Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: mresistor on June 09, 2012, 08:41:21 am
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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.
(http://i122.photobucket.com/albums/o250/privateacct/20120609_0745.jpg)
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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
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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.
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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.
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If you would draw it out it would be easier to figure out what he was trying to do.
Brad :icon_biggrin:
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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.
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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.
(http://i122.photobucket.com/albums/o250/privateacct/20120609_0748.jpg)
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Very nice find. Did you figure it out along the way?
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Not a clue Ed - must have been a government funded project...
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congrats & nice!
happy pikkin' :icon_biggrin:
--DL
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Not a clue Ed - must have been a government funded project...
:l2:
Brad
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Not a clue Ed - must have been a government funded project...
I'm sure there is a lot of paperwork documentation. But finding it... :icon_biggrin:
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Not a clue Ed - must have been a government funded project...
No wonder it was left unfinished...