Yep, those resistors are important! ?My TR-4Cw RIT has excellent cosmetics and the cathode resistors were all 17.5 to 18.5. Screen resistors were around 80. Output on 40m went from 150 to 180.?
I¡¯ll now be reviewing all of my transmitters and replacing anything out of tolerance.?
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Thu, Apr 10, 2025 at 15:14, Craig W8CS via groups.io <
craig_severson@...> wrote:
I'm not the first to have done this, just reporting this to help if anyone is on the fence.?
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I noticed some poor performance on my T-4XC that I pulled out of mothballs this year after a long siesta.?
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Did the heathkit shop AC-4 upgrade, no difference in output, more of a preventative thing with 48 year old caps.?
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Started poking around the finals section and noticed that the cathode resistors were 17.2 and 19.3 ohms, pretty out of spec for 15 ohm resistors. This week I got around to looking at the rest of the circuit including screen, screen supply, and meter shunt resistors.?
- R49 2W 1.5Kohm was heat-swollen and running 1600 ohms
- R50/R51 screen resistors (68 ohm) were measuring 73/76 ohms
- R59 meter shunt resistor (3.3 ohm) was measuring 4.5 ohms
Replaced all of these with upgraded/over-spec components and WOW what a difference. Easily hits 100W output on 10M, 150W+ on lower bands.?
No, I'm not going to run this unit at those numbers but nice to see the potential. And this is with what I consider to be "soft" final tubes.?
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Also installed a couple of binding posts on the rear panel which pigtail across the meter shunt resistor for easier bias set/checks.?
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I could post pictures of the mods if anyone is curious.?
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Craig/W8CS
Greenville, SC
