DX-60B has excessive drive

[WA9ZWA]

Hello all.
I picked up a Heath DX-60B at a Hamfest. It was working with about 50 watts out. It was all original with original electrolytic caps. I decided to recap it. I finished up...checked the plate voltage all seemed good. I put it all back together and hooked hooked up my HG-10 VFO and antenna proceeded to tune it up. I switched the meter to grid pushed the key and the Grid current pegged. I can get it to come down a little by turning the drive control all the way down. The Drive tune has a little or no effect. I thought maybe the HG-10 developed a problem so I tried a crystal with the same results.
I've checked my work and the power supply voltages, including the negative voltage supply and all seems OK. I'm pretty sure everything is correct. I have put it on the bench and hooked it to a dummy load. The drive is still high. I was able to get a slight dip and it puts out about 7 or 8 watts. I notice when I key it, the out put is about 15 watts and quickly drops to 7 or 8 watts.
I did drill a hole in the chassis to mount a terminal strip to mount the new filter caps on. I left the tubs plugged in while drilling...I know I probably should have taken them out. I wonder if I could have damaged a tube or jiggled a connection?
This one has got me scratching my head.


Barry
WA9ZWA

[Pete, WA2CWA]

I could check all the solder connections made when replacing the caps.

[WB2RJR]

Did you change the electrolyics in the bias supply? The caps have + side going to ground, not the - side. Do you have -130 volts for the bias supply?

I suspect you changed something wrong but you may not have. What is the grid voltage on the 6146 when this is happening and when you just have it on but not keyed?

[DMOD]

One of the causes of Excessive Drive can be the result of a failed "Drive" potentiometer:

http://amfone.net/Amforum/index.php?topic=40809.0

HK did not do a reliable design of the drive circuit:

Below is a schematic for a Screen Drive Circuit if the 25k drive pots are not available.

Phil - AC0OB

[W2PFY]

I would suggest you try another 6146 and see if the condition remains the same?

[WD8BIL]

If it is the drive pot you can actually find one here:

http://www.elliottelectronicsupply.com/5-watt-wire-wound-potentiometer.html


I've got one in my Viking 1 and it works great!

Buddly

[w1vtp]

One of the causes of Excessive Drive can be the result of a failed "Drive" potentiometer:

http://amfone.net/Amforum/index.php?topic=40809.0

HK did not do a reliable design of the drive circuit:

Below is a schematic for a Screen Drive Circuit if the 25k drive pots are not available.

Phil - AC0OB

I vote for a good look-see at the circuitry around R7 / R8.  I'm guessing the ground end of R7 has lifted (maybe internally inside R7 pot) which would result in little control on the 6CL6.  Careful about just replacing the 6146 without checking this out first 'cause 6146 CG's don't like excessive drive.  Might wreck it.  Those drive pots take a heck of a beating.  The EICO 720 suffers from the same problem.  I have three replacement pots at the ready for my 3 720's

Gl, Al

[K4RT]

Looks like ZWA found & corrected the problem: http://antiqueradios.com/forums/viewtopic.php?f=5&t=309440 (Post dated Oct Sun 23, 2016 7:46 pm).

[W3GMS]

Its sure would be nice if he would have come back and told us what the problem turned out to be.  Got a lot of good suggestions from all the comments here on AMfone.
Joe-GMS

[W3RSW]

He did in the "Wireless" next to last post. Corrected a floating ground of a 20uf cap he'd previously installed by soldering it in conjunction with pot ground lug.

[W3GMS]

He did in the "Wireless" next to last post. Corrected a floating ground of a 20uf cap he'd previously installed by soldering it in conjunction with pot ground lug.

So we are expected to look around the internet looking for his post as to see what fixed the problem?   

My point is, if someone asked for help on this site, then common courtesy would be for that person to respond to the original post about what fixed the problem.  Brad did post the link to the another internet site where he did explain what happened, so yes we found out due to Brad coming across it.     

This is not the first time this has happened and I am sure its not the last. 

Hit and run!!

Joe-GMS

[W3RSW]

Out of the park!   
Point taken.

[W3GMS]

Out of the park!   
Point taken.

 

Catch you on 40M soon.....
Joe-GMS

[K4RT]

I saw ZWA's post here on AMFone and then later happened upon the thread on the other site.

