Greetings,
It has been quite awhile since I've had time and motivation to put any radio chassis on my bench, about 8 years to be exact. I have a friend who is more into vintage TV's than radios and has asked me to help with a Model 70 - early. He replaced the EC caps and tried the it but no sound. Now it on my bench and I've rebuilt the bakelites, Replaced out of spec resistors, including bypassing sections 4,5,6 and the power resistor, section 5 to 6 was at 240 not 180. I powered it up slowly and noted that the 10w 180 resistor I used is getting really hot and no sound. I noticed a wire cut from Cap 33 between the bakelite connection and the speaker plug. According to the schematic there is a connection between the + side of EC number 41 and the 33 resistor. I would, if possible like to see how this wiring is connected. The original EC's were gone when this unit was acquired so any help you can give is greatly appreciated.
Glenn
Unpowered - measure the possible shorts at the rectifier tube output, that is across the 1st electrolyic.
Take the tubes out, power just the transformer, check all voltages, see so nothing heats up or smokes.
Check the electrolytics.
Check the connections in the rectifier/filter agains the sch.
Check all tubes.
Power up with just the rectifier tube, measure the B+ voltage, keep it awhile (your electrolytics should be rated apprppriately for about 500V), see that nothing gets hot.
Be carefull - the charge will linger. You might discharge it with a 10K resistor held with some insulating tool.
240 ohms to ground of the final candohm section is correct. Post a pic of chassis if you can.
Actually the spec is 180 from 5 to 6 and 70 from 4 to 5 on the early models.
Needless to say after rebuilding the bakelites and replacing the bad resistors, it talking again.. and the overheating problem is gone
Aligned it and its pretty good, sometimes it's tough to tell because I'm in the basement with CFL's and LED's all around once it's upstairs with a long antenna it should be good.
Interesting, could you point me to that early schematic to see the changes they made?
Brobertson,
Depending on the Ryders edition you have, it's either pg 466-D (original) or 1-18 in the revised. It gives the tubular resistor values for all the terminals, terminal to terminal.
Hope that helps, Have a great Thanksgiving.
Thanks, and it does get confusing,
I see the Rider's BC Resistor data you mention listed at 180 ohms on this site page 18,19:
https://worldradiohistory.com/Archive-Ri...31-PQR.pdf
I also see part for BC Resistor here part 03079 (which I cannot find specs anywhere as of yet) - this might possibly be the one with 180 ohms.
https://philcoradio.com/library/download...l.%201.pdf
But delving deeper it gets more confusing as on this site it lists part 5125 which I can find on the Philco library as 240 ohms.
Library 5125 -
https://philcoradio.com/phorum/showthread.php?tid=21836
These service bulletin pages show date of May,1931 and the 70 has 240 ohms listed, page 51,52:
Service Bulletin -
https://worldradiohistory.com/Archive-Sc...letins.pdf
If yours measured 240, maybe it was replaced perhaps? Or is this a mistake where they took the 180 from BC resistor 5667.
The later 70's above the b22 show another part number as well.
The Philco library all show 1933 as the beginning year for the BC Resistors.
Maybe someone can find the original part number. Being that where it is in the circuit, how much difference would it make?
Edit: Page 55 of this site ,dated Dec. 31, lists it as part 03079, different from May 31 bulletin.
https://worldradiohistory.com/Archive-Sc...letins.pdf
I have a couple of 70 chassis, the 5-6 terminals on the B-C resistors in both read close to 240 ohms. Being a wire wound resistor, it is not likely to change value from what it was when it was originally manufactured. Unless the thing is burned to a crisp. I would leave as is.
Steve
Steve,
Yes I thought the same but this section was getting very hot (smoking, 130+ on my infrared thermometer before I shut it down) so I figured it wasn't worth taking a chance on it as every reference I had showed 180 on the WW resistor. I pulled 4 and 5 from the WW and added a terminal point to connect the leads, so the readings would be in spec for the 5 to 6 and the 4 to 5 with 5 being attached to ground.
Brobertson,
This is a WireWound resistor with multiple (6) connections. I didn't look at all the links you listed, but looked at the original and at revisions and the 180 number is where I headed. The set runs well now and that's a good thing...lol
Glenn
well you proved me wrong....I went by the reference I had available to me.
Happy Thanksgiving to you
Feel better?
It's not a contest, Glenn.
I understand that it's not a contest, but you seemed like you needed to prove your point. All I ever asked for with my initial post was if someone could post a pic or a link to a pic for me to look at. The fact that the Riders I have show a certain value so I took that as gospel not thinking I needed to look at many other places to get a resistor value.
I am done with the set, it works well and I know my friend will be happy with it, isn't it all about saving sets so they can be enjoyed and are functional. I look forward to the next one on my bench which will be a Crosley Super 8. We can stop beating this dead horse and move onto different things.
Again take care and have a happy Thanksgiving.
Okay, boys...just don't let things end like this:
Glenn.....I did not have any point, this was my only post about this, this in fact was Steve's point.
You want to feel that way - suit yourself.