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2sc2999 and Schottky diode swap

Posted: Monday 12th Feb 2007, 7:01
by carl
How to perform the 2sc2999 and Schottky diode swap for increased receive gain and less noise.

As many of you know there are a few ways to boost the incoming signal, generally this is done with a pre-amp style device; the drawback to a preamp is that it also boosts all other noises as well. It works the same as turning up the volume on your radio, as you can tell it does not help much if at all. What can you do to help? Well by swapping a few parts for upgraded parts you can make your radio more sensitive by boosting the incoming signal and helping to make the radio quieter on receive. The best part is that sense we will be working with the first IF stage of the radio all the garbage that would normally be boosted with a pre-amp will be filtered out so only the other radios carrier will be boosted. We will also help out the noise blanker section of the radio for quieter operation. This will not change the signal you receive on your meter but it will make a 3 s-unit signal as loud as a 4.5 s-unit signal. It also does not make your radio more prone to being overdriven up close. The swap is relatively quick, taking anywhere between 10 minutes for the experienced to 40 minutes to the first timer.

Today I will be using a Uniden Grant XL but the same applies to the Grant LT, Cobra 148 GTL, Uniden Washington, Cobra 2000 GTL, General Sherman, Texas Ranger 296, and countless other clones.

Tools needed
soldering iron
solder sucker, or c0pper braid
silver solder
small side cutters
right angle pic (makes removing small parts easier)
#2 phillips screw driver

Parts needed - less than $15
1- 2sc2999 High Gain, Low Noise Transistor ( or nte107**)
4- 1N6263 Schottky Barrier Diodes (or nte583, ecg583, sk9975)
1- Transistor removed from the TR-14 position

You can begin by removing both the top and bottom case half?s, There is a total of 12 screws that need to be removed (4 per side, 1 on top and bottom, and 2 in the rear). I find the speaker easier to unsolder rather than clip the nylon zip ties and unplug from the main board. If you chose to unsolder the wires at the speaker remember that the White wire is the Positive (+) lead.

Take a look at the component side of the radio and find the positions outlined below. They are TR-14*, TR-19*, D1, D2, D21, And D22. These areas are where we will be working. Also take note of the orientation of the transistors (TR?s) and note that the flat side faces the rear of the radio, It is important that the new parts be installed the same way, The same holds true for the Diodes (D?s) as the stripe must be facing the correct side on the new diodes.

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I like to start with the transistor at position TR-14, this is the Am Detector. You need to unsolder this from the backside of the board; it?s easy to find its location on the rear by holding the radio up to a bright light and using a pen to mark one of the legs. Make sure it?s a pen and not a pencil. Once you have the Transistor lose, you can place it aside as you will be using it again in a second. Place the new 2sc2999 transistor in the TR-14 position with the flat side facing the rear of the radio. Flip the radio over and solder each leg. Heat the joint for 2-3 seconds before applying solder. A good joint is shiny joint not dull and grey. If it is you need to heat the joint longer.

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Move over to the Transistor at TR-19 and remove it. Take the Transistor you removed from the TR-14 position and solder it in place, Again the flat side will face the rear of the radio. This is the ssb detector.

You can now replace the diodes at D1, D2, D21, and D22 with the new 1N6263 diodes. These are low noise diodes that help quiet the natural hiss of the radio. The bands on the D1 and D21 diodes will face towards the mic connector, the bands on the D2 and D22 diodes will face away from the mic connector.

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you may want to have the recieve section of your radio aligned, i have found that most radios will not need one if the radio has been aligned before.

*early model radios will be marked with a Q instead of a TR, they are the same component.

**the nte107 can be either hit or miss, when nte bins there parts they have a few transistors that cross over to the nte107 part (including the stock piece) so there is a very good chance you will not be receiving an upgraded part. The 2sc2999 however is an upgraded part and you should find one before using the nte107 if possible.

Posted: Monday 12th Feb 2007, 7:02
by carl
TR-17, D1, D2, D23, D24

Galaxy DX 33, 44, 55, 66, 73, 77, 88, 99, 11b, Pluto, Super Galaxy, Galaxy II, Saturn, SSB, Melaka, RCI2980, Eagle 2000, Connex 3300 (all), Superstar 3600, 3900 (all), Osaka 3900, General Lee, Voyager VR9000, Alan 87, Nortstar Galaxy clones and other radios that use the EPT-3600 series Main Board.

