[Hammarlund] Hammarlund HX-500 Transmitter...

Mon Sep 16 17:45:38 EDT 2013

Hi Jack,
	Like Glen said, "good for you".  And I agree with all the rest that he 
said.  One thing to remember, you've got, probably, close to 125vac 
coming in, vs maybe 118 as designed, so voltages will be a bit high. 
Unless  you've compensated with a variac, bucking xfmr, etc.
	I also have an HX-500, and went thru it several yrs ago (6-8?).  It had 
the xfmr and mods.  I'll look in my folder and see what I've got for 
docs, but like you said, they're abysmal lat best.
	I used mine yesterday in the CX QSO party, on 40m SSB.  I was having 
some intermittent problems in the antenna switching ckts for "quick 
changeover" for several rigs, but it performed very well.  I did get the 
usual comments like, "HX-500, I expected a 500 watt signal level".  I'll 
have it on CW next Sun., I hope.
	The SB filtering system always amazes me, I hope it never goes bad. 
Switching freqs of the IF transformers rather than just switching 
carrier osc. freq. seems like the complicated way to do it.
I'll let you know if I find anything useful for you in my files.
73,

Al, W8UT
www.boatanchors.org
www.hammarlund.info

"There is nothing -- absolutely nothing -- half so much
worth doing as simply messing about in boats"
Ratty, to Mole

On 9/16/2013 4:24 PM, Jack Harper wrote:
> Greetings to the List:
>
> As I mentioned before, I am slowly bringing a Hammarlund HX-500
> transmitter back to life.
>
> My goal is for the HX-500 coupled with my R390A and the TO-Keyer to be
> the primary rig for the rest of my not so much remaining life - so, I am
> being careful and perhaps a bit overly fanatical about "getting it
> right" - and hope to also learn a thing or two along the way...
>
>
> Questions:
>
> (a) I am astonished to see that Hammarlund runs the +780VDC line from
> the power supply (5R4) up through the chassis to the 6146 pair simply
> through a hole in the chassis steel. The hole was drilled just slightly
> larger than the plain red hookup wire and so literally the only thing
> that keeps the +780VDC from the chassis is the old insulation on that
> wire - and that insulation is now wearing through (fan vibration?).
>
> The interesting thing is that under the chassis, a very nice porcelain
> standoff with a lug supports the connection to the power supply filter
> choke. But, then the wire for the filtered HV just zooms up through that
> drilled hole with just a few thousandths of clearance around the
> insulation.
>
> I have a spare HX-500 parts unit and checked that thinking the one that
> I am working on had been totally hacked - but, it is the same with that
> red wire just going through a hole in the steel.
>
> I suppose that I am not a very brave soul and so just bought a used
> porcelain feed-through on eBay and plan to install that by drilling a
> 3/8" hole through the chassis for the feed-through with proper lugs top
> and bottom etc with the top inside the RF cage topside.
>
> Question:  Am I missing something here??  Why would Hammarlund do that
> sort of thing on a HV line?  Just to save a buck at the orders of a
> "cost accountant"? Surely not... This certainly reinforces, by the way,
> the practice of automatically installing a modern 3-way power plug on
> any boatanchor. One never knows what evil might lurk under the hood...
>
>
> (b) Hammarlund originally had a 6AL5 rectifier to generate the "bias
> voltages" (6146 et. al.) but came out with a Service Bulletin in about
> 1962 that called to replace that tube with a solid state rectifier "to
> provide instant bias for the 6146 tubes to prevent possible excessive
> cathode current at power-up" (waiting for the tube to warm). The same
> mod also called to replace the original pair of 12AX4 rectifiers (for
> HV) with a single 5R4, which required also a different power transformer.
>
> My HX-500 had that modification made, which essentially meant rebuilding
> the power supply, which was done.  The correct power transformer (by
> specified stenciled part number) was also installed to replace the old.
>
> The thing that has been throwing me is the fact that the original
> unmodified schematic had one set of power supply output voltages (there
> are seven:  -100, -50, +350, +780, +300, +215, and +150), but the
> Service Bulletin had a very different set of power supply output
> voltages (-90, -45, +270, +780, +230, +150). That does not make sense to
> me - nothing else in the transmitter was modified by the Service Bulletin.
>
> To make matters worse, someone manually penciled in different power
> supply resistor values (dropping resistors) on the Service Bulletin
> schematic (the "new" schematic) - e.g., 750-ohms instead of the
> Hammarlund 15-ohms etc.
>
> So, there are three sets of possible voltage/resistor values - two
> formal Hammarlund and one informal penciled in every copy of the Service
> Bulletin that I have ever seen.
>
> The HX-500 that I have had the Service Bulletin mods made and the
> dropping resistor values are the ones penciled in (that penciled scanned
> schematic, by the way, appears to be the only one available anywhere on
> the Internet).
>
> Problem is that the voltages coming out of my doubly modified power
> supply are wildly out of spec (which spec?) - e.g., +360VDC instead of
> +270VDC etc.
>
> One thing that I have learned on this project is that I cannot trust the
> HX-500 documentation - especially, apparently, as the company began to
> come to an end.
>
> I begin to believe that the Hammarlund published output voltages in the
> Service Bulletin are WRONG - why would Hammarlund change those output
> voltages when nothing else in the transmitter changed? In addition,
> whoever did the power supply mod in my HX-500 fiddled the dropping
> resistor values to meet the penciled in values - and gummed the thing up.
>
> So, my theory is that I should get resistor values in the power supply
> that generate the voltages on the original Hammarlund schematic - and
> ignore the WRONG voltages specified in the Service Bulletin.  I have
> done that, though they are different from what Hammarlund wanted: e.g.,
> 68-ohms rather than the published 15-ohms - that sort of thing.
>
> Question:  Does it make sense for me to get the output voltages
> specified in the original unmodified schematic? I believe the Service
> Bulletin numbers are bad.
>
>
> (c) I notice that Hammarlund also left off a bleeder resistor on the
> +300VDC section of the power supply. I have checked the original
> schematic and do not see a path for that to bleed down at power down
> (i.e., maybe a resistor somewhere outside the power supply to ground). I
> would like to insert a bleeder (40K?). Does that make sense???  Why
> would Hammarlund leave off that bleeder? Again, an evil "cost
> accountant"...?
>
>
> I appreciate any input -
>
>
> Regards to the List -
>
> Jack, WØYJ ("Friend to all Things Hammarlund")
> Evergreen, Colorado USA
>
> ps - By the way, you can see this transmitter running at
> http://www.youtube.com/watch?v=ybJ1LsCU0xg  (as published by the seller).
>
>
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