Help with 73.5 Voltage regultor

[mike walker]

I'm trying to find a VR for a 73.5 T. Pelican had two but neither looks like the one on the car. Its a Marchel. Can anyone direct me where I can buy one? thanks

[Gumby]

The new replacement one does work but looks "different" I'm guessing that your's is not a Bosch. Ron

[mike walker]

The one on the car is a Marchel. The ones I got from pelican is a black "H" looking thing that does not look like the original its part number is 911-603-901-00. The other kind of looks like the original but the terminals are not oriented the same. It is a Bosche part number 901-603-206-02. Will it work??? Thanks for your help.

[Gumby]

Mike, The correct replacement looks nothing like the orginal but works just fine , I think that you cannot switch between types , so if your car had a Marchel, then you have to stick with a Marchel replacement. What Pelican sent you should be fine , it's a little fiddley to connect tho . my Marchel replacement looked like a 1/4 thick X 2 peace of plastic !!! with 2 connections at the top "tabs" and I hooked up the ground to the bottom center of the unit . If you need a photo let me know . Ron

[mike walker]

Mike, The correct replacement looks nothing like the orginal but works just fine , I think that you cannot switch between types , so if your car had a Marchel, then you have to stick with a Marchel replacement. What Pelican sent you should be fine , it's a little fiddley to connect tho . my Marchel replacement looked like a 1/4 thick X 2 peace of plastic !!! with 2 connections at the top "tabs" and I hooked up the ground to the bottom center of the unit . If you need a photo let me know . Ron

Ron, Please attach a photo....thanks

[Gumby]

Mike here is a photo I hope this helps . Ron

[mike walker]

Thanks Ron that helps a lot...I thought that was the wrong kind.

[304065]

That's a Huco by the look of it.

VR's are pretty simple. Only two wires in and one out, D+/61 input from battery, D- ground and the DF wire to the alternator brushes, into the slip rings, through the field and then to ground. Every VR has a "set-point" which is a predetermined voltage below which the DF wire receives whatever voltage the D+/61 is receiving. In the old days, this was done electromechanically with a bimetallic strip that heated up at a certain voltage and opened the connection between D+/61 and DF. Once the field current shut off the strip cooled down and closed the circuit again and off you go. Modern Solid-State VR's use a transistor or something to switch the field in and out. I used to believe that they continuously varied the output voltage to the field to match the set-point, but was disabused of that notion by an expert who claimed that to continously vary would require a huge resistor.

Anyway, what varies among manufacturers, and the reason Porsche admonishes us, on the little sticker on the engine compartment latch panel, to use the same manufacturer of voltage regulator as alternator, is because the set-point varies. You wouldn't want to use a Bosch reg with a Marchal alt because the design is slightly different and the set-point is different. The way around this (non-concours) is to use an adjustable VR like the Transpo IB301A.

Anyway, the Marchal box is a white plastic can that mounts sideways on the board. If you can't find one OE send me a PM.

[Gumby]

John , When my orginal VR went "bad" I took it apart and cleaned the contacts, It worked but... the tach did not like it! much bouncing so I went with this replacement . Ron, ps. spot on the discreption of operation.