TR-18 (Q), D1, D2, D34, D35

RCI-2950 & 2970 (non dx) Mirage 2950, Sommerkamp 2000, Galaxy Saturn Turbo, Galaxy DX 22B, Galaxy DX 2527, RCI-2990, Eagle 5000, And other radios that use the EPT-2950 series Main Board.

Re: 2sc2999 and Schottky diode swap

Posted: Monday 12th Feb 2007, 12:05
by Rick
The problem with this mod is the front end transistor (which this is not an IF stage) will have a floor noise improvement of .3 to 1db which is just not worth the effort, if you do some test with RF signal generator which will go down to .2uv and up to 100mv and use a SINAD you will see that I am right. The best way is to try and improvement the dynamic range is to try changing the AGC attack, have you ever tried trapping the AGC but careful doing this as you can blow the front end transistor up. Some radios I have done for my self have adjustable AGC.

I am not trying to run you mod down I am just pointing out it is very little to be gained from such a mod.

You need to look at this for a manufacturer point of view, if they could make improvement to there radio they would, it sales more units and that is the name of the game, it not to do with cost has as some people may think one transistor is the same cost as the current one when you are buying in quantity.

Rick (Euro Radio Co).

Posted: Sunday 20th Jan 2008, 18:19
by countryboy
witch one on a uniden washington 8719 pll???

Posted: Sunday 20th Jan 2008, 18:21
by countryboy
and is this right for a cobra 29 ltd classic. tr7,d5,d6,d24

Posted: Tuesday 11th Mar 2008, 16:12
by Z28
I have this mod and I don't like it. Can you please tell me the original values of the components so I can put it back to original?

Or a parts list/diagram.

Fyi, to all wondering why I want to put it back, its because it really just makes the radio act like it has a pre-amp in line. The actual noise ratio is just the same. The part that really makes me not like it is the fact that the S meters range is ruined. Basically everyone hits me S9, even if its weak or strong. I do lots of tracking and can't use the S meter like a normal radio. RF gain down, same problem.

Re: 2sc2999 and Schottky diode swap

Posted: Wednesday 12th Mar 2008, 21:36
by Rick
What radio are you trying to put back to stock?
What is the PCB number?

Posted: Wednesday 12th Mar 2008, 23:28
by dxswe
I have done the SC2999 and 1N6263 mods in my Galaxy 95t2 with good results.The best thing to make noticed with this mod is when you have the radio installed in my car.But when you have your radio connect to a base antenna you make any different.I have realignment the S-meter with an rf-generator and the receive.


Re: 2sc2999 and Schottky diode swap

Posted: Thursday 13th Mar 2008, 6:21
by Z28
Rick wrote:What radio are you trying to put back to stock?
What is the PCB number?

I have General Lee, which is the same as a Galaxy radio. I want to put all the components used for this mod back to stock.

In regards to re-aligning the s meter, it still doesn't work. If you set s9 = 50uV, it won't be correct for S5 ( a different uV level, not sure what it is at this time, but you get my point).

Re: 2sc2999 and Schottky diode swap.

Posted: Thursday 13th Mar 2008, 8:09
by Rick
Which Galaxy? The last time a looked there was 30 models. Was is the PCB number? What diode ref numbers?

Posted: Monday 7th Apr 2008, 22:25
by StrightClaw
I agree with Rick I tried this on my Ranger Moble and it seems about the same to me. Its not realy worth the effort.

Posted: Saturday 19th Jul 2008, 0:03
Can anybody pleae tell me which is the IF amp transistor in the President Adams? as i have a bagfull of new 2sc2999's,would like to swap the original & see if there is a dramatic improvement, as this mod worked superbly in my old Lincoln :D ,cheers.

front end

Posted: Saturday 19th Jul 2008, 0:47
by warhorse
tr5 2sc1730 rf amp going by the diagram'' played with transistor swaps i totaly agree with ricks coms above all depends what transistors u tweak i mean u cannot go by Hfe gains what so ever. highgain transistors most times have the reverse gains''. if you dont believe take a standard mids or uk cb and do swaps''.

Posted: Saturday 19th Jul 2008, 2:44
Hi warhorse :) yep i did the mod & it had the reverse effect as you suggested it might,coz when i swapped the transistor rx sensitivity went down so i have replaced the 2sc1730, was worth a try,cheers for your input on this,Shaun :D

Posted: Saturday 19th Jul 2008, 7:59
by Rick
There is a lot more to it than just changing a transistor and a few diodes, to find good transistors you really need access to transistors curve tracer.
I have some times tested 10 or so transistors with the curve tracer before I have found what I am look for, and even when you have found the right one it not just a case swapping the transistor, you also need to do a full re-alignment using a RF signal generator and SINAD meter.

