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Author Topic: USB problem on Hammarlund HX-50  (Read 5670 times)
K7WXK
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Posts: 68




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« on: March 28, 2013, 05:22:21 PM »

Been working for a few weeks on a recently acquired HX-50 and it has been challenging, to say the least.  I'm on the home stretch now and I have a problem with just the USB.  It has a carrier I am unable to suppress.  I have tried all the procedures in the manual and no success.  LSB works like a charm with a clear and clean signal.  There must be an imbalance somewhere in the crystal filter network or related circuits.  Tried all the usual suspects, so I am appealing to the experts.

I have a rather long thread on Antiqueradios.com, but I thought I would increase my exposure by posting here as well.  Any suggestions are welcome.

Marc
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N3DT
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Posts: 561




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« Reply #1 on: March 29, 2013, 06:29:44 PM »

I can't help you, but I'll be watching this. I have an HX-50 I got a long time ago, did mess with it a bit, but it's got a few bad crystals in it and needs a good going over.  It's waiting for me to finish with my 2 R-390A's. I need the band change knob for it if you know a source.

Did you get your neutralization done? I have a DX-40 with the instructions for that if it would help.  I've heard a 6146 will work in them too with re-wiring of course.  The power supply will probably not handle the full power though. I think they only put out about 30 watts, or was that input?
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K7WXK
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Posts: 68




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« Reply #2 on: March 29, 2013, 08:42:53 PM »

I got the neutralization fixed, and even worked Alaska on 20 meter "LSB".  The audio quality was excellent, so I was quite pleased to say the least.  USB is still a work in progress.  The neutralization problem was operator induced, because I tried to align the rig using my antenna vice a dummy load.  It still took some tweaking, but I think I have it now.  The power out is a consistent 70 watts as long as the SWR is reasonable. 

You may very well find some problems with your rig.  It has a shady reputation, but with a thorough going over you should end up with a really fine sounding rig. I had the station in Alaska give me a very critical evaluation, and she said don't touch anything.  It sounds great. 

I'm looking to pair it up with my HQ-160, but now it is working pretty well in concert with my R-388.   I'm a sucker for old Hammarlund's, and the HX-50 is one of only a handful of transmitters that they made.  I also think it is quite handsome, but it was never very popular.  When I came up in the 1960's, most of the popular rigs had 6146 finals and worked pretty trouble-free.

Good luck on yours whenever you get started.

Marc
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G3RZP
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Posts: 4721




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« Reply #3 on: March 30, 2013, 04:10:00 AM »

Did they not have a reputation for drfiting, thus getting known as the "Drifty Fifty"?
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K7WXK
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Posts: 68




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« Reply #4 on: March 30, 2013, 08:11:27 AM »

Drifty fifty... that's good.  I suspect after all the factory changes and mods one could understand why its reputation was a bit tarnished.

Incidentally, I think I have solved the problem with the carrier.  It seems that maybe the crystal filter has drifted, so I had to de-tune the crystal oscillator (USB) in order to reduce the carrier.  On air checks will verify.

Marc
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W2WDX
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Posts: 188




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« Reply #5 on: April 18, 2013, 06:15:02 PM »

I would check the crystals specifically Y102 and its trimmer cap C108 and make sure they are working properly. Also check the function switch S101A Rear which switches these two crystals into the grid of V101c (pin7). Sometimes if it gets dirty this can cause problems. These two crystals and trimmers need to generate equals levels at the grid. After you check this move on.

However, the most likely candidates are CR101, CR102 and R112 potentiometer. Make sure these components are functioning correctly. Then make sure this pot is set correctly. Since this is a suppressed carrier it may be a matter or reducing the carrier to equal levels of suppression split between USB and LSB. The best way is to use a receiver and adjust the carrier balance to equal minimum on each mode. Remember this is suppression, not elimination. In radios of this type you can tune your carrier balance to have no carrier on one sideband at the expense of higher carrier on the other. The idea is to "balance" the suppression between the two. This is because each sideband shares a common passband filter. This is why more modern designs use individual filters for each mode.

One other point to consider is that the filter (ZF101) may have slightly different slopes on each side of the passband which would affect suppression of each sideband. This is why balancing is important,

A slight amount of carrier is acceptable on SSB as long as it is suppressed well enough below the modulated signal since it will most likely be be below the noise floor on receive. A spectrum analyzer is great for this task, but an s-meter on a receiver near the transmitter will work as well.
« Last Edit: April 18, 2013, 06:37:24 PM by W2WDX » Logged

K7WXK
Member

Posts: 68




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« Reply #6 on: May 01, 2013, 11:00:43 AM »

WDX,

I just got around to reviewing your response and it is making a lot more sense now that I more fully understand how the system works.  Thanks for the explanation.  I have it well balanced now and there are equal amounts of carrier on each side.  I guess I was expecting total suppression....not so.  Audio reports have been universally good.  Now onto the VOX.  Hopefully, I will have this thing working like the factory intended soon.

Marc 
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