Heathkit SB-200 Collins 30L-1 kit

The Heathkit SB-200 and Collins 30L-1 share almost identical design backbones. Both have dc floating control grids, -120 Vdc resistor voltage divider bias systems, and DPDT relays. Both amplifiers are AB2 (conduction angle slightly more than 180 degrees and having grid current). The 30L-1 and SB-200 are cathode-driven with tuned input circuits, both covering 80 through 10-meter primary Ham bands.

Other than layouts, the main difference between the 30L-1 and SB-200 is original tube choice. The 30L-1 uses four 65-watt ICAS dissipation cathode-driven thin-anode 811 tubes running at nearly 1900 volts, the SB-200 uses a pair of T160L/572B cathode-driven graphite anode tubes. The SB-200 thus has a total of 320-watts plate dissipation while the 30L-1 has 260-watts.

The Collins and Heathkit amplifiers are so similar in backbone one could rightfully assume the SB-200 is simply a modernized 30L-1 circuit copy.

I cover the details of both machines in two papers. The first paper deals mostly with biasing:


The second paper deals mostly with arc protection:


While we sell many RF tubes and parts, I have five basic parts kits and systems common to both amplifiers:

  1. An arc protection and bias upgrade for both the 30L-1 and SB-200 (located on this page) the SB200KP
  2. A modern fast properly-sequenced 120-Vdc relay board system
  3. A step-start system
  4. A tuned parasitic suppressor board good for 811 and 572 style tubes located on this page
  5. A relay line buffer that is more stable with better threshold than other types

The SB200KP covers both the SB-200 and the 30L-1 amplifier groups. This kit contains:

  1. Two 150V GDTs for the filament
  2. Two 230-volt GDTs, in the SB-200 one directly from each grid pin to chassis ground, in the 30L-1 on the grid resistor common point
  3. Two 1N4007 or heavier meter protection diodes (these protect the meter in any severe arc)
  4. One 1N5408 grid positive clamp diode (in a fault the grid goes positive)
  5. One 1N5408 power supply negative rail clamp (prevents the negative supply rail from rising in a fault)
  6. Two .1uF (or greater value) bypass capacitors for the meter diodes and the negative rail diode
  7. Four high surge capacity 33 ohm 1W metal composition resistors for tube grids
  8. One 10-ohm, 9kV surge-rated 9-watt fault resistor
  9. Two 3.9V 5-watt Zener diodes for grid bias (the 30L-1 should use two diodes with 811 tubes, 572 tubes can use one or two)
  10. Four orange .001uF (1000pF) HV pulse rated disc capacitors for improved grid-to-chassis bypassing

This entire kit is $30 shipped to any USA postal address. I am still in the stone ages so you have to email me at this link Email to Order