Thoughts on DX-40 restoration
On on an impulse, I just bought a decent looking Heathkit DX-40 on eBay for $65 with
free shipping - poor guy should have thought that one through a little better! At any
rate, this is my new winter restoration project. I've always been a boatanchor / tube
guy until just this year (sold off over 100 collected radios in the last few years!).
This one was just too tempting - not to sit on a shelf, but to put on the air on 80 and 40 CW.
Maybe try AM (grid modulated.... hmmm) on 75 as well
From the eBay photos and description it seems pretty complete - obviously a recap and realign is
in it's near future. I have TONS of old FT-243 rocks still around so that end isn't a problem.
But what to do about the finish.... should I even try to redo the original two-tone paint job
on the face? Pretty hard to duplicate the curvy shapes and make it look even close to original.
Or should I maybe just leave it "rat rod radio" on the face, and just repaint the cabinet? As
a last option, just repaint entirely and make no effort to match original - just go with a nice
overall light gray, making it look nice without any trace of the original Heathkit paint job look?
[screen capture below - if you search under 'completed listings' you can find it on eBay]
The panel looks okay, but I'd definitely give the cabinet a coat of paint. I had a DX-35 (very similar, but older) as a novice rig. Don't try to use a VF-1 unless it is powered by its own supply -- they're well known for chirp when tied into the transmitter for power.
So true on the VF-1! Not a very stable VFO no matter what you do with it. I never had success with one anyway.
Originally Posted by WA7KKP
I know the HG-10 was essentially the same thing but for whatever reason was a much more solid performer.
But I'm not too concerned - I've got rocks that cover every 5kc segment of the 40-Meter CW band, Extra portion
to the end of the Novice band! The rig holds 3 - so I'll just populate with some good options (7.040, 7.060 and
something in the Extra segment - 7.020 maybe)
So your vote is "let it ride" on the front panel and let it be something of a "rat rod radio"? I'm leaning that way too...
My VF-1 worked fine, taking power from my olde DX-60B xmtr. The 6AU6 would start to pull when the tube got tired. Otherwise, it was FB.
Originally Posted by WB7AWK
You'll likely find out about that "poor guy" payin' for the shipping when you plug it in...
First, if you want to repaint the cabinet, the Sherwin-Williams formula for the paint (any good paint store can use this formula) is available in the article at
Next, the power transformer in the DX-40 is running on the "ragged edge" and powering either the VF-1 or HG-10 series VFOs from the transmitter will definitely overload. The transformer in the DX-35 is even more overloaded. Heath finally used a power transformer with sufficient capability in the DX-60 series.
There are several things that can be done to the VF-1 which improves the stability considerably and none of those changes require any wiring changes to the VFO. The first is to replace the 6AU6 oscillator tube with a 6AH6. This "tames" the frequency stability. Heath went to the 6AH6 instead of the 6AU6 in the TX-1 Apache to get the VFO stable enough for SSB. The only thing is that the 6AH6 has a slightly different inter-electrode capacitance than the 6AU6 and the trimmer capacitors (not the slug tuned coils) have to be adjusted slightly to get the calibration correct. Then, replace the screen regulator tube (0A2) with an 0B2. This drops the screen voltage to 108 VDC instead of 150 VDC. Next, use the 0A2 removed from the screen circuit to regulate the voltage of an external power supply feeding the VF-1 to 150 VDC. Using 150 VDC regulated instead of 250 to 300 VDC (or so) from the transmitter stabilizes the VF-1 even more.
If one looks closely at the manual for the HG-10 series VFOs, they will see that Heath recommends using a separate, regulated, power supply for optimum stability of that VFO series. This is recommended even though "robbing" the power from the DX-60 series transmitters will not overload the power transformer.
If phone operation of the DX-40 is desired, I strongly suggest cutting the power back from the rated input. If the transmitter is to be used only for CW, remove the modulator tubes from the transmitter. Transformer failure is VERY common in the DX-40 and doing everything possible to reduce the load on the transformer is prudent. For every 1 DX-40 still operating with the original transformer there are at least 3 transmitters that have had a transformer failure. The DX-35 is even worse with probably less than 10-percent still running with original transformers. Heath replaced a lot of transformers in the DX-35 and DX-40 under warranty because of the fact that the transformers were just plain not really capable of handling the load.
With the aforementioned changes made to the VF-1, that VFO is generally more stable than the HG-10 series.
Another thing is not to key the VFO when using CW. This is true of virtually every external VFO. Just let the VFO run continuously when in transmit and then key the transmitter. When the VFO is keyed, there is a very good chance that it will "chirp" whereas letting it run continuously eliminates chirp.
I put a DX-40 transformer in a DX-35 and it worked great. Same voltages and form factor. maybe they were the same transformer. It took me 3 DX-40s to get one to work. parts robbed out of all 3 to collage into one. Some of the DX-40 parts were used for a DX-35. the 2 units are very similar.
The transformer for the DX-40 is not the same as in the DX-35. The DX-40 transformer has the same voltages but is a little bit better than the DX-35. However, it still is not really capable of handling the real load under full power. The transformer in the DX-60 series is much better.
Thanks for posting that information Glen. I'm not sure I understand all that I see - under the DX Cabinet section there
Originally Posted by K9STH
appear to be TWO formulas - I assume one is the cabinet itself, and the other is the dark gray tone on the front panel?
So am I correct in assuming that the face plate is just bare aluminum with the dark gray parts as the second "recipe" in
your article? Or am I not reading this right? Or is there a third gray color? Or the face is the same gray as the box,
but with the darker gray accents?
Also, how would you go about redoing the face panel - or would you even try? It seems it would be VERY difficult to
make it original, given the silk-screening of the various nomenclature. I'm thinking I'm just going to repaint the outer
cabinet only and let the front pane ride as it is.