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  #31  
Old 02-25-2010, 02:20 PM
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one other thing... there doesn't seem to be any short between those 2 coils using the same system I just explained.
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  #32  
Old 02-25-2010, 02:44 PM
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and yet another update... Measuring from one end of the 200 Ohm coil to the chassis, I get 198 Ohms and on the other side of that coil wire I get 187. On the wire going to the .2 Ohm coil to the chassis I got .2 to .3 Ohms then I double checked it a minute later and I get no reading at all and haven't since. Hmmm
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  #33  
Old 02-25-2010, 03:59 PM
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Have you disconnected the transformer secondary leads from the radio ? If they are still wired into the set when you take your measurements, you could be getting bad readings due to wiring or component problems down the line.
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  #34  
Old 02-25-2010, 04:09 PM
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Nope! I had better do that. Thanks. 'taking one step at a time...
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  #35  
Old 02-25-2010, 04:13 PM
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If you turn on the power switch and measure between the pins of the power plug you should get around 6.4 ohms. You should get an open circuit between either pin of the power plug and the chassis.

Between pin 4 of the 5Z4 socket and the chassis you should get about 200 ohms. Between pin 6 of the 5Z4 socket and chassis you should also get about 200 ohms. This seems to jive with what you mention in your last post.

Between pins 2 and 8 of the 5Z4 socket you should get 0.2 ohms. You should get an open circuit between either pin and the chassis.

Between pins 2 and 7 of the 6F6 you should get 0.2 ohms. Between one of these pins and the chassis you should have a dead short. Be sure to remove the dial light before taking measurements for this winding.

If you disconnect the center tap of the B+ secondary (winding connecting to pins 4 and 6 of the 5Z4) that should isolate all the windings from one another and you should not get any continuity between any of the windings.

On your PMV you do have the light bulb wired in series with the radio and not in parallel, right?
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  #36  
Old 02-25-2010, 04:25 PM
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That's detail. I'll get to it.

Yup, the PMV is in series. I have used it many times for other projects. 'Works great.

Thanks
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  #37  
Old 02-25-2010, 05:44 PM
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OK...

Your first and second paragraph tests out OK.

If I am counting the pins correctly on the 5Z4 (the schematic is illegible and marked with letters P1 P2 H S can't read the others) then I am getting between .5 and .6 ohms between pins 2 and 8.

On the 6F6, I get between .3 and .4 ohms between 2 and 7 (again if I am getting the pins right). Both pins are grounded to chassis as a matter of fact only pin #5 and #6 are not grounding to the chassis.

The dial light is clipped and pin #6 is disconnected on 5Z4
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  #38  
Old 02-25-2010, 08:42 PM
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On the matter of the 6f6, here is a tube diagram of that little feller:

http://www.nostalgiaair.org/tubes/6f6.htm

pins 2 and 7 being the filament, you will pretty much have your multimeter reading as a short to ground for both of those pins while the tube is installed, as the filament is of very low resistance. If both pins 2 and 7 still read as a short to ground when the 6f6 tube is pulled, then you could have a problem.

On the issue of all of the other pins, save for 5 and 6 being grounded; pin 6 isn't used on this tube, though there may still be things soldered to it, being used as a tie point for other parts in the circuit. Pin 5 is the signal input grid, so that makes sense that it wouldn't be grounded. Looking at the schematic, it appears that pins 3,4, and 8 should not be grounded. But we'll mess around with that issue a bit more once your transformer issues are cleared up.
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  #39  
Old 02-26-2010, 12:20 AM
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Guys.. Thanks for the help. I learned how to track down a circuit without a PC board. I was able to use the detail as well as the bits and pieces of info about tubes and the pin setup and I found 2 wiring mistakes, my mistakes of course, that put my PMV (dim bulb tester) to sleep!

The 60W dropped right back but it didn't start out very high as I am used to for getting those caps jump started. Then after about 2 seconds, I started to hear something very faint and my gut reaction was to flip the switch on the PMV which I did. It wasn't like a crackle or a fizz but more like a faint hiss. Anyway, there was no smell or smoke or heat that I could tell. I still have no tubs in, but that pin 2 and 7 on the 6F6 are still showing ground to chassis. After figuring out which pin is which... 3, 4, 6 and 8 are not grounded... 1, 2, 5 and 7 are. 6 isn't used.

