Notes and other info:
Cobra 138 XLR
VR1: AM RX Audio Level
VR12: AM/SSB RX Meter
VR9: SQ. Threshold
VR5: RF Gain (Internal)
VR8: AM Power
VR8: AM Power
RX Peak and Tweak Cans:
TX Balance Cans: (ie tune for even output on low and high channel(s):
L39 and L37
RF peak-tweak coils:
This radio is listed to be the same as:
Cobra 139XLR, Palomar SSB500 (early), President Adams, Grant (old), Madison (old), Washington (old), Realistic TRC449, TRC457, TRC458, Robyn SB510D/520D, Stag 357, Teaberry Stalker 101, 102, Teaberry Stalker 202, WKS 1001:
so information should generally apply to these, too.
JIL Citizen B524
(23 Channel Crystal-Controlled Base Station)
<L7, L11, L12, RV2-AMC>
Purple zener behind RV2 can be bypassed for more mod.
Common failure is channel indicator backlight bulb.
Replace with Large red LED from Radio Shack.
Royce I-653B 23 Channel "Module Transceiver"
"Sardine Can" contains T5080P PLL, which is impossible to get at unless the PLL board is unsoldered. Not worth the time. A few "upper" channels in the legal FCC 40 band can had by controlling state of the N=16 pin which comes out of the sardine can and onto the main circuit board, and is then wired to the channel selector. Again, not worth the trouble. Hard to get at the coils to peak radio, too. Tune <T402, L403, L404> for output power, <Q301> is Mod Limiter. Cutting the Mod Limiter out of this radio isn't so bad, because it would be very hard to make it overmodulate without a hard driving power mic.
A great radio. Has uPD858 PLL. Pll and mixing crystal contained on "daughterboard", making programming pins only somewhat visible. Cut edge of mainboard near PLL (this will be obvious after you open the radio) with moto-tool to reveal pin 19. Cut-out needs to be large enough to get soldering iron tip in. Isolate pin 19 with eXacto knife or equivalent. Find ANL switch. Unsolder wires from ANL switch, clip them back so no bare wire is showing (do NOT connect them together) and put a little shrink tube on the ends for a professional-looking job. ANL is now always "ON". You'll need 3 qty. 4" pieces of 22-24 ga. wire. Strip ends of these wires and tin w/solder. Solder a wire between ANL switch top pin and +5v on the channel selector board. (+5v on the channel selector is where the grey wire goes into the ch. selector board.) Solder a wire between pin 19 of the PLL and the middle pin of the ANL switch. Solder a wire between mainboard ground and the bottom pin of the ANL switch. Now, with the ANL switch in the down position, you have the normal FCC 40 channels. With the ANL switch in the "UP" position, channel 1-15 = 26.565-26.735 and channel 16-40 yields 27.555-27.805. Tune output power by tweaking coils L212 and L214. Mod. control is VR401, which is not labeled on all chassis. It is the VR near the large transformer near the back of the radio. This unit has excellent modulation when turned up, power mic rarely necessary. After tweaking, you may have to turn the TX meter adjustment down to keep needle from pinning up against end of meter travel.
240 to 110VAC Conversion Instructions for EPS-21012M
and like inexpensive 220 Volt input, 12-15 VDC output, 10-12 Amp power supplies many internet dealers have on closeout.
Use these instructions at your own risk. No guarantee is expressed or implied. Observe normal safety precautions for handling electricity.
1 medium wire nut, 1 standard US 110v grounded plug. (three prong). Some electrical tape or shrink tube (for a more professional job).
1. Cut funky European 220v plug from end of power wire.
2. Install regular 110vac standard US plug on end of now cut wire. Connect the Brown wire to positive (+) 110v. Connect the blue wire to Neutral 110v. Connect the Yellow wire with the green tracer to ground.
3. Remove cover from power supply. Find Blue wire coming out of power cord running to the power switch. CUT this wire in the middle of the exposed insulated part of the wire, leaving enough on each end of the cut to strip back the wire (and eventually) put these wires together.
4. On the INPUT side of the transformer, find the blue wire that is connected via a shrink tube to a brown wire. CUT the connection between these two wires. Put a shrink tube or electrical tape over the end of the brown wire and put aside. You will not be using the brown wire.
