). .

So yes, the plates are over 1/2" wide.

The filament-to-plate separation, spacing distance is 1/16" (0.0625").

I think you misread or misinterpreted this. We're talking about the wires at the TOP of the tube. Call them connecting "over-wires" or crossover wires if you will:

"The 5R4WGB “potato masher” tubes have a larger filament wire distances between the filament wires and the plate (0.250”) at the top, whereas the 5R4GYB “Brown-Base” has a shorter separation distance (0.125”) between the filament wires at the plate at the top."

No, you said this: "Newer 5R4GYB can arc at the plate to filament."

You didn't say anything about the arcing being at the top.

I can believe the 5R4GY series could arc sooner since: ""The 5R4WGB “potato masher” tubes have a larger filament wire distances between the filament wires and the plate (0.250”) at the top, whereas the 5R4GYB “Brown-Base” has a shorter separation distance (0.125”) between the filament wires at the plate at the top."

Where ea\lse could I possibly see the 5R4 arcing in a Viking II? At bottom of tube, no. Inside the plate to filament- no. How about some common sense.

How about some clarity such as detailing your descriptions and explanations. We can't read your mind.

One could see the arcing between filament and plate down inside by looking at it from the top.

If you two want to be argumentative and piss and moan, please take it off line and somewhere else.
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