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Author Topic: Back to Hammarlund HX-50...newer schematic available?  (Read 1086 times)
W5SU
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Posts: 35




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« on: November 22, 2018, 06:03:20 AM »

(Sorry if I wasn't supposed to make this a new post about the HX-50, but this is a new question)

Apparently there was a series of updates to the HX-50 before the "A" model came out.  One of the subsequent models (mine included) has a second OA2 regulator, plus a solid state diode bridge in place of the rectifier tube.  I don't know whether those models have other changes in the circuitry and am not finding any schematics on line for those models.  I don't believe these are user-modifications.  Would anybody out there have a handle on a schematic for a plain HX-50 (not "A" model) that has a solid state rectifier and 2 voltage regulator tubes? 

Many thanks and '73!

Carl - W5SU
Dallas TX
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WA2CWA
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Posts: 559


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« Reply #1 on: November 22, 2018, 06:46:58 PM »

(Sorry if I wasn't supposed to make this a new post about the HX-50, but this is a new question)

Apparently there was a series of updates to the HX-50 before the "A" model came out.  One of the subsequent models (mine included) has a second OA2 regulator, plus a solid state diode bridge in place of the rectifier tube.  I don't know whether those models have other changes in the circuitry and am not finding any schematics on line for those models.  I don't believe these are user-modifications.  Would anybody out there have a handle on a schematic for a plain HX-50 (not "A" model) that has a solid state rectifier and 2 voltage regulator tubes? 

Many thanks and '73!

Carl - W5SU
Dallas TX

There was Issue 1 of the schematic. I don't believe the HX-50 schematic was ever re-issued and updated.
Somewhere in one of the numerous Hammarlund HX-50 bulletins/updates (probably what they designated as Bulletin code 2 or 3). they added a CR-111 zener diode and a resistor. The zener was prone to failure and under another bulletin/update, CR-111 was replaced by the second OA2 tube. The resistor remained.
The HX-50A schematic is probably your best bet for trouble shooting your HX-50 especially if the previous owners followed and implemented all the changes, updates, additions, modifications, etc.  that Hammarlund issued on this transmitter.

Pete, wa2cwa
www.manualman.com

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W5SU
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Posts: 35




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« Reply #2 on: November 23, 2018, 10:03:54 AM »

Paul -
Great response; makes sense.

Thanks!
'73

Carl - W5SU
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WA2CWA
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« Reply #3 on: November 23, 2018, 12:19:52 PM »

Where's Paul?  Grin Grin

People work on HX-50's when they want total frustration and aggravation. It was not one of Hammarlund's better designs.

Pete, wa2cwa
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N3DT
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Posts: 1657




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« Reply #4 on: November 24, 2018, 02:57:29 PM »

Yeah, I've been having a lot of trouble with the crystals and crystal osc. slugs as I remember. When I get rid of this Apache I'll start working on it again, but it's probably been 20 years. The Apache was a piece of cake, it helped that everything was working, it was mostly some mechanical issues and cosmetic stuff, changed the 6AU6 to a 6AH6 as I remember and that really calmed it down. The HX-50 has that stupid sweep tube in it and all the ones I find are junk. Nothing like a pair of 6146's.
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KE0ZU
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« Reply #5 on: November 24, 2018, 08:41:23 PM »

I will certainly agree the "50" wasn't one of their better designs, electrically.   I do like the styling however, but wonder why they didn't use the dual window format like the receivers?

I'm going to start on mine in a few weeks.

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https://mikeharrison.smugmug.com/
Pics and bold print are usually links.
G3RZP
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Posts: 1228




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« Reply #6 on: November 25, 2018, 02:31:40 AM »

If the crystals are solder sealed HC-6/U, they may well have developed flux contamination over the years - the flux vapourised and gradually settled on the crystal blank, moving the frequency LF and dropping the activity. With care, you can unsolder the can, wash the crystal in acetone or alcohol (not the drinkable sort!) get it dry and re-solder the can. Not guaranteed but it has worked for number of people - that problem led to manufacturers moving to either cold weld or resistance welding in the 1970s. High stability crystals were often in evacuated glass envelopes such as the 7 pin miniature tube style or glass versions of  HC-6/U or HC-49/U.
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N3DT
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« Reply #7 on: November 25, 2018, 07:48:12 AM »

Those crystals are not plug in, they're wired in and I see they have a green bottom to them, so It looks like they are not soldered. But yes, if they don't work it would probably be good to open them up and see if they can be cleaned. Seems I had a few that didn't work, but then the slugs are probably way out of spec. Only reason I got it was it looked cool. Little did I know it had a stupid sweep tube in it. I'm sure the price was right, I hardly ever gave more than $20 for anything if even that much.
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WA2CWA
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« Reply #8 on: November 25, 2018, 12:07:08 PM »

Those crystals are not plug in, they're wired in and I see they have a green bottom to them, so It looks like they are not soldered. But yes, if they don't work it would probably be good to open them up and see if they can be cleaned. Seems I had a few that didn't work, but then the slugs are probably way out of spec. Only reason I got it was it looked cool. Little did I know it had a stupid sweep tube in it. I'm sure the price was right, I hardly ever gave more than $20 for anything if even that much.

