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[KM4AH]

Friend brought me his this morning. Only one of the filaments working, turns out the solder was melted out of that pin. The other filament lit OK. Has HV. Pulls some idling current. But, absolutely nothing out. Zero.
He said the output dropped in half, and then went to nothing.
Anyhow, I ordered him a new set of tubes that should get here Feb 4.
I'm thinking I will be lucky if it is just the tubes.

Seems like I remember something about these amps not operating on one tube. Am I just remembering things ?

[AA7IS]

If you look at the schematic you will see it should still have output with drive with one good tube, there is no reason it wouldn't.
Solder melting from the pins happens a lot if folks try to run FT8 or similar modes without a tremendous amount of air flow across the socket pins.
It's why when they are used properly with the pressurized socket and Pyrex chimney they don't do that.

[KM4AH]

Thanks. I'm thinking, hoping that he lost the one tube and kept driving the amp at the same tune and with the same drive and destroyed the other tube.

In my limited experience once those pins start dripping the only permanent cure is replacing the socket.
I have some new Johnson porcelain sockets for 3-500Z. Not sure if they mount the same.

[VE7RF]

On the TL-922, the cathodes are in SERIES.  The CT of the 10 vac @ 15 amp fil xfmr is returned to the junction point of the cathodes via small ga wire, and a small choke. With one tube dead, or pulled out, the 15 amps now has to flow though that puny ga wire and choke.... which will destroy it. 

IF the amp is oem, it really needs all the various mods done to it.  Some of the TL-922 mods are on W8JI's site.   All 29  of the TL-922 video's  on amprepairguy.com's  u-tube channel.  He has lots of video's on the TL-922.

Video's at     https://www.youtube.com/@amprepairguy/videos

[KM4AH]

On the TL-922, the cathodes are in SERIES.  The CT of the 10 vac @ 15 amp fil xfmr is returned to the junction point of the cathodes via small ga wire, and a small choke. With one tube dead, or pulled out, the 15 amps now has to flow though that puny ga wire and choke.... which will destroy it. 

IF the amp is oem, it really needs all the various mods done to it.  Some of the TL-922 mods are on W8JI's site.   All 29  of the TL-922 video's  on amprepairguy.com's  u-tube channel.  He has lots of video's on the TL-922.

Video's at     https://www.youtube.com/@amprepairguy/videos

Thanks. I looked at several videos. Problem is that it is not my amplifier and not likely that I will get paid for working on it. And, I know about enough about it to keep digging myself a bigger hole.
The choke going to the filament sockets is pretty cooked, but DC goes through just fine. The terminal strip from the output of the filament transformer is pretty cooked.
I don't see any voodoo in it.
I think I will take some Caigs and a Q-tip and clean the filament sockets on the one that dripped, put the new tubes in and if it doesn't work send it to somebody who knows what they are doing.

[KM4AH]

Thought while I am waiting on tubes I would post this and maybe somebody would have an idea what cooked that choke. Thanks



https://hosting.photobucket.com/images/ah308/rgerringer/IMG_0743.JPG

[VE7RF]

Thought while I am waiting on tubes I would post this and maybe somebody would have an idea what cooked that choke. Thanks



https://hosting.photobucket.com/images/ah308/rgerringer/IMG_0743.JPG

I assume that's the bifilar choke ?  It's burnt cuz of either HV arcing the windings..or excess current.

On a another note, dumb question.   IF 2 x tubes have the cathodes wired in SERIES,  is the input Z now double as well ?
IE: each 3-500Z is aprx 100-110 ohms.  In parallel, the tuned input's are tweaked for 50 ohms.   Are they tweaked for 200-220 ohms when cathodes in series ??

[KM4AH]

The filament choke is hidden under the piece of polycarbonate. Much larger gauge wire. The burnt choke is in that filament circuit as well .

I have seen many videos of TL922's with all kinds of issues, but that choke did not appear to be discolored in any of them. Curious.

The owner doesn't know how to tune an amp any more than the man in the moon, and I think he was driving it with a TS950SDX at probably 150 watts . Even after he had lost one tube.
So, who knows.

