[R-390] Crystal Oven Heater Resistance

[Roy Morgan]

On Apr 22, 2008, at 6:19 PM, Mike Hardie wrote:
> I tracked down the resistance to be the heater in HR202.  With  
> HR202 pulled the resistance at J208-F is infinity.  Can anyone  
> confirm whether or not the manual figure of 100 ohms figure is  
> correct?

Mike,

Check your oven. Normally, the heater voltage is on the label.  The  
R-390A/URR uses a 6.3 volt oven, and the R-390/URR (the "non-A") uses  
a 26.5 volt heater.  There may have been a swap.

It appears from info I have here that the heater is from pin 3 to 1  
and the switch is from pin 1 to 7.

I have four 26.5 volt ones handy: they measure 143, 140, 158, and 316  
ohms, pin 3 to  pin 7.  The first three are Ovenair type RT-2.  The  
last is Bliley typeTCO-1C and is marked 0.3 amps.  There may be  
something amiss with its switch since pin 1 to 7 measures about 100  
ohms.

Normally these things use about 5 watts.  The Bliley above will use  
about 8 watts.

  A Bliley typeTCO-1A marked 6.3 volts 0.85 amps has no continuity to  
pin 3.  Pins 1 and 7 show a couple tenths of an ohm. I'd guess the  
switch is ok but the heater is open.  This one would use about 5.4  
watts.

The James Knight unit I just pulled out of an R-390A is type JK09,  
6.3 volts, and measures 6.7 ohms pin 3 to 7.

Notes:
- You didn't say which radio you have (maybe the oven is not HR-202  
in the "non-A")
- The A radio has two crystals in one oven, 17 mc and 200 kc. The non- 
A radio has only the 1 mc crystal in the oven, which is mounted below  
the chassis on the calibrator module.
- These oven units were used in mobile radio service too, and some  
are meant for 12 volts, while others can be inserted in a two-keyway  
socket to allow for both 6 volt and 12 volt operation.
  - The Heaters switch on the back of the R-390A does not control  
HR-202.  It only runs the crystal oscillator deck oven and the PTO  
heater.

Roy


Roy Morgan
k1lky at earthlink.net
Lovettsville, VA 20180