Ok Lee, > NB is off...not that it matters, now...listen carefully...of course you > hear the garbled opposite sideband...BUT also you hear a lot of > clicking/arcing like noise on voice peaks especially. > Loud enough to be a bother..
This is absolutely NOT reproducable(?) here. > Why is this a problem since we don't really listen to the wrong SB? > Well, IF you are listening to a nice signal AND right next door a > signal is pounding in and the RX hears the wrong SB for it (and it will > based on the location as to the good signal you want) you get the > clicking etc that is loud because the interfering signal is strong. Well turn off the NB. IF your desired signal is now covered in noise, turn it back on and suffer ;-) Really, I have never gotten any clicking or distortion with the NB off, definitely DO get it with NB on. 73, Gary WB6OGD ----- Original Message ----- From: kc9...@aol.com To: gpola...@cinci.rr.com, drakelist@zerobeat.net Sent: Sat, 14 Jan 2012 18:23:35 -0000 (UTC) Subject: Re: [Drakelist] Interesting discovery/problem about R-4A & R-4B Gary, Here is my original post: While working on a Drake R-4A..(11 tube) .I discovered something that > bothered me...and thought for sure it was a problem needing fixing! > Yeah...I do like things to work well. > > OK...find a nice STRONG signal...maybe S-9 ++ (20 over) tune it in it > sounds great...OK...now carefully tune to the opposite sideband of that > same signal. > NB is off...not that it matters, now...listen carefully...of course you > hear the garbled opposite sideband...BUT also you hear a lot of > clicking/arcing like noise on voice peaks especially. > Loud enough to be a bother....IF you PULL the Noise blanker tube V9 and > or V10...the noise goes away! Huh! the NB is OFF, so why do we hear > that racket?????And why does pulling the tube fix it? > > Well go off looking to see what's wrong so I can fix it....spent quite > a lot of time....looked at lots of things with the scope. > Discovered what was going on is: > If you scope the grid or plate of V9 the 50 kc NB amp...you see a > relatively small signal when the signal is tuned into the correct > SB...BUT if you look at it when tuned to the wrong SB...WOW huge signal > level (maybe 5-10 times as strong) ...and that signal level is getting > through the NB amp, shaper and amp...and clamping the plate of V4 the > IF amp right before the PB tuning...thus creating the annoying clicking > sounds. That's why it stops when you pull the NB tube(s). > > So, got to looking at the AVC signals and how it works at the grid of > V9 the 50 kc amp going into the NB section....found out the AVC does > not throttle back as much with a wrong SB sigal as the properly tunes > one! So the signal. > > Why is this a problem since we don't really listen to the wrong SB? > Well, IF you are listening to a nice signal AND right next door a > signal is pounding in and the RX hears the wrong SB for it (and it will > based on the location as to the good signal you want) you get the > clicking etc that is loud because the interfering signal is strong. > > Now that I understood what was happening...I looked for a bug....not > easy to find for sure.... > > Ah Hah! I thought let's look at my R-4B I have here to compare the > scope patterns and voltages in question. Maybe I'll learn something > helpful? > And does my R-4C do this? > > Answer is: Oh no...the R-4B does exactly the same thing! (R-4C does not) > > This R-4A is not really broke! or both the R-4A and the R-4B I have > here are both broken?? > > Looks to me like a design issue in the AVC circuits. > > > 1) Hey gang...try iy out, let me know what you discover. Please. > 2) Anyone already fixed this with a MOD? > Lee Simmonds Summit DCS LLC 260-799-4077 Office 260-403-6936 Cell -----Original Message----- From: Gary Poland To: kc9cdt Sent: Sat, Jan 14, 2012 12:47 pm Subject: Re: [Drakelist] Interesting discovery/problem about R-4A & R-4B I have all three “ TWIN “ lines, what is it you want tried out?? _______________________________________________ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
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