[R-390] Heater Dropping Resistor R536

[Jon Schlegel]

Hello All,

I'm working on the IF module from my R-390A and just noticed that 
V507 (Limiter, 5814A) has a 4 ohm resistor (R536) in series with the 
heater.  For the moment assuming that the heater's resistance doesn't 
change over temp, this means that V507's heater draw is about 250 mA 
@ 5.3 VAC instead of the nominal 300 mA @ 6.3 VAC.  Heater power is 
about 70% of nominal.  Anybody know what's going on here?  Isolation 
from the rest of the heater string?  Does the Limiter depend on soft 
emission?  Don't think we're at a frequency where cathode back 
heating is an issue <G>.

Also R536 looks to be about a 5 watt WW and it's dissipating a cool 
1/4 watt.  Guess they wanted the stability of a WW.

Regards,
Jon Schlegel WA3MVM