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The die-cast plug with the curved body and the matte finish was more popular 40 or 50 years ago. I like it because the contact insulator and the body have a more-robust mechanical bond than the cylindrical-body plug with the polished finish. I would guess it costs a little more to fabricate. 73

That's the deal. The High/Low switch bypasses the two driver tubes altogether in High side. The radio drives the four final tubes directly. That's why it needs two input-matching circuits. One for driving two driver tubes, and one to drive four finals directly. 73

That's the plan. Removing the pink wire feeding 11 Volts DC from the common lug on that section of the band switch will allow splicing it to the power wire for the module. A ground wire will go to the switch lug. The idea is to minimize how much stuff gets altered in the receiver. The fewer...

I agree, but we encountered a fatal personality quirk in the five-tube version. It would go into fatal oscillation and kill one or more tubes before tripping the fuse. Converting it to the four-tube version was the only cure I found for this. A built-in driver stage sounds good, but it caused a...

If you use enameled wire to wind a combiner, the insulation-breakdown voltage of the enamel might cause the RF voltage to arc if placed directly onto a grounded copper foil surface. Some folks use teflon-insulated wire. It has a higher breakdown voltage and probably doesn't need this extra step...

RTFM they say. In this case I really should have. Turns out the three binary inputs that select one of eight frequencies stored in this gadget are internall pulled *UP*! NOT down. Whups! If that's the case, this hookup should not have worked. But more to the point, I don't need to feed a...

Yep, like he said. The display does respond to the setup of your clarifier, er "voice lock". The factory made it a receive-only control. Transmit frequency was set to the center of the channel by a trimpot inside. Most specimens of that radio have had the clarifier "unlocked", so that you...

Almost. The coil is across the two low-side lugs of the switch, not between the switch and the final cathodes. And the output from the driver PI-net coil goes to a High-side lug, not to a common lug. I drew it up years ago and plastered it over the factory schemo's High/Low switch. Haven't seen...

Ought to be, but I don't have it the can to whip out. The schematic shows the mode switch connecting the ground side of the external and internal speaker only for AM and FM modes. In PA mode it breaks the ground to the internal speaker and ext jack, connects ground to the PA jack. Bypassing...

The 468 trimmer cap on the input to the driver tubes is just below the input coil on the schemo. Isn't marked or identified. Pretty sure it's 5 or 6 turns on a half-inch inside diameter. 73

Oh no, Mr Bill! The perennial arithmetic puzzle. Four doesn't equal five. The Cobra SSB radios had five pins to provide a separate ground pin each for audio and for transmit/receive switching. This served to keep noise voltages out of the mike audio, since pin 2 carries only the mike's audio...

Used to be able to buy the die-cast version of that plug. Haven't seen it offered for years. The suppliers where we got them have all closed long ago. 73

Schematic's wrong. The compression trimmer soldered to the High/Low switch is the input-impedance matching adjustment for Low side. This amplifier does something out of the ordinary. The Low side feeds the radio drive directly to the four final tubes. You can remove the two driver tubes and...

Closest that's posted online would be the Teaberry T240D. Same on the inside, mostly. https://cbtricks.org/radios/robyn/t_240d Also covered in Howard Sams volume CB-187. If you're sure the receiver frequency is right, the 9.785 MHz crystal X3 may be off frequency. Might require replacing a...

That frequency display does something you don't see very often. It has two inputs. In SSB modes, it reads the carrier crystal frequency and the 34 MHz PLL output and does the math. This compensates for the offset. In AM receive, it substitutes 7.8000 for the missing carrier input. When you...

I wish him long life, good health and brisk business. All prerequisites for self employment. 73

The weekend is when design projects get tried out. And: EET VERKS! Mounts where the original board with two crystals went. Only connection to V3 is pin 2, where the hot side of the original crystals went. The tiny orange ceramic blocking cap has unnaturally long lead wires. Not totally...

Got a suggestion to just use a zener diode to hold the module's select-input voltages below 3 Volts. Duh! Sometimes you just gotta acknowledge advice from Captain Obvious. Credit where credit's due. Thanks. Had some issues years back with 1-Watt zener diodes below 5 Volts. Had to push a minimum...

Whoa! I had forgotten that this model lacks a mike gain control. Not a lot of Cobra models are missing that control. Just makes any mike trouble twice as aggravating. 73

I sell an overpriced solution to the 4-pin mike/5-pin radio dilemma. https://www.ebay.com/itm/116584159949?mkcid=1&mkrid=711-53200-19255-0&siteid=0&campid=5336136228&customid=&toolid=10001&mkevt=1 The original 5-pin socket comes out, and the five wires get soldered to this board, along with a...