Paul,

Do you think 5% resistors are OK?

Yeah, even 10% would be fine.

Well, I had to order these resistors. So it'll be a couple of days before I get them. So, I would like to thank you guys, Paul, Gary, and phlogiston, and others who have helped me trying to knock this problem out. I'll see what these resistors do and will definitely be back with you guys because I know there's more problems. Being this is my 1st Zenith, I know I'll need to tap you guys' brains again shortly.

Greg

Let us know your progress.

Well Paul and Gary, I'm back. Replaced candohm with fixed 5w resistors. Thought for sure I would have corrected something. But still have this B+ problem. If I have the 6F5G and the 6H6G in B+ ok. But if I add any one of the remaining tubes, (the 6A8G, or the 6K7G, or the 6F6G, by themselves. Just 1 at a time.) the B+ takes a dive. Anyone want to suggest anything else?

Greg

Greg,
Can the 6A8, 6K7, or 6F6 be installed individually without loading down the B+? Or only the 6F5 and the 6H6?

No Paul. If I individually put in the 6A8, the B+ gets dragged down. If I individually put in the 6K7, the B+ gets dragged down. If I individually put in the 6F6, the B+ gets dragged down.
This is having the 6H6 and the 6F5 both in while I'm inserting these tubes 1 by 1.

When I have the 6H6 and the 6F5 in together, the B+ is OK.

I hope I'm being clear with my description. If not, please let me know.

Just to be sure, your are using "G" tubes- glass, not metal ones?

2 of them are metal. The 6F5 and the 6F6.

Can you measure the DC voltage at the junction of C15 (- term) and the 300 ohm resistor, referenced to ground?
Take the first measurement with only the 5Y4 rectifier installed.
Then take the measurement at the same point while adding th 6H6, the 6F5, and then the 6F6, 6K7 and 6A8. Install the tubes in the order listed.

OK Paul. I'm not at home now, but will be there about 1:00pm and then will try that. I'll talk to you then

Thanks,
Greg

Paul,

Did you mean C16?

Paul,

Took measurement at junction of C-16 and 300ohm resistor.

1. 5Y4 only -.21v

2. 5Y4 and 6H6 -21v

3. 5Y4, 6H6, and 6F5 -.41V

4. 5Y4, 6H6, 6F5, AND 6F6 -7.24 (After it settles down. Climbs real slowly until it reaches -7.24v_

5.5Y4, 6H6, 6F5, 6F6, AND 6K7 -9.0V

6. 5Y4, 6H6, 6F5, 6F6, 6K7, AND 6A8 -8.76V

Yes, sorry that's what I meant.

Based on the max. voltage drop across R12 of 9 volts, that equals a total plate current of only 20 mA.

Someone else can chime in, but that seems reasonably low, considering something still seems to be loading down the B+ supply voltage?

Have you checked the values of any of the carbon resistors to see that they are at least close to spec? I am thinking of plate and grid biasing resistors, although it does not hurt to check them all.

Not to clear here but dows have voltage chart. Make sure C8 in hooked up posive to ground

http://www.nostalgiaair.org/PagesByMode ... 025209.pdf

C8 does not appear to be an electrolytic. Is that the one you meant?

Paul wrote: Have you checked the values of any of the carbon resistors to see that they are at least close to spec? I am thinking of plate and grid biasing resistors, although it does not hurt to check them all.

+1

Also, when you replaced the candohm, did you entirely disconnect all of its terminals?
Are you sure the tubes don't have shorts? It would be "black cloud luck" that three would, but it would be good to test them or sub them.

If none of the above works, my next step would be to print out the schematic, and go over the radio wire by wire highlighting the schematic as you go. I've heard there could always be a wrong connection, although I've never made one myself.

Yes, I entirely disconnected the candohm. Replaced them with 1% resistors. I will check all of the resistors. I know it's kind of hard to believe that 3 tubes could be bad all at once. I'll let you know after I check all of the resistors.

Hey you guys. Am still checking ALL of the resistors. I will talk to you guys tomorrow. I have to get up early in the morning.

And again Thanks a bunch for your help. I need it.

Greg

Greg,
its very possible your 5Y4 G is weak... it wont hold up to any load beyond the two very light load tubes you have in. Try pulling those two back out and put just a 6A8 or 6K7 in. Bet the B+ holds up. The 6F6 is the heavy drawing B+ tube , since its the output tube, as per normal in any radio.
The when you unhooked the Candohm, you were disconnecting the B supply circuit... so that was normal for the voltage to jump. You could have checked the Candohm easily without having to replace it.
BTW, you can use a 5Y3G or GT in place of the 5Y4 if you have terminals on the socket that match for a 5Y3 which is a MUCh more common tube. Then you have to rewire pin 8 over to pin 2 and move the HV plate connections one pin over each, I forget its either up or down.
No big deal if the pins are there on the socket. Often they are not.

Mark Oppat
www.oldradioparts.net