Garey Barrell <[EMAIL PROTECTED]> made an utterance to the drakelist gang
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Tom -
Only the 80M reading looks incorrect. Obviously these readings are all
subject to alignment AND S-Meter calibration adjustments.
The 160M band requires an accessory crystal at 12.6 MHz, usually
inserted into Position 1 of the XTALS switch. The XTALS switch must
then be set to Position 1 instead of NORM the BAND switch set to 1.5 -
3.0 and the preselector peaked. If there is no 12.6 MHz crystal in
Position 1 (or) then don't bother looking for a peak! :-)
A properly working and aligned R-4B should produce a discernible
increase in background noise on all bands with the calibrator OFF and NO
antenna connected. You'll also notice that each harmonic of the
calibrator can vary by as much as 10 dB from _the one next to it_ as
you tune through each band.
In your situation I would suggest a quick run through of Section 6.4.6,
ignoring for now the 10k resistor and the 68 ohm input resistor. No
antenna connected, if you have a dummy load, connect it to the antenna
jack of the receiver. Adjust the trimmer caps along the top of the
chassis with an INSULATED tool. If you must use a metal screwdriver,
put a piece of shrink tubing or tape around the shank to prevent
shorting the trimmer cap to the chassis when adjusting through that
hole. Be VERY CERTAIN of your measurements before adjusting the height
of the four tuning slugs, and only adjust them if you feel you must!
Then skip to Section 6.4.9 and do the Bias and S-Meter adjustment.
Then recheck your calibrator signal levels on all bands and see how they
compare.
If they look OK, then I would suggest a complete realignment per the
manual, skipping 6.4.4, para. 8 for now. Unless someone has been
"fixing" the receiver, these wires should not require adjustment
That product detector was originally intended for the R-4C, and is what
later morphed into the Sherwood PD. There is nothing wrong with the
MC1496L product detector circuit, as long as it is implemented
properly. If it was my R-4B I would replace it with the original,
subbing Schottky diodes for the original 1N270's, but then I'm stubborn
that way! Most mods of this type that I come across are either poorly
conceived or poorly implemented, or both, and usually do more harm than
good. I have a copy of the original article if you don't have it.
Keep us posted!
73, Garey - K4OAH
Atlanta
Drake 2-B, 4-B & C-Line Service Supplement CDs
<www.k4oah.com>
Tom Weigel wrote:
----- Original Message -----
*From:* Tom Weigel <mailto:[EMAIL PROTECTED]>
*To:* richard radke <mailto:[EMAIL PROTECTED]>
*Sent:* Sunday, January 28, 2007 3:07 PM
*Subject:* Re: [drakelist] R-4B PreSelector Issue
Rick:
Here are the calibrator marker s-meter readings for the various bands
on my R-4B:
1.5 - 30.0 mhz no readings found
3.6 mhz S7
7.3 mhz 35-Over S9
14.2 mhz 20-Over S9
21.1 mhz 15-Over S9
28.6 mhz 20-Over S9
Thanks,
Tom, ABØJ
----- Original Message -----
*From:* richard radke <mailto:[EMAIL PROTECTED]>
*To:* Tom Weigel <mailto:[EMAIL PROTECTED]>
*Sent:* Sunday, January 28, 2007 1:53 PM
*Subject:* Re: [drakelist] R-4B PreSelector Issue
Tom,
How strong is the calibrator marker on the other bands?...Should
be at least S9, even on 10
Rick W9WS
Tom Weigel wrote:
Hello:
With the exception of 40M, where the set performs very well, my
R-4B has extremely weak or nonexistent PreSelector peaks
and extremely weak receive. This happens whether operating
standalone or in transceive with my T-4XB.
The previous owner installed a small breadboard circuit described
on an accompanying hand-drawn schematic as "Improved Product
Detector Using MC 1496L," from the December, 1977 issue of /Ham
Radio/. I think that this mod was originally meant for the R-4C,
but I really don't know. I also suspect that the previous owner
could have only used these Twins on 40M. Again, I am guessing!
I have gone through and cleaned all of the bandswitches with
Q-Tip and DeOxit, lifting off some tarnish from the circular
switch surfaces.
Is a complete realignment session in order for my R-4B? Bad
crystals? Anyone else have additional ideas?
Thanks in advance,
Tom, ABØJ
Minneapolis, MN
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