1974 Champ strangely modified

[mresistor]

Picked up a 74 Champ, from an estate sale and the owner was obviously a tinkerer. Take a look at this photo, what was the guy doing here? Was he running DC filaments to the 6V6 and had them elevated? I wonder if this modification was actually working as it looks like it was still in process or he had problems with it, white wires not connected. I'm wondering if the 5 volt filament winding is good on this original PT. Trying to figure out why this was done. I thought I'd give you guys a look before I restore it to normal condition.

[Fresh_Start]

What the heck is that slider switch on the board for?

I notice that someone scorched the insulation on at least one red wire...

Chip

[mresistor]

Hi Chip - Scratch the DC filament - I think he was lifting ground with the switch and orange wires. (don't think I will plug it in like this). The output of the switch goes to pin 7 of the 6V6. But pin 2 is still connected to 6.3vac filament voltage. Darn strange. There are two diodes and a 33uf e-lytic cap added on the additional terminals. What the purpose was of this modification completely eludes me.

[Ed_Chambley]

The only thing I can see is maybe he was trying to make a variac with the slider just because there is a fairly large resistor in series.  I don't think I would power it up.  I have no idea of the reason for the diodes on the heater or the additional caps.  Attempting DC would be my only guess.  If I had an old SE PT lying around, I might stub it is and fire it up to see what happens because it is one of 2 things.  It is either really cool or really stupid.

Plus it is a Champ.  You can put back original in about 45 minutes.  Makes me curious, so I would have to check it out as is.

Anyway, Great score picking up a champ as I am sure you got it for next to nothing.

[Willabe]

If you would draw it out it would be easier to figure out what he was trying to do.


                            Brad     

[mresistor]

Thanks, but, I'm just going to take the stuff out...   make it work normally again. Starting in a few minutes. Got a feeling I might find out the "why" along the way.

[mresistor]

Well, I took all that mod stuff out and soldered up a ground at the 6V6 pin 7 to chassis, added a wire from the rectifier to the 1K resistor, added the tubes, put a fuse in it, stuck it back in the cabinet, connected the speaker and turned it on. It's got a Jensen C8R in it, and it sounds very nice. I had some old rusty 66 chassis straps I donated to the cause as it came to me with none. I like the blue lamp jewel too. Not a bad investment.

[Ed_Chambley]

Very nice find.  Did you figure it out along the way?

[mresistor]

Not a clue Ed - must have been a  government funded project... 

[DummyLoad]

congrats & nice!

happy pikkin'   

--DL

[Willabe]

Not a clue Ed - must have been a  government funded project...

             


            Brad   

[sluckey]

Not a clue Ed - must have been a  government funded project... 

I'm sure there is a lot of paperwork documentation. But finding it...   

[darryl]

Not a clue Ed - must have been a  government funded project... 

No wonder it was left unfinished...