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572B input impedance?


The only info I could dig up was that the driving impedance of a single 572B is around 215 ohms. Dentron made the Clipperton L amp with four 572B's and no tuned input circuit and it had a half decent input impedance so that would seem about right whereas four 572B's should show a driving impedance of 215/4 or about 54 ohms give or take a little for other circuit components.
 
Thank you. Guy just brought over a Warrior HA-10. has filament and plate voltage, but no TX. uses foot pedal to activate. has a PI input network, going to see if input matching is correct or close. If it is, chances are the tubes are shot. Feedthru thru relay is 1.5, but when amp is active, SWR input is 9.99. pretty sure it is tubes, but wanted to double check. Nice amp, 4 572B's.
 
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I had an FL2100b on the bench a while back, input VSWR were sky high, turned out to be a bad cap on the grid, replaced that and re aligned the input tune network.

The Chinese tubes can vary alot on the input impedance.
 
Crusher said:
Thank you. Guy just brought over a Warrior HA-10. has filament and plate voltage, but no TX. uses foot pedal to activate. has a PI input network, going to see if input matching is correct or close. If it is, chances are the tubes are shot. Feedthru thru relay is 1.5, but when amp is active, SWR input is 9.99. pretty sure it is tubes, but wanted to double check. Nice amp, 4 572B's.
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The HA-10 was built for four 811A's. Someone must have swapped them out for 572B's. You could have a bad grid capacitor C3, C4, C5, or C6 on one of the tubes or possibly a bad input capacitor C1 or C2. Also this amp never had a tuned input so if this one does have one I would look real close at it as it is an after market installation.
 
I will have to check all these caps later. As to the input matching, it has a PI network. 2 doorknobs and a small inductor wrapped around form with an adjustable slug in center. Just like what you might find in the FL2100B same doorknob capacitors as well. One thing I did notice is that when I adjusted the plate tuner, 1 tube got real bright or dim depending where I turned plate knob. Weird. The HV switch definitely needs replaced as well. Has a lot of play and I thought I heard it arc internally. Someone has definitely worked o it before, has 8 electrolytic caps for filter supply. Can tell, it was store in a damp place for awhile as some of the inside cabinet shows rust and water spots from condensation. When I saw this, I turned just filaments on and let it sit for awhile. And don't worry, I have HV gloves I use when working on something that I am not sure of it's condition.
 
Monobander just one tuned slug?

It looks like a good canidate to start at the input and go through all of it to the output.

How many of them have you had hit the bench. "Can you look at this the guy said it was working?" find out it is a total rebuild job after all the "mods" are removed and put back to stock.

I got an old globe amp on the bench right now that is total rebuild, EL38's are neat though.
 
The guy was over yesterday and dropped it off. He got it in a trade. Guessing the guy beat on it before he traded. Even gave him 4 extra tubes. Going to dig a bit deeper and see what I find. I have had one of the 2100B's on the bench before. Just had to replace tubes. Guy beat up on pretty bad as well. If only people would understand the limits of the tube they were using and not trying to get every last watt out of it.
 
Crusher said:
The guy was over yesterday and dropped it off. He got it in a trade. Guessing the guy beat on it before he traded. Even gave him 4 extra tubes. Going to dig a bit deeper and see what I find. I have had one of the 2100B's on the bench before. Just had to replace tubes. Guy beat up on pretty bad as well. If only people would understand the limits of the tube they were using and not trying to get every last watt out of it.
Click to expand...


Well that eliminates about 50% of the hams out there and about 98% of the CB'er's. :whistle:
 
well, changed all the input caps, C1 and 2. bypass caps on filament choke as well. they all tested good, but not taking any chances. have several hundred laying around. changing the blocking cap as well. Had a 500pf 5kv, tolerance was 20%. It was reading right around 400pf. figured it got hot. Putting a 1000pf at 12kv russian job in it's place. Fairly certain it is the tubes though has 4 taylor tubes and they have writingon them like someone tested them and sold them as used.
 
Perhaps this to check the input vswr and see if it is the input tuned or something else.

Disconnect the rf input at the tubes connect a 54 ohm resistor or something close to that 50 ohm will do.

Connect the antenna analyzer to the input and hold the input relay down
( no electrical or rf power applied of course) sweep the analyzer to find out exactly where that "tuned input" is resonant at with the 54 ohm load representing the four tubes.

I built my tuned input for the 4-1000 with this method using a 100 ohm resistor, After I got the tuned input built and tried a "hot" run input vswr was just as the analyzer said with the 100 ohm resistor.
 
yeah, i did this for input. wasn't too far off from where it should have been. Thanks for the heads up. The tubes are toast. the blocking cap was cracked. looks like someone glued it together. from the blocking cap to the plate tuner, the metal strip was black. it used to be silver plated. it was only 1/4 inch wide. i used a 1/2" piece of brass to connect it. heavier and much better electrical connection. went overkill on the doorknob cap, but should never be a problem. cou[le of parasitics are toast. need to replace yet. they havegrid tied straight to ground. no cap like schematic. so it the neutralizing circuit has been bypassed.
 
Sounds lke you about got the bugs worked out.

The grid to ground, sort of makes it hard to monitor grid current that way.

What type of cut off bias is it using if grids are striaght to ground? That bias circuit may be toast also.
 

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