[Boatanchors] Thoughts on Reviving the Heathkit DX-100

Wed Jan 6 14:35:10 EST 2016

Hi Bry,

I suspect they can handle the voltage. In fact they have been. What 
about the pair of electrolytic cpas each rated at 450 volts for a totla 
of ...um..900 volts. Too close to the bone. The heater supplies will be 
only a few per cent higher than they were before. That's okay too if the 
original voltage wasn't already at the high end of tolerances.

73,

Bill  KU8H

On 01/06/2016 02:08 PM, Bry Carling wrote:
> Interesting. I am pretty sure that the 6146 tubes can handle 900V OK.
>
> We used to routinely run our ceramic based 807 tubes at 1200V DC to get a little more out of themin our WS 19 on the CCF (Combined Cadet Force) net in Britain in the old days!
>
> Nice red glow on a cold day.
>
> Bry
>
>> To: boatanchors at mailman.qth.net
>> From: wrcromwell at gmail.com
>> Date: Wed, 6 Jan 2016 13:45:37 -0500
>> 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
>> ______________________________________________________________
>> Boatanchors mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/boatanchors
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:Boatanchors 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
>> Message delivered to af4k at hotmail.com
>   		 	   		
> ______________________________________________________________
> Boatanchors mailing list
> Home: http://mailman.qth.net/mailman/listinfo/boatanchors
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Boatanchors 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
> Message delivered to wrcromwell at gmail.com
>