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Author Topic: Just fried my AL-80B  (Read 12350 times)
N3DT
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« Reply #15 on: February 04, 2015, 02:03:49 PM »

If you poke around on the interweb, there's a guy in Western MD that has the updated schematic of the QSK board, but it should be easy enough the check the pin diodes with a good meter. The rest of the circuit is a real bear to check, I got a bad one and couldn't get anywhere with it, lots of timing circuits in it.

Oh, here it is. http://faculty.frostburg.edu/phys/latta/ee/qsk5/schematic/schematic.html#receive
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AA4HA
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« Reply #16 on: February 05, 2015, 06:17:37 AM »

It sounds like you might of done two inadvisable at the same time, overdriving the amp AND running it without a proper connection to the antenna.

Is there a glitch resistor on the anode? Might you have opened that up? Do you have good B+? If not maybe you zapped the rectifiers. With the power off and the caps chicken-sticked (discharged) do the coils all ohm out as good?

You should be able to do many of these checks with everything unplugged (and discharged) using an ohmmeter to step through the amp from coax connector to coax connector (going through all of the tank circuits, switches, resistors, etc...).
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Ms. Tisha Hayes, AA4HA
Lookout Mountain, Alabama
Free space loss (dB) = 32.4 + 20 × log10d + 20 × log10 f
W8JI
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« Reply #17 on: February 05, 2015, 09:19:44 AM »

Every symptom he described points to the QSK module.

Nothing he did would open the fault limit resistor or damage the tube.
Nothing he described points to bad rectifiers, which only can short (and blow the line fuse).
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KK5DR
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« Reply #18 on: February 05, 2015, 03:59:26 PM »

Now that you have said you have the QSK board in the amp, I would be highly suspicious of it. As was said, it is easy to burn a PIN diode with high output SWR, which sounds like due to the conditions described at the time of the "event".
I have not looked at the design of the QSK board but it is possible that you can still have a recieve signal path, but the transmit signal path is damaged. From what I know of PIN diode T/R systems, there are PIN diodes in the recieve signal path as well. They may still be good. It's the TX side that sounds burnt. More testing is in order.
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W9GB
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« Reply #19 on: February 05, 2015, 04:48:43 PM »

Previously noted by N3DT

Electronic T/R Switching and the Ameritron QSK-5
by Greg Latta AA8V
Schematic Diagram and Circuit Descriptions
http://faculty.frostburg.edu/phys/latta/ee/qsk5/schematic/schematic.html#receive
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K1ZJH
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« Reply #20 on: February 05, 2015, 04:51:51 PM »

Driving your amp with 100 watts, while not necessary, should not hurt it at all. As others have stated, it is something in the input network, the infinite input SWR should be the clue. However, if you want to believe that the tube is bad, I'll be happy to give you $10 for the old one! Grin

It can if you overload tube. While 100 watts into a pair of 3-500's is no concern but into one tube if your ducks are not all in a row you can damage tube.

Gawd,  you are clueless.
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KK5DR
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« Reply #21 on: February 05, 2015, 06:21:37 PM »

I took a look at the schematic in the previous posts. Yep, right there it is. Check the larger transmit diodes on that board. I'd bet money they are smoked.
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N3DT
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« Reply #22 on: February 05, 2015, 07:51:31 PM »

$12.27 ea. at Mouser and DigiKey, Don't know what Ameritron charges.
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W4AMP
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« Reply #23 on: February 05, 2015, 09:20:18 PM »

Try it without the qsy board like W8JI suggested. He designed the amp.
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W8JI
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« Reply #24 on: February 06, 2015, 09:34:43 AM »

I designed that board maybe 25-35 years ago.

The most likely diodes to be damaged are the RECEIVE diodes. They are sensitive to the transmission line voltage, because they are subjected to slightly more than the transmission line voltage. There is a fuse system with a lamp, but it does not always save the diodes.

The transmit diodes can be damaged, but since they are "on" and have minimal voltage across them it takes a whopping steady high current fault to hurt them.

The receive diodes are interlocked to the transmit diode system, so the TX diodes can never be on without the RX diodes at normal cut off voltages. A failure in the RX diodes or biasing transistor will sometimes let the TX diodes partly turn on.

There were several changes in that board over the years, the most recent I'm aware of in was the 90's. I plan on revisiting the board sometime soon and updating it, since it is pretty old.

 



 
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W9FIB
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« Reply #25 on: February 06, 2015, 11:17:39 AM »

I plan on revisiting the board sometime soon and updating it, since it is pretty old.

I, for one, would be very interested in what you design. And thanks for your web site. It has given me a lot of info that is greatly appreciated!
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W4AMP
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« Reply #26 on: February 06, 2015, 09:50:12 PM »

I designed that board maybe 25-35 years ago.

The most likely diodes to be damaged are the RECEIVE diodes. They are sensitive to the transmission line voltage, because they are subjected to slightly more than the transmission line voltage. There is a fuse system with a lamp, but it does not always save the diodes.

The transmit diodes can be damaged, but since they are "on" and have minimal voltage across them it takes a whopping steady high current fault to hurt them.

The receive diodes are interlocked to the transmit diode system, so the TX diodes can never be on without the RX diodes at normal cut off voltages. A failure in the RX diodes or biasing transistor will sometimes let the TX diodes partly turn on.

There were several changes in that board over the years, the most recent I'm aware of in was the 90's. I plan on revisiting the board sometime soon and updating it, since it is pretty old.

 



 

Good to see you Tom.Hard to believe it had been that long already. 73
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W9OY
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« Reply #27 on: February 07, 2015, 07:06:27 PM »

check Q5  I used to blow this a couple times a year when I had a QSK-5 in a AL-1500 about 30 years ago.  Also check the lightbulbs, (a very clever solution).

73 W9OY

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