5. Strip about 1/2" of the insulation off of the blue wire you just disconnected. Connect this blue wire to the other blue wires you exposed in step 3 via a wire nut.
6. Plug power supply into standard 110v outlet and cross your fingers. If nothing pops or smokes, you're done. Reinstall cover.
Other procedures for great results:
Hook quality VOM to external output of power supply. (The red and black binding posts.) Adjust black voltage "knob" until dc voltage on VOM reads precisely 15v. Adjust RV3 on rectifier board inside power supply until Voltage meter on power supply itself reads precisely 15v. This will give precise readings on the internal Power Supply meter and also has the added bonus of the 12 o'clock position of the black knob on the power supply equaling more or less 13.8 VDC. How convenient.
RV1 and RV2 are probably OK at factory settings, which should be somewhere near the center of the potentiometer.
Replace line fuse (accessible on front of power supply) with 3.0 amp fuse.
"Super Swing" Galaxy Pluto.
Standard disclaimer: These modifications (and radios and
HF linear amplifiers mentioned herein) are not legal nor type accepted for use
on the Citizen's Band in the US of A. They are for educational purposes only.
One other note: I realize that most, if not all, of the modifications I
write about can be performed by alternately drilling a hole somewhere in the radio and putting a switch or pot therein. I'm just not into that sort of thing. I like for my radio to look 'stock', if that is possible for some 'big ole' export radio.
I am going by memory here, so screwdriver expert beware.
If you break it, YOU broke it.
This modification work on just about any Galaxy / Galaxy Manufactured or Korean/Japanese manufactured clone thereof.
I know nothing of this 'Pluto radio' (love the way that
specifically, so I'll be assuming a few things:
1. It is built like just about every Galaxy radio on the planet.
2. It is similar to the SuperStar 3900 GT and
3. It has dual final output transistors. (10w AM Model).
4. It does NOT have variable RF Power accessible from the front panel.
Most folks I talk to and sources I have read do NOT recommend a 'swing kit' in this type of radio because of the good to excellent modulation properties and resultant swing inherent in this type of radio. I agree.
Here is a modification you can do that will give you:
1. QRP ((super) Low Power Mode)
2. Variable RF output adjustable from the front of the radio and
3. A kind of 'super swing' mode, especially when teamed up with a small
kicker in the 200-250 watt range.
Here is what you will LOSE: Adjustable RF Gain control.
All righty, here we go. The short version of this whole exercise is this (for those of you who want to get right at it): Make sure the audio limiter is intact. Turn the Mod pot all the way up. Remove wires from RF Gain control and wire so that RFG control is always wide open. Remove AM POWER Pot from radio and wire the RF Gain control such that it is now the AM Power Pot. That's about it!
Details and commentary of this hack job are as follows.
The first thing you must realize is that you will LOSE the ability to attenuate the INCOMING RF signal to your radio. In other words your RF Gain control will no longer function. So what?, most of you ask. I never use that thing anyway!!! (Me, too.)
If TR32 (The audio limiter transistor or 'mod shunt') has been removed/negated in this radio, PUT IT BACK.
Find the Modulation control for AM, which is typically VR14 in this style of radio. Turn it all the way up. You can tell which way to turn the pot by observing a wattmeter or SWR meter whilst turning the pot and saying 'ahhhhhhhhhhdeeeeeeeOOOOOOOOOOOO'. Turn this pot until the needle deflects the maximum amount.
Next, find the RF Gain potentiometer on this radio (it's on the FRONT and has a shaft sticking through the front faceplate and is controlled by the knob marked 'RF Gain') and note the wires attached thereto. Usually they are gray, red and black. Unsolder the wires from this potentiometer. You will now need to determine which two of the three wires you have just unsoldered, when touched together, turn the RF Gain control to its 'always wide open' position. Do this by turning the radio to a busy channel (19?) and observing the meter and listening to the audio through the speaker. When you touch two of the wires together, the needle will deflect to the right with an incoming signal and you'll hear the audio through the speaker. Solder these two wires together and protect with shrink tubing or black electrical tape. Also protect the remaining wire in similar fashion, as we don't want it flopping about inside the radio wreaking potential havoc. (no pun intended.)
