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Sintronic_Cpu
| | Posted on Wednesday, September 04, 2002 - 7:31 pm: | 
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I recently barrowed a friends Palomar 300A and as soon as it is hooked inline, a radio that keys 4 and swings 20... power is dropped to almost nothing swinging 3 watts, I didn't know what was causing this. My friend said he had the same problem, but has been using it for years and never hurt anything. So I though, ok... hooked up my Galaxy 99 and WOW, dead keyed like 200 and swung about 600 on my Astatic 700's on the Average scale! So I thought I'd try my DX 959... that was the radio I was going to run on it while I borrowed the linear anyways.
Anyhow, I hooked it up and talked to a friend for a total of 3-5 minutes and my Galaxy 959 lost all key up, keying it cuts the receive off, but will not key transmitter. I thought my Galaxy just bit the dust as unrelated to the 300A, I hear lots of stories about the 959 being cheap.
Then I decided to risk it one more time, quickly, too see if the Galaxy just died on it's own... I hooked up an older Connex 3300, zap, keying it for under 3 seconds... out went the key up.
Now I don't know what to do with my Galaxy and Connex, I tried replacing the Final, the driver, the AM regulator, the mod regulator, and the TX switching transistor... nothing, both are as good as dead!
Aside from any fixes for my radios, does anyone know what could be wrong with the linear? It wasn't hooked up backwards, and WAS in the 10 meter slot, not any other. I wasn't driving the poop out of it or anything, what could it be? It still has it's full output? Can't be a tube.
HELP ME PLEASE!!!  |
Sintronic_Cpu
| | Posted on Saturday, September 07, 2002 - 11:53 am: |
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Well, I guess everyone is asleep then. Sorry to bother. |
Conecuh
| | Posted on Saturday, September 07, 2002 - 3:28 pm: |
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I believe I borrowed that same amp one time |
Sintronic_Cpu
| | Posted on Saturday, September 07, 2002 - 5:47 pm: |
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Do you know what could cause this to happen though? |
2600
| | Posted on Sunday, September 08, 2002 - 12:47 am: |
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Yeah, I do. It's the dreaded "Little arcs across worn-out relay contacts" problem. I don't know just exactly why the 300A in particular is so likely to do this. I have seen it over and over. The relays in this amplifier are closing only partway because of wear and tear (and age). This causes a small, blue arc to jump across this small gap between the contact points. The RF energy in this arc gets amplified by the tubes, and causes a lot of RF power to appear between the driver cathodes and ground. So what, you say? That's where the transmitter is tied in, to those driver cathodes. This creates the rare, but famous and legendary "Back-Feed" literally jumping out of the amplifier back upstream into your radio final.
It doesn't have to do this for very long. One thousandth of a second is plenty long enough for this excess RF voltage to exceed the breakdown rating of a 12-volt RF transistor like a 2SC1969 or 2SC2312. The final's base resistor and/or bias circuit can get sideswiped along with the final.
Watching the output of this 300A on a 'scope (using a tube radio to drive it) will usually show a fuzzy trace briefly at key-up, revealing a short burst of arc on one or more of the relays.
You didn't say which version 300A you have. The one with three identical relays on a plug-in circuit board behind the meter is a real pain. The R10-E3604 relay was made custom, and became unavailble when RF Parts finally ran out of them about 10 years ago. We use a more mundane relay sold by Rat Shack and others, using wire jumpers soldered to the relay lugs, and routed to the correct PC board hole. Pretty annoying. The Rat Shack DPDT 10 Amp 12 Vdc relay is rated at 10 amps, and should last a while, at least.
The later version has the relay circuit board soldered in, bolted to the deck beneath the meter. The plug-in relay R10-E1-Y2-12Vdc is pretty generic, made by lots of competitors and sold a lot of places, like Mouser. The two little square, short white or yellow plastic relays that are soldered down are expensive when you can find them. Candyman used to have a generic substitute made by "American Zettler" with a number that started "AZ-931". An outfit called "Master Distributors" had some Potter and Brumfield R50-E2-Y2-12VDC like the originals for $35.00 EACH last year. I didn't buy any at that price.
One of these is the preamp relay. You can save a little by replacing that one with a jumper wire, and kissing off the preamp. The other one of these two short relays is likeliest to be the culprit. It does two things: 1)keys the plug-in relay, and 2)turns on the tubes. When it arcs, it sends accidental BROADBAND RF drive into the tubes, and they try to oscillate. They really don't have to do this for very long to assasinate a final. The "one-key radio assasin" syndrome (OKRA ??) calls for replacing both the relays used for transmit. Good luck finding them. If it's a problem, say so. I'll check back on this thread later. I can probably find a source, if I know which relay type(s) yours has in it.
Oh, and on the Galaxy/Connex radios. Did you check the small resistor that feeds the base leg of the final? If it's bad, the bias diode and the bias trimpot are both under suspicion. If those two parts were damaged, they can kill a new final even without the 300A in line. The easiest first test of a radio with no wattmeter reading on transmit is another radio in the room on the same channel. If it can hear anything when you key, even a weak dead carrier, this narrows the troubleshooting a LOT.
Just don't be tempted to replace just one. Both the relays used for transmit should go, whichever version you have.
73 |
Sintronic_Cpu
| | Posted on Sunday, September 08, 2002 - 11:36 am: |
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What should I look for in my Galaxies? |
2600
| | Posted on Monday, September 09, 2002 - 4:11 pm: |
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Well, did you try the trick with a spare receiver next to it on the same channel? Does the transmit LED come on when you key the mike? You said "Now I don't know what to do with my Galaxy and Connex, I tried replacing the Final, the driver, the AM regulator, the mod regulator, and the TX switching transistor... nothing, both are as good as dead!"
Not to put too fine a point on it, but did you check any of the old parts when you removed them? Did you use new parts, or used ones from a junked radio? If any of the replacement parts WERE used, did you test them before they were put into the radio ? Knowing which of the parts you removed really WERE bad is a LARGE help in looking for hidden damage.
The very first test point (IF your Transmit LED comes on when you key) is the final/driver BIAS test jumper. It should have between 11 and 13 volts on it while keyed on SSB, roughly half that on AM. Until I know how the "spare receiver" test turned out, and if your transmit LED comes on, there's nothing to go on, really. You tell me what you DO have, I'll suggest the next likely place to check.
73 |
Sintronic_Cpu
| | Posted on Monday, September 09, 2002 - 8:43 pm: |
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I got the 959 fixed, there was a resistor on the first leg in front of the final that had a burnt place on it. I replaced it and now it works, but I still couldn't find out on the Connex. All the parts I used are brand new from B & D Enterprises, and they are not NTE they are all Mitsubishi parts. |
2600
| | Posted on Wednesday, September 11, 2002 - 1:57 am: |
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Okay, but we still don't know if you hear anything weak leaking out of it on a nearby receiver when you key it, or what the transmit light does when you key it...........
Do you have a voltmeter that you can use? It sounds like the Connex is gonna take more than just a wattmeter to troubleshoot.
73 |
Sintronic_Cpu
| | Posted on Wednesday, September 11, 2002 - 3:15 pm: |
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Yes, I have a volt meter. Yes it does pick up in another receiver, just like the 959. Fixed it though. I can't see any burnt parts like in the 959, but I did replace the final, driver, AM regulator, and voltage regulator. Even though those aren't the problem, I put all the new parts in there anyways, this 3300 is about 10 years old. So newer parts can't hurt too much, lol.
Where to begin now? |
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