The AM Forum

Lately I've replaced the 872's in my Junkston Desk with some 4B32's. One of the xenon rectifiers is a Cetron and I'd like to know if it is getting gassy.

The cathode, or what I think is the cathode is a small cylinder with a hole on the top that appears to be about 1/2 inch in dia. Looking into the space through the 1/2 inch hole, this area lights up lite blue in color when HV is turned on! No color on the outside of the cylinder what-so-ever. Is this toob gassy?

The other rectifier is a Chatchem (sp), it's built different and can't see inside of this area. No color here anywhere with HV.

Thanks,
wd8kdg
Craig

are they supposed to have gas?
You would get better voltage regulation with solid state rectifiers.
add a neon bulb if you miss the trippie glow.

I'm not familiar with 4B32. If they are like 3B28's there is just a tiny glow inside when operating. Not very impressive rectimfyers.
The bluer the better is my motto.
Ohhh for the days of an old BC Tx with huge bottles............. I have to love my ceramic tubes for now
Fred

http://www.mif.pg.gda.pl/homepages/frank/sheets/061/2/2G-472B.pdf

Just Xenon

Can't see the glow when the works are in the pedestal, not at all like my junkston 500 PS/Mod. ;D

Checked out the replacements/specs before, BUT the blue color? :-\

Craig,

They have more like a dim, violet glow, as opposed to the bright pale blue glow of mercury.  The glow is just barely perceptible deep inside the plate/filament structure.

Xenon gas rectifiers are less spectacular than MV tubes, but less cantankerous.  I have ample spares, both in the form of 872's and 4B32's, so have seen no reason to change to solid state in my homebrew TX's.  4B32's will tolerate colder ambient temperatures, and don't have to be burnt back in after being tilted away from the vertical position like MV's.  But I seem to recall reading somewhere that the expected life of a properly operated xenon rectifier is but a fraction of that of the equivalent, properly-handled, MV tube operated under condx recommended by the manufacturer.   Mine all seem to last about as long as 872A's, but alas, most of my tubes are "good pulls."

In the Gates, I replaced both 8008's and 866A's with solid-state direct plug-in replacements.  This freed up floor space in the cabinet by allowing me to remove the filament transformers.  I needed extra space for the new (silent) modulation reactor.  I placed it where the power supply filter choke used to go, and moved the filter choke to where the old mod reactor went.  The 8008 filament transformer had to go to make room for the new reactor, which is a potted unit in the shape of a cube just a little less than 1 ft each dimension.

Hi Don,

Thanks for the info, looks as though a dim violet color is normal. Must be what I'm seeing. The first time I turned on the HV with 872's there was a flash/arc/hiss and I hate that when it happens. So switching to xenon toobs was expected.

The nights have been dropping into the 20's here in the Willamette Valley at night. I did let the 872's warm up for at least an hour the first attempt at HV. no-go

The desk is a different animal than the 500. I can glance over at the 500 PS/Modulator and watch the toobs. Can't do that with the desk, everything is hidden in the pedestal. Gotta get it right the first time or pay the price. I'll stock up on several spare 4B32's.

Knew someone here on amfone.net has been down this road before. ;D


Tnx & 73's
wd8kdg
Craig

Yea, I'm not sure on the 'gassy' part since they already have gas in them, but I'm curious to know their failure mode. I can tell you they don't arc like mercury vapor tubes do, nor do they require the extended warm up times, as mentioned. When I swapped out the ones in my transmitter, it settled right down and has been pretty happy since. Same goes for me.  :)

So Don, others - how does a Xenon rectifer tube fail? Contamination? Leakage? What actually makes them go bad, and why would they crap out more often than mercury vapor tubes? Other than plugging them into a working tx, how do you test them or know when they are approaching 'beat'? I have to be honest, other than swapping the 872s for 4B32s, I've never had to replace one. But then, much of my on air time involved smaller transmitters.

I have had 4B32's to arc over inside, much like 872A's.  Instead of the familiar blue flash, I recall a bright white flash like a small firecracker, near the top of the plate structure in the tube.  Same effect - it craps out the fuse.

This morning I woke up early and couldn't get back to sleep, so decided to do some very rare (for me) pre-dawn 75m phone operation.  The heat had been off all night, so the shack was cold.  I  let things warm up for a few minutes, but when I tried to transmit, one of the 866A's in the driver power supply (runs about 1000 volts @ <100 ma) started pulsating.  I could hear a wam-wam-wam-wam sound, and could see the  grid current meter actually pulsating up and  down.  I looked at the 866's, and in one of them the blue glow inside was blinking on and off about twice a second.  I have never seen anything like that before.  I turned it off and waited a few more minutes, and next time, the tube came on normally.  At first, the power groaned for a few seconds, but then everything calmed down to  normal.