Have you tried measuring the voltage output under a load? I'm guessing at 5 amps the max output might be at around 6 volts but is it regulated or suppose to be regulated?
SG

I did place a load on it. Near as I can figure, it is not regulated as it does drop with varying load. I am sure it will scale to 6V at full load.

 

Ok Ideally you need to make a circuit diagram of it by Reverse Engineering it, follow the wires from the transformer and do the PCB as well, it's probably a center tapped supply, bridge rectifier using two 5Amp diodes and two transistors in a Darlington pair using the 2N3055 for the 0 to 6V supply.

Here is a Possible circuit diagram for the 0-6V supply...

Dodgydave, you are correct for the most part, but I did not see a Darlington pair anywhere. There is only one other transistor in the whole unit. I see in your drawing you realized the 6V is actually being fed by 9VAC from the transformer. I got it wrong my first time as well.

 

You will find there are 10 power supply circuits for the fixed voltages. It looks like a 1N400X family of diodes (1 amp) in the half wave rectifier topology with a resistive pi filter and a bleeder resistor. In a period, long time ago, bleeders served two purposes, one was safety and the other was a minimal form of regulation. The maximum spec i found by doing the maximum calculations based on the resistors. The bleeder typically consumed 10% of the total load current for regulation.

The variable will have higher diode current to satisfy the 5A specification.

JoeJester, right on the mark. The primary and the 9VAC that feed the variable supply are on one side of the transformer, and the other voltages that feed the fixed supplies are on the other side of the xfmr. I placed a picture above.

 

Dodgydave, you are correct for the most part, but I did not see a Darlington pair anywhere. There is only one other transistor in the whole unit. I see in your drawing you realized the 6V is actually being fed by 9VAC from the transformer. I got it wrong my first time as well.

The two transistors together make a Darlington pair.

 

Loaded with a 20 Megaohm input impedance will show the maximum peak voltage minus the diode drop of the 3055. So yeah, it will be up around that 11 volt DC level.


Have you drawn and labeled the components in the various power supplies yet? That will clue you into the fixed supplies.

It would be beneficial if you measured the ac voltages at the higher voltage taps and post them.

 

@CBTech_Joe

here are two of the fixed voltage power supplies that I could discern from the pictures minus the capacitor values. The less than 500 volt supplies share a topology You can use one schematic that would work for every supply to build your component list. I would like you to make a list of component values for each of the supplies, including the 6 volt variable.

 

@CBTech_Joe

here are two of the fixed voltage power supplies that I could discern from the pictures minus the capacitor values. The less than 500 volt supplies share a topology You can use one schematic that would work for every supply to build your component list. I would like you to make a list of component values for each of the supplies, including the 6 volt variable.

View attachment 217498

JoeJester, I will definitely get all the information to you. It is the least I can do for all the help. I will be travelling for work for a bit, but I will get on this as soon as I can. Your drawing looks very close to what I am trying to document in my chicken scratched drawings. I will verify as quickly as I can. I also have another thread running for a sweep/function generator repair which is waiting on parts. Apparently Newark only stocks some parts in Europe.

 

There is a reason the 6V supply is operating at such a high value. Back in my early days, the shunt resistor you see on the schematics was called a bleeder. It typically would draw about 10% of the maximum supply current.

It served two purposes, one was to discharge the capacitor when the main power was removed ... to save your ass should you touch them. The second purpose was basic voltage regulation. In fact the voltage regulation was the best answer on the FCC 2nd Class Radiotelephone license in the 1970s. In your supply, it would reduce the voltage to about 6 volts without a load. But that is inefficient for the low voltage supply. It's fine with those supplies that are milliamps, but not the ampere kind.

The better way would be to put a 6.8V zener between the base of the 2N3055 and ground.

What do you think would happen under a varying load without any regulation, without the bleeder or other regulation? ... the supply would move excessively.