[Hammarlund] Hammarlund HX-500 Problems...

Wed May 1 13:15:09 EDT 2013

     A couple of things, its possible the change in load on 
the power supply between Stand By and operating could 
account for the higher voltages of the low voltage supply. 
Not the bias, I can't figure that out unless there is a bad 
component there.  Its also possible the meter used to 
generate the voltage chart was lower resistance than the 
DMM. DMM's typically have about a 10 megohm constant input 
resistance while some VOM's were only 1000 ohms/volt.  I 
found the charts for the Hammarlund SP-600-JX were all taken 
with a 1K ohm/volt meter except for grid bias which 
specifies a VTVM.  When checked with a DMM or 20K ohm/volt 
meter the voltages mostly read high.
     The 150V line is regulated by a VR tube and should be 
very close although these tubes can vary by at least five 
percent in voltage so 153V is quite reasonable.
The bias is adjustable, where are you measuring it?
     The schematic shows voltages at several points in the 
power supply, I would check those as well as tube pin 
voltages.
     If you have an older analogue meter like a Simpson 260 
or Triplet 630 see if it agrees with the DMM, if it doesn't 
I would trust the analogue meter.
Check in both "standby" and "operate to see what difference 
it makes.
     In my ancient RCA AR-88 receiver the standby position 
takes almost everything off the B+ line which goes high by 
something like 50%.

--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com
----- Original Message ----- 
From: "Jack Harper" <jharper at secureoutcomes.net>
To: <hammarlund at mailman.qth.net>
Sent: Wednesday, May 01, 2013 9:35 AM
Subject: [Hammarlund] Hammarlund HX-500 Problems...

Hello to the Hammarlund List...

I have been a member of the BoatAnchors List for
the last 17-years (almost to the day - 25 May
1996 - Tempus Fugit!) and posted on that List my
trials and tribulations of beginning to bring a
Hammarlund HX-500 transmitter back to pristine (hopefully) 
life.

A BA List member kindly listed that post on this
Hammarlund List - which I just joined yesterday.
After reading through some of the archives, I am
delighted to be here amongst fellow Hammarlund Aficionados.

I posted that I was seeing several tube pin
resistance measurements that are different from
the published Hammarlund specs - six, in fact,
out of, what, 175 pins or so, which is not bad at all...

I resolved two of those - caused by Hammarlund
recommended modifications that were added to my
transmitter. However, #3 did not make sense and I
was convinced that the measured value is actually
correct according to the HX-500 schematic and the
actual wiring. A couple of Hammarlund List
members agreed that the published number is wrong
(the consensus is that Pin-8 of V6 6U8 should
actually be about 2.3K rather than the published 350-ohms).

I also mentioned that the transmitter blows its
6A fuse after a minute or two operation in
STANDBY mode. Several people suggested that I
check the power transformer, which I did last
night by removing all the tubes and then
connecting a 100-watt light bulb in series in the
main power cord. The pilot lamps came on so I
know that the transmitter was getting power -- 
and the 100-watt bulb had no glow at all, even
with the Shack lights off - so, Good News, at
least the power transformer appears to not be
shorted etc (the light bulb, by the way, is good
- I measured 10-ohms across that, which I think
sounds about right).  This was the first time
that I have applied power to the transmitter
since I first got it and realized that it was blowing fuses 
several months ago.

The power supply is putting out the following measured (DVM) 
voltages:

Should Be           Actual Readings
---------------           --------------------------
-90 VDC                         -70 VDC (!?)
+270                             +383 (!?)
+780                             +760
+230                             +350 (!?)
+150                             +153

The HV is good, but the lower voltages are
totally out of whack, which explains, perhaps,
why the 6A fuse pops after about a minute in
STANDBY -- +383 rather than +270 ?  These
measurements were taken in STANDBY mode...

Someone, before me, hacked the power supply by
adding the Hammarlund power supply modification
with ugly orange wire, blobby solder joints,
higher value than specified resistors in parallel
- that sort of thing. I ripped all that out and
replaced all of the electrolytics with new Mouser
units, better wiring, with better (I hope - at
least I twisted the wires together :) solder
joints etc. There was also a resistor in the
supply with a totally wrong value, which I replaced.

Anyway, after re-wiring the power supply with new
components, the voltage measurements remained about the same 
as above.

Before I did the rewiring, I carefully traced out
the power supply circuit that was in the
transmitter when I got it and it met the power
supply mods (other than a wrong resistor) that Hammarlund 
published.

The original power supply, when the HX-500 first
came out, used a pair of 12AX4 rectifiers - which
were changed to a single 5R4 and a solid state
diode for the bias rectifier circuit to provide
instant bias for the pair of 6146s. This also
involved a different power transformer - I
checked the stamped part number on the replaced transformer 
and it is correct.

I replaced all of the power supply electrolytics
with new and left the original cans in place. I
also checked all of the resistance measurements
and they were good (other than the wrong one). I
added a new terminal strip for the new axial
electrolytics, which are all, of course, under
the chassis. I did double the value of C164 and
C165 to 80uuf (inductive input filter on the +780VDC HV).

Anyway, the fundamental problem with the supply
is that it is putting out weird voltages. I have
not yet checked the AC output voltages of the
power transformer - though, surely those are not wrong...

Now that I have all the tubes out, I will try to
check those on my tester either tonight or
tomorrow night (I work 80-100 hrs/week as part of
a tech startup, which chews up a lot of my time -
I usually only get to work on Fun Things on
Sunday afternoon - but, I got a bit less sleep
last night :).  Then, I will see if I can resolve
the other three strange tube socket pin
resistance values - and then get to work on the
weird power supply output voltages.

Question for the List:  Any thoughts as to why
low voltage DC outputs of the power supply might
be so cock-eyed:  +383 instead of +270; +350 instead of 
+230...?

I also notice that the Hammarlund power supply
modification changed the supply output voltages as follows:

Original           Modification
-----------           -----------------

-100                     -90
-50                       -45
+350                    +270
+780                    +780
+300                    +230
+215                    +200
+150                    +150 (reg)

I find all that odd...

Even though I have been a ham since 1967, I am
not really all that strong on diagnosing and
correcting problems - Any advice and counsel
greatly appreciated.  My hope with the HX-500 is
to pair it, in great operating condition, with
the R390A that I have as my primary operating
station - along with the Hallicrafters TO Keyer :)

Regards to the List,

Jack, WØYJ
Evergreen, Colorado USA

ps - It is madly snowing like crazy here at 8,000-feet 
elevation  :)

______________________________________________________________
Hammarlund mailing list
Home: http://mailman.qth.net/mailman/listinfo/hammarlund
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:Hammarlund at mailman.qth.net

List Administrator: Duane Fischer, W8DBF
** For Assistance: dfischer at usol.com **

This list hosted by: http://www.qsl.net
Please help support this email list: 
http://www.qsl.net/donate.html 