I have a 40-190 that is running a 5Y3 rectifier and an aftermarket power transformer that is under rated even for the 5Y3. I can fix all of this.
But all the Riders and Beitman schematics I'm looking at show a 7J7 Det.-Osc. tube. Mine has a 6J8 in it and everything associated with it looks original. Is the 6J8 original and is there any schematic showing it? A lot of different connections and component differences between the two.
Thanks,
Pepper
Thanks Glenn! I've got all the NA Riders paperwork and my own original Beitman schematics. All showing the 7J7. I know the 5Y3 isn't correct and why it was changed I don't know. 84 has a 5 pin socket and it was changes to a standard octal to support the 5Y3. Okay to run the 5Y3 but not with an aftermarket power transformer that's rated 250-0-250 on the hi-voltage outputs. If my memory serves me well the 5Y3 wants plate voltage of 350-0-350 for the hi-voltage. The transformer that's on it now has a big puddle of wax under it so I know it got very hot. Haven't checked winding resistance yet. Puddle of wax could have been from the original transformer. Just gettin' started on it and wanted to figure out this 7J7 issue 1st. A couple of resistors coming off of the 6J8 are color coded grn. stripe with brown body but they don't read anything with a "5" at the beginning. In fact they both read completely different by hundreds of ohms.
I'll get in touch with Chuck. His paperwork is always great.
Thanks again,
Pepper
Pepperoni Wrote:Thanks Glenn! I've got all the NA Riders paperwork and my own original Beitman schematics. All showing the 7J7. I know the 5Y3 isn't correct and why it was changed I don't know. 84 has a 5 pin socket and it was changes to a standard octal to support the 5Y3. Okay to run the 5Y3 but not with an aftermarket power transformer that's rated 250-0-250 on the hi-voltage outputs. If my memory serves me well the 5Y3 wants plate voltage of 350-0-350 for the hi-voltage. The transformer that's on it now has a big puddle of wax under it so I know it got very hot. Haven't checked winding resistance yet. Puddle of wax could have been from the original transformer. Just gettin' started on it and wanted to figure out this 7J7 issue 1st. A couple of resistors coming off of the 6J8 are color coded grn. stripe with brown body but they don't read anything with a "5" at the beginning. In fact they both read completely different by hundreds of ohms.
I'll get in touch with Chuck. His paperwork is always great.
Thanks again,
Pepper
A 5Y3 doesn't care whether it has 250 volts on the plates or 350 volts on each plate the only thing that matters is what the current load is on the output of the tube, in the case of a 5Y3,5Y5, and an 80 the maximum current is 125 milliamps. Quite clearly the original transformer packed it in and someone could not find, or could not bother to find a duplicate of the original. If the original was a type 84 the filament voltage is 6.3 volts and is normally powered from same filament winding as the rest of the tubes, unlike the 84 the 5Y3 does not have an indirectly heated cathode so it needs it's own 5 volt filament winding. The filament current of a 5Y3 is 1.5 amps, which is pretty standard, so if the new transformer has a 5 volt winding it should be able to take that tube. If the transformer is running hot it may be that either the high volatge winding or the 6.3 volt filament winding cannot handle the current load of an eight tube set with push pull type 41s.
Regards
Arran
Thanks Arran! The puddle of wax on the cabinet I believe is from the original power transformer. There's no evidence of wax coming out of the transformer that's on it now. There's still a label on this transformer. It's a Stancor PM8403. 250-0-250 @ 70mA, 5.0 volts @ 2 amps for the 5Y3 filament and 6.3 volts @ 2.5 amps for the rest of the tube filaments.
I add up all the filament currents for each tube including the 41's but not the rectifier, and it's 2 amps. According to the above data and what you're saying this transformer that's in here should work fine with the 5Y3 that someone has installed in place of the 84.
Is this a correct assumtion on my part? Do the 41's in push-pull configuration increase the filament current for those two tubes?
Pepper
You should be fine with this lineup. If it's playing OK, and transformer is not getting hot, you're in pretty good shape. I'd add a fuse to the set to protect your efforts. If the filament voltage is too hot, I would consider adding a bucking transformer to tame things and get the maximum life out of your tubes.
Thanks Fox! Find out when I get it up and running. I didn't realize a 5Y3 could run on 250-0-250. I just looked at the tube specs and the plates called out 350-0-350. Learn something new everyday. Been doing this for a good six years now and have worked on a lot of radios. Guess it takes a lifetime to even get close to being considered a pro at it. If there is such a thing.
EDIT: Thought I'd add this. It's my dilemna with the components associated with the 6J8. Pin 6 of the 6J8 has a violet, yellow, red resistor attached to it. 7.4K? It reads 4.6K. Out of tolerance? Who knows. Also on pin 6 of the 6J8 is a resistor with one end green and a brown body. It reads 226 ohms. What's the green for? Another resistor, same color code, green stripe at one end and brown body coming off of pin 7 of the 6J8 reads 165 ohms. Again what's the green for? These readings were taken with one end of each resistor isolated from the circuit. Can't wait to get Chucks paperwork and see if there's any addendum to the 6J8 addition.
Pepper
The only problem that I can see is that the plate voltage may be too low with a 250-0-250 volt high voltage winding, but in these set the plate and screen voltages on the output tubes was under 200 volts anyhow, 170 or 180 volts I think. The schematic will tell.
Regards
Arran
This thing's getting a complete overhaul anyway. It looks like a Zenith with all the dried and cracked rubber wire in it. Wire coming out of the IF cans is bare etc. I may just yank the octal socket, install a loctal and run a 7J7. At least I'll have a set that matches a schematic.
Johnny
Pepperoni Wrote:I may just yank the octal socket, install a loctal and run a 7J7. At least I'll have a set that matches a schematic.
Why would you do that? There is no need for such an extreme measure unless the tube socket is bad, in which case it would make sense to switch to a loctal socket and a 7J7 if you wished to do so. Otherwise, you would just be making extra work for yourself that is unnecessary.
Here's how I suggest you solve your dilemma: Go to the NJ7P Tube Database and look up the 7J7 and 6J8 tubes. Makes notes of what elements connect to which pins in each tube. Then, once you get your schematic package from Chuck, just make notes on the schematic indicating the pin numbers of the 6J8 on each appropriate tube element.
http://www.nj7p.org/Tube4.php?tube=7J7
http://www.nj7p.org/Tube4.php?tube=6J8G
Thanks Ron! I've done that and I'm disassembling the radio. As i mentioned earlier I've never seen a Philco with this much bad rubber wire. Almost every wire in it is dried and cracked. I should have Chuck's paperwork soon and can make those notations. I guess I was a little frustrated when I said swap the octal to a loctal. You'd think that if Philco made a run of radios with the 6J8 they would have at least released a supplement reflecting that tube and it's associated components. But it's not a perfect world. With the exception of the power supply and 5Y3 socket/tube change this radio appears un-tampered with. My plan is to just put it back together the way it was. Just new components and wiring. Should work great. The audio output transformer is DOA (completely open on the primary side) and I see someone has answered my request for help finding a replacement. Go check that now.
Pepper