Rectifier Replacement on my Blaupunkt tube radio

[omegaman]

My Blaupunkt 40400 Vollestereo console restore

I recapped the unit and changed some resistors


I have now read up on rectifiers and think I understand more about them and their application

http://en.wikipedia.org/wiki/Diode_bridge

http://w3hwj.com/index_files/RBSelenium2.pdf

First, about me. I am a neanderthal, mouth breather, barely able to walk upright when it comes to Electrical Radio service. I have never measured a voltage live and mostly just replace capacitors and resistors

What I learned:

Many electrical devices are powered from AC but actually run on DC, so AC has to be converted to DC.

Diodes limit AC to one direction, causing DC. This is called "rectification"

Rectified DC power "pulses" from the output cathode, holding back the reverse AC, and surging on the forward AC as AC alternates current. This is called "Ripple". A capacitor can smooth this pulsing out.

http://en.wikipedia.org/wiki/Reservoir_capacitor


Modern diodes used for rectifiction are more efficient then those of yore and the DC '+' output needs a resistor to drop the voltage back to specification. The voltage is on the schematic. Start with a 100ohm and adjust the ohms up or down till you get the required voltage from the spec. Use a high watt like a 3 or 5 watt resistor

My '+' voltage says 300v on the schematic

That would be DC volts. Make sure your meter can read that high a voltage



A half wave recification is just a single diode and a resistor

The full wave rectifier is used so that you can plug in the cord any way and the diodes will sort it out and deliver correct DC to the + and - lines

Full wave bridge rectifiers are marked with ~, ~, +, -

The ~ are AC inputs and the +/- are DC outputs


This radio's original silicon or selenium rectifier was replaced by the 4 diodes making a full wave bridge rectifier circuit. One diode has a broken lead

I believe I can replace the broken IN4007 diode and get the recification working

I also believe I can replace the whole 4-diode set up with a "NTE5316 R-SI,BRIDGE,800V, 8A" device as rectification


I will put a 100ohm 5 watt power resistor on the + side to compensate for the more efficient silicon diodes in the bridge and measure the voltage on the +/-and adjust the resistor to get my 300v

The radio already has a 100uf Electrolytic capacitor that the - line goes to. I think that is the ripple smoothing capacitor

I THINK THAT SPONGY LOOKING THING IN THE SILICON BEEFUP PICTURE IS A CAPACITOR. There are no markings. It is conncted to the '-' side

Questions:
Any guess what that spongy capacitor value might be? What would that capacitor do for the '-' side

What capacitor should I use to smooth the pulsing? Electrolytic? Value? Voltage? Is that connected between the + and - output lines?

Should I incorporate a bleeder resistor? What value? I could not calculate the value from the formula. How would that be included in the circuit?

Any input would be helpful, especially the "Don't do that, you'll kill yourself" kind