[AMRadio] R 388

John Lawson jpl15 at panix.com
Wed Jul 11 21:45:36 EDT 2007

On Wed, 11 Jul 2007, kk4tr wrote:

> THe problem is the band spread seems to be too wide on all bands and it has 
> been this way all the time.

  By "change the slide rule dial" tdo you mean that you are adjusting the 
'ZERO" screw, or are you actually changing the location of the pointer 
along the dial cord?

   At any rate, I would suggest a bit of 'triage': Remove the bottom cover 
of your rig, go to the place in your schematics where it shows the PTO 
injection point ( I'm on business travel and can't recall the VT-number of 
the tube). Using a known-accurate 5-digit frequency meter, connect to that 
point, to observe the output frequency of the PTO. I stress that the freq 
meter must have sufficient digits to read megahertz to 10 cycles, and of 
known accuracy.

  Find a strong WWV signal, 2.5, 5, or 10 Mhtz, and set the dials 
mechanically so that they read properly - ie. if you're centered up on WWV 
at 10 Mhtz, the slide rule should be on '10' and the KHtz dial on 0'.

   Now roll down to the low end of the dial, go to '0' on the KHtz knob at 
the exact end of the slide rule - note the frequency of the PTO.  Roll up 
to the top end of the dial, be sure the Khtz knob is on '0', and measure 
the PTO frequency at this point.

   This will tell you immediately if the PTO frequency span is too narrow, 
as I suspect it is.  If it is grossly 'narrow, it is likely that you will 
need to R&R the PTO for further work... the crystal calibrator, BTW, is 
it's own signal source and is independent of the PTO.  The PTO is the only 
source for frequencies for tuning in the R-388.

  But first collect the 'real' data so you can make that determination. 
Also, it should be a matter of course that you check the power supply 
voltages to be sure they're in tolerance.

   And for sure let's keep this on the List - you never can tell when 
someone else might be having the same problem and need the exact 
info/experience that you're going to dig up.  A lot of my BA Radio Lore 
came from exactly this kind of 'mail copying', if yahknowhuttamean...

   I imagine others will add to this, suggest other ideas, etc.




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