Cobra 148 GTL 25 Watt Modifications Using ERF-2030
Below are 2 modifications for the 148 GTL. Both modifications are approx. 25 watts. Modification #1 only replaces the final. Modification #2 replaces both driver and final. This modification is for the latest production 148 GTL with 4pin microphone plug. It is unknown if this modification will work on previous 148 GTL units. 148 GTL Modification #1 - Final Transistor Replacement Only Required Parts: 1pc ERF-2030 1pc EN-369FN 1pc 470pF ceramic disc capacitor 1pc 33K ohm, 1/4 watt resistor jumper wire 1) Remove L40 2) Remove C149 3) Remove R181 4) Remove TR36 and replace with ERF-2030. Note: ERF-2030 mounts identically to the removed 2SC1969. Make sure to use all the same hardware, insulator, thermal grease, etc. 5) Install jumper wire at R181 6) Add 470pF ceramic disc capacitor across C152 7) Install EN-369FN at TR36 (on solder side of PCB). Solder the positive lead (+) to the ERF-2030 gate. Solder the negative lead (unmarked) to the ERF-2030 source. 8) Add 33K ohm resistor (1/4 watt) from ERF-2030 gate leg to RGTL Modification #2 - Driver and Final Transistor Replacement Required Parts: 2pcs ERF-2030 1pc EN-369DR 1pc EN-369FN 1pc 1000pF ceramic disc capacitor 1pc 33K ohm, 1/4 watt resistor 1pc 470K ohm, 1/4 watt resistor jumper wire 1) Remove L40 2) Remove C149 3) Remove C156 4) Remove R209 5) Remove L43 6) Remove C200 7) Remove C151 8) Remove R181 9) Remove TR36 and TR38. Replace both with ERF-2030s. Note: ERF-2030 mounts identically to the removed 2SC2166 and 2SC1969. Make sure to use all the same hardware, insulator, thermal grease, etc. 10) Install jumper wire at R181 11) Add 1000pF ceramic disc capacitor across C152 12) Install EN-369DR at TR38 (solder side of PCB). Solder the positive lead (+) to the ERF-2030 gate. Solder the negative lead (unmarked) to the ERF-2030 source. 13) Install EN-369FN at TR36 (solder side of PCB). Solder the positive lead (+) to the ERF-2030 gate. Solder the negative lead (unmarked) to the ERF-2030 source. 14) Add 33K ohm resistor (1/4 watt) from ERF-2030 gate leg at TR36 to R180 15) Add 470K ohm resistor (1/4 watt) from ERF-2030 gate leg at TR38 to JW48 16) Remove the 270pF capacitor soldered from junction of C151, C152, R181 to ground. This 270pF capacitor is on the solder side of PCB.

R416 6K8 VR401 100K SQUELCH

PC - 412

To improve noise blanker performance change the following components C1 from (33p) to (18p), C2, 3, 4, 7, and 13 from (222) to (103), C6 from (222) to (472), R1 from (3K3) to (10K) R2 from (18K) to (33K), R4 from (470R) to (680R), D1 and 2 from (1N60) to (1N6263).

NOISE BLANKER

CTR4 2SC945 TR5 2SC945 TR7 2SA733 TR6 2SC945 TP6 R11 10K CTR8 2SC945 X1 7.3450 MHz CR17 3K3 R18 5K6 R19 10K R20 1K C17 100p C15 100p 2nd RX OSCILLATOR TR9 2SC1675

AM IF STRIP

L3 LA163 R26 1K5 D S R24 1K CR25 220R CCR29 220R FL1 FLKHz FET 1 3SK45 2nd MIXER G1 G2 R22 10K R27 1K8 R28 3K3 TR10 2SC945 R33 3K3 D8 IS1588 FET 2 2SK19 AGC AMP D5 IS1588 C24 4u7 C26 39p D3 IS1588 R30 1K2 R31 330R R32 3K3 R34 3K3 C23 0.47u D6 IS1588 D7 IS1588 R35 180K D9 IS1588 TR11 2SC1675 TR12 2SC945 TR13 2SA733 R234 150K TR48 2SA733 D67 IS1588
R3 330R L1 LA038 R6 47K TR3 2SC1730

USB AM LSB

S403-1 MODE

L2 LA179 R10 100K

D10 IS1588

C29 2u2 R37 1K R38 1K

R232 1K5

R2 18K R1 3K3 C1 33p

TR1 2SC1675 R4 470R C2 222

C4 222

C5 TR2 100pF 2SC1675 R7 2K7 CR5 22OR CR8 150R R9 68R

R41 2K2

R42 1K

D2 1N60 CD1 1N60 C9 82p

R13 470K

R15 330R

R16 10K
D66 IS1588 D71 1N60 R40 5K6 VR3 1K SQUELCH PRE-SET R235 15K D11 IS1588

C10 0.22u

R12 10K

C11 102

C12 100p

R33 1K

C25 0.47u

R36 1K D70 IS1588

C27 222
VR1 5K AM S/METER PRE-SET
VR2 5K SSB S/METER PRE-SET

C16 222

R21 100R

C21 222

8.0 VDC IN AM MODE
8.0 VOLTS WITH (N.B) SWITCH ON 7.8 MHz IF INPUT TO S METER OFF ANL
CD23 IS1588 R86 47K R87 1K D65 IS1588 R88 3K3 CC72 33u TR19 B = 1.30 VDC E = 0.70 VDC C = 5.60 VDC All voltages 2% CR85 560K TR19 2SC945 R91 2K7 R90 1K R93 22K CCR84 68K R89 10K R92 1K C74 47u C73 22u
ANL OFF S405-1 NB/ANL SWITCH

Euro Radio Co

NB/ANL D68 IS1588

euroradio.net

D20 IS1588 C48 5p L5 LA260 C41 2p L6 LA259 TR15 2SC1675 1st RX MIXER L7 LA258 7.8 MHz L8 C47 2p LA257 L9 LA268 FL2 FL046 7.8 MHz L10 LA269 D19 IS1588 D18 IS1588 R58 3K3 CFL3 FL067 R62 22R R66 15K TR16 B = 1.02 VDC E = 0.50 VDC C = 8.40 VDC All voltages 2%

AGC LINE

NB/ANL

S405-2 NB/ANL SWITCH

To improve the receiver bandwidth and signal to noise change the following components C41, 47 from (2p) to (3p), TR14 from (2SC1674) to (2SC2999), D21, 22 from (1N60) to (1N6263),

L12 LA270

CD13 MC301 L4 LA261 R43 150R TR14 2SC1674 RX RF AMP
TR17 B = 0.70 VDC E = 0.00 VDC C = 2.95 VDC All voltages 2%

R74 1K5 TR52 2SC945

TR18 B = 2.32 VDC E = 1.60 VDC C = 8.00 VDC All voltages 2%

L15 LA264

R34 3K3
R81 68K D22 1N60 D21 1N60 R82 100K

R80 1M

C64 220p R222 1K
R Ja Eu c ro ks R on ad io C
FET 3 2SK19 7.8 MHz 7.8 MHz 27 MHz CR53 10K CR257 680R R59 1K R253 1K5 R61 150R CR68 3R3 R54 180K R55 100R R56 1K R57 470R CL11 100uH R69 3R3 TR17 2SC1675 R73 33K CTR18 2SC1730 L14 LA271 R79 100K R60 220R R52 100R L51 L52 CR63 68R R64 1K5 R65 10K L13 LA272 D24 IS1588 C65 5p TP3 CC45 100p D17 IS1588 CR67 470R CR70 3R3 CR75 150R R76 68R CC62 1u R78 10K C66 220p C67 1u CTP4 CL57 470uH CCVCO MODULE PIN VOLTAGES PIN 1 = 7.8 VDC PIN 2, 3, 4, AND 7 PIN 5 = 3.4 VDC PIN 6 = 0 VDC PIN 8 = 8.00 VDC PIN 9 = 7.3 VDC PIN 10 = 4.02 VDC All voltages 5% CR106 100R TX + 8.0 vdc C68 15p TO INCREASE TX AUDIO CHANGE R124 AND R126 TO 4K7, AND ADD 1K RESISTOR R2E TO THE COLLECTOR OF TR26 R207 2KTP9 L20 LAMHz 3 2

