Heathkit DX-100 "Squegging" only on 10, Sometimes

[N8ETQ]

Yo'

      Got a DX-100 here with all the "Normal" issues,
you know what they are. Biggest one was HOT Chassis.
Cleared that up and during checkout I found the usual
Low/No Ig. on 10m.

      Flipped on the bench RX to listen for the VFO X 4
signal and it sounded like a band opening!  So I fired
up my HP 141 and saw this.

      The first time it's on the Ig meter does peak
with the Grid tuning control and the signal sounds and
looks ok. Changing NOTHING I can switch off the osc.
by moving the CW-PHONE Sw. to phone. Put it back in CW
and I see and hear a bunch of signals.

      I reheated a bunch of solder joints, cleaned the
12BY7 and 5763 pins and sockets, checked power, reheated
all the wire connections to the buffer coil. I subbed
in diff. set of tubes too. No Joy.... Coupling caps seem
OK as well but I haven't changed them yet.

    Pix .001 is the "Expected" 28.275 signal. (First
time on)

    Pix .002 is the second time on, No Ig reading.

    Pix  .005 is what it looks like squegging away.


       PS:  I kind of took the summer off, Hope Y'all had
a good one, Were all still standing here.

73

/Dan

[w4bfs]

ugh !  somebody unstable !

it may take various things to find this cause :

experience sez grounding issues most likely therefore i saw where you went after some of these ....good

some of these can be hard to find .... did you clean rotor connections on tuning caps ?  ...lube first and de ox rotary grounds .... solder bond grounding to chassis with solder gun and non-acid flux after scraping .... go back and check threads about contact servicing using cleaners, etc.

it saves time in the long run to just go thru stage-by-stage with careful inspection of conditions and component values .... then activate and check voltages

after saying all that ...swap a few toobs .... could do the trick

[WD8BIL]

Hi Dan...... check the bias on the oscillator stage. See ifn it's a resistor heating or something. Like, there's a 22K grid resistor in there off the VFO bandswitch lead.

Also the keying line runs thru the VFO/Crystal switch AND the Phone/CW switch. Maybe bad contact there too.

Good luck...... good hunting!

[N8ETQ]

  Hey Beefus and Buddly,

       This thing really kicked my Arse... I found 3 ohm Thermisters
 on both sides of the "PLATE" Sw. which I removed, really thought
that would get it, NoJoy...  After several more hours of head scrathin'
I figured I would check the bias rectifier 6AL5 and the 0A2 via
substitution. My Hickok 532 will check them but I had spares so
I chose that route.

        Turns out the 0A2 was actually an 0B2 !  150V vs 105V.
The correct regulator tube really "Tamed the Beast". 

Thanks

/Dan

[WD8BIL]

Good deal, Dan!! Another note for the books.
Happy AMing.

[w4bfs]

wow ...that was unexpected ....just gotta check it all ....nice werk

[N8ETQ]

Yo'


   Just to wrap this up.. It's a Good ole' DX-Hundy
again.  Along with the stuff already covered, I ended up
removing a soft 5R4, a crappy 5V4, also a 1100 ohm 18W
"R" in series with the LV PSup. output. (Attempt to control
excessive Line voltage I suspect).  I also added a 12V xfmr
and relay for PTT. Someone modified the Loading per the "B"
scheme but used a 2 X 500pF Cap. It's about 500 pF too small
for 160 but OK otherwise. (Into 50 Ohms). Another thing about
that loading cap, It was mounted in such a way that the
Rotors came in close proximity to the chassis and the center
wall. So as you tried to load it up it would begin to load,
then start to reduce loading, then load up again. I re-
oriented the cap so the Rotors would swing out into space
and it's much better now.

        I also added a #14 wire from the driver tuning cap,
through the center shield to the PA compartment for
Neutralization and he pulls 2 ma Ig on 10M now. He makes
about 100 W on 80 - 20m, about 90W on 15 and 80W on 10.

        I as always, installed back to back diodes across
meter, three wire cord, internal 6 A line fuse and a 2A
job just for the LV xfmr.

        Hopefully the owner will make the effort to control
the line voltage to this thing either with a Variac or bucking
xfmr. I noticed that any line voltage over 115 provides
over 6.3 V to the fils. At normal ac line voltage here
(120 to 123) the fil voltage exceeds 7.3V ! Yikes!

   "And another thing" (Going all Mary Lou Reton on ya)
when installing the 2 circuit TRS jack to accommodate the PTT
I found that EVERY "R" in the speech amp/driver was out of
spec. Some by as much as 50%.  I changed em all as well as
all the caps in those stages. A complete PIA, but after
getting that Shield out of there I couldn't see not doing it.


73

/Dan