[HBR] Re: 7360 HBR product detector

[LeeCraner at aol.com]

Kurt, Jay and the HBR Gang:

To bring everyone up to speed, my recently resurrected/completed HBR-16 had 
the 7360 product detector "modification."  However, the BFO signal bled into 
the AGC line so bad that it desensitized the receiver severely.  It was the 
collective wisdom of a few on this reflector that the 7360 mod should be abandoned 
in favor to Ted's 6BY6 product detector (see Ted's comments on the 7360 mod, 
below, compliments of Jay, W6HHT).

Yesterday, I pulled the 7360 mod out of my HBR-16 and installed the 6BY6 
product detector.  Success!  AGC functions just as it should.  S meter works.  
Strong CW/SSB signals don't overload the product detector.  Sensitivity (on 40) 
is 0.28 uv 10dB s/n.  This receiver is hot!  All that's left is to mount the 
Jackson Bros dual drive and calibrate the dial.

The bottom line is if you're thinking about using the 7360 in your HBR-xx 
don't bother, IMHO.  Just isn't worth the aggravation.  

Thanks to Kurt and Jay for their input and encouragement.  And a special 
thanks to Jay for digging up a forty year old letter from Ted and typing it out 
for my benefit!

73
Lee WB6SSW

In a message dated 06/02/07 21:55:50 Greenwich Standard Time, 
amargosaent at iscweb.com writes:

> Saturday afternoon
> 
> Lee -
> 
> I told you earlier I would advise if I found anything in the old letter 
> collection about the 7360 product detector.  I did find something, while 
> I was looking for AGC information, and I pass it on to you here.  It 
> will not solve anybody's problem with the 7360, but it may make you feel 
> better about abandoning that tube.  An extract from Ted's text to "Bill" 
> follows:
> 
> Ted Crosby letter 18 Nov 67
> To: Jay, Alex, Bill [I have no last name nor callsign for Bill]
> 
> "First, that audio developed AGC circuit, and crazy acting S-meter you 
> are complaining about.  Of no help to you here, sorry.  These circuits 
> not of my doing, and something I know nothing about.  But that your 
> S-meter performs in such a crazy non-conforming manner as to be a 
> complete pain the ass, from what little I saw of its performance while 
> you were down here, I most certainly will agree.  If what I saw can be 
> accepted as a criterion, I wouldn't have that 7360 product detector, 
> audio AGC, S-meter circuit of yours up my rear, even if I had room for a 
> saw mill at that spot.  I haven't forgotten that you told me this thing 
> wouldn't work at all until that time you finally wen to Cec Caves with 
> your troubles, with old Cec finally managing to get it going for you.  
> Actually , knowing little about this entire matter as I do, I'm in no 
> position to question the correctness of your claim that Caves corrected 
> your problems.  Even so, still my opinion that there remains much room 
> for improvement.  I further recall that while you were down here, it was 
> agreed between the two of us that it was completely impossible to keep 
> your unpredictable S-meter operational while attempting to make any type 
> of test run, even through the mixer and IF gains be so far advanced, 
> impossible to be certain as to just what was happening to the marker 
> signal we were endeavoring to focus upon.  This being true, it was 
> further agreed, quote "To hell with the S-meter.  Instead, crank the 
> audio gain to a near fully-advanced position, and then use only that 
> minimum amount of mixer and IF gain necessary to provide a solidly 
> readable marker-signal at the output of the receiver" unquote.  
> Obviously, if you had followed this particular method of monitoring your 
> up to now "unsatisfactory " 10 meter test runs, could be that you'd have 
> had slightly better luck, regardless of the fact that crazy acting 
> S-meter of yours would have been completely inoperative the entire time, 
> due to insufficient overall-receiver gain.
> 
> "Second, I'll agree as well to the difficulties of making a series of 
> accurate test-run dial-logging s insolong as that dial-drive-system of 
> yours continues to be as slippage prone as it was when I saw it.  I'll 
> continue to hope that in some manner you will be able to rectify this 
> defugelty."
> 
> My comments, 40 years after the above was written:
> 
> A.  Someone named Bill had used a 7360 product detector in a circuit not 
> developed by Ted, and had some serious trouble with it.  It further 
> seems that "Bill" had visited Ted with his receiver, prior to this 
> letter, and Ted was aware of these problems, and had observed the 
> circuitry and wiring.  It also seems clear that "Bill" had some kind of 
> main tuning arrangement that was not a National or Eddystone, perhaps 
> his own design (one of that category is shown on today's HBR web page), 
> and the mechanical shortfall in that dial prevented him from making 
> temperature test runs.
> 
> B.  Any substitute for the mechanical precision of a National or 
> Eddystone dial must, as a minimum, meet the backlash performance of the 
> National (which is inferior to that of the Eddystone).  If the 
> substitute doesn't meet that criterion, you are simply not going to 
> temperature compensate your Hartley coils.
> 
> C.  If Ted could not quickly find the problem with the 7360, it would 
> take serious time and effort for anybody else (including me) to complete 
> that task.  The probable result of  task completion would most likely be 
> "the 7360 is not well suited for the HBR product detector application".  
> Just that simple.  I worked with Ted, knew him pretty well, and yes, he 
> was that good at seeing "fixes" in other people's circuitry and layout 
> (including mine).  He saw the 7360 thing, didn't "see" an immediate fix, 
> and felt his own product-detector circuit really worked just good enough 
> for everybody else.  I can testify that it did and does.
> 
> Important point - YOU WERE NOT THE FIRST TO HAVE 7360 PROBLEMS, AND YOU 
> MADE THE RIGHT DECISION WHEN YOU ABANDNED THAT TUBE.
> 
> At any rate, I thought these tid-bits might make you feel better.
> 
> Whatever you do with your main dial, make sure it has NO BACKLASH, and 
> it permits you to LOG VERY PRECISELY the  mechanical rotation of the 
> tuning capacitor shaft.  This requirement is essential if you are to be 
> successful in temperature compensation, and if you want to minimize your 
> post warm-up drift for serious on-the-air use of the HBR. 
> 
> Good luck, and persevere.  This HBR adventure is really fun (although it 
> does have its moments of near-terminal aggravation) and I will attest to 
> the fun part 40 years ago, and again starting in 2006 after a 30-year 
> absence from ham radio.  In fact, the HBR was the major lure to come 
> back (I had actually let my Extra Class license expire, and had to take 
> the exams all over again so I could get my 1948 call-sign W6HHT 
> re-issued to me).   Once the HBR book is completed, I will be back on 
> the air QRP with hot-cathode transmitter, J-38 straight key,  
> hot-cathode  Hammarlund Super-pro single conversion superhet receiver 
> built in 1944, and last (but certainly not least) my HBR-XX hot cathode 
> 1968 double superhet receiver!  Since I am myself an antique (I would 
> qualify for the half-century wireless club, if such existed) I will 
> simply march on with my antique vacuum tube equipment plus paleolithic 
> Morse, and - have fun!.
> 
> 73 de W6HHT
> 
> 




**************************************
 See what's free at http://www.aol.com.