Most DIY types do not have the equipment to do the job in the first place that why they get bad results and that why people like me charge a good price to do the job.

To improve the RX performance on the Adams, change the following TR6/7 to 2SC2999, C32 to 6pF, TR15 to 2SC1675 one for TR6 or 7 will do, D10/11/15/16 to 2N6263.

If you change the above, you will need to do a full re-alignment using a RF signal generator and SINAD meter.
You should be able on SSB to get 0.28uV for 10db S/N, and on AM it should be about 0.45uV for 10db S/N.
This chassis is not very broadband so you will only get the above sensitivity over about 60 channels (E.G 30 channels each side from the channel you do your alignment from).


Posted: Saturday 19th Jul 2008, 22:09
by warhorse

Posted: Sunday 10th Aug 2008, 10:58
by Unit 67
When i have done the RX modification for improve the radio reception capabilities i uses the NTE23 transistor,because the NTE23 transistor is a high gain transistor and has a noise filtering on it,but the pin out is different.

You will need to reorient the NTE23 transistor pins to work.I uses a piece of a #24 wire plastic cover to isolate the pins.With the flat side of the transistor facing to you and leads pointing down.

Transistors pinouts


I am talking about the NTE107 for a example only,because the first IF transistor in the CB radios has the same pinout as the NTE107.And this includes the 2SC1674,2SC1730,Etc,Etc.

I have done this mod in The Uniden Washington with the MB8719 PLL,the Cobra 148GTL,the Cobra 139XLR and many other radios in the first IF transistor with great results,but you have to readjust the RX meter pot.

2sc2999 and Schottky diode swap

Posted: Sunday 19th Oct 2008, 15:03
by thundir
Hey Rick or Carl if i did this mod on my ranger 2950 old school Non DX radio will i have to align the receiver or is it a plug and solder deal. PleAse let me know. Im actually doing this mod in about a week from today.......

2sc2999 and Schottky diode swap

Posted: Monday 1st Dec 2008, 17:12
by ralph60
very nice.

I used the NTE 107 and the four NTE 583 Schottky diodes. I didn't have to do a front end alignment.

I have an filed expedient antenna that I use every now and then to check that ever thing is in working order. its a small 3ft Fire stick mounted on a 3ft 1 1/2 EMT conduit a top a tripod with a ground rod. the whole set up stands a little more then 6ft off the ground. it has a good SWR.

I couldn't believe how far I was able to receive, and quiet. I am going take ever thing out of storage. set up my Shakespear Big Stick wiht the full wave Fire stick on the 60ft mast.

2sc2999 and Schottky diode swap

Posted: Sunday 18th Jan 2009, 15:34
by cmbb
I have tried to do this change in an old CB radio Truetone CYJ4837A-87 but the 2999 is impossible to find in mexico, and I've tried about 20 nte107 of different providers and cities and do not work, I think they are of the same origin, the question is that another transistor can use to make less noise and better reception with my radio? Thank you


Posted: Wednesday 18th Mar 2009, 4:01
by texan
I have the trc 457. It has the upd 858 like the 139xlr {same board number to I think} I changed the diodes in am detector and have the 2sc2999 transistor. I need to know which transistors to change.

[quote ]
I have done this mod in The Uniden Washington with the MB8719 PLL,the Cobra 148GTL,the Cobra 139XLR and many other radios in the first IF transistor with great results,but you have to readjust the RX meter pot.[/quote]

Re: 2sc2999 and Schottky diode swap

Posted: Saturday 21st Jun 2014, 13:38
by domedew

I have a Cherokee CBS-1000, that I would like to install the Schottky Diode swap too... but don't know the locations the transistors or the diodes in this radio... ANY HELP ??

Re: 2sc2999 and Schottky diode swap

Posted: Wednesday 1st Apr 2015, 0:44
by jimbowilly
When I perform this modification (receive upgrade). I really have to take the time and really listen before I realize just how much of a difference this mod makes. I usually listen on Sunday mornings (08:00 to 10:00)to the skip on channels 6 and 11 to get the best example of how much more I am receiving. And to realize how much more clear the reception is.
I've been testing this mod by including this mod with select operators I have worked for over the last couple of years. These CB and 10 meter radio operators can't stop telling me just how happy they are with their reception. And how quiet their radios now are with this upgrade.
One thing to add. The radios from the 1990's have less noise period.
I run 4' Francis antennas. 18ft of coax.