Rick, I received your FB QSL card in Friday's mail.  Enjoyed our AM QSO.

Brad

[DMOD]

He did in the "Wireless" next to last post. Corrected a floating ground of a 20uf cap he'd previously installed by soldering it in conjunction with pot ground lug.

So we are expected to look around the internet looking for his post as to see what fixed the problem?   

My point is, if someone asked for help on this site, then common courtesy would be for that person to respond to the original post about what fixed the problem.  Brad did post the link to the another internet site where he did explain what happened, so yes we found out due to Brad coming across it.     

This is not the first time this has happened and I am sure its not the last. 

Hit and run!!

Joe-GMS

  and it would be nice if he came back here and at least acknowledged the help and told us what he found.

He was on three other sites doing the same thing.

Phil - AC0OB

[WA9ZWA]

I'm back.  Thanks to Phil AC0OB for the email informing me that you guys wanted to know what I found.
I did find the problem.  It was a loose ground on the bottom terminal of the drive control.  There is a ground lug from the mounting nut on the drive pot that bends around and is soldered to the terminal on the pot.  The ground side of the 20 uf electrolytic is also soldered to that same terminal on the pot.  When I changed that cap the ground lug came unsoldered and sprung out.  It was so close it was hardly noticeable. I bent the ground lug so it physically contacted the terminal on the pot better and soldered it and all is well.
I recently acquired another DX-60.  I am getting ready to recap it. I will make sure that doesn't happen on it.  Someone had replaced the meter on the second DX-60. It worked but the scale on it was 0 - 10.  I was lucky enough to find a DX-60 meter on Ebay.  I got it and have it installed and now it looks original.
I got a Johnson 122 VFO with the second DX-60.  It works but needs alignment.  I am going to tackle that soon.  I don't like the way it operates with the DX-60 powering it.  I am going to build a external supply for it.
Here's a list of my old iron:
DX-60B W/HG-10 VFO
DX-60 W/Johnson 122 VFO
DX-40 W/VF-1 VFO
Hallicrafters SX-99
Hallicrafters S-85 W/Heath Q-Multiplier
Hallicrafters S-38B
Hallicrafters S-41G
Homebrew 6AG7/6L6 transmitter

73
Barry
WA9ZWA

[W3RSW]

Nice stchuff Barry. Now for an HG-10 receiver to compliment the Dixie.

Brad, Tnx fer yours too. I've got to make up some more decent cards other than the notecard I ginned up for you. Don't often get cards these days.

[DMOD]

...I did find the problem.  It was a loose ground on the bottom terminal of the drive control.  There is a ground lug from the mounting nut on the drive pot that bends around and is soldered to the terminal on the pot.  The ground side of the 20 uf electrolytic is also soldered to that same terminal on the pot.  When I changed that cap the ground lug came unsoldered and sprung out.  It was so close it was hardly noticeable. I bent the ground lug so it physically contacted the terminal on the pot better and soldered it and all is well.
I recently acquired another DX-60.  I am getting ready to recap it. I will make sure that doesn't happen on it.  Someone had replaced the meter on the second DX-60. It worked but the scale on it was 0 - 10.  I was lucky enough to find a DX-60 meter on Ebay.  I got it and have it installed and now it looks original.
I got a Johnson 122 VFO with the second DX-60.  It works but needs alignment.  I am going to tackle that soon.  I don't like the way it operates with the DX-60 powering it.  I am going to build a external supply for it.
Here's a list of my old iron:
DX-60B W/HG-10 VFO
DX-60 W/Johnson 122 VFO
DX-40 W/VF-1 VFO
Hallicrafters SX-99
Hallicrafters S-85 W/Heath Q-Multiplier
Hallicrafters S-38B
Hallicrafters S-41G
Homebrew 6AG7/6L6 transmitter

73
Barry
WA9ZWA

Thanks Barry, nice stash. 

I am a boat anchor-classic radio-vintage transmitter junkie and have to attend BAAA meetings.    Fun stuff.

BTW, down at http://amfone.net/Amforum/index.php?board=46.0 there is a Transmitter Forum for upgrades, tips, etc.

Phil - AC0oB