[Masonparker]

Working on a A72T3  and I have a question about a Condenser.    The condenser Part # 505454 states the following - (.05 Mfd. 400 volt (low impedance at 455kc -- do not substitute ordinary condenser)

I look on Just Radios and I didn't see any condensers listed as low impedance.  What type of condenser should I use to replace the existing one???

Thanks 

[David]

With the build quality of todays caps I would just go with a .047 at 630 volts. http://www.nostalgiaair.org/Resources/128/M0021128.htm

[Mondial]

Sometimes manufacturers of AC/DC radios used bypass capacitors which were designed to be series resonant at the 455kc IF frequency. They were used to AC ground circuit common (which was connected to one side of the AC line) to chassis ground. This type of cap will have a very low AC impedance at the IF frequency and therefore make an excellent bypass.

Philco did something similar by wrapping turns of insulated wire around a regular paper bypass cap.

Typically you can replace the special cap with a similar value modern film cap, but you may have to experiment if you run into problems with squeals, or oscillations of the IF stage.

[morzh]

Тоday's caps, especially the ceramic ones (and you do not need high voltage, it is a Cathode bypass) have very low impedance overall, and so you might not need to worry about the resonance as the impedance overall might be lower than the resonance one for the origianl cap.

[Masonparker]

thanks for the help