New guy DX-60 problems.

[W5BFE]

I decided a Heathkit DX-60 would be a first good tube radio since there seemed to be plenty of them on Ebay. Well after the once over, I replaced the the electrolytic capacitors. I replaced the 8.2 ohm resistor on pin 6 of the 6146 cathode since it was bulged and charred. Well after a bit of tuneup, I committed the cardinal sin of all DX-60s and the function switch finally sparked itself to death. Well after some headscratching I  managed to replace the function switch with a series of toggle switches. I'm switching the HV line now with a 6 volt DC relay.

Back at it I started to tune it into a dummy load on 40 meters. R35 the 270 ohm resistor which I think is a bleeder for C40 and 42 started smoking. Replaced that with a 5 watt resistor.

Finally got a signal out of the radio. On 40 meters I'm getting about 10 watts output. In AM it sounds as if an electric razor is humming away. Only when I back the gain way down does the electric razor stop. Of course with the gain that low I can't even modulate the thing. I was wondering if the mic input being so close to that neon power light might somehow be coupling into the audio chain somehow.

I've replaced all the tubes, and have tried two 6146s (the one that came with the radio and the NOS I ordered.) I still can't seem to get any power out of them.  I was careful to not let the grid over 2.5~3 ma, and always kept the plate current under 200 ma. At one point with the original 6146 the plate current may have gone over 200 but I quickly backed down the drive. I don't think I smoked it.

Any help or pointers at common DX-60 pitfalls or faults? I'm kind of sheepish of taking live voltage readings while on but I guess at some point I'll have to get readings to properly diagnose this thing.

I'd also like to try some audio mods (simple ones), but haven't done any, I don't plan on connecting this to a linear at any point either.

I'd appreciate any input you may have, I know y'all have seen plenty of DX-60 threads but I couldn't find one that might describe what's happening to this radio.

Jake

[w4bfs]

hello Jake .... welcome to the am forum .... DX60 fun .... a lot of different things happen in the function switch, as I recall ... its been awhile

the real basics are about component quality .... you said you have replaced  electrolytics ... what about coupling caps ?  how about the carbon comp resistors ?  .... if you don't want to start troubleshooting by measuring voltages and currents, that's where i would start ... if a tube tester is available check tubes for leakages / shorts

it takes a while to get your sea legs .... be sure to work safe and discharge caps before the hands go in ....gl & 73   ... John

[K9DXL]

I got my DX-60 going last winter.  The first step was putting in new power supply electrolytics from Hayseed Hamfest.  They're nice folks with fast service.  Then, I added a 3 wire AC cord and chassis mount fuse in the hot lead.
With a solid power supply, troubleshooting began.  I had intermittent/low RF output that was resolved when I found a ground lug that was extremely loose.
When I tried the rig on AM, there was AC hum and no modulation.  My tube tester indicated a short in the 6DE7 modulator tube so I replaced it, and was rewarded with intermittent modulation/AC hum.  Wiggling the 12AX7 seemed to help sometimes, so I thought the socket pin contacts were the problem.  After a long frustrating time barking up that tree and getting nowhere, I turned my attention to the components around the tube socket.  Pin 3 of the 12AX7 goes to ground through a 3300 ohm resistor, and even though the ground lug looked solid, when I tried to tighten it up, I discovered that the screw was stripped!  New hardware and cleaning the chassis connection point with a piece of fine sandpaper fixed the problem, and audio was now clear as a bell.
There are several articles in back issues of Electric Radio that may be of interest to  you, by (SK) Bill Breshears WC3K and others.  I found it helpful to keep notes and write a narrative when each stage of the troubleshooting was done. 
Be careful and don't give up (but don't keep working on it when you're tired) and you'll be rewarded with a great rig!

[Steve - K4HX]

http://amwindow.org/tech/htm/dx60aud.htm

http://amwindow.org/tech/htm/wc3kmods.htm

http://amwindow.org/tech/htm/dx60k4tax/dx60k4tax.htm

http://amwindow.org/tech/htm/dx60ptt.htm

http://amfone.net/Amforum/index.php?topic=26603.0

[wa5ddz]

Hi Jake  --  John has it right, work safe, one hand behind your back,
600+ volts gives a hard jolt. I have four DX-60's and a DX-60B on
the work table. For me it is best to get everything working in the cw
mode then on to am. A good vtvm ( I use a heathkit im-10, it has a large
face ) is a must. Keep posting your results. Good luck--they are a nice
little rig.  Bruce

[DMOD]

Finally got a signal out of the radio. On 40 meters I'm getting about 10 watts output. In AM it sounds as if an electric razor is humming away. Only when I back the gain way down does the electric razor stop. Of course with the gain that low I can't even modulate the thing. I was wondering if the mic input being so close to that neon power light might somehow be coupling into the audio chain somehow.

I guess the obvious question is: What kind of microphone are you using and have you changed the chassis Amphenol Connector to a phone jack?


High impedance (= > 50k) microphones are generally used to drive the speech amp stages of these older rigs. That means a high impedance dynamic mike or a crystal mike such as the D-104. A 500 ohm microphone will not generate a high enough voltage for driving those tube stages unless you use an audio transformer.

Many of the older Amphenol "flat button" microphone connectors have the internal button flattened out and don't make a solid connection.

Phil - AC0OB

[W5BFE]

Hello Gentlemen and thank you for all the wonderful replies.

I never did think of replacing the coupling capacitors or carbon comp resistors. My only thought was that the electrolytics should be swapped out as they may have become dry. I also changed out the two prong lamp cord for a three prong grounded plug. I still don't know what that neon bulb looking thing on the hot line is. The schematic says it's a circuit breaker but it looks more like a neon lamp than anything else.

The microphone I'm using is a radio shack omni directional XLR microphone rated at 600 ohms, which then goes into a 1/4" TRS low to high impedance transformer. From there I made up a custom audio cable which is a 1/4" phono jack which then terminates into a PL-259 with only 3/16" of an inch of the center pin jutting out. It should be making pretty good contact with the solder blob from what I can gather.

The chassis is quite crunchy in terms of oxidation so I didn't think of shoddy ground in terms of the hardware connections, that might actually be part of my problem. That being said is there any danger in gently wiggling the tubes while the radio is in operation (other than the 6416 lol) other than getting burned?

Oh and those steel sleeves that cover the octal tubes, are those there as heat sinks? Or is that for RF shielding?

I'll let you all know what my voltage readings turn up next.

Thanks!

[DMOD]

That being said is there any danger in gently wiggling the tubes while the radio is in operation (other than the 6416 lol) other than getting burned?

Oh and those steel sleeves that cover the octal tubes, are those there as heat sinks? Or is that for RF shielding?

I would use Deoxit spray on the tube sockets, wait few hours, and then reinsert the tubes and let them dry out while hot.

The shields are used primarily for RF shielding, however, I usually dispense with the 6DE7/6DR7 shield after I make my mods because it runs pretty hot in AM.

Phil - AC0OB

[W1RKW]

if you use DeOxIt on the tube sockets be sure to clean off residue between the contacts. Any HV will create a carbon track over time. Use the cleaner sparingly on the intended target and avoid over spray.

[K1JJ]

If I had a DX-60, after it was working correctly, I would do these AM hi-fi mods ASAP.


http://amfone.net/Amforum/index.php?topic=26603.0


I almost bought a DX-60 off eBay last month to try them out and use as a low level linear exciter.  Probably use my ricebox as a low level 100mW VFO and receiver.

T

[W5BFE]

Welp,

I think I found my problem. The voltage that goes to the HV plate choke and pin 1 of the 6DE7 is measuring around 320 volts. I do see 680 or so volts coming out of the voltage doubler circuit but it's not getting to the plate of the 6DE7 or the 6146 somehow. I replaced the old diodes with 1N4007s so I'm wondering if I screwed something up somewhere. I need to go over the schematics again and see where I went wrong.

[K1JJ]

Measure voltage along the HV path until it drops off. Then get out the ohmmeter to see where the high resistance is.  Maybe there is a poor set of switching contacts in line?   Screw terminal rusted at the plate choke?

Play with the connections by banging them with an insulated rod while measuring.  This should be an easy thing to find.

Another technique is to turn out the lights and look for arcing of any kind. You know to be super careful doing all of this when the HV is on!  Sometimes your hand can slip off a tool, probe, etc.


T

[W5BFE]

I think I'm getting close. R35 was originally charred and reading 500 or so ohms. I replaced it with a 270 2 watt ceramic resistor, after more troubleshooting I noticed that the new 2 watt ceramic was discolored, but still on tolerance. I beefed it up to a 270 ohm 5 watt. I have a feeling the 100 ohm resistor R34 is open or damaged somehow. Hopefully this is it!

[W5BFE]

Sure enough R34 was burned open. I replaced it with a 100 ohm 10 watt resistor now I'm getting 620+ volts to the plate of the 6DE7 and the 6146.  I'm not sure if my noodling around killed it or not but it's back. Now I'll see if I can tune it up.

[DMOD]

For some potential ideas on modifying the audio circuits and power supplies for these controlled-carrier transmitters, see my post at:

http://amfone.net/Amforum/index.php?topic=34555.0

Phil - AC0OB

[W5BFE]

The QIX mods from Steve sound great, but I don't have any rack gear. So I'm going to try a mod that keeps the audio chain from the mic button on. I finally got the hang of tuning this thing up, and if you're not careful about the grid and the plate switch position things can go POP really easily I've found! I've already smoked the 8.2ohm bias resistor on the cathode of the 6146 AGAIN. Oddly enough after replacing that and forcing myself to look at the switch whilst tuning I've gotten it up and running with the original tubes from fleabay. It's pushing about 65 watts on 40 meters yay!

I'm currently trying to figure out which of the mods will yield the best results without taking the chainsaw to the thing too much. It's already been drilled on enough!