Missing capacitor values on Radiola 18

6/22/2010 1:08:16 AMKen K.

I'm recapping a Radiola 18 for a friend. I've got the power supply and the four .5 mfd bypass caps done. However, there are three small, open-cased mica capacitors in the RF stages that the schematic does not list a value for, nor is there anything printed on them. I know mica caps don't normally go bad but this set has an unusual oscillation and I feel that one may be breaking down under strong signal levels. Does anybody know the values of these mica caps? Thanks!

6/22/2010 2:03:05 AMWarren

Might have a look at this for the "Mystery Componet" It could be the oscillation problem.

http://www.nostalgiaair.org/References/Articles/Singles/Radiola18-2.htm

6/22/2010 10:40:08 AMNorm Leal

Here is information on Radiola 18:

http://www.nostalgiaair.org/References/Articles/Singles/Radiola18-2.htm

The mystery cap mentioned may be your problem? It's actually for neutralizing the stage. Tubes have capacity between plate and grid which couples signal through. This cap adjusts the amount of signal in the opposite polarity to cancel.

Cap to grid of detector can be 250pf. Plate cap on this tube can be .001 mf. These should be ok.

You may not be able to turn strong stations all the way down. Adding a shield under the RF chassis helps eliminate this problem. This may also stop unwanted oscillation.

Norm

:I'm recapping a Radiola 18 for a friend. I've got the power supply and the four .5 mfd bypass caps done. However, there are three small, open-cased mica capacitors in the RF stages that the schematic does not list a value for, nor is there anything printed on them. I know mica caps don't normally go bad but this set has an unusual oscillation and I feel that one may be breaking down under strong signal levels. Does anybody know the values of these mica caps? Thanks!
:

6/22/2010 5:50:22 PMDoug Criner

Have you tried shuffling the '26 tubes? They may have a bit different value of interelectrode capacitance and thus more prone to oscillation.

6/22/2010 6:08:55 PMKen K.

:Have you tried shuffling the '26 tubes? They may have a bit different value of interelectrode capacitance and thus more prone to oscillation.
:

6/22/2010 6:16:15 PMKen K.

::Have you tried shuffling the '26 tubes? They may have a bit different value of interelectrode capacitance and thus more prone to oscillation.
::
:

6/23/2010 2:11:50 PMKen K.

:::Have you tried shuffling the '26 tubes? They may have a bit different value of interelectrode capacitance and thus more prone to oscillation.
:::
::
:I guess it's time to take the plunge and spend $40 on a digital capacitance meter...