EPT690010Z Main Board Modifications
(Galaxy DX2517, Ranger RG66, RG99, Cobra 148F GTL DX+, Texas Ranger, TR6900, TR6900 Jumbo, TR6900F and others)
This article has been reproduced which permission from the author (Firebreather).
For a more up to date version take a look at his website, he tends to make additions and improvements from time to time.
This is the new generation main board being used in the above mentioned 10-meter radios.
Before you read any further, you must know
that the website displaying this article, the author (Firebreather), John
Mahoney, and Panther Electronics will accept no responsibility for any
damage, physical or legal, which may incur as a result of performing any
or all of these modifications. Although each of these modifications has
been performed and tested by the Author, they were done so in a testing
environment and are provided here solely for informational or Export use
EPT690010Z Variable Adjustments
VR1 AM/FM S-Meter VR12 Driver Bias
VR2 SSB/CW S-Meter VR13 SSB ALC
VR3 SSB/CW Squelch VR14 AM/FM High Power
VR4 AM/FM Squelch VR15 AM Modulation Meter
VR5 FM Deviation VR16 AMC
VR6 SSB Carrier Balance VR17 SSB Power
VR7 TX Frequency VR18 AM/FM Low Power
VR8 CW Sidetone Monitor Vol.
VR9 RF Meter
VR10 Final Bias
VR11 Final Bias
Modulation Limiter - Q39
Q39 (TR39) is the modulation limiter for the EPT690010Z board. For the AM/FM models only, you may remove the limiter. For the SSB rigs, I recommend placing a 1K resistor in series with the emitter leg of Q39. Removing the limiter on the SSB models causes severe "garbling" while in the SSB mode. Ample performance may be achieved by simply turning up VR16 and wiring a good aftermarket power microphone for use with the radio.
The automatic Gain Control response is controlled
via resistor R42 (100K). If you find that your local buddies sound "garbled"
on SSB, you can remedy this by changing R42 to anywhere between a 33K to
a 56K resistor. All radios seem to respond differently depending on the
value used. You may have to experiment with different values within this
range. You can make the AGC variable by installing a 100K potentiometer.
Power Amp Improvement (2SB754) - Q54
This is the best improvement you can make
to this chassis. The stock device is a 2SB754, which is a 60-watt, 7A power
amp device. This does fine for stock radios. However, in order to stabilize
the voltage on the board after improving the RF output and boosting the
modulation, the 2SB817 becomes the better choice. The 2SB817 is a 100-watt,
12A device which allows greater voltage stability for the entire radio
as a whole. I ran my test radio (RG66) with the stock device and noticed
quite a bit of wobble and light dimming. After replacement, the radio responded
with almost no blinking, zero wobble and a healthy increase in RF output
as well as swing.
AM Modulation Amplifier Improvement - Q55
This is another improvement, which has previously
been published for the EPT690010Z. The stock AF Amplifier is the 2SA473 (Q55).
Replacing this with the 2SA1012-0 or the ECG153 will improve the clarity
and volume of the modulation. It will also run much cooler which provides
stability for the device. If you plan to use the radio with the provided
stock microphone, this upgrade is highly suggested for maximum AM modulation.
Receive Improvement - D30 & D31
The stock AM Detection diodes are 1N60P devices.
These are adequate but can be greatly improved by replacing them with the
ECG583 Schottky devices. The replacement diodes allow greater copy of distant
stations without allowing your local buddies to overdrive your radio. I
have obtained a gain increase of approximately 3db on stations more than
20 Miles away. This modification is especially noticeable in mobile installations
where you are forced to use an inferior antenna system (as compared to
a base station setup).
Noise Blanker Improvement - D1 & D2
The Noise Blanker diodes can also be replaced with the ECG583 Schottky devices. The improvement over the stock diodes can be rather dramatic, depending on how noisy the environment is around the operating location. Again, this modification is most noticeable in radios being used in mobile installations.
HereÕs one that many folks ask me about and I was hesitant to include it here. This modification significantly lowers the effectiveness of diode D9 and greatly increases the injected received signal to the radio. This was very popular when the Galaxy 10-meter radios first hit the market (D7 on the Galaxy DX-series EPT3600 chassis). The modification requires that you remove the banded end of diode D9 and add a 1/4W, 1.5K resistor in-line with the banded end and the now vacated board location. This actually works very well for any distant station giving you an S-1 to an S-5 signal. A typical example is a station giving you an S-3 will increase to an S-9 (relative) without any increase in background noise (as is the case with most preamps). The downside is that anyone in your immediate vicinity keying up will tremendously overdrive the front end of your radio, possible causing damage to the receive portion of the board. Because of this, I ALWAYS perform this modification with a SPDT sub-miniature or micro-mini switch so that the modification can be turned ON and OFF as needed.
DISCLAIMER: Although this modification works great, I can not stress enough the care that must be taken when using it. Careless use of this modification can lead to radio damage. Engage this circuit modification only when copying distant stations. I take no responsibility for any damage incurred as a result of this modification.
Having said that, go ahead and experiment with this carefully.
You will be surprised at the results.
Super Swing Modification - R264
Again, since it is asked for so often, I have included the Super Swing modification for this radio. Locate resistor R264 and lift the right leg (as you are viewing the radio component side up and front of radio facing you) of the resistor from the board. Install a 1N4001 diode in series with the resistor, being sure to place the banded end of the diode in the vacated main board hole. This will allow you to lower the dead key and still have the full swing capability of this radio. If you plan to use this radio with an external low drive amplifier, I do not recommend performing this mod. It makes it next to impossible to match the radio to a low drive amp. Also, if you performed the RF Output Increase Modification above, this modification may not be necessary. I tested this modification first and then reversed it before performing the RF Output Modification (to preserve the validity of the output modification results). Since I was very pleased with the results of the RF Output Modification, I did not re-do the Heavy Swinger Modification. If anyone does both of these, I would be interested to hear the results.
Under the echo board is a two-wire connector
(JP36). It carries a brown and a black wire from the ON/OFF echo control
switch. Pull this connector from the ept690010z board and talkback is a
thing of the past. The echo circuit will still work and you will be able
to turn the modulation up as high as you please without feedback from the
+10 kHz Switch
Some of the radios using the EPT690010Z have
a +10 kHz switch built in. For those that don't, adding one is fairly simple.
Near the two 4008 Binary Adder ICs you will find a compliment of jumpers.
The +10 kHz jump is obtained by tying JP253 and JP249 together. In my test
RG66, I used the ANL/NB switch for this purpose.
Full Modification Compliment Part Listing
Here is the parts list for performing all of the modifications listed in this article. All of these parts are available through Panther Electronics. To order any or all of these parts, contact John Mahoney at Panther Electronics:
73s and Happy Modifying!!!!
EPT690010Z Makeover Parts
Modification Component Required
Modulation Limiter: ¼-watt, 1K resistor
AGC Improvement: ¼-watt, 33K resistor
Power Amp Improvement: 2SB817, 100-watt, 12A
AM AF Amp Improvement: ECG153 (2SA1012-0)
AM Detection Improvement: ECG583 Schottky Barrier-type
Noise Blanker Improvement: ECG583 Schottky Barrier-type
Super Ears Modification: ¼-watt, 1.5K resistor
SPDT Submini switch
Super Swing Modification: 1N4001 Diode
Galaxy Service Manual Highly Suggested
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