Trials of restoring Heathkit DX-35

[Ed Joseph]

I was given an old DX-35 CW/AM transmitter by a friend. This thing has been sinking my time for the last 2 months.

It had several mods done to it, including a large meter (since replaced with a square of sheet metal) and also had the wrong rectifier tube.

A couple things about this beast:
- The power transformer in this is running at max by design, and if you look at one wrong, let alone try to run the VFO off the included socket, it will melt down. (This is also an issue with the DX-40)
- There are THREE *different* schematics in the manual online.
- The schematics have no part designators, such as R2, C6, etc. That just strikes me ad odd.

Anyways, at this point, I corrected all the mods (I think!), recapped it and got this thing to do about 60W CW into a light bulb. I would not recommend doing that amount of power for any length of time due to the transformer issue. I've not even attempted to try AM mode yet as dead carrier seems to have some raspy buzz to it I need to figure out. I think this thing will still take a while to work the kinks out of, and I likely will end up putting some mods back into it. For such a simple design, this is probably the most frustrating rehab I've ever done on a boatanchor in my life!

[CK-722]

Ed, check your Inbox. There's a link to Facebook Page of the former Heathkit Technical Editor. Maybe he can help you.

[audiophile]

You're working on what they call a "GriefKit"

[Turkeytop]

Always wanted to build a Heathkit. Back in those days we were dirt poor and I didn't have five cents to spend on any frivolous hobby stuff. By the time I reached the point in my life when I could afford such things, Heathkit was no longer in business.

[Ed Joseph]

Greifkit, indeed...

I've built a handful of them in my life... I was pretty poor myself growing up, seems that when I *could* afford that stuff, other things always too precedent. Now, I find myself poor again, and basically doing radio from the curbside.

Frankly, if I cannot get this thing to run right "by the book", I always have the option to just gut it and homebrew something from the parts.

[innate-in-you]

I was given an old DX-35 CW/AM transmitter by a friend. This thing has been sinking my time for the last 2 months.

It had several mods done to it, including a large meter (since replaced with a square of sheet metal) and also had the wrong rectifier tube.

A couple things about this beast:
- The power transformer in this is running at max by design, and if you look at one wrong, let alone try to run the VFO off the included socket, it will melt down. (This is also an issue with the DX-40)
- There are THREE *different* schematics in the manual online.
- The schematics have no part designators, such as R2, C6, etc. That just strikes me ad odd.

Anyways, at this point, I corrected all the mods (I think!), recapped it and got this thing to do about 60W CW into a light bulb. I would not recommend doing that amount of power for any length of time due to the transformer issue. I've not even attempted to try AM mode yet as dead carrier seems to have some raspy buzz to it I need to figure out. I think this thing will still take a while to work the kinks out of, and I likely will end up putting some mods back into it. For such a simple design, this is probably the most frustrating rehab I've ever done on a boatanchor in my life!

Most likely, you need to change the electrolytic capacitors in the power supply.

Either that, or you have to desolder a wire that the sixteen-year-old builder wrapped around the power cord to keep a wire in place

[Ed Joseph]

The power supply was the first thing I did, the caps were physically leaking. I changed the bleeder resistors as well. I generally change the PS caps by default in anything more than a few years old.

I also found a shorted ceramic B+ bypass cap in the plate circuit and replaced all other paper and electrolytics in the thing.

Soldering... I bet I've taken a pound of excess solder and solder blobs floating around in this thing. I've removed several shorts from too much solder. I've also found a dozen or more loose wires, wires hanging on by one strand (in the B+ circuit no less!). It has had a rough life. The fact I can get RF output from it is kinda amazing itself.

When I first got this thing up, the B+ was 40 volts high because they had a 5U4G instead of a 5U4GB, which does make a big difference!

[FET-500]

You're working on what they call a "GriefKit"

Some of them are easy and awesome...

[Ed Joseph]

I considered solid-stating the power supply, but I decided that having the B+ on the plates immediately with this rig would be a bad thing... I've been toying with the idea of just homebrewing it into a kinda "URR navy transmitter" looking rackmount rig, 2 band screen mod AM with like 20 watts PEP output. Maybe make one band 11m and the other 43m. It only had one crystal in it, 43m, 6925kHz which I'd just use if I have company over and want to hear music on one of my old shortwave radios. With 11m I'd at least have a band for some occasional ragchewing. My main goal with this would be to see how good I can make it sound on air. I really don't have any desire to do the ham license thing, to be honest.

[audiophile]

The raspy buzz reminds me of the RCA BTA-5T going back on the air after being dark for a almost a decade. It never sounded right, and you could hear 240 Hz intermod with certain voices. I finally got to bottom of it after thinking about it. On a dead carrier the hum was acceptable.

Filter caps weren't connected in the modulator section. Wow what a difference.

[Ed Joseph]

Which BTA5, audiophile? The only one I've personally had experience with was at WTRX. That was the main TX at least until Cu bought the place. Not sure if they run it or replaced it since then.

[CK-722]

This one I think.

http://licensing.fcc.gov/cgi-bin/prod/c ... r_id=51703

I think Don McComb worked on both of those transmitters. I think Dave Gale said WOOD had one also.

http://licensing.fcc.gov/cgi-bin/prod/c ... r_id=66019

Yup.

[CK-722]

https://www.necrat.us/wsyr-5.jpg

Weren't the panels on the one at WTRX blue?

My next door neighbor had been the accountant in Lapeer. One day early in her tenure there, she opened a door thinking it was a storage cabinet. She was full of hilarious radio stories. I listened to her stories for hours a few times.

[Ed Joseph]

Yes the panels were dark turquoise I recall... forgot about the WDEY transmitter... totally
Was there also one at WFEN or was that a Continental? I'm thinking the latter now...

There was a BTA 1 at WGRY when I was there. I could never get that thing past 85% positives, but I wasn't there very long to really mess with it. There wasn't an AM limiter, just a blue-face Orban 418 limiter with no assymetry, looked a bit like an 8000A but just had a row of knobs on it. I guess it worked well enough to be heard in the parking lot, LOL!

[Ed Joseph]

This, exactly... Only left channel was wired up.