MMM transmit 'slide-in' for Dwight D, Cobra 1000, 89GTL etc

[nomadradio]

Here's the hookup for adding the MotorMouthMaul-style "slide-in" trick to the Uniden Dwight D, Cobra 1000GTL or 89GTL.

Shoulda jotted down the pc-board number. Seem to remember "PC409". Woulda been even easier to snap a shot of the number while documenting the trick.

Woulda, coulda, shoulda.

But the single thing that makes this type radio different from 'just adding a cap' to a Cobra 29LTD radio is the arrangement of two parts. R84 and D20 are in series, controlling the voltage feeding the "Delta Tune" circuit while in transmit mode. That knob is disabled while transmitting.

The two parts get swapped, D20 goes where the factory placed R84, and R84 gets moved to where D20 was first installed.

The capacitor shown here is a 220uf 25-Volt part. The positive leg goes to the foil trace that runs between R84 and D20. The negative lead goes to the handy ground foil alongside it.

Here's a wider view of where that closeup covers.

This made the Dwight D radio take around three seconds to 'slide' in to the channel center frequency. It starts about 4 kHz below channel center.

A smaller cap will be faster.

73

 

[Shockwave]

Years ago people use to pay me to improve the voltage regulation in older tubes transmitters that would display this type of VFO drift on keyup. I find it amazing that they are paying all over again to install the same "defect". While it sounds cool, too many people that don't know what they are doing, are trying it themselves. My only complaint is if you do this, make sure the darn thing lands on center slot frequency when the cap reaches normal voltage. I hear many of these mods pass right by the frequency or never even reach it. Holding a hetrodyne whenever someone else is keyed, that is actually on frequency. Thanks for providing accurate modifications and preventing those mistakes.

 

[nomadradio]

Years ago people use to pay me to improve the voltage regulation in older tubes transmitters that would display this type of VFO drift on keyup.

Kinda like paying your mechanic extra to make your daily driver misfire on one cylinder.

People want what they want.

73

 

[543_Dallas]

Don't think of it as a misfire but a back fire. You old guys remember shutting off the ignition when rolling down hill.