[Boatanchors] Thoughts on Reviving the Heathkit DX-100

Wed Jan 6 14:21:02 EST 2016

On one workbench I have a group of outlets that are behind a variable
autotransformer that
due to its size sits on the floor with a simple servo motor setup to turn
the crank.

On Wed, Jan 6, 2016 at 11:09 AM, Jim Liles <hallicrafterssr2000 at k9axn.com>
wrote:

> 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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