Paul - OK, progress! :-)
The meter circuit is essentially a voltmeter measuring across the shunt resistor (R36). The "select at test" resistor (R38) is a series multiplier to convert the mA meter to a voltmeter. Since your 2.2 resistor is "low", you have to decrease R38 to make the "voltmeter" more sensitive.
250 mA at 650 VDC is 163 W, which for 100 W output means about 61% efficiency. That's about as good as it gets. That IS low current for a T-4XB transmitter. I believe if you touch up the alignment trimmers along the left side per the manual you will get more like 130 W output on 40M. If not, then the next step is to check R26 for value and condition, and then sub the 12BY7 Driver. Be sure and use an INSULATED tool to adjust the trimmers. Even a momentary short from the trimmer to the chassis puts the entire +250 VDC supply across R26.
How much output can you get if you switch to CW, increase the GAIN, and TUNE & LOAD. There is no Final screen current limiter in CW, so keep the PLATE control dipped. If still less than 130W at about 340 mA, your Finals may be a little soft, or perhaps another weak tube in the chain.
73, Garey - K4OAH Glen Allen, VA Drake 2-B, 4-B, C-Line& TR-4/C Service Supplement CDs <www.k4oah.com> Paul Gerhardt wrote:
Thanks for the info on meter Calibration. Today I put a 6 ohm (closest to 5 that I had) and using .070a x 6 ohm = .40v at the TP in the B- line. I then removed R38 and replaced it with a 0-200 ohm trimpot. I got the meter to read on the hash mark and then measured the pot (about 27 ohms). I then installed a new R38 with a value of 24 ohms (close as I had). I then removed the 6 ohm from the AC4 B-. Now The meter is reading just a tad high on idle and at 100 watts into the Cantenna I see about 240-250 and in tune I find I can squeeze a few more watts out of it and by increasing the load a bit get it to peak out at 120W out and the meter reads about 280ma. I think this is close enough for me and will contine on. FWIW today I used my Drake W-4 and checked it at 100W with two MFJ meters that I have and they are all very close at 100W on 40M. The original R38 value was 120 ohms so something has changed maybe the meter being abused by the 'hard pegging' with the open Meter Shunt resistor. Paul Gerhardt K3PG http://pgerhardt.blogspot.com QRP ARCI 6674 FP 274
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