Forums :: NEW! Web Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives
Support This Site: Contributors :: Advertise


It is currently Jan Sat 16, 2021 12:03 am


All times are UTC [ DST ]





Post New Topic Post Reply  [ 17 posts ] 
Author Message
 Post subject: Cathode Voltage Equals Plate Voltage
PostPosted: Nov Wed 18, 2020 12:40 am 
Member

Joined: Jun Fri 27, 2008 3:10 am
Posts: 136
Location: Damariscotta, ME
I'm stumped.

I am working on a Heath HR-10B. I know, not the most popular receiver, but I have always liked the looks of them. This one is beautifully wired and no apparent mistakes or bad components.

Brought it up and heard the AF OK, but no sigs. So I started working backwards and could inject into the detector and peak up the last IF. But as I moved back no signal through the last IF tube, Replaced tube with NOS and no change. Then I checked voltages. After much reviewing, I determined that the output at the DC filter and dropping resistor the voltage was much higher then it should be, almost like there is no load.

Then, working back, every tube fed by that DC line had generally the same voltage showing on the plate, screen and cathode. Attached is a portion of the schematic showing the last IF, expected voltages and measured voltages. All wiring is spot on and resistors pretty much within tolerance.

Any thoughts?


Attachments:
HR10B.JPG
HR10B.JPG [ 102.38 KiB | Viewed 489 times ]

_________________
Carl
WA1KPD
Top
 Profile  
 
 Post subject: Re: Cathode Voltage Equals Plate Voltage
PostPosted: Nov Wed 18, 2020 12:47 am 
Member
User avatar

Joined: Sep Wed 10, 2014 2:01 am
Posts: 2285
Location: Costa Mesa, California
Does the accessory socket have a jumper to allow the cathodes to connect to ground through the RF gain pot?

Norm

_________________
KK6IYM


Top
 Profile  
 
 Post subject: Re: Cathode Voltage Equals Plate Voltage
PostPosted: Nov Wed 18, 2020 12:50 am 
Member

Joined: Jan Tue 10, 2012 8:39 am
Posts: 1965
It does appear that the cathode circuit has no path to ground.


Top
 Profile  
 
 Post subject: Re: Cathode Voltage Equals Plate Voltage
PostPosted: Nov Wed 18, 2020 3:24 am 
Member

Joined: Jun Fri 27, 2008 3:10 am
Posts: 136
Location: Damariscotta, ME
Ok, in an attempt to retain whatever shred of dignity I might have, the voltages snapped right in place when I wired up an external plug for the 8 pin accessory socket with pins 1 and 6 shorted together.

I used to tell my brother in law, Harry WE1X (SK), look first for the simple things. I should have listened to myself...

Thanks, guys

_________________
Carl
WA1KPD


Top
 Profile  
 
 Post subject: Re: Cathode Voltage Equals Plate Voltage
PostPosted: Nov Wed 18, 2020 3:37 am 
Member
User avatar

Joined: Sep Wed 10, 2014 2:01 am
Posts: 2285
Location: Costa Mesa, California
We have all been there. I spent several hours on a Hammarlund one day before it finally occurred to me to read the manual--which brought the problem into focus.

Norm

_________________
KK6IYM


Top
 Profile  
 
 Post subject: Re: Cathode Voltage Equals Plate Voltage
PostPosted: Nov Wed 18, 2020 10:36 am 
Member

Joined: Mar Tue 10, 2020 5:11 am
Posts: 445
Location: Mission Viejo, CA
I wasted 2-1/2 hours one night right after I'd removed the front panel from my SX-101A, then immediately dug into recapping the power supply without bothering to turn it back on before replacing capacitors to check it still worked after removing the knobs and front panel. I turned it on when I was done and lo, no signals. There was audio but it didn't sound loud. Then I disgustedly made room on the bench for my scope, signsl generator, DMM, picked that heavy chassis up and placed it this way, then awhile later had to move it that way when I still hadn't found the problem, etc. etc. ad nauseum.

Then while following the diagram and wires under the chassis, mine eyes fell on...

... the Send-Receive switch.

:oops: :oops: :oops: Uh-huh.

Removing the front panel required removing the four toggle switches on the panel. Then without any front panel to show what the switches were, nor which direction they should be...

SteveH


Top
 Profile  
 
 Post subject: Re: Cathode Voltage Equals Plate Voltage
PostPosted: Nov Wed 18, 2020 11:09 pm 
Member

Joined: Jun Mon 24, 2013 3:00 pm
Posts: 1695
Location: Champaign IL 61822
That's terrible design. 175 volts is far too high on an ordinary tube cathode.
Only special ones like CRTs and tubes for cascode RF amps are really designed
to take that.

Its OK to cut off tubes that way, but the voltage should be clamped to somewhere
in the 20-40 volt range.


Top
 Profile  
 
 Post subject: Re: Cathode Voltage Equals Plate Voltage
PostPosted: Nov Wed 18, 2020 11:14 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 15335
Location: S. Dartmouth MA 02748-1225 USA
External contact on T-R relay to mute receiver...

_________________
List' & I will Enchant Thine Ear


Top
 Profile  
 
 Post subject: Re: Cathode Voltage Equals Plate Voltage
PostPosted: Nov Thu 19, 2020 11:35 pm 
Moderator
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 22185
Location: Somers, CT
I am surprised the cathode would soar above the the grid cutoff voltage... Maybe a zener diode to clamp the cathode just above cutoff?

_________________
Just because it can be done doesn't mean it should be done.


Top
 Profile  
 
 Post subject: Re: Cathode Voltage Equals Plate Voltage
PostPosted: Nov Fri 20, 2020 3:59 am 
Member

Joined: Jun Mon 24, 2013 3:00 pm
Posts: 1695
Location: Champaign IL 61822
Peter Bertini wrote:
I am surprised the cathode would soar above the the grid cutoff voltage... Maybe a zener diode to clamp the cathode just above cutoff?


As-is the cathodes are connected to B+ through a 100K resistor. Even at that
max current its not good for the heaters. One little resistor from the bottom of the
RF gain control would clamp it at just above cutoff. But it and the two lines
in the assembly manual would cost money.


Top
 Profile  
 
 Post subject: Re: Cathode Voltage Equals Plate Voltage
PostPosted: Nov Fri 20, 2020 4:03 am 
Member

Joined: Jun Fri 27, 2008 3:10 am
Posts: 136
Location: Damariscotta, ME
Quote:
One little resistor


Of what value?

_________________
Carl
WA1KPD


Top
 Profile  
 
 Post subject: Re: Cathode Voltage Equals Plate Voltage
PostPosted: Nov Fri 20, 2020 1:09 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 2231
Location: Potomac, MD 20854
In the interest of Carl's shred of dignity, and echoing the embarrassing tales from other posters, yesterday I panicked while working on a Jackson 658 tube tester. I wanted to check the B+ fuse and unscrewed the cap from the fuse holder. The cap has a socket that snugs around the end of the fuse, but the fuse did not come out. It was jammed in the holder. What would I do?

I tried several times to get the cap to grab the fuse with no success.

Then, finally, the aha! moment: I turned the tester over and the fuse fell right out.

If Carl will permit me to join him in pursuit of dignity, I'd be grateful.

_________________
Avery W3AVE


Top
 Profile  
 
 Post subject: Re: Cathode Voltage Equals Plate Voltage
PostPosted: Nov Fri 20, 2020 5:14 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 9804
Location: Beaver Falls, PA. USA
Another one that will fool you is the switch for a separate receive antenna, on some transceivers. Been there, done that... :oops:

_________________
Tim KA3JRT


Top
 Profile  
 
 Post subject: Re: Cathode Voltage Equals Plate Voltage
PostPosted: Nov Fri 20, 2020 7:45 pm 
Member

Joined: Jun Mon 24, 2013 3:00 pm
Posts: 1695
Location: Champaign IL 61822
Avery wrote:

Then, finally, the aha! moment: I turned the tester over and the fuse fell right out.


Fine, except for TVs or certain German boatanchors weighing what ... 100 kilograms?

My tip: there is sticky stuff intended for sticking notes on walls, in the school or stationary
section of the drugstore. Little bits are great for pulling out such things. Or, even stickier
but harder to cut to size, double sided masking tape or duct tape.

Doug McDonald


Top
 Profile  
 
 Post subject: Re: Cathode Voltage Equals Plate Voltage
PostPosted: Nov Fri 20, 2020 8:18 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 2231
Location: Potomac, MD 20854
dtvmcdonald wrote:
Avery wrote:

Then, finally, the aha! moment: I turned the tester over and the fuse fell right out.


Fine, except for TVs or certain German boatanchors weighing what ... 100 kilograms?

My tip: there is sticky stuff intended for sticking notes on walls, in the school or stationary
section of the drugstore. Little bits are great for pulling out such things. Or, even stickier
but harder to cut to size, double sided masking tape or duct tape.

Doug McDonald


Good tip. But I was so fixated on why the clip on the back of the cap wasn't grabbing the fuse that it wouldn't have occurred to me to try to pull it out with something sticky. I have no idea why I thought of tipping the instrument forward.

_________________
Avery W3AVE


Top
 Profile  
 
 Post subject: Re: Cathode Voltage Equals Plate Voltage
PostPosted: Nov Fri 20, 2020 10:40 pm 
Member
User avatar

Joined: Oct Tue 11, 2016 4:41 am
Posts: 251
Location: Alexandria, Virginia
WA1KPD wrote:
Ok, in an attempt to retain whatever shred of dignity I might have, the voltages snapped right in place when I wired up an external plug for the 8 pin accessory socket with pins 1 and 6 shorted together.

I used to tell my brother in law, Harry WE1X (SK), look first for the simple things. I should have listened to myself...

Thanks, guys


Hi Carl. I recently was trying to sort out the side tone circuit in a Swan transceiver and after getting that working thought I had a bad tube or other failure in the IF stages. I got as far as the grid of the first IF tube with the scope when I saw the accessory plug on the desk. I had disconnected the outboard VFO so I could turn the transceiver upside down and forgot to insert the plug into the accessory socket. :D

73,

Brad K4RT


Top
 Profile  
 
 Post subject: Re: Cathode Voltage Equals Plate Voltage
PostPosted: Nov Fri 20, 2020 11:10 pm 
Member

Joined: Jun Fri 27, 2008 3:10 am
Posts: 136
Location: Damariscotta, ME
A good friend who can remain nameless was working on an early Atwater Kent model 42 TRF when it suddenly died. He spent untold hours checking every bit of the circuits and just would occasionally hear a slight signal in the speaker. He posted his problem and emailed several friends and although he got a ton of ideas, he tried out, nothing would fix it.

He asked if he could drop it off so I could put a new pair of eyes on it. I put it on the bench and without even thinking before I started it up I put an ohmmeter on the model E (the big round one) speaker leads,- 480 megs!

Opened up the speaker and one of the internal leads on the speaker, factory fastened with a stud and nuts, had come loose, Tightened it back up plugged it all in and it worked like a charm. I felt bad calling him......

_________________
Carl
WA1KPD


Top
 Profile  
 
Post New Topic Post Reply  [ 17 posts ]  Moderator: Sandy

All times are UTC [ DST ]


Who is online

Users browsing this forum: w3jn and 23 guests



Search for:
Jump to:  


































Privacy Policy :: Powered by phpBB