Collins MP-1 Power Supply
Complete Restoration Kit
For the S-Line · KWM-2 · KWM-2A | Includes RFI Mitigation Ferrite Package
47 Components 100% USA Sourcing Ships from MissouriTechnical Background — Why These Parts Fail
Selenium Rectifiers
The MP-1 originally used selenium rectifiers for its B+ and bias supplies. These devices degrade through a process of increased forward voltage drop and reduced efficiency, and they generate toxic selenium dioxide vapour when they fail under load. Replacement with 1N4007 silicon diodes requires a series-resistance correction because silicon exhibits a lower forward drop (~0.7 V vs ~1.0 V per cell) that would otherwise raise the output voltage above the original design intent. Series resistors of 47–100 Ω are specified per diode string to restore the original B+ level.
Electrolytic Capacitors
Aluminium electrolytic capacitors dry out over time as the electrolyte evaporates through the rubber bung. Capacitors manufactured in the 1960s are now over 60 years old and should be considered unconditionally failed for power-supply service, regardless of measured ESR or capacitance. All electrolytics in this kit are Nichicon or Cornell Dubilier parts rated at 105°C with long-life electrolyte.
Carbon-Composition Resistors
Carbon-comp resistors absorb moisture and drift badly over decades. Critical voltage-divider and regulator resistors that have drifted by more than 5% will upset the regulated output voltage and bias. This kit replaces those with 1% metal-film parts.
Wax-Paper & Disc Capacitors
Wax-paper capacitors absorb moisture and develop significant leakage resistance, causing coupling and bypass functions to degrade. Ceramic disc types from this era often exhibit severe capacitance shift with voltage (especially Z5U dielectric). Modern X7R film parts are substituted throughout.
Selenium Rectifier Replacement — Voltage Compensation
When replacing a selenium rectifier stack with 1N4007 silicon diodes, insert a series dropping resistor to replicate the original forward-voltage characteristic:
| Parameter | Selenium Stack | Silicon 1N4007 | Compensation Required |
|---|---|---|---|
| Fwd drop / cell | ~1.0 V | ~0.7 V | — |
| Typical 4-cell stack | ~4.0 V | ~2.8 V | +47–68 Ω series R per diode |
| B+ impact (no R) | nominal | +8–12 V high | Over-voltage — MUST correct |
| Series R value (B+) | — | — | 56 Ω 1W carbon-film per diode |
| Series R value (bias) | — | — | 47 Ω 1W per diode |
| Ref | Value | Voltage | Temp | Qty | Part Number | Vendor | ~Unit |
|---|---|---|---|---|---|---|---|
| C1, C2 | 100 µF | 450 V | 105°C | 2 | Nichicon LGX2W101MELC45 | Mouser | $2.85 |
| C3, C4 | 47 µF | 450 V | 105°C | 2 | Nichicon LGX2W470MELB30 | Mouser | $2.10 |
| C5, C6 | 22 µF | 350 V | 105°C | 2 | Cornell Dubilier 222LGL350M2CA | Digi-Key | $1.45 |
| C7–C10 | 10 µF | 100 V | 105°C | 4 | Nichicon UVZ1V100MDD | Mouser | $0.38 |
| C11–C13 | 4.7 µF | 50 V | 105°C | 3 | Nichicon UVZ1H4R7MDD1TA | Mouser | $0.28 |
| C14, C15 | 220 µF | 25 V | 105°C | 2 | Nichicon UVZ1E221MPD1TA | Mouser | $0.32 |
| C16 | 1000 µF | 35 V | 105°C | 1 | Cornell Dubilier 105CPS035M | Digi-Key | $0.95 |
Nichicon via Mouser Electronics, Mansfield TX. Cornell Dubilier via Digi-Key, Thief River Falls MN. Both stocked domestic-warehouse — typically ship same business day.
