R390 non A problems

[iw5ci]

Finally i got my first Collins Radio. A Collins 390 ser. no. 90

The radio is in good shape and it appears to be in original conditions.


As far as i could test the radio vis a vis with the best european tube receiver ever made
(Rhode & Schwartz EK07-D2) the 390 shows the same sensibility and overall the same performance
in receiving BC stations.

Anyway i have to problems and i need help to fix.

Problem A: BFO .
When i tune on an am signal in 0.1 bandwidth for maximum s-meter deflection, and the in turn on the BFO
i aspect to have zero-beat. Unfortunately i have to turn the bfo pitch completely CCW to have zero beat
so the bfo is misaligned.
This cause some problems in SSB reception because if i tune lsb signal i receive it quite well but of usb signals
i have to turn the bfo completely CCW to make it readable.
So what i have to do it to realign the bfo to have zero beat in the zero position, I suppose there is a trimmer
inside to do that?!

Problem B: Calibration of the scale.

the zero adj control is intended to match the digital scale with the real frequency, i can compensate in almost
any 1 mhz segment , but on some segments i can't' do that (i would probably need 2-3 khz more of excursion of
the vfo), how can i correct those bands to make it possible to match the reading?

thank for any help.

[w3jn]

You can correct the BFO problem easily.  Remove the BFO knob.  Tune in a carrier with the .1 filter for max s-meter deflection.  Turn on the BFO.  Turn the BFO adjust shaft for zero beat.  Replace the knob with the pointer straight up at 0, and tighten the setscrew.  Be careful - the set screws are NOT Allen heads - they're Bristo (sometimes called Bristol) spline keys.  If you use an Allen wrench you'll ruin the set screw.

As for the 2 KHz off on the bands, the crystals have drifted a bit in frequency.  Common problem.  You can adjust them a *little* by adjusting the trimmer for each crystal (each crystal is used on 2 or more bands), but at the same time the trimmers should be peaked for max oscillator output.

To get around this, you can loosen the shaft coupling on the PTO and, holding the PTO shaft stationary, move the KC Adjust knob a few KC in the correct direction.  That will give you enough adjust (hopefully) for each band).  Again, the set screw on the shaft coupling is a Bristo spline key, not Allen.

[iw5ci]

Hi, unfortunately i cannot remove the bfo knob center and put again the knob, because the zero beat is obtained turning the knob completely ccw, so it's the bfo frequency that is not correct and there is noway from outside to solve the problem. I suppose there is a trimmer or variable cap to realign it.

[iw5ci]

mhmhm i see that the bfo pitch should be a inductor with a core inside with no end travel position.... my bfo have min and maximum stop position... so maybe it's why i cannot use the instructions you gave me

[w3jn]

The stop for the BFO is behind the knob.  The shaft itself has no stop at all.  Just pull the knob off, reset the BFO shaft as I described above, and replace the knob in the proper position.

[iw5ci]

wow !!! it worked.. now i have pefectly centered the bfo
...

for the second problem if i have understand, i have to look for the band where there is the worst disalignment then put the tuning a pair of kc in the right direction, then disengage the pto, rotate the main tuning knob in the right direction and engage again the pto, i have correctly inderstand?

[WV Hoopie]

Although the question is about the R-390 and not the R-390A, Chuck Rippel has some info on alignment of the R-390A IF section that might apply here as well.

In effect after a complete twisting of the IF cans and Mechanical Filters, (yeah I know the 390 doesn't have any), leave the sig-gen set to 455KC and zero beat the BFO to the sig-gen, then with the BFO shaft loose, set the knob at ZERO.

http://www.r390a.com/html/technical.htm

Craig,

[The Slab Bacon]

Be careful - the set screws are NOT Allen heads - they're Bristo (sometimes called Bristol) spline keys.  If you use an Allen wrench you'll ruin the set screw. 
 Again, the set screw on the shaft coupling is a Bristo spline key, not Allen.

Johnny,
           You left me scratching my head on this one as i have always heard of / called them "Bristol" wrenches. Are you sure about the "Bristo" thing??    

http://www.bristolwrench.com/

[w3jn]

wow !!! it worked.. now i have pefectly centered the bfo
...

for the second problem if i have understand, i have to look for the band where there is the worst disalignment then put the tuning a pair of kc in the right direction, then disengage the pto, rotate the main tuning knob in the right direction and engage again the pto, i have correctly inderstand?

Yes, exactly.  The idea is to get the adjustment range of the zero set back to where you can get it into range on every band.  You need to do this by loosening the coupler on the PTO and holding it steady while you're adjusting the KC knob.

Frank, yes the manufacturer seems to call them Bristol wrenches but the R390 and Collins manuals always seem to call them Bristo wrenches.  I seem to recall a big debate on an online forum about this, but don't remember where....

[WQ9E]

Frank, yes the manufacturer seems to call them Bristol wrenches but the R390 and Collins manuals always seem to call them Bristo wrenches.  I seem to recall a big debate on an online forum about this, but don't remember where....

That was on the boat anchors mailing list and I finally just started deleting every email with that subject line since the debate seemed to go on forever.  I believe Bristol is correct, see:  http://www.bristolwrench.com/  and click on about us.   I was first familiar with these through some mil manuals which do call them Bristol but Collins seems pretty consistent in dropping the l, probably because of an original manual mistake that propagated throughout their product line.

[The Slab Bacon]

Hmmmm.......................... got me on that one  

I do have an original military manwell for the 'A, I'll have to take a close lookie and see what it says. I never payed any attention to it. If it was an original manwell misprint / typo, it will go on forever???

[The Slab Bacon]

this has bugged me, so I did a Google search for "Bristo Wrench", it immediately asks me if I mean "Bristol Wrench". I ignored it and searched bristo, it came up with a boatload of hits for "Bristo Wrench". One of which was a Collins 75S-3 manwell.

I quickly skimmed through the manwell and sure enough they called it a "Bristo Wrench" in the first chapter referencing the accessories that came with the receiver!!   

So I guess if you are working on Collins gear it's a "Bristo Wrench", but if you're working on anything else it's a "Bristol Wrench".    

Stranger things have happened!!

                                                  The Slab Bacon

[aafradio]

Bristo is the name that Dwight Goodwin gave in his 1913 patent, though one of the manufacturers listed is the Bristol Company, who obviously took umbrage with the spelling later on.  Apparently the military didn't agree with Bristol. :-)

http://www.datamp.org/patents/displayPatent.php?id=42304&pn=1,075,710 is the link.

Given the common usage of the term Bristo by the military in WWII, I wonder whether it obtained the patent production rights within the eminent domain rules that the government exercised extensively during the national emergency.  I can think of no other reason that the military manuals seem to all be consistent in calling it a Bristo wrench.

In a way, the debate is like referring to kHz or kc - depends on the era you are from....

[ke7trp]

The cheap Bristol wrenches on ebay that come in the blue pack, work perfectly for all of these old radios.  I ordered a set last year and have used it dozens of times now.

C