The next step is documenting the AM power potentiometer
and de-installing same. Locate the AM Power control pot on the main circuit
board of the radio. It is usually VR13 in the Galaxy-type radios. Turn the pot
to about 50%. Key transmitter, making mental note of Deadkey. Make note of any
resistance markings on this potentiometer. (normally 5K). Get Volt-Ohmmeter (VOM).
Range of VOM should be set to about 20v DC. Attach black lead to chassis ground.
With radio in the ON position, Mode AM and in RX , measure (and take note of)
voltages at three connection points of VR13. You should measure something like:
0v, 14v and ~8v. The two points with +DC voltages we
will call HOT. The 0v we will call Ground. REMOVE THIS POTENTIOMETER FROM THE RADIO BY CAREFULLY DESOLDERING IT.
Now that the AM power pot has been removed, you will need
three wires, ~20ga and ~10" long. Locate the RF Gain control potentiometer
you desoldered the wires from a few minutes ago. (I'm now assuming the radio is
positioned such that the control shafts on the front of the radio are pointing
toward your belly.) Run a wire from either one of the HOT connection points where The
AM power potentiometer was on the circuit board the the leftmost connection on
the RF Gain potentiometer. Run a wire from the other HOT connection of the
AM power pot to the middle connection of the RF gain potentiometer. Solder a third wire between the GROUND connection of the previous AM power pot to the remaining (rightmost) connector of the RF gain control potentiometer.
At this point, your RF gain control should now act like a variable RF POWER control on the front of your radio. COOL. Turn radio on, turn linear off, Mode should be 'AM'. If you've done everything right, turn 'RF Gain' control clockwise and the wattage should increase accordingly on your wattmeter. If turning the RF Gain control clockwise results in DECREASING power output, you have the leftmost and rightmost leads on your RF Gain pot reversed. Desolder these connections, reverse and re-solder. If you hear popping noises or get NO power output whilst testing, something is wrong. Check your connections. Pray.
You should notice, as a byproduct of this exercise, that you may now turn your AM/FM power WAY down into the milliwatt range when you dial the RF Gain control counterclockwise. Why does this work? Typically because the RF gain pot can inject about 10Kohms resistance whereas the AM power pot could only muster about 5Kohms resistance. As you increase the resistance by turning your RF Gain control counterclockwise past the 5K resistance limit of the old AM power pot, the wattage drops EVEN FURTHER than possible with the internal adjustment. I love this country.
FYI, to control 'swing' on SSB, your Mic Control should
effectively do that,
as it always has in the past. By limiting the amount of audio input, you
will limit the RF output on SSB.
Now for the fun part: The 'Channel 6 Super-Swing Mode'!!!
Hook up radio into your system as Normal.
Mode: AM, Channel: 6 (or channel of your choice)
Linear: (~225 watt) in whatever power mode (L/M/H/WFO) you like and in the ON position.
Wattmeter installed between the linear and the antenna. Range: low position (~20w)
Your new RF 'Gain' control in the minimum (fully counterclockwise) position.
Key Radio. (linear relay will probably NOT engage. That's
Turn RF Gain control SLOWLY clockwise until linear relay engages and reading on Wattmeter is about 2-3 watts.
Increase range of Wattmeter to ~200.
Speak into microphone: AaaaaaaaaaadeeeeeeeeeOOOOOOOooooooooooo.
Notice huge swing, from about 2 to 150 or so watts. Now that's a swing!!!
Now you've got that patented 'Channel 6 Sound (TM)'...
Other cool things to do with this mod:
1. Talk to the guy across the neighborhood without the linear in super low power mode. People with think his CB has some kind of super-duper-ears kit in it.
2. Whilst using an Antron 99 and low power, tell the receiving station you are
going to 'turn the beams around and point 'em at them...', then SLOWLY rotate
the RF Gain control clockwise. (do NOT overdrive the linear). Your signal
will seem to come out of nowhere as you increase your carrier power from 1
watt to 100 watts or more (measured post-linear).
(Please, no lectures on S-units here...the object is a slow increase in signal strength, which you will achieve. If you've got a much bigger linear and can make their S meter go from 1 to 30+, good for you.)