The Slider Buffer Installation Guide Copyright 2002 Nomad Radio
|--> Introduction: What's it good for? Why bother?
Three questions here. Do any of them sound familiar?
1) When I turn the channel selector on my Browning Mark III SSB transmitter to select my Glenn slider, the power will drop. Even when I set it to (for example) channel 20, the transmitter is stronger on CRYSTAL channel 20 than it is with the Glenn set to 27.205
2) When I switch my Siltronix 90 slider from 'CB' band to 'HF' band, the transmitter power drops WAY off.
3) This little resistor under the chassis just beneath the channel selector overheats and burns up every time I replace it.
This is a pretty simple proposition, really. All the sliders sold in the mid-to-late seventies BUT a couple were made to properly drive a solid-state radio. The two exceptions to this were 1) the PAL slider. It could be persuaded to drive a tube radio okay on its own, and had a small trimpot inside to reduce the drive, making it correct for a solid-state radio, as well. And 2) Maco made a 5 MHz slider that fed directly into one of the two oscillator tubes on the Mark III SSB. It had other annoying problems we won't cover here.
You plucked a crystal out of the radio, and wired in a cable. The slider would feed a variable frequency into that cable, taking the place of the fixed quartz crystal. A solid-state radio runs from 12 volts, more or less, and the drive level from the crystal is a couple of volts, about one-sixth or so of the power supply that runs it.
Tubes, on the other hand run from 100 to 200 volts, and the same one-sixth fraction of that is a LOT more than a couple of volts. That's all the Siltronix and Glenn sliders would deliver. This causes the transmitter to be "wimpy". It just isn't getting enough drive.
|Mr. Glenn, Whoever he was,
had a solution for this. his model number was "326-1", a small circuit
board with a "buffer amplifier" on it
that would increase the drive level out of his
famous 326-G slider so it would be sufficient to
drive a tube radio.
|Our version of this toy, the Nomad Radio
Slider Buffer, installs inside a Mark III SSB
transmitter, allows the use of a three-foot long
cable to the slider, and takes care of boosting
the drive level coming out of a wimpy slider. It
is designed to bolt directly inside the
transmitter, and comes with the slider cable, and
all the mounting hardware needed.
2) 4-40 x 1/2 in. threaded standoff
Before changing anything under the radio, it's a good idea to check for a routine weak spot. Just underneath the channel selector, under the chassis is a slug-tuned coil, L5. It has two solder lugs on it. The front-facing lug has a 1/2-watt resistor with brown-black-orange color-coding stripes. There may be a silver or gold band after the orange one. This is R34 on the schematic. The original value is 10K (10,000 ohms). If the orange band is faded or dark, this indicates stress. The part may be okay, but if it is darkened or discolored, dont' trust it. R34 routinely gets overheated when a Siltronix slider is used with a direct hookup. If it doesn't look PERFECT, replace it with the one we provided with the buffer. It's a really good idea to check V6 the 6GH8A tube. If R34 gets stressed, V6 does, too.
|Decide WHICH CHANNEL on the front-panel
selector you want to use for the slider. Remove
Under the radio, find the two
screws directly under the SSB
Slide a #4 inside tooth lockwasher over the
end of both the
|Screw the two half-inch tall standoffs down onto the lockwashers.|
|Slide the buffer board over the ends of the standoffs with the black coax toward the Channel Selector, the brown wire toward the meter end of the radio. Slide a lockwasher onto each standoff stud and screw on the mounting nuts, but not TOO tight.|
|Find pin #4 of V2, type 6BA6 (the only one of that number in the radio). Pin 4 will usually have two skinny (solid) black wires and one fatter green wire, probably cloth-insulated.|
|Heat this pin and the wires with the soldering iron, and add a SMALL amount of fresh solder to the old solder on the pin and wires.|
|The end of the brown wire is already solder-tinned. Lap-solder it to pin 4 on V2.|
|Fish the coax from the buffer board between the sockets V8 and V9, under the wires that run between them.|
|Route the end of the coax as shown into the rubber grommet and up to the rear of the Channel Selector.|
|Solder the end of the coax TO THE SWITCH LUG adjacent to the crystal you have removed. DON'T SOLDER IT TO THE CRYSTAL SOCKET ITSELF. Pulling out the crystal on each side of it may make this easier. Note which socket each one came out of, so they each go back into the same socket as before.|
|Insert the stripped/tinned end of the shielded cable from the top side of the chassis into the chassis hole in the very back corner next to the power transformer.|
|Pull the shielded cable through underneath the chassis and route it as shown to reach the buffer board.|
|Insert the stripped end of the center conductor into the larger hole shown. It will solder in place fine from the top side.|
|Insert the tinned end of the cable shield into one of the two ground holes at the edge of the board and solder it. Solder the center wire to the large center hole. Be sure to leave slack in the center wire, so it won't get pulled out.|
|Secure the shielded cable at the chassis corner with the nylon wire tie through the adjacent hole as shown.|
|Re-install the bottom cover.|