A Linear Amplifier

I will be adding a full portfolio of pictures as I go alone.

Power supply board. Not foreign metal parts.

Caps have low ESR and show proper capacitance on the digital cap meter.

Opened up the diodes to get a valid check. The right side diodes are hard shorts.

Each diode is rates at 3A 600 PIV. The schematic calls for 3A 1200v piv diodes.

This is the diode that I like and ordered.

3 amps, 1000piv, 15 Deg C/W (cooler running).

Mouser Part #:	621-1N5408-B
Manufacturer Part #:	1N5408-B
Manufacturer:	Diodes Inc.
Description:	Rectifiers 3.0A 1000V

	Data Sheet

Eight new 1N5408 installed.

On the Varriac. 12 volts AC in.

On the Varriac. 12 volts AC in.

Dim Bulb Tester w/ 200 watt lamp.

Dim Bulb Tester.

Full Line voltage and no blown fuses.

Full Line voltage and no blown fuses. Keep your hands OFF!!!

Low RF power input test.

Low RF power input test.

Here is what I figured happened. This is a vintage amp. Any silicon junction breaks down over time from the flow of electrons through the PN materials. It is like shooting BBs through a sponge. Eventually the BBs will stack up from front to back of the sponge. A vaguely similar thing happens in the PN material. It will eventually short out. This has been extensively explained in an IEEE article that I read this summer (2011).

Additionally I believe the diodes to be a tad under rated. That is they are 600 volts inverse voltage rated. That supply puts out 1500 (1100 measured) volts plate dc. The manual parts list calls for 3 amp 1500v reverse voltage rectifier diodes. Two 600 in series should withstand 1200volts. That is 300 over voltage according to the parts list.

I will get the Hi Voltage AC secondary voltage with a meter (using 1/10 the input AC 12.6 vac). And figure out what the real peak voltage with modern 120vac and the PA code the lighting line voltage (residential) is allowed to rise to 126 volts. See: Elmer Meter project for more information.

Some times I go overboard with details. But I like details.

1N5408 are the diodes that I purchased. All eight are being replaced. I am really liking the Diodes Inc products. Looking at the Data sheet I see this product runs significantly cooler (15C/W) than the other manufactures (~53C/W). Heat hurts junctions.