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I just checked the cathode resistors in my TR-4 and they probably should be replaced.? They're not equal and are 20% to 40% over 15 ohms.? Is it recommended to stick with carbon comps for those or will film resistors be okay?? If I remember correctly, these should be kept at 1/4W but not 100% sure on that either.

Thanks for the reminder!

Barry - N4BUQ

Craig:

Congrats on the resistors already checked and replaced.? Those parts are standard checks and "replace as required" for me, which in those particular cases is often.

If you still have the T-4XC open, check the voltage on pin 1 of V-9a and pin 6 of V-9b.? If voltage is low, check resistors R-91 and R-81 (you'll need K4OAH's Service manual to find these easily) as I have found these tend to drift high as well,?especially R-91.? I have seen voltage on pin 1 as low as 68 VDC before changing R-91.

73,

Peter

VE7PS

On Fri, Apr 11, 2025 at 6:08?AM Steve Wedge, W1ES/4 via <w1es=[email protected]> wrote:

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.

Sent from for iOS

On Thu, Apr 10, 2025 at 15:14, Craig W8CS via <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.?

--

Craig/W8CS

Greenville, SC