04-04-2021, 11:58 AM
A couple of pointers on the old Philco tetrode trf sets.
1. When rebuilding the filter block (big black metal can) stick to the mfd value of the caps. If you don't it can significantly raise the B voltage.
2. Use film caps not electrolytic type. E caps can't take the ripple current and will short after a few months of operation. The 80 will turn a very angry red color! See pic below.
3. Check the resistance of the untuned side of the rf coils. Not uncommon for them to be open do to a chemical reaction.
4. Check resistance between any of the four pins on the spkr plug (unplugged). Should see nothing higher than 4k. Field coil is abt 3200 ohms and the the opt pri is abt 500 ohm. You can rewind the fc, spkr comes apart part pretty easily. If your a glutton for punishment you can rewind the transformer. A member just did one a few weeks ago.
5. Check the 250 ohm side of the volume control. It controls the cathode current on the rf amps. A lot of times they are intermittent or open @ the low end. The 5K side is always good which doesn't do much.
Don't know if you saw this diagram but it's got the parts values on it.
https://philcoradio.com/library/index.ph...chematics/
I have It's older bro the 76. The only difference is you've got a tone control and I've got a local/distance switch.
GLOM
de N3GTE
1. When rebuilding the filter block (big black metal can) stick to the mfd value of the caps. If you don't it can significantly raise the B voltage.
2. Use film caps not electrolytic type. E caps can't take the ripple current and will short after a few months of operation. The 80 will turn a very angry red color! See pic below.
3. Check the resistance of the untuned side of the rf coils. Not uncommon for them to be open do to a chemical reaction.
4. Check resistance between any of the four pins on the spkr plug (unplugged). Should see nothing higher than 4k. Field coil is abt 3200 ohms and the the opt pri is abt 500 ohm. You can rewind the fc, spkr comes apart part pretty easily. If your a glutton for punishment you can rewind the transformer. A member just did one a few weeks ago.
5. Check the 250 ohm side of the volume control. It controls the cathode current on the rf amps. A lot of times they are intermittent or open @ the low end. The 5K side is always good which doesn't do much.
Don't know if you saw this diagram but it's got the parts values on it.
https://philcoradio.com/library/index.ph...chematics/
I have It's older bro the 76. The only difference is you've got a tone control and I've got a local/distance switch.
GLOM
de N3GTE
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Terry