CC31 12p D12 MC301

C52 222

TR16 2SC1675 C55 222

C58 222

C70 102

R83 100K

HI S407 TONE

27 MHz D16 IS1588 D15 IS1588 R48 1K R49 1K R50 2K2

R46 4K7 CC33 1u

D14 IS1588

C35 102

C37 102

C38 4p

R51 100R

C39 102

TX + 8.0 vdc R94 680R R47 3K9 RX + 8.0 vdc R45 1K5 PLL PIN VOLTAGES PIN 1 = 3.4 VDC PIN 2 = 4.28 VDC PIN 3 = 5.16 VDC PIN 4 = 3.45 VDC PIN 5 = 3.45 VDC PIN 6 = 8.0 VDC PIN 7 = 4.22 VDC PIN 8 = 4.46 VDC PIN 9 = 8.0 VDC PIN 10 = NC PIN 11 to 16 CH SWITCHED 8.0 VDC PIN 17 = 3.66 VDC PIN 18 = GROUND All voltages 3%

RX + 8.0 vdc

R241 100R

VR403 10K VOLUME

VR404 1K RF GAIN
R95 1K5 C201 C103 ALL RESISTORS 680R PC-416 IC1 MB15 S401 CHANNEL SWITCH D401 TLR11 CC1 HAGND FIN P1 P2 P3 P4 P5 P6 ** AO2 AI2 AO1 AI1 PD LD RI RO VCC 9 D31 IS1588 R97 2K2 R96 33K

Euro Radio Co

C95 47u R108 100R 1 IC3 AN612

CR98 12K

MIKE AUDIO
34.765 MHz = Channel 1 35.205 MHz = Channel 40

R124 10K

R126 10K

C108 0.47u

VR405 1K DYANMIKE

PC-426

L16 100uH

C99 2u2

R100 6K8 C81 2u2

C88 47p

C80 2u2

L17 470uH

R101 10K

TR20 2SC1675 LOOP MIXER

IC2 UHIC 007 VCO MODULE

TR22 2SC945

C104 0.47u

BALANCE MODULATOR 3

R107 100R

C98 10p

R206 270K

L19 LA216

R113 10K
TR21 2SC945 AM AUDIO SWITCH

C101 0.1u

TR23 2SC945

TR24 2SC945

D59 IS1588

D60 IS1588

L404 1u8 R134 3K3 D501 and VR501 Not fitted on early models TR26 2SC945 D501 AMC IS1588
J404 MIKE SOCKET AUDIO TX GND RX

C208 102

On some early models C18 is 47u change to 330u at 16 volt R128 15K

TR25 2SA733

R2E 1K

R133 47K

D61 IS1588

C405 102

C407 102

X2 10.240 Mhz

R104 1K

C89 47p

R102 2K2

R103 2K2

R105 100R

R205 1K2

C92 4u7

R110 150K

C93 103

C82 473

C84 1000u

C85 10p

C86 18p

C91 472

C97 103

C96 103

C207 47p
VR4 10K BALANCE MOD PRE-SET

R114 27K

R115 1K

R116 3K3

C100 22u

R117 470R

R118 47K

R119 10K

R120 5K6

R122 15R

C102 472

R123 10K

R125 56K

R129 33K

R163 22K

C90 0.47u

C94 472

R109 3K9

R112 1K5

C105 103

C107 103

C18 47u

R127 1M
R132 10K R130 1K5 R131 10K
TR27 2SA733 PA AUDIO SWITCH
CB S404-1 CB/PA AM AUDIO IN CB MODE PA AUDIO IN PA MODE

C46 222

C103 10u

R121 1K

C109 10u

VR501 1K AM AMC

C110 103

ALWAYS 8.00 VOLTS

R111 560R

R165 1K5

L59 LA284

AM TX AUDIO LINE

TR28 2SC945
LSB = 33.9765 MHz AM = 33.975 MHz USB = 33.9735 MHz
TR30 B = 3.80 VDC E = 3.20 VDC C = 7.90 VDC All voltages 2%