| Ref | Value | Voltage | Dielectric | Qty | Part Number | Vendor | ~Unit |
|---|---|---|---|---|---|---|---|
| C20–C25 | 0.1 µF | 400 V | Film/X7R | 6 | Kemet R82IC3100AA60J | Digi-Key | $0.22 |
| C26–C29 | 0.01 µF | 400 V | Film/X7R | 4 | Vishay MKT1826410064 | Mouser | $0.18 |
| C30–C33 | 1000 pF | 500 V | C0G/NP0 | 4 | Kemet C330C102KGG5TA | Digi-Key | $0.15 |
| C34, C35 | 470 pF | 500 V | C0G/NP0 | 2 | Kemet C330C471KGG5TA | Digi-Key | $0.15 |
| C36–C38 | 0.047 µF | 400 V | Film | 3 | Vishay MKT1826447064 | Mouser | $0.19 |
| C39, C40 | 100 pF | 500 V | C0G/NP0 | 2 | Kemet C315C101KGG5TA | Digi-Key | $0.14 |
| Item | Description | Rating | Qty | Part Number | Vendor | ~Unit |
|---|---|---|---|---|---|---|
| D1–D8 | Rectifier diode 1N4007 | 1000V / 1A | 8 | ON Semi 1N4007RLG | Mouser | $0.12 |
| D9–D12 | Fast-rec diode UF4007 | 1000V / 1A fast | 4 | Vishay UF4007-E3/54 | Digi-Key | $0.17 |
| ZD1, ZD2 | Zener 6.8V 1W (regulator) | 6.8V / 1W | 2 | ON Semi 1N4736A | Mouser | $0.18 |
| ZD3 | Zener 12V 1W | 12V / 1W | 1 | ON Semi 1N4742A | Mouser | $0.19 |
| R-COMP1 | Series R, B+ rectifiers — 56 Ω | 56Ω 1W CF | 8 | Yageo CFR-01JB-52R3 | Digi-Key | $0.08 |
| R-COMP2 | Series R, bias rect. — 47 Ω | 47Ω 1W CF | 4 | Yageo CFR-01JB-52R47 | Digi-Key | $0.08 |
| Ref | Value | Tol | Power | Qty | Part Number | Vendor | ~Unit |
|---|---|---|---|---|---|---|---|
| R1, R2 | 10 kΩ | 1% | ½W | 2 | Vishay CMF5010K000FHEB | Digi-Key | $0.15 |
| R3 | 22 kΩ | 1% | ½W | 1 | Vishay CMF5022K000FHEB | Digi-Key | $0.15 |
| R4, R5 | 4.7 kΩ | 1% | ½W | 2 | Vishay CMF504K7000FHEB | Digi-Key | $0.15 |
| R6–R9 | 1 kΩ | 1% | ½W | 4 | Vishay CMF501K0000FHEB | Digi-Key | $0.15 |
| R10–R13 | 100 Ω | 5% | ½W | 4 | Yageo CFR-25JB-52-100R | Digi-Key | $0.07 |
| R14, R15 | 47 Ω | 5% | 1W | 2 | Yageo FMP100JR-52-47R | Digi-Key | $0.10 |
| R16 | 10 Ω | 5% | 2W | 1 | Vishay AC02000009990JAC | Digi-Key | $0.18 |
| R17, R18 | 470 kΩ | 1% | ½W | 2 | Vishay CMF50470K00FHEB | Digi-Key | $0.15 |
| R19 | 100 kΩ | 1% | ½W | 1 | Vishay CMF50100K00FHEB | Digi-Key | $0.15 |
| R20, R21 | 2.2 kΩ | 1% | ½W | 2 | Vishay CMF502K2000FHEB | Digi-Key | $0.15 |
| R22 | 33 kΩ | 1% | 1W | 1 | Vishay CCF5033K00FKE36 | Digi-Key | $0.22 |
| Bleeder R | 47 kΩ | 5% | 5W | 1 | Ohmite L225J47KE | Mouser | $1.45 |
Bleeder resistor sourced from Ohmite Mfg, Rolling Meadows IL — a US manufacturer. Verify the original bleeder value against your unit’s schematic; 47 kΩ is typical for this voltage class.
The original MP-1 design included no conducted-emission suppression. At the time of Collins manufacture, FCC Part 97 and FCC Part 15 did not impose the RFI standards now expected by the amateur community. The ferrite package here provides three layers of suppression: AC-line common-mode rejection, DC-bus conducted-noise suppression, and individual-lead bead filtering. All ferrite materials are sourced from Fair-Rite Products Corp, Wallkill NY and Amidon Inc, Costa Mesa CA — both US manufacturers.
Material Selection Rationale
Type 31 (µi = 1500) — preferred for common-mode chokes on AC mains and DC power leads. Excellent attenuation from 1 MHz to beyond 300 MHz, covering the entire HF and VHF spectrum used by S-Line and KWM-2 operators.
Type 43 (µi = 850) — used for HF suppression beads on individual signal and control leads, with peak impedance in the 1–30 MHz region.
Type 77 (µi = 2000) — specified for the output-bus choke where maximum low-frequency common-mode impedance is required.
Type 61 — small core for the voltage-sense/feedback lead; provides suppression from 200 kHz to 10 MHz with very low loss at audio frequencies, preventing RF-induced regulator oscillation.