Hammarlund runs the 6DQ5 conservatively in the HQ-50 so unless the transmitter is a total screw up, the tube should last as long, if not longer, then some of the other tubes in the transmitter. And, if it's a concern, change it out for a 6146B with a change out of some parts and socket. What's another mod to this documented highly modded, updated, fixed, make it better to work, etc. -type transmitter.

Pete, wa2cwa
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N3DT
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« Reply #9 on: November 25, 2018, 06:30:48 PM »

I probably had some really funky 6DQ5 tubes. As I remember the power would come up and drop off immediately, CW mode, hardly a chance to tune it. I'd like to see the 6146 mod, at least the schematic. It's spec'd at 150W CW input. Output must be about 30W. There's certainly no duty cycle to that 6DQ5 unless this thing is really screwed. But I didn't mess with it much.
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WA2CWA
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« Reply #10 on: November 25, 2018, 08:34:47 PM »

I probably had some really funky 6DQ5 tubes. As I remember the power would come up and drop off immediately, CW mode, hardly a chance to tune it. I'd like to see the 6146 mod, at least the schematic. It's spec'd at 150W CW input. Output must be about 30W. There's certainly no duty cycle to that 6DQ5 unless this thing is really screwed. But I didn't mess with it much.

I have no clue if anyone ever changed out, or documented, the 6DQ5 for a 6146 in the HX-50. Personally, I see no advantage other then for the people who dislike sweep tubes in any amateur radio application. And, unless you diddle with the power supply voltages, there is no power advantage.
Obviously, key down time is very important in order to keep the 6DQ5 from going to Never-land and not returning. Initial tune-up probably should be done in the AM mode unless you have very fast wrist and finger movements to do it in the CW mode.

Pete, wa2cwa
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KE0ZU
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« Reply #11 on: December 02, 2018, 07:47:25 PM »

I have some PDFs regarding what appear to be various running production modifications to the HX-50.   They include audio/vox mods, the Zero Beat mod, instructions for installing the 160 meter option, and a few others.

I don't know how common these docs are but if anyone wants a copy, post or PM your email address, and I'll gladly send copies.

Mikeinkcmo
KE0ZU
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https://mikeharrison.smugmug.com/
Pics and bold print are usually links.
WB3JIH
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Posts: 2




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« Reply #12 on: December 13, 2018, 09:59:48 AM »

I rebuilt a HX-50A, and it gets fine reports.  The 6DQ5 is a pretty robust tube -- not sure why there's so much maligning of it.  The Hallicrafters HT-44 and SR-160 both used them, and the SR-500 Tornado uses a graphite plate version of it.  It's also a lot cheaper than a 6146 or other sweep tube...

There's no "updated" schematic for the HX-50A -- I looked.  There are some service bulletins for it, but for the most part, you will be able to troubleshoot and get by with the HX-50 schematic.  I've got an original manual if you need a high res scan.

The audio out it is really nice. Although it does OK by itself, I think Hammarlund intended for it to drive the HXL-ONE linear. I have the amp connected to mine, and I just started rebuilding a second one (amp).

Agree though -- tune it in AM mode.  You can get a lot of carrier out of it in CW mode... for a short period...

Jeff
WB3JIH


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WA2CWA
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« Reply #13 on: December 13, 2018, 12:35:24 PM »

There's no "updated" schematic for the HX-50A -- I looked.  There are some service bulletins for it, but for the most part, you will be able to troubleshoot and get by with the HX-50 schematic.  I've got an original manual if you need a high res scan.

Jeff
WB3JIH

The HX-50A schematic was printed and is available.

If the previous owner(s) took all the the various Hammarlund service bulletins and updates and applied them to a particular HX-50, there is no one HX-50 schematic that would encompass all the changes. Hammarlund never printed an updated HX-50 schematic. If you apply many of the updates and service addenda to a HX-50, the HX-50A schematic is probably a lot closer to what you now have.

Pete, wa2cwa
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