Need some guidance here... raplaced several tubes (42 - audio) this brought sound to the unit. Then replaced 57 detector and one 58. Seem to get the stonger stations at times.

(I suspect the volume control might be whacky.)

Then howling and motorboating kick in. My labrador retriever doesn't like this at all.

Terry F St. Louis

You must, at very least, replace the original electrolytics. When these develop high internal series resistance, they are no longer capable of filtering high frequencies out of the B supply.

This radio also requires shields on the tubes, though it will work alright without them. Howls and motorboating will develop at higher volumes without the shields. The volume control controls the amplification of the RF stages.

I completely recapped my 148, with metalized film caps stuffed in the 'Cub' condensers (a bit of work), and new electrolytics hidden in an old electrolytic box capacitor underneath, and the set performs very well.

:You must, at very least, replace the original electrolytics. When these develop high internal series resistance, they are no longer capable of filtering high frequencies out of the B supply.
:
:This radio also requires shields on the tubes, though it will work alright without them. Howls and motorboating will develop at higher volumes without the shields. The volume control controls the amplification of the RF stages.
:
:I completely recapped my 148, with metalized film caps stuffed in the 'Cub' condensers (a bit of work), and new electrolytics hidden in an old electrolytic box capacitor underneath, and the set performs very well.
:
----------------------------
Still working on the set. I found a "double" 0.1mfd capacitor with one wire broken. If I replace can I just use two 0.1 mfd 600V caps?

The one I found with the broken wire has a band around the middle and it looks like this band is chassis ground with one lead back to the volume control and one lead to a #58 pin 3.

Can anyone confirm?

Thanks for all of your help.
Terry F - St. Louis

Hi Terry,
Looking at the schematic, one 0.1MFD capacitor goes to the screen grid of the first 58. The other goes to the antenna input transformer.
The schematic does not state that they are housed in the same container, but it wouldn't show up on the schematic.
Broken wire or not they need to be replaced. Using two 0.1uF capacitors will work just fine.

All the Best,

Bill Grimm

A broken wire could cause this condition in any case. If the ground were broken (unlikely), it could cause signal connection between the different parts of the circuit. If the screen grid B+ filtering were lost due to a broken wire here, this could cause howling and feedback.

....etc.

Tom,

Got the radio working. It was a combination of the problems you, as well as others, described.

THANK YOU VERY MUCH!
Terry F. St. Louis

:Need some guidance here... raplaced several tubes (42 - audio) this brought sound to the unit. Then replaced 57 detector and one 58. Seem to get the stonger stations at times.
:
:(I suspect the volume control might be whacky.)
:
:Then howling and motorboating kick in. My labrador retriever doesn't like this at all.

Terry:
Motorboating is almost always caused by a large capacitor not...er, well...capacitating. Check filter caps and anything bypassing to ground.
Lewis

P. S. The temperature in the Atlanta area is in the sixties, too cold for the cat, but my lap is warm and I am trying to repair something with a cat in my lap. Interesting practice.
LL

:
:Terry F St. Louis
:

Also be sure 57 and 58 tubes have shields which make good contact with the chassis. Poor shielding on these tubes can cause oscillation.

Norm

:Need some guidance here... raplaced several tubes (42 - audio) this brought sound to the unit. Then replaced 57 detector and one 58. Seem to get the stonger stations at times.
:
:(I suspect the volume control might be whacky.)
:
:Then howling and motorboating kick in. My labrador retriever doesn't like this at all.
:
:Terry F St. Louis
: