Yeah, I had a bit of a time trying to find R192 the first time or, actually, finding out the reference designator was of “that burnt resistor on the relay board”. ?The schematic, if I remember, showed a lower number for highest ref. des. used.

The resistor in question is on the relay board, near the rear-centre. The resistor is right up near the top, so it’s easily replaced. ?It should be a 28 ohm, 1/2 watt. ?Most of the MV for the set goes through that resistor, and I can’t help but think that Drake put it in there to be a fuse. ?That resistor will save you if the cap fails shorted. ?I have replaced some of the cans with discrete parts, so there is room in there but using a Hayseed preserves all the wiring in place. I reckon that going the Hayseed route is quite a bit more expensive in Brazil.

I have seen some of these rigs with R192 replaced by a 1W or even a 2W resistor! ?Those were not done by the factory.

73,

Steve Wedge, W1ES

Time flies like an arrow. Fruit flies like a banana.

On Thu, Jan 23, 2025 at 7:49 AM, Marcus PY2PLL <py2pll@...> wrote:

Hi Steve et al

Em 22/01/2025 22:35, Steve Wedge, W1ES/4 via groups.io escreveu:

There are two relays. One controls changing over the antenna and mute functions and the other, smaller one changes enabling voltages from receive to transmit.

The schematic will show K1 and K2 relays.?

I read somewhere that there was 2 slightly different diagrams for TR-4C, I mean above and below certain serial number. I never found this "newer" diagram version (mine have serial 38636). On it one relay is a quad one K1 (antenna, T/R cathodes grounding, linear amp key) and K2 at the 9MHz oscillator (insert/short a 68pf cap to generate CW carrier).

Another note:!if this is a TR-4C of any type, and it doesn’t have a new can capacitor, plan on replacing it either with a Hayseed replacement or by discrete parts. The original can cap has a very high failure rate and usually fails shorted — taking R192 with it. It’s a good thing that that resistor is there on the relay board, as it saves the wiring from melting. If that resistor blows, replace with the same value and rating to keep the protection.?

This made me ask about this two diagrams. On the diagram I have the highest resistor value is R183, highest cap C220. The quad one at this schematic is C145. Still the original here, I'll measure-it one of this days but I'll "build" a new can with newer parts ?. But inspecting the diagram R192 seems to be there, near the power supply connector. Image not clear.

73 Marcus PY2PLL