R236 8K2

D33 IS1588
MB3756 PIN OUT PIN 1 = ALWAYS 8.0 vdc 100mA PIN 2 = SUPPLY 13.8 vdc PIN 3 = VREF 8.0 vdc 100 mA PIN 4 = GROUND PIN 5 = RX/TX CONTROL PIN 6 = RX 8.0 vdc 100 mA PIN 7 = NC PIN 8 = TX 8.0 vdc 200 mA All voltages 3%

L23 LA285

L25 220u

X3 11.325 Mhz

R173 1K

L21 LA256

TR29 B = 1.46 VDC E = 1.08 VDC C = 8.10 VDC All voltages 2%

D34 IS1588

R148 8K2

6.8 VDC IN AM MODE

R203 10K

R137 1K

TR29 2SC1675 TRIPLER

TR30 2SC1675

C118 103

D32 IS1588

TR31 2SC945 AM SWITCH

TR32 2SC1675

X4 7.8000 Mhz

D39 IS1588

D40 IS1588 LSB

D41 IS1588 AM

R224 3K3

LOOP OSCILLATOR

L22 LA051

C119 103

R150 220R
CARRIER OSCILLATOR R151 22K

TR33 2SC945

L26 220u

R161 10K

VOLTAGE REGULATOR WITH RX/TX CONTROL

TR35 2SC945

R147 8K2

L58 470u

C116 2p

C117 470p

L24 220u

C120 103

D38 IS1588

R158 3K9

TR34 2SC1675 SSB ALC
IC4 MBR162 3K3 13.8 VDC S402 ON/OFF T1 TF147 C133 10u C134 10u C135 0.47u D43 IS1588 L401 LD013 CD55 1N4003 L402 LD013 DC 13.8 VOLTS C172 1000u CCCJ403
D35 IS2687 R239 10K R238 10K R237 10K

L27 470u

C123 220p
AM 7.8000 MHz LSB 7.7985 MHz USB 7.8015 MHz

R155 56K

L30 LA266 R156 22K

L31 LA265

R138 1K

R139 100R

R140 1K

R141 2K2

R142 10K

R143 220R

C111 103

C112 103

C113 103

C114 103

R144 1K

C212 470p R145 10K

R152 10K

R146 1K

C229 C228 C227

C213 18p

L60 470u

R149 18K

D36 IS1588

D37 IS1588

C106 0.47u

C125 5p

CT2 20p

R157 10K

R223 10K

R159 18K

C136 473

D44 1N4003

R164 560R

D42 IS1588

C124 222

R153 1K

C122 100p

R154 10K

L28 470u

C127 82p

D69 IS2687

L29 470u

C128 27p

L32 470u

C130 1p

C131 10p

L33 100u

C132 472

C215 222

C129 103

VR11 10K SSB ALC PRE-SET

R160 8K2

ALWAYS 8.00 VOLTS S403-3 MODE LSB AM USB 13.8 VDC R44 8K2

C199 103

C126 103

LSB AM USB

TX + 8.0 vdc

13.8 VDC

LOCK DETECTOR LINE (HI = LOCKED, LOW = UNLOCKED)

L49 LD077

D52 KB262

D75 KB262

R191 1K5

VR402 20K VOICE LOCK

D51 IS1588

R166 3K3

13.8 VDC On early models C181 is 10u I change this to 1000u at 16 volt. R258 1M NOTE: Filter cap C181 can be any size from 100u to 2200u at 16 volt it all comes down to what you can physically mount on the PCB. The higher the capacitance the better the filtering.

