Motorola 6y ~1937 -- I.F. Coil problem and an unidentified power transformer lead

Virtually everything in this radio was taken out and put back in incorrectly by the last person to work on it. It's been pretty painstaking getting it all back together. lol I've got pretty much everything matching the schematic now except for a couple of things. There is a yellow lead coming from the power transformer that I can't account for anywhere on the schematic. It is next to the red lead marked "ctap" in the photo. Any Idea what that is? All of the other leads are accounted for and hooked up. I got continuity from the red lead marked "ctap" to both plates of the rectifier tube with similar resistance, so it would seem that it is the center tap shown in the schematic.



Also... The schematics indicate what I "think" is a center tap on the I.F. coil (part 9 on the schematic). There is no corresponding lead coming out from the can under the chassis and there is no top lead for this one either. Any Idea what that's all about? I've checked continuity on the coil and at least based on that, it is otherwise hooked up correctly. In the pic, the leads are coming up through the hole next to where the pot. is mounted. And by the way, the electrical tape is temporary until I can come up with something more clever.... It's tough getting all the parts in there when you don't know where they originally were.



Here's the schematic:
http://www.nostalgiaair.org/PagesByModel/786/M0006786.pdf


These are at least in theory the only two things stopping me from getting this radio going. Any help will be greatly appreciated.

-Jason

How many of the electrolytic caps do you have installed.
On can do you mean 2nd if coil. Looks like you might have wires missing. Others will join in with help.

Thanks for the reply. I have all six e. caps installed. In the black plastic box in the 1st pic there is a 15uf and two 2uf caps. Just beneath it is a 25uF, and elsewhere, there is an 8uF and another 2uF. That was the thing changed the most. The original person had two 4.5uF film caps (they were massive) working in combination with the old component cap for filtering. There were also several incorrect film caps (both value and voltage tolerance.) That's all gone now. Also, you're correct. It's the 2nd I.F. coil assembly, or part 9 on the schematic. If anyone would like me to get any measurements on anything (preferably without plugging it in) i'll be happy to do so. Thanks again!

Ok on the left over wire what all do you that is supposed to come off the transformer . Then see what is left. This happened to me on a philco set. Found it to be dial lamp.
Did not show it on schematic. On the IF hope some body will
Jump in and help. I just started working on a crosley
It is a mess like this one wires loose , caps missing ect .
hope i get help.When i start.

A little update.. I opened up both i.f. coil cans and had a look. All leads are hooked up and the taps are connected. I doubt they have ever even been opened before. Both have only 4 leads.

Hi on the IF make several copies of the schematic.. Trace out only the IF in color red yellow ect.Then check your set do it IF by IF acount for all wires.You can use tape to mark each wire on each IF ...That helps to see where each one goes ect.In general each IF should feed the next.They may have used a center tap on the IF if so i have never seen them do that befor ,but hey you never know.Some transformes if replaced may have a extra center tap...Sprman : )

Look at your 5Y3 you will see they use a voltage divider ,using resistors to drop voltage befor it goes to the IFs! Marked number 9 IF.Sprman

Oh yeah. I've traced all the leads back on the schematic with a highlighter to make sure everything is hooked up. All of the resistors are hooked up now. Got all metal film 1% types. The voltage divider was also missing when i got the radio so I guess I'm lucky it isn't toast. Continuity checks out. I'm beginning to wonder if the "center tap" can be wired directly to the lead it's closest to. It looks kinda like there's a dot there connecting them. It's hard to see. In the cans there are simply two coils of wire spun around a plastic core with two leads each. Nothing to hint that there would have been a 5th lead on either assembly. Just paranoid about doing something wrong and subsequently frying something irreplaceable... I'll get another xcopy of the schematic and trace all the if coil leads to see what they're doing. Thanks for the help so far!

Ah i see now yeah best to use a varac when you go to fire it up start off low voltage like 50 volts .You can leave 5y3 in but pull all other tubes.Get to 107 to 110 and see what each tube have voltage wise on each pin..I run all my sets at 107 to 110 volts.They run cooler and work just fine.A good schematic sure helps.Once done.Ohm out power plug to ground shouyld be no shorts to ground. Sprman

Sorry I've been such a pain. lol I just hate to see this radio broken. The cabinet is in almost flawless condition and it belonged to my grandparents. Didn't just pick it up on ebay. But anyway... I appreciate all the advice so far. I'll be sure to let you know what happens.

I hooked it up as mentioned with the red lead as the center tap and the yellow one unhooked. The I.F. coil's "center tap" is joined to the lead it's closest to on the schematic. I plugged it in and the 5y3 rectifier tube got extremely hot very quickly. I decided to get some measurements on the power transformer...

The two possible center taps:
To each other - 150 vac, no continuity
red to ground - 56 vac, no continuity
yellow to ground - 89 vac, no continuity
red to 5y3 plate - 397 vac, 150 ohms
yellow to 5y3 plate - 467 vac, no continuity

Other leads:
5y3 plates to each other - 800vac, 315 ohms
5y3 filaments - 5.79vac, 1 ohm
either rectifier filament to either regular filament - 315 ohms

Basically, I'm confused as to which lead is the power transformer's center tap. The yellow lead is clipped very short, so I can only assume that it's been hooked up several times in the past. When I used the yellow lead as the center tap, the 5y3 did not get as hot and voltages in the radio were still low or 0. I plugged in all the tubes out of frustration and got no sound whatsoever from the radio.

On a side note, After the radio is turned off, I still get 3vac at 60hz on the rectifier plates. It only goes away after I unplug the radio.

Anyway...I guess that's it for now. Any ideas?

Souunds like power transformer is wired wrong, and, you have a short.
Do you have a schematic on this set?
Bill Cahill

That certainly wouldn't be out of the question. There are just a few joints that look original, but most everything in this section was messed with. They have a schematic at nostalgiaair here http://www.nostalgiaair.org/PagesByModel/786/M0006786.pdf . I also ordered a better copy from justradios to clarify a few component values. Both are identical, and I have one more lead coming from the power transformer than I should...at least according to the schematic. Thanks for your input!

Hi have you checked all resistors ?Dont forget to check the speaker field coil,800 ohms cold.Look for solder drops shorting to ground. 5Y3s get very hot! Power Trans should have 2 leads for heaters,2 leads for heaters on the 5Y3 and 2 leads for the 5Y3 plates and 1 lead for center tap!Look at 5Y3 tube data max ratings,go by that for voltages on it...Sprman

There are 10 resistors coming off the Power supply plus field coil for speaker. Check them all ,you may have to life one end to get a good reading.Remove tubes first! Another thing you can do is remove all leads from output of power trns and measure them for voltage ,dont forget to measure input to transformer too.Sprman