Referring to the schematic:
http://www.nostalgiaair.org/PagesByModel/330/M0001330.pdf

Can I replace the two R19 flexible resistors with
separate 25 ohm resistors and 2 lengths of wire?
If so what wattage would you suggest?
The wire insulation is crumbling and they measure
only about a third of the rated resistance they are
suppose to have. I have not disconnected them to measure them. I am measuring them while still connected...
Wondering why they used this type of resistor?
Bob E.

Bob: you can't measure those filament resistors while in the ckt. Study the schematic, and I think you will see why - there are various components in parallel with the resistors, including the filament winding of the xfmr. You can lift one lead and measure.

Those flexible resistors are most often OK.

If you need to replace them (which I rather doubt), you can figure the required wattage. The two R19 resistors are in series across the 6.3-V filament winding of the xfmr, so they see 3.15 V each. Power = V^2/R = 3.15^2/25 = 0.4W. Double for safety, so use 1W or higher.
Doug

:Referring to the schematic:
:http://www.nostalgiaair.org/PagesByModel/330/M0001330.pdf
:
:Can I replace the two R19 flexible resistors with
:separate 25 ohm resistors and 2 lengths of wire?
:If so what wattage would you suggest?
: The wire insulation is crumbling and they measure
:only about a third of the rated resistance they are
:suppose to have. I have not disconnected them to measure them. I am measuring them while still connected...
: Wondering why they used this type of resistor?
:Bob E.

Doug,
Thanks,
I thought that might be the case...but another question. These dual resistors have thick rubber
insulation rather than cloth type. They have hardened and crumbled away in spots sometimes an inch or so in places exposing the very thin wire..What,
if after testing them correctly and they test ok should I do to the wire/insulation. Should I just put some shrink tubing over the length of it?
Thanks, Bob

:Bob: you can't measure those filament resistors while in the ckt. Study the schematic, and I think you will see why - there are various components in parallel with the resistors, including the filament winding of the xfmr. You can lift one lead and measure.
:
:Those flexible resistors are most often OK.
:
:If you need to replace them (which I rather doubt), you can figure the required wattage. The two R19 resistors are in series across the 6.3-V filament winding of the xfmr, so they see 3.15 V each. Power = V^2/R = 3.15^2/25 = 0.4W. Double for safety, so use 1W or higher.
:Doug
:
:
::Referring to the schematic:
::http://www.nostalgiaair.org/PagesByModel/330/M0001330.pdf
::
::Can I replace the two R19 flexible resistors with
::separate 25 ohm resistors and 2 lengths of wire?
::If so what wattage would you suggest?
:: The wire insulation is crumbling and they measure
::only about a third of the rated resistance they are
::suppose to have. I have not disconnected them to measure them. I am measuring them while still connected...
:: Wondering why they used this type of resistor?
::Bob E.

Those resistors will get hot. Shrink tubing should be OK, I think - the resistors' heat should shrink it. Or maybe a light coating of silicon sealer? If you try the silicon sealer, wait for it to cure (and become non-conductive) before powering up the radio.

As long as the resistors aren't touching anything, the liklihood of a problem is low.

I believe those flexible resistors were wirewound. So, they should either be OK or open.
Doug

:Doug,
:Thanks,
:I thought that might be the case...but another question. These dual resistors have thick rubber
:insulation rather than cloth type. They have hardened and crumbled away in spots sometimes an inch or so in places exposing the very thin wire..What,
:if after testing them correctly and they test ok should I do to the wire/insulation. Should I just put some shrink tubing over the length of it?
:Thanks, Bob
:
:
:
::Bob: you can't measure those filament resistors while in the ckt. Study the schematic, and I think you will see why - there are various components in parallel with the resistors, including the filament winding of the xfmr. You can lift one lead and measure.
::
::Those flexible resistors are most often OK.
::
::If you need to replace them (which I rather doubt), you can figure the required wattage. The two R19 resistors are in series across the 6.3-V filament winding of the xfmr, so they see 3.15 V each. Power = V^2/R = 3.15^2/25 = 0.4W. Double for safety, so use 1W or higher.
::Doug
::
::
:::Referring to the schematic:
:::http://www.nostalgiaair.org/PagesByModel/330/M0001330.pdf
:::
:::Can I replace the two R19 flexible resistors with
:::separate 25 ohm resistors and 2 lengths of wire?
:::If so what wattage would you suggest?
::: The wire insulation is crumbling and they measure
:::only about a third of the rated resistance they are
:::suppose to have. I have not disconnected them to measure them. I am measuring them while still connected...
::: Wondering why they used this type of resistor?
:::Bob E.

Another idea - paint them with "Electrical Insulation in a Can." That's not the exact name, but it's something along those lines. Comes in a small yellow can with a brush mounted on the inside of the cap (like rubber cement cans). Sold at hardware stores.

If I'm correct about those resistors being wirewound, shouldn't be necessary to test them - they would either work or not.
Doug