[Boatanchors] Thoughts on Reviving the Heathkit DX-100

Wed Jan 6 14:09:49 EST 2016

Bill,

Why not run the shack behind a Variac?  Everything here is behind em.

Have an extra 40 amp 115v if there is any interest.  You can run the whole 
system with it.

Regards Jim

-----Original Message----- 
From: Bill Cromwell
Sent: Wednesday, January 06, 2016 12:45 PM
To: boatanchors at mailman.qth.net
Subject: Re: [Boatanchors] Thoughts on Reviving the Heathkit DX-100

Hi Dave,

I have been experiencing the same sorts of trouble with my DX-100. I
recapped it and found the final plate voltage hanging at about 900
volts! The line voltage here gets over 125 and closer to 130 volts
sometimes. The series wired caps as a unit are rated at um..900 volts!
Whatever margin was included when they were 'rated' is all the margin
there is. I have disconnected the plate supply transformer and I run a
pair of 2E26 tubes on the "low" voltage as finals. My DX-100 no longer
has the modulator section (maybe I'll restore that and maybe not). It
was gone before I got the transmitter. I haven't missed it. Can you
spell CW. I run my gear on the conservative side and I even crank the
power down to "official" QRP levels sometimes. I do NOT need 900 VDC on
the final plates. The Kenwood, running on the same AC power line also
leans on those 6146s with ~900 volts.

I am thinking of the bucking transformer solution for the final plate
voltage just as you have suggested and solid state regulation of the
"low" voltage which is also on the high side in my rig but well withing
the ratings of the parts. I may put caps with higher voltage ratings in
the final B+ filter and maybe a solid state regulator after that. My
DX-100 is still using the vacuum tube regulators. Replacing those with
silicon would make the voltages even higher - Yikes! If your DX-100
still has the modulator bits you may have to be more creative finding
interior space for a small bucking transformer. Maybe an isolation
transformer and bucker for the operations table would be more appropriate.

I do have other options for running reduced power on 160 meters
including a Johnson Ranger. I would just as soon have most of the power
from the pair of 6146s available from the DX-100. Sometimes I would like
to have more - maybe 50 KW <evil grin>. I'm sure the guys who do have 50
KW wish they had more, too. C'mon now..we know they are out there. Is
anybody missing their local pole pig?

73,

Bill  KU8H

On 01/06/2016 09:59 AM, David Stinson wrote:
> Morning.  I just finished restoring a Heathkit DX-100
> for a good friend.  The information I needed was supplied
> by the kindness and generosity of several of our members.
> Our people are the best!.
>
> Many of the grounds had gone "Hi-Z." A small "tweak"
> of the ground screws usually fixes that. It's a common problem with old 
> radios and the first thing I address when one hits my bench.
>
> This transmitter had a bad LV transformer.  It had also
> been chopped and lopped to use the SB-10 Sideband adaptor.  The previous 
> owner had done other things "his way" and it was quite a puzzle to undo 
> all the mayhem.
>
> It's a pretty transmitter, but I'm not a fan of the DX-100.
> The DX-100 runs everything on the "hairy edge," putting
> max voltages on modulators, PAs and even the LV stages.  One of the 5R4 HV 
> rectifiers had a failed and
> arcing tube base- not surprising given how hard Heath pushes everything in 
> this rig.
> http://home.netcom.com/~arc5/5R4arc.jpg
> The set was designed when the AC line voltage averaged 110-112 VAC. 
> Today's lines run 122-125 VAC.  That's better than 10% high and runs the 
> HV north of 800 Volts.  Not nice.  Things start arcing easily at 800 
> Volts.
> No wonder people report 115W out on 75 Mtr AM;
> they're kicking the stuffings out of everything in there.
> I'd bet breakfast that a bunch of blown-up DX-100s
> were fried for just this reason:  High primary voltage.
> If it were my rig, I'd buck the line down under 110V,
> take my 80W average out on 75 AM and call it "good."
>
> Moreover- the terminal strips used to build the set are cheap and prone to 
> breakdown.  I had the 6 VAC buss
> from the transformer try to weld it's terminal post to the chassis and I'm 
> lucky I didn't lose the replacement
> transformer.    I think one should coat the terminal
> strips and the chassis around them in Corona Dope,
> just for safety's sake.
>
> The 5V4 "Low Voltage" rectifier: I noticed that one of the wires that 
> crosses the 5V4 socket had a burned spot and the replacement transformer 
> also had a burn spot in the same place.  I put shrink tubing over
> the burned spot.  Well, I got a new burn spot because
> the wire crosses above a filament pin and the insulation
> was breaking-down, causing an arc! http://home.netcom.com/~arc5/5V4arc.jpg
> I double-shrink-tubed the entire length of the wire, plus the wires going 
> from the LV filter choke near the chassis because I thought I saw an arc 
> to ground there as well.
> The DX100 is the "arcing-est" transmitter I've ever seen.
> When transmitting, one needs a good ground because
> RF where it doesn't belong encourages arcs in this rig.
>
> All this leaves me with the impression of the DX-100
> as a fragile beast, just itching to let its smoke out and roll over on 
> you.  If you run one, I think toning the primary voltage down around 110V 
> and accepting
> a little less output, applying Corona Dope to all the terminal strips in 
> the power supplies and checking all you grounds would be excellent 
> investments.
>
> GL OM ES 73 DE Dave AB5S

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