06-25-2016, 01:34 PM
<is a big positive.>
Yes it is, about 300v.
I didn't mention last night I had a little fireworks. 91 the dual mains bypass cap blew it's top BANG!!!!! So that was exciting. I haven't done an ortopsy but I think I may have over heated one of the leads inside the bakelite block when soldering on the outside connections. One of the leads may have been touching the outside of the other cap and with some heat added it could melt the yellow mylar and shorted to the foil innards.
After poking around a bit I found that the plate voltage on the mixer and 1st IF was low like 80vdc, should be 200vdc. Did a little investigation to find that I had done a little miscalculation. #47 is in parallel with the shadowmeter coil and is 2000 ohms. I replaced it with a 2300 ohm resistor. At first thought I was thinking that 47 was used to set the amount of current thought the shadowmeter's coil. Make it higher and you'll get more deflection lower and you'll get less deflection. But upon looking a bit closer it also controls the plate voltage for the mixer/IF amp. With a good coil and resistor you should have about 800 ohms. My coil is open. I had 2300 ohms. Replaced it with a 750 ohm resistor (had it on hand) and did some voltage check, things looked a lot better.
Flipped it back over and realigned the IF stages. Before didn't have much gain, had to crank up the output of the generator to get a signal and the adjustment didn't peak very well was really broad. With the right voltages the peak is much more pronounced and have the generator output all most all the way down. All this is good!
Had pulled the 76 tube out while I was troubleshooting put it back in and hooked my 25ft test ant (cord for the Eletrolux sweeper) and we got stations!!!. Volume is still a bit low and volume control is dirty so it's next on the list for cleaning.
Terry
Yes it is, about 300v.
I didn't mention last night I had a little fireworks. 91 the dual mains bypass cap blew it's top BANG!!!!! So that was exciting. I haven't done an ortopsy but I think I may have over heated one of the leads inside the bakelite block when soldering on the outside connections. One of the leads may have been touching the outside of the other cap and with some heat added it could melt the yellow mylar and shorted to the foil innards.
After poking around a bit I found that the plate voltage on the mixer and 1st IF was low like 80vdc, should be 200vdc. Did a little investigation to find that I had done a little miscalculation. #47 is in parallel with the shadowmeter coil and is 2000 ohms. I replaced it with a 2300 ohm resistor. At first thought I was thinking that 47 was used to set the amount of current thought the shadowmeter's coil. Make it higher and you'll get more deflection lower and you'll get less deflection. But upon looking a bit closer it also controls the plate voltage for the mixer/IF amp. With a good coil and resistor you should have about 800 ohms. My coil is open. I had 2300 ohms. Replaced it with a 750 ohm resistor (had it on hand) and did some voltage check, things looked a lot better.
Flipped it back over and realigned the IF stages. Before didn't have much gain, had to crank up the output of the generator to get a signal and the adjustment didn't peak very well was really broad. With the right voltages the peak is much more pronounced and have the generator output all most all the way down. All this is good!
Had pulled the 76 tube out while I was troubleshooting put it back in and hooked my 25ft test ant (cord for the Eletrolux sweeper) and we got stations!!!. Volume is still a bit low and volume control is dirty so it's next on the list for cleaning.
Terry
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