CJ401 PA

R174 12K

D53 IS1588

R187 2K7

R175 3K3

VR5 3K TX FREQUENCY PRE-SET

R188 100R

34.765 MHz = Channel 1 35.205 MHz = Channel 40 PLUS OFFSETS IN SSB
7.8000 MHz IN AM MODE PLUS OFFSETS IN SSB

R225 100K

CC166 472

R195 1K

TR47 2SA733

C230 0.47u

J405 ANT
How to unlock the VOICE LOCK. 1 Remove DRemove RRemove R174 and solder a jumper in its place. 4 Unsolder the red wire that comes from the Voice Lock pot from the PCB and solder in to pin 1 IC4 MB3756. 5 Change R175 to a 1K
C139 0.5p R176 330R R177 470R L35 LE051

R226 47K

TR53 2SC945
J402 EXT SPEAKER RX LINE C403 102

L37 LE051

L38 LC019

TR36 2SC1969 FINAL

L48 LA219

D45 1N60

CC7 CTR43 2SC458 AF BUFFER R227 3K9 CR199 680R R200 6K8 CR201 3K3 R202 22K C187 104

C150 330p

R181 10R

TR38 2SC2166 DRIVER

TR39 2SC2314 BUFFER

C162 47p

C163 2p

D73 1N60

D74 1N60
C141 68p C225 4n7 L36 LE051

C142 27p

C143 180p

D48 IS1588 C146 390p

L39 LD098
TR37 2SC496 BIAS REG C154 473

L42 LD098

C156 220p

D50 MV1Y

D49 MV13YH

D46 1N60

R178 10K 1/2 WATT

C147 47p

C149 120p

C148 104

VR8 5K BIAS

D76 IS1588

C155 100n

VR9 500R BIAS

C226 100p

C158 472

C164 103

R183 12R

C159 472

R184 330R

C160 472

R185 C161 330p 1K5

R189 100R

IC5 SO42P TX MIXER

5.60 VDC IN AM MODE 13.75 VDC IN SSB MODE

C144 1u

C138 472

C140 472

VR6 100K RF METER PRE-SET

R179 100R

C153 47u

C165 472

R228 560R

D63 IS1588

VR10 5K AM POWER

C177 104

C178 102

R198 68R

R256 560R

D47 IS1588

C154 1p

L40 LD087

C152 470p

L41 LD101

L44 LD096

C203 33p

L45 LA254

L47 LA160

TR42 2SC945

C174 1u

C175 470u

C176 47u 9

L46 LA220

IC6 AF AMP

SP401 SPEAKER

C151 472

L43 LD087

C157 472

R186 100R

R193 220R 1 WATT

TR41 2SC1419

TA7222AP

C169 472

R194 1K

R208 1R

R197 3K3

C186 220u

CB S404-2 CB/PA

R180 270R 1/2 WATT

R187 330R

C179 22u

C180 4u7

C173 10u

R196 4K7

C191 1u
ADJUST VR10 IN AM MODE FOR 5.60 VDC AT THE EMITTER OF TR41.

R169 47R

1/2 WATT
S/RF CAL SWR S408-1 SWR S/RF SWITCH

VR406 5K CAL SET

R418 100R

VCO MODULE UHIC007

S403-2 MODE

BRIGHT DIM

There are small 10-volt electrolytic caps dotted all over the various 8V supply rails, change them to 16-volt types for better reliable. Diodes IS1588 can be replaced with 1N4148.

S408-2 SWR S/RF SWITCH

LP2 LAMP

S406 DIMMER SWITCH

C1 10p

R2 6K8

R5 100R

TR2 2SC1675

R8 10K

M401 S/RF/SWR METER

D2 1N4148

D3 1N4148

R9 220R
If you find any errors or omissions, please let know the value of the component and or circuit reference. Please E-Mail me and I will correct them.
Known faults -------------------Warble on SSB, and the PLL chip running hot. Check Pin 9 the PLL it should be at 8V but you will probably find it at 10 to 11 volts in which case change IC 4 (MB3756) Warble on SSB. Check Pin 9 the PLL it should be at 8V if the voltage is bit low check C84 know to go low. Warble on SSB and low power. Check TR37 (2SC496) Bias regulator know to go o/c. Drift off frequency after warm-up. Replace C212 and C213 with 1% caps.

R1 3K3

D1 SVC251

C2 56p

C4 320p

R3 5K6

TR1 2SC1675

C8 102

R4 5K6

C5 120p

C6 102

C7 5p R6 5K6

R7 8K2
DRAWN BY: Rick Jackson Euro Radio Co Size Date: Document Number Cobra 148 GTL.SCH Tuesday, March 11, 2008 Rev 1.5 of 1