[Drake] Early R-4B?

Sat Jan 22 12:37:06 EST 2005

Hi Chris,

The consensus is that this one is an R-4B prototype, often offered by Drake 
to experienced hams (like W6AM, who was known to have received such items) 
for field testing prior to a new model introduction . This would account for 
the lack of chassis and cabinet markings, the different passband tuning 
setup (likely same as the R-4A), the kit-like workmanship, and the 
unterminated/unused wiring.

Wayne, VE3EFJ, (who has a great site for Drake product info at 
http://www.zerobeat.net/drakelist/drakemod/drmodtoc.html by the way) offered 
specifics as to determination of model by observation of the noise blanker 
circuitry (self derived AGC on the R-4B) and the FET driven PTO.  The 
presence of these circuits proved the receiver to indeed be primarily an 
R-4B.

The missing L6 in the low pass filter at the PTO output looks to be the 
result of someone having removed and reinstalled the PTO and, for some 
reason having eliminated the LPF by removing L6 and connecting the coax lead 
directly to the PTO output lead.  Wayne's recollection was that these LPF 
circuits were designed with Q=1, so the reactance of L6 would be the same as 
one of the caps (330pf) at 6MC. I calculated the value to be about 21 uH, so 
I may try to make or buy one and restore the filter circuit.

Wayne agreed that the extra wire from the PTO is indeed likely the FSK 
connection shown on the schematic. A shielded connection to this wire would 
be brought out to an RCA jack if the receiver were to be used for FSK in a 
transcieve mode with a T-4X.

I repaired the shaft coupling for the passband tuning shaft using 
appropriate diameter SS tubing from ACE hardware. The replacement required a 
slight modification of the flat on the shaft to accomodate the flat 
retaining spring, and  I used a hex crimper (used for F connector crimping 
on RG-59) to secure the tubing to the switch shaft (a purist would have made 
a coupling with an ID which would produce a press fit on the switch shaft, 
but I was not motivated toward undetectable originality).  I remain puzzled 
as to how the original coupling became damaged and split.

73 de Stu  W7FE

----- Original Message ----- 
From: "Chris Codella, W2PA" <w2pa at arrl.net>
To: "w7fe" <w7fe at cox.net>
Sent: Saturday, January 22, 2005 8:06 AM
Subject: Re: [Drake] Early R-4B?

> Stu,
>
> This was an interesting post.
> I was wondering if you ever got a reply to this posting.  I didn't see 
> anything further, except one short comment, on the reflector.
>
> 73,
> Chris, W2PA
>
> w7fe wrote:
>
>> To those familiar with the R-4B:
>>
>> I recently acquired a somewhat corroded but working R-4B.  During my 
>> initial inspection and subsequent cleaning and repair process, I've run 
>> across some rather puzzling things:
>>
>> 1.  This one has no chassis markings at all, not even a serial number. 
>> There is enough of the original copper plating left to indicate that no 
>> markings had ever been applied.  There are no silk-screened 
>> switch/jack/pot i.d. markings on the case exterior either. Unusual?
>>
>> 2. The passband tuning/selector assembly is not as described in the 
>> alignment procedure or as pictured in the manual.  The passband tuning 
>> shaft is connected to a little butterfly variable capacitor, not to a 
>> mechanism to vary the position of the slugs in the coils.  This is 
>> visible because there is no can over the passband tuning circuitry, just 
>> a u-shaped mounting bracket, open on the right and left sides.  The 
>> passband selector is actually a rotary switch, with a lot more components 
>> around it than are shown on the schematic. Does this perhaps suggest a 
>> very early model, maybe before they developed the mechanism to tune the 
>> coil slugs and simplified the circuit for passband selection?
>>
>> 3. L6 in the output filter on the PTO is not present at all. The center 
>> conductor of the co-ax (which goes to the xtal-vfo slide switch) is just 
>> lap-soldered to an unshielded wire which comes from the PTO output. 
>> C132 and C149 are in place (on the nearby audio board), however.  I can 
>> see where L6, the co-ax, and the PTO output lead should probably have 
>> been connected on the adjacent audio board, but it appears that nothing 
>> has ever been connected to those points. Does anyone know what value L6 
>> should be, or its physical characteristics?
>>
>> 4. There is a black/white wire coming from the PTO and connecting to 
>> nothing.  This must be the FSK connection as per the schematic, but it's 
>> just flying free.  Should it connect somewhere, like to one of the lugs 
>> on the adjacent audio board?
>>
>> 5. Generally, many of the solder joints are poor, some cold, most with 
>> excess solder, and several places exhibit wire insulation which has been 
>> melted by an errant iron.  The wire harnessing and lead dress are quite 
>> sloppy; in fact, there are wires attached to the filament pins on V2's 
>> socket which have been clipped off to about 1/4" and left in place, 
>> connecting to nothing. Also, there is a wire attached to a ground point 
>> near V8's socket (which is the same color as V8's filament lead which 
>> connects at an adjacent terminal point) which is clipped off to about 1" 
>> and goes nowhere. Is this lack of  good workmanship  weird, or what?
>>
>> 6. Finally, another goofy observation for those who have were interested 
>> enough to read this far:
>>
>> The brass shaft coupling to the passsband selector switch shaft was 
>> cracked and split!  I'm baffled as to how this might have happened. It 
>> looks almost as if water got into it and froze, splitting the coupling. 
>> Has anyone seen this condition before?  Anyway, it results in 
>> unacceptable excess play in the little lever actuator for the passband 
>> selector. Now that I have removed the coupling (in several pieces), I 
>> think that they used 5/16 OD brass tubing, with a little flat spring 
>> wedged inside to produce a tight connection between the two 
>> shafts...looks fixable with some hardware store tubing. Has anyone else 
>> had occasion to do this repair?
>>
>> 73 de Stu   W7FE
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