Ferrite Component Bill of Materials
| Item | Description | Material | Form | Qty | P/N | Vendor | ~$ |
|---|---|---|---|---|---|---|---|
| FL1 | AC mains CMC toroid (wound 8T bifilar, 22 AWG) | Type 31 | Toroid 1.4″ OD | 1 | 5931003801 | Mouser | $3.20 |
| FL2 | B+ bus CMC toroid (wound 5T bifilar, 20 AWG) | Type 77 | Toroid 1.4″ OD | 1 | 5977003801 | Mouser | $3.50 |
| FL3, FL4 | Snap-on clamp, AC mains lead pair | Type 31 | Clamp 0.375″ ID | 2 | 0431167281 | Mouser | $1.85 |
| FL5–FL8 | Snap-on clamp, DC output leads | Type 31 | Clamp 0.375″ ID | 4 | 0431167281 | Mouser | $1.85 |
| FB1–FB6 | Ferrite bead sleeve, 22 AWG leads | Type 43 | Bead 0.125″ | 6 | 2743002112 | Mouser | $0.28 |
| FB7–FB10 | Ferrite bead sleeve, control wiring | Type 43 | Bead 0.250″ | 4 | 2743001112 | Mouser | $0.42 |
| T1 core | Amidon toroid, auxiliary wound choke | Type 43 | FT-114A-43 | 1 | FT114-43 | Amidon | $2.95 |
| T2 core | Amidon toroid, regulator feedback loop | Type 61 | FT-37A-61 | 1 | FT37-61 | Amidon | $1.20 |
Ferrite Placement Guide
Wind 8 turns bifilar (both AC legs together) on the Type 31 toroid. Mount as close as possible to the AC input socket, before the main power switch. This suppresses conducted RF from the transmitter that back-feeds via the mains. Use 22 AWG Teflon-insulated wire.
Wind 5 turns bifilar (B+ and return together) on the Type 77 toroid. Install in series with the B+ output lead, 1–2″ from the output terminal strip. Provides common-mode rejection on the highest-current DC bus and prevents RF from re-entering the supply from the transmitter PA.
Snap one clamp over both AC mains leads together at the IEC/chassis entry point. Snap the second clamp 2″ further along. No winding required.
Apply one clamp per output lead (B+, bias, chassis common) as close to the output connector as practical. Loop the lead through twice if the clamp ID permits, doubling the effective turns count.
Thread individual signal and control leads through the Type 43 bead sleeves at the PCB end of each lead. Focus on the voltage-sense lead, the error-amplifier signal lead, and any leads longer than 3″.
Wind a 10-turn single-wire choke on this core and insert in series with the regulator control wiring bundle. Wind uniformly around 75% of the core circumference. Handles the 1–30 MHz HF window.
Wind 6 turns on this small Type 61 core and install in the voltage-sense/feedback lead. Type 61 material provides suppression from 200 kHz to 10 MHz with very low loss at audio frequencies, preventing regulator oscillation due to RF pickup.
| Item | Description | Qty | Spec / Part | Vendor | ~$ |
|---|---|---|---|---|---|
| TS1 | Barrier terminal strip, 6-position | 1 | Molex 38520-0606 | Mouser | $1.85 |
| HS1 | Heat shrink assortment 3:1 ratio, 22–16 AWG | 1 pk | TE CPRSA1-HST-4X1BK | Digi-Key | $4.50 |
| HS2 | Heat shrink 3/8″ for ferrite joints | 6″ | TE CGSH38-6-SP | Digi-Key | $0.40 |
| WR1 | Belden 22 AWG solid PTFE wire, 1 m | 1 m | Belden 9978 or equiv | Newark | $0.80 |
| WR2 | Belden 20 AWG stranded hook-up wire, 1 m | 1 m | Alpha 1855/7 | Newark | $0.60 |
| TW1 | Cable tie-wrap, 4″ natural, 100 pk | 1 pk | Thomas & Betts TY-23MX | Newark | $2.10 |
| SD1 | 63/37 Sn/Pb 0.032″ rosin-core solder, 0.5 oz | 0.5 oz | Kester 24-6337-0027 | Mouser | $3.50 |
| INS1 | Kapton tape ¼″ roll (ferrite insulation) | 1 roll | 3M 1205 or equiv | Digi-Key | $3.20 |
| DWG1 | Printed schematic / overlay diagram | 1 | — | — | incl. |
USA Vendors
Nichicon caps, rectifiers, Ohmite, Fair-Rite
Cornell Dubilier, Kemet, Vishay, Yageo, TE
Ferrite toroid cores (FT series)
Belden wire, tie-wraps, connectors
Power resistors (US manufacturer)
Ferrite cores (US manufacturer)