I found the problem! I was thinking RF and ALC when the problem was really AF. I replaced V9 with a cheap Chinese 12AX7A and all is well. I learned that tune mode uses the mic amp as an audio oscillator in tune mode (I read that on Drakelist). Apparently the tube got weak enough it would only start oscillating with the gain turned up. It was still OK in SSB mode.
73, Bob WW3QB --- On Sun, 12/27/09, Robert Ladden <[email protected]> wrote: From: Robert Ladden <[email protected]> Subject: [Drakelist] Change in T-4XC Tune Mode To: "Drakelist" <[email protected]> Date: Sunday, December 27, 2009, 8:33 PM My T-4XC has changed behavior in Tune mode. It was that as I turned up the gain the plate current and output would increase gradually. Now there is no increase until the 12:00 position, where it is almost full power. Then I have to turn in down to decrease power. SSB and CW modes seem to work as before. I can get full power, it is just a little harder to tune up because I have to turn the gain way up and then down. At first it led me to think I had a final PA problem, so I did try swapping the 6JB6s. Also swapped the driver and V1. Then I put it back as before. I fear that this is a preview of a total failure (which would be easier to find). 73 and Happy New Year, Bob WW3QB -----Inline Attachment Follows----- _______________________________________________ Drakelist mailing list [email protected] http://mailman.zerobeat.net/mailman/listinfo/drakelist
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