This is where some of the confusion arises. R1127 is called the "AGC Pedestal", and the service manual fails to complete the adjustment, as you describe. The service manual copy that I have says to set R1127 to the center of it's range in the "coarse tune", and the IF gain is left at one extreme if it's setting. If you proceed to the "final adjustmet", this is where R1127 is left "fully clockwise". Someone (I don't recall who, but it should be in the Drakelist archives) suggested that the adjustment to R1138 for maximum audio output, then -3 dB, is a typo and should be R1127. This seems to make sense. R1127 can also be adjusted in a similar manner to R1129 in the TR-7. Although the circuits are not identical, the effect should be the same.
I found a graph at http://www.cliftonlaboratories.com/receiver_agc_curves.htm that shows the AGC knee in the R-7, which seems to be around -100 to -110 dBm. IIRC, this came fairly close to adjusting R1127 via the "TR-7 method" in my unit. The IF gain setting is more critical to proper operation in the R-7 than the TR-7, and too much IF gain will cause the distortion effects that have been described, especially in FAST AGC; FWIW, I have seen at least two TR-7s that had likely been in for factory service, and came back with the IF gain set to max with no apparent issues. My R-7 still seem to be a little too high, I suspect,because the radio still doesn't sound quite right. Too little IF gain will result in a receiver that sounds "deaf" and/or low S-Meter readings, and readjusting the IF gain will probably require the other adjustments to be re-touched. I'll have to dig through my notes and see what I finally came up with for an adjustment procedure, although my observations are colored by my quest to get the S-Meters to read reasonably close to each other between the TR-7 and the R-7 when "twinned". That may be a pipe dream. Proper adjustment of the IF gain in the R-7 is still somewhat of a mystery. Does anyone know John Kriner well enough to ask if he can shed any light on this subject? It is important to note also that before any alignment is attempted, the +10V regulator should be spot on. Proper adjustment of the +10V is also critical to proper AGC adjustment in both radios. 73 -Jim On Sun, 04 Sep 2011 16:29:39 -0400, Garey Barrell wrote: >Jose - > >There are a couple of AGC setup 'rules'. One just says to set R1127 'fully >clockwise' and then >never mentions it again. This is the AGC 'delay' setting, think the -1.34 VDC >setting in the 4 >series. This is the 'threshold', and the idea is to turn the AGC 'on' just >slightly so it doesn't >'step' on , but rather just increases smoothly when a signal appears. > >With no antenna, and the IF GAIN (R1138) fully counterclockwise, adjust R1127 >counterclockwise until >the output noise JUST decreases. This tells you that the AGC is 'on', just >barely. > >The reason MEDIUM and SLOW 'look' better is that the AGC doesn't have time to >get all the way back >to ZERO before the next syllable comes along. > >Maybe someone else has a better explanation, but this is what works for me! > >73, Garey - K4OAH >Glen Allen, VA > >Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line >and TR-4/C Service Supplement CDs ><www.k4oah.com> > > >Jose V. Gavila wrote: >> Hi all, >> >> Thanks everyone for your help on this!. I have realigned the AGC and now it >> is better, even if not >> as good as I would like, as there is an slight cracking noise still >> sometimes on SSB and, on CW, >> with AGC set on FAST, the effect, as seen on an oscilloscope connected in >> parallel with the >> speaker, is very noticeable (as a distorted envelope). MEDIUM and SLOW >> 'look' lots better. >> >> If I set AGC OFF and reduce RCVR GAIN, all is OK, so it really seems as an >> AGC problem. >> >> Regards, >> >> JOSE >> -- >> 73 EB5AGV - JOSE V. GAVILA - IM99sm La Canyada - Valencia(SPAIN) >> Radio and Test Equipment....... http://jvgavila.com >> RadioRepair BLOG............... http://radiorepair.blogspot.com >> >> > >_______________________________________________ >Drakelist mailing list >[email protected] >http://mailman.zerobeat.net/mailman/listinfo/drakelist -- Ham Radio NU0C Lincoln, Nebraska, U.S.S.A. TR7/RV7/R7A/L7, TR6/RV6, T4XC/R4C/L4B, NCL2000, SB104A, R390A, GT550A/RV550A, HyGain 3750, IBM PS/2 - all vintage, all the time! "Give a man a URL, and he will learn for an hour; teach him to Google, and he will learn for a lifetime." HyGain 3750 User's Group - http://groups.yahoo.com/group/HyGain_3750/ http://incolor.inetnebr.com/jshorney http://www.nebraskaghosts.org _______________________________________________ Drakelist mailing list [email protected] http://mailman.zerobeat.net/mailman/listinfo/drakelist
