It looks like I'll be doing some quick comparisons with the CD this weekend. The previous owner was sort of known for doing odd changes to the AGC circuit, so I'm still thinking that I've missed a change in a grid resistor somewhere.
It's interesting that I can juuuuusssssstttt get it to 40-over-9 with the AGC at -15V, but continuing the RF GAIN to full CCW doesn't really advance the meter any more than that - even though the voltage continues to go more negative. Looks like I've got to go through every resistor in the bridge first. 73, Steve, W1ES/4 -----Original Message----- >From: Garey Barrell <k4...@mindspring.com> >Sent: Jan 12, 2012 9:25 PM >To: Steve Wedge <w1es1...@earthlink.net> >Cc: Drake List <drakelist@zerobeat.net> >Subject: Re: [Drakelist] S-meter balance: ain't the tubes. > >Steve - > >Well, a couple of choices. > >1. The bridge is not balanced. One or more of the 'legs' is not what it has >to be. > >2. The current being drawn by the Plates of V4 and V5 is NOT equal to the >Plate and Screen current >drawn by V2 and V3. > >Have you measured element voltages on the four tubes in question? Value of >Cathode resistors? >Value of larger decoupling resistors? > >Did you determine what fried R89 & R42? > >The two bridge legs design value looks to be 820 per leg, so the two currents >in question should be >equal for the bridge to balance, resulting in zero delta, ergo (always wanted >to use that word!) 0 >Volts on the meter. > >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> > > >Steve Wedge wrote: >> R-4B, s/n in the 9000's (I'm too lazy to peek around the back). Had >> previously fried R89 and the >> S-METER ZERO pot and had to replace the pot with a 200-ohm padded with a >> 390-ohm CC. It barely >> reaches S-1 with the pot maxed still. The S-METER SENSITIVITY pot which is >> supposed to be 1k was >> reading 600 ohms, so I padded it with 390 ohms. I can't get the needle to >> reach 60-over with the >> RF GAIN fully CCW. >> I tried replacing V4 an V5 with NOS tubes and there was no change. V2 and >> V3 were likewise >> replaced with no improvement. (V2 was already a new 6HS6 anyway but I >> swapped to be sure). Put >> all the original tubes back in. >> It's a simple bridge, fercryinoutloud! What am I not seeing? _______________________________________________ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
