The Amplifier Power Supply

Part B - The Transformer Side

The second power supply circuit diagram shows the HT and LT transformers and associated circuitry including the HT capacitor board and the HT Divider / monitor board. 

A couple of bits are different to that shown in G3SEK's control card design:

  • The HT divider is different. As I was limited in physical space I used two 10M ohm @ 7.5kv resistors rather than 16 1M ohm resistors!

  • The 240v blower is driven from a secondary winding on the HT transformer so that the amplifier could still be used with 120v mains (line) supply.

Click on the component to see a photograph

The Power Supply, transformer Side

The key parts of the above circuit are:

  • The HT and LT transformers

  • The 8877 cooling blower

  • The HT bridge rectifier and capacitor bank

  • The HT monitoring board

  • The R104 HT surge current limiting resistor

Parts List

Power Supplies - Transformer Side
Supplier      Part     Number     QTY   


RS R201-210  199-5836 10 47k, 9watt resistor, wirewound, vitreous enamel
RS C1-10 381-9374 10 ALS30, 450Vdc, 220uF aluminium electrolytic, screw terminal
RS R106a/b 296-0572 2 10M ohm Resistor, high voltage, 7.5kv
RS R107/8 214-1406 2 Resistor, metal oxide film, power, 1W, 100k
Heritage T1   1 HT transformer, 2,800v, 240v @ 120mA secondaries. Made to specification.
Heritage T2   1 LT transformer, 15v and 5v @ 10A secondaries. Made to specification.
Silicon Alley D1-4 HV14-1 4 EHT rectifier sticks
RS   408-397 4 Fuseholder, panel mount, low profile, 25x6.3mm, screw cap, tag connection, 13A
RS R104 252-6431 1 Resistor, 75W, 47R
RS R105 159-966 1 Resistor, metal cased, power, 10W, 1k, 5%
RS   223-089 1 Blower, single inlet, 240Vac, 110CFM
RS   581-307 1 Blower, accessories, filter assembly, 110-165CFM
RS   211-0941 1 Connector, power, plug, shrouded, 4 way (for blower supply)
RS   211-0957 1 Connector, power, socket, shrouded, 4 way (for blower supply)
RS    213-7564 2 Fuseholder, open base, 1.25in
RS   18-9539 1 Fuse, anti surge, Siba 70-059-61, 2A