Should I turn the thing back on? I'll wait for now.
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  #40  
Old 02-26-2010, 07:51 AM
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Quote:
Originally Posted by de.facto7 View Post
I still have no tubs in, but that pin 2 and 7 on the 6F6 are still showing ground to chassis. After figuring out which pin is which... 3, 4, 6 and 8 are not grounded... 1, 2, 5 and 7 are. 6 isn't used.
Do you see a physical connection between pin 2 and the chassis and between pin 7 and the chassis on the 6F6 socket? If you are saying they are both grounded because of the resistance readings then you are measuring through the filament winding of the transformer (or a short circuit in the wiring). Disconnect the wires coming from the transformer from pins 2 and 7 on the 6F6 socket and measure between these two leads from the transformer. This measurement should be low (0.2 ohms according to the schematic). With these leads disconnected measure between pin 2 and pin 7 on the socket. This measurement should be open.

Pin 1 and either pin 2 or pin 7 should be grounded. Pin 5 should not be grounded. There should be about 500k ohms between pin 5 and ground due to the grid resistor.

With no tubes in it you aren't going to get any voltage on the electrolytics. The 5Z4 rectifier would need to be installed to get voltage to them. BTW, as a word of warning for when you get to this point don't ever run the radio with the 5Z4 installed without the speaker connected. Since the speaker has a field coil that is used as a filter in the power supply not having it in the circuit can cause the voltage to get too high on C13 and C14 and they can pop. Been there, done that.
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  #41  
Old 02-26-2010, 03:12 PM
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The wires are disconnected and show .6 ohms. The measurement between 2 and 7 is open. The resistor between pin 5 and the chassis was a flexible one. I thought it was good but it wasn't. I replaced it with a 500K and now it shows no grounding. There is a physical connection to the chassis from pin 8 via a 500 Ohm resistor and is not grounded. There is a direct connection to ground from pin 1.

I guess what's at issue now is whether .6 ohms is close enough to the .2 ohms that is called for on that transformer coil; I wouldn't know. The other coil that is supposed to be .2 shows .4 and it connects to the panel lights if I remember correctly. (disconnected at the moment)

Oh.. and thanks for the 5Z4/speaker tip!!
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Last edited by de.facto7; 02-26-2010 at 03:17 PM.
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  #42  
Old 02-26-2010, 04:05 PM
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I think those resistance measurements are fine. What is shown on the schematic is not going to take into account the resistance of your meter leads. What you might do now is to plug the chassis in without tubes and measure the AC voltage coming from the B+ winding. You would measure between pin 4 and the chassis and pin 6 and the chassis. Be careful with this measurement. The schematic shows about 370V AC from each pin to ground but it will probably be a little higher since the transformer isn't being loaded down. Also check the voltages on the filament windings. Between pin 2 and pin 8 of the 5Z4 you should get about 5V AC. Between pin 2 and pin 7 of the 6F6 you should get about 6.3V AC. If you start getting the hissing sound you mentioned earlier, try to see where it is coming from.
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  #43  
Old 02-26-2010, 07:21 PM
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I powered up with the 60W bulb and I found the hiss and shut down. There is a small arch underneath the 5Z4 plug. But it doesn't look like it's between it and the chassis necessarily but the arc is coming from a small moon shaped hole that seems to be where the solder point for pin 5 would be if there was a pin 5; there is not a pin 5. I have no idea what it is or why it would happen but there is definitely a hot, smoking arc flashing from within that hole.
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  #44  
Old 02-26-2010, 08:04 PM
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I'm curious-does the 60W bulb light up as a short during the hiss?

You'll need to order a new socket now-once that carbon starts to build up where it arced, it will continue to do so. Do not run that radio until you get that socket out of there.

I had a radio with a similar problem-a little bit of moisture was retained from when I had cleaned the chassis, it caused a small arc, and I had to pick up a new tube socket. Once I did that, the radio played perfectly.
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  #45  
Old 02-26-2010, 08:35 PM
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Yes, the bulb lights up like a lamp. Thanks for the socket info. I suppose these are available at some of the antique radio sites. I'll look around. Maybe I should see if I can clean or dry out the others somehow. Blow drier?
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