[VE7RF]

The filament choke is hidden under the piece of polycarbonate. Much larger gauge wire. The burnt choke is in that filament circuit as well .

I have seen many videos of TL922's with all kinds of issues, but that choke did not appear to be discolored in any of them. Curious.

The owner doesn't know how to tune an amp any more than the man in the moon, and I think he was driving it with a TS950SDX at probably 150 watts . Even after he had lost one tube.
So, who knows.

This is what I originally thought. The choke that is burnt up in the pix, is the extra (single winding) choke that's used for the B- return. ( It's wired between the junction of the series cathodes...then back to the  bias, cutoff bias, then to CT of fil xfmr).   The reason it burns up is simple. With either the filament gone open in either tube, OR either tube is UN-plugged,  the remaining good tube will still light up.  With 10 vac across the entire  secondary winding, their is still 5 vac between the CT and each outer end of fil xfmr sec.   You end up with 5 vac across the good tube.... BUT the return for one side of the good tube's cathode is now through that single winding choke...... which is obviously  not rated to handle 15 amps CCS.  (that  single winding choke that got zorched only has to handle cathode current, which is the sum of dc plate current + dc grid current, so maybe 800 ma + 300ma = 1100 ma).

That single winding choke being zorched, happens a LOT more than you think.  Hams have a problem with what they think is a grid to fil short on one of the tubes, so UN-plug one tube at a time to isolate the bad tube.  With one tube UN plugged, blamo, there goes the single winding choke.

[KD6VXI]

Thought while I am waiting on tubes I would post this and maybe somebody would have an idea what cooked that choke. Thanks



https://hosting.photobucket.com/images/ah308/rgerringer/IMG_0743.JPG

I assume that's the bifilar choke ?  It's burnt cuz of either HV arcing the windings..or excess current.

On a another note, dumb question.   IF 2 x tubes have the cathodes wired in SERIES,  is the input Z now double as well ?
IE: each 3-500Z is aprx 100-110 ohms.  In parallel, the tuned input's are tweaked for 50 ohms.   Are they tweaked for 200-220 ohms when cathodes in series ??

The DC line for the filaments is in series.

The RF current on the cathodes is in relation to the grid.  Which is in parallel with each other.

Making the input impedance 110 / 55 ohms.

--Shane
WP2ASS / ex KD6VXI

[ZS5WC]

Make sure the cooling is sufficient in this amp, the Fan should suck a mini storm out of it because the cooling is compromised.
Also , the solder in tube pins will melt if fan run on timer when amp is turned off does not function, or series dropping resistor to fan circuit is open in this condition.
As suggested above, the earthing etc. mods are very valuable and increases amp. stability by ten fold.

73 de William, ZS4L / ZS5WC

[KM4AH]

Thanks. I really don't know what to do with this amp. The fan delay is working. The plate voltage is around 3400 checked with a Fluke 87 and a HV probe. Filament voltage is good. Plate blocking cap is good. Coupling cap to the filament choke is good. Relay closes. Pulls idling current.
No output on any band.
I talked to AmpRepairGuy on the phone. I'm sure his price is fair, but the owner of this amp can't afford it.
Seems like all of the amp repair types that I might trust are too far to drive, especially when they are dead.
Anyhow, there is no signal passing through it for some reason.
I would think if it was the band switch it would at least work on some bands.
But, me thinking is a problem.

[KM4AH]

Well, after piddling with this some more, it is the band switch.  I can get a drop in replacement for a couple of hundred bucks off eBay. Man, I think I would rather have a root canal.

[W4JFA]

Can you describe what happened to the band switch?

[KM4AH]

Can you describe what happened to the band switch?

Good evening, actually it is the tuned input portion of the band switch, not the output. And, I have no idea. There is just no continuity on 40 or 80 meters. I can push it slightly, or turn it slightly, and get continuity. But, when in the detent position it's open.

Turns out the owner has never taken it off 75 meters since he bought it. So, I disconnected the output and input, put some heat shrink on the disconnected wires , and straight wired the 75/80 meter tuned input.

Works fine.  I'll put a note in there so that if some future owner wants to replace the tuned input portion of the band switch it should be simple but tedious.