[R-390] Bugeye BFO removal

[nryan at mchsi.com]

Hi, Roger, Ben, and Group,

Roger is right about the stop tab.  You need to have it in place to prevent damage to the BFO slug or bellows.

Here is how I center the BFO knob on 455 KC:

Warm up receiver.

Set FUNCTION control to MGC.  

Tune receiver to 00.000.  CARRIER LEVEL meter will read very high.  

Set BANDWIDTH to .1 KC.  

Limit the RF GAIN to approximately 3/4 full scale reading on CARRIER LEVEL meter as you peak the signal with the KILOCYCLE CHANGE.

Switch on BFO.  Zero beat tone with BFO PITCH knob.

BFO PITCH knob should be at 0.  If not, loosen knob setscrew, set at 0 and tighten setscrew.  Check that BFO PITCH knob turns freely, but is limited by the stop tab to + or - 3 KC.

73 de Norman, KG4SWM


----- Original Message -----
From: Flowertime01 at wmconnect.com
To: r-390 at mailman.qth.net
Sent: Sat, 11 Jun 2011 19:42:21 -0500 (CDT)
Subject: Re: [R-390] Bugeye BFO removal

Ben,

Once you remove that bug eye you may send it to me here in South Carolina. 
My disposal site paper work is all in proper order.

Do remove the three screws.
The outer ring and counter part will then pull off.
Then you need to find a very small hex Allen to loosen two set screws in 
the aluminum big ring knob that serves as the BFO knob on the counter.

Loosen the set screws and pull the big ring knob off the shaft.

The big back black plate is held to the front panel with the BFO shaft 
bushing and nut.

Find a couple 1/2 or 9/16 wrenches and remove the nut from the bushing.
The big black plate can then be removed.

So now how you going to adjust your BFO?

You need to locate a stop tab washer and knob.

No stop tab washer (looks like the one behind the function switch) and the 
BFO shaft will do several rotations. This will expand and compress the 
bellows coupler between the BFO shaft in the IF deck (and front panel extension) 
and the BFO slug shaft that screws in and out. Keep this up and you will 
break something. Murphy says it will be the most un- obtainable part that 
breaks. What ever part you do not have a spare for.

So make a stop washer or acquire one and retain it to the front panel with 
the front panel bushing. The bushing used on the micro dial (bug eye thing) 
may be longer than the original. Put the bushing nut on the inside of the 
front panel. Install a Large BFO knob.

Why not just un-assemble every thing, give it a good bath, relube it all, 
and reassemble it with reasonable spacing so it works nice and smoothly. Tell 
every one you own a previous spook receiver and not just a stock signal 
corp receiver.

The extension shaft from the IF deck through the front panel is standard 
stock issue. It was not changed to install the micro dial and thus needs no 
changes to get back to a stock knob. 

One conspiracy theory is that the micro dials were introduced to provide a 
source of spare replacement knobs. By installing a micro dial one knob was 
free from the BFO shaft to be applied else where on the front panel and thus 
no one needed to admit a part had been lost. This is just a theory as spare 
knobs were available. The stock number in the parts manual was good. Both 
R390 and R390/A knobs could be ordered.

Go ahead, ask me how you get the counter to zero with the BFO at exactly 
455.

And then ask how you get the big knob to run smooth in the counter.

Those two questions are in order.

What keeps you from screwing up the bellows coupler with a micro dial? 
Nothing but common sense. How far a micro dial will dial up or down is dependent 
on the mechanical limits of the particular bellows in an IF deck and its 
current placement. After years a bellows may be stretched or compressed. This 
thus limits the range of the device under examination. Changing to a micro 
dial does not change how far you want to twist the BFO. That 180 - 270 
degrees or rotation is the same for a stock knob or micro dial. The counter just 
makes a better position indicator than the stock knob against the stock front 
panel.

Roger AI4NI