Hello All,
Recapped all caps and replaced out of tolerence resisters. Radio motorboats slowly on broadcast and very rapidly in shortwave. Motorboating goes away when 6K7 is touched. Reception is understandable but garbled. I have been trying to figure this one out for a couple of years- try to get it going, get frustrated, put it up,try it again etc.....
Any advice gratefully accepted.
Many thanks,
Jon.

Jon, you say: "motorboating goes away when 6K7 is touched." I assume that you're touching the grid cap?

When you touch it, is it garbled or OK?

Temporarily bridge the output filter cap #49 with another cap of similar value, observing correct polarity - any change?

Check the grid resistance from grid to ground on the AF tube and the audio detector - make sure it's not open.

Here's the schematic:
http://www.nostalgiaair.org/PagesByModel/374/M0024374.pdf

:Hello All,
:Recapped all caps and replaced out of tolerence resisters. Radio motorboats slowly on broadcast and very rapidly in shortwave. Motorboating goes away when 6K7 is touched. Reception is understandable but garbled. I have been trying to figure this one out for a couple of years- try to get it going, get frustrated, put it up,try it again etc.....
:Any advice gratefully accepted.
:Many thanks,
:Jon.

Doug, Thanks for responding. Yes, I meant the grid cap. When touching grid cap all reception goes away.
I will bridge # 49 cap and see what happens. Many thanks, Jon.
:Jon, you say: "motorboating goes away when 6K7 is touched." I assume that you're touching the grid cap?
:
:When you touch it, is it garbled or OK?
:
:Temporarily bridge the output filter cap #49 with another cap of similar value, observing correct polarity - any change?
:
:Check the grid resistance from grid to ground on the AF tube and the audio detector - make sure it's not open.
:
:
:Here's the schematic:
:http://www.nostalgiaair.org/PagesByModel/374/M0024374.pdf
:
::Hello All,
::Recapped all caps and replaced out of tolerence resisters. Radio motorboats slowly on broadcast and very rapidly in shortwave. Motorboating goes away when 6K7 is touched. Reception is understandable but garbled. I have been trying to figure this one out for a couple of years- try to get it going, get frustrated, put it up,try it again etc.....
::Any advice gratefully accepted.
::Many thanks,
::Jon.

Doug, Thanks for responding. Yes, I meant the grid cap. When touching grid cap all reception goes away.
:I will bridge # 49 cap and see what happens. Many thanks, Jon.
::Jon, you say: "motorboating goes away when 6K7 is touched." I assume that you're touching the grid cap?
::
::When you touch it, is it garbled or OK?
::
::Temporarily bridge the output filter cap #49 with another cap of similar value, observing correct polarity - any change?
::
::Check the grid resistance from grid to ground on the AF tube and the audio detector - make sure it's not open.
::
::
::Here's the schematic:
::http://www.nostalgiaair.org/PagesByModel/374/M0024374.pdf
::
:::Hello All,
:::Recapped all caps and replaced out of tolerence resisters. Radio motorboats slowly on broadcast and very rapidly in shortwave. Motorboating goes away when 6K7 is touched. Reception is understandable but garbled. I have been trying to figure this one out for a couple of years- try to get it going, get frustrated, put it up,try it again etc.....
:::Any advice gratefully accepted.
:::Many thanks,
:::Jon.
Doug, Tried other caps at # 49, no change. When checking resistance grid to ground, do I check between grid cap and chassis? I assume radio is off?
Jon.

Yes, Jon, unplug the radio, and measure resistance from grid to chassis. There should be some kind of measurable resistance. Otherwise, the grid can build up a negative charge, until it leaks off somehow - everytime this happens, you get a "putt" like a motorboat's putt-putt.

:Doug, Tried other caps at # 49, no change. When checking resistance grid to ground, do I check between grid cap and chassis? I assume radio is off?
:Jon.

:Yes, Jon, unplug the radio, and measure resistance from grid to chassis. There should be some kind of measurable resistance. Otherwise, the grid can build up a negative charge, until it leaks off somehow - everytime this happens, you get a "putt" like a motorboat's putt-putt.
:
::Doug, Tried other caps at # 49, no change. When checking resistance grid to ground, do I check between grid cap and chassis? I assume radio is off?
::Jon.
Doug,
With tube grid caps attached, got about 2 meg. Nothing on each tube grid to chassis with grid cap disconnected. Is this normal? Can,t tell from schematic. Jon.

Yes, measure with grid caps attached. What tubes are you measuring the 2M?

Look at the schematic. The 6V6 has R27 from grid to ground, 470K. 2M is way too high.

Have you checked the values of all your set's resistors? Depending upon what each resistor is connected with, you may need to lift one lead to get a legitimate reading. Any ones more that about 20-30% off should be replaced.

:Yes, measure with grid caps attached. What tubes are you measuring the 2M?
:
:Look at the schematic. The 6V6 has R27 from grid to ground, 470K. 2M is way too high.
:
:Have you checked the values of all your set's resistors? Depending upon what each resistor is connected with, you may need to lift one lead to get a legitimate reading. Any ones more that about 20-30% off should be replaced.

Doug,
I replaced all resisters and there is no change in performance. Still rapid motorboating in shortwave, and broadcast is still garbled but understandable and in certain spots on the dial I get a slow put-put.
Jon.
:
:

Jon, I'm out of ideas. If you want to ship me the radio I'll take a look at it. You can contact me by email.

:Jon, I'm out of ideas. If you want to ship me the radio I'll take a look at it. You can contact me by email.
Doug,
Thank you for your gracious offer but I am not giving up yet. I hope to figure this one out and in the process learn something.
Many thanks ,
Jon.

::Jon, I'm out of ideas. If you want to ship me the radio I'll take a look at it. You can contact me by email.
:Doug,
: Thank you for your gracious offer but I am not giving up yet. I hope to figure this one out and in the process learn something.
:Many thanks ,
:Jon.

I noticed that decoupling capacitor 22 is a dual cap. How did you replace it? Two .1 caps to ground would be OK. If a .1 cap was used between the two points a put-putt would be probable.

:::Jon, I'm out of ideas. If you want to ship me the radio I'll take a look at it. You can contact me by email.
::Doug,
:: Thank you for your gracious offer but I am not giving up yet. I hope to figure this one out and in the process learn something.
::Many thanks ,
::Jon.
:
:I noticed that decoupling capacitor 22 is a dual cap. How did you replace it? Two .1 caps to ground would be OK. If a .1 cap was used between the two points a put-putt would be probable.

Terry, That was it! I guess I mis-read the schematic when re-capping. The radio had been pretty well butchered when I got it and missed the dual cap. I had wired the cap directly to the band switch from the # 4 pin on the 6K7 tube. The radio performs very well on both bands and now I have learned something.
Many, many thanks to you and Doug Criner for your time and suggestions.
Regards, Jon

Terry, nice catch!