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zenith 5-R-236 help please
#1

  I just finished recapping & replacing some out of tolorance resistors. E caps also replaced. I need help with how to verify if the 5Y4 rectifier tube is working. When powered up all I get is a very low hum out of speaker that has no change with volume control, basically nothing. Buy the way it played before I worked on it Icon_redface
 with tube in socket I get 262v. ac and 261v. ac on each plate to chassis ground. But the filament I only get .oo5 dc to chassis ground. From center tap of transformer to rectifier filament I get 183v/dc neg.
 I'm asking this because I have no plate voltage on any of the tubes
 I ohmed out the power trans. and got 580/ohms plate to plate
                                                        276/ohms & 302 ohms on each side to center tap.
 The 5Y4 tube filament of power tranny ohms out at .003.
  All the tubes light and have been tested. I changed 5Y4 with another known good one.
Speaker feild coil ohms out at 1800 ohms and output transformer at 450 ohms.
     I have been over the wiring at least 10 times and find nothing in error. Here is a schematic of the radio.
 
  http://www.nostalgiaair.org/pagesbymodel...024982.pdf

 Any help with this would be greatly appreciated.
#2

Your R7 or R8 could be open. (Or which is unlikely your field and R5 or 6 open...not likely at all). Or wires unsoldered.

In short, there is no connection between your cebtertap and the chassis.

People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
#3

Thanks morzh. I did change R5&R6. R7 & R8 are within a few ohms of 80 & 150. I will change them to be sure and recheck the wiring. One question, I get 195v if I test from the center tap to the chassis. Does this seem correct to have that much difference in potential voltage btwn center tap and chassis ground?
#4

Hi Mike and Seasons greetings, (Both Mikes)

> with tube in socket I get 262v. ac and 261v. ac on each plate to chassis ground.
That's good.

> But the filament I only get .oo5 dc to chassis ground.
The heaters are powered by AC current, if you measure it with a DC meter you will get an inaccurate reading.

> I'm asking this because I have no plate voltage on any of the tubes
Well strictly speaking you do have plate voltage on the 5Y4 tube. Like Mike sez R-7 or 8 could be open (he types faster that me)

Just for grins you could ground to the chassis the  minis side of C-10. This will restore the HV but you won't have negative bias for the audio tubes if R7 or 8 are open. You don't want the leave it like that but just to see if you have HV.

> One question, I get 195v if I test from the center tap to the chassis.
That's way high. Should be 20v or so. Something is open between the HV ct and the chassis .

Terry
#5

Thank you and seasons greetings to you. I'm probably not clear as I should be.
The no plate voltage was to the other tubes and also the positive of c-9/c10. and I thought that there should be 208v dc coming off the filament of rectifier to the positive of the e-caps. The schematic seems to show.
I will try your idea of grounding c10 minus side to chassis and see if I get HV. Thanks
#6

> I thought that there should be 208v dc coming off the filament of rectifier to the positive of the e-caps. The schematic seems to show.
The HV at this point would be measured from the HV ct - lead to the rectifier filament + lead.

Terry
#7

That makes sense now. I will resume work on it tomorrow and see what I find out. Thanks
#8

Why are we complicating things....why not just measure ohms between the filament and cassis? Obviously wit power FF and caps discharged.

People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
#9

Well sometimes I think if I had a brain I'd be dangerous. Going over the wiring for the twelth time I fianlly found where I went wrong.
There was a 1-tab solder junction where the Ecap positive wires and several other wires joined that was attached to the chassis via the Ecap can stud & nut. I had replaced that solder junction tab with a two tab when I restuffed the large Ecap. I don't know why but I thought it was one where the two solder tabs were seperate from the part that bolted to chassis. It wasn't and so I had grounded the B+ to the chassis.
Radio playