[R-390] R-390 Problems Update

[Drew Papanek]

In a message to David Hallam, James Miller wrote:

>With just a paper clip jumper you may be putting too much voltage on the 
>BFO
>and VFO tube filaments.  A 22 ohm (5-10W) resistor is preferred...<snip>

The transformer winding supplying the PTO and BFO tube heaters supplies 
nominally 25.2 VAC.
In the original configuration; the ballastube drops about 12.6 volts, 
leaving 12.6 volts for the seriesed
6BA6 tube heaters in the PTO and BFO.

With "Two 12BA6 and a Paperclip", 25.2VAC is applied to the seriesed 12BA6 
tube heaters in the PTO and BFO.  Each 12BA6 receives its rated 12.6 volts.  
No additional series resistance is required.

That is the simplest Ballasubstitution.  12BA6 is probably the most common 
tube ever made, being the IF tube of choice in millions of radios with the 
"All American Five" tube lineup.  No trouble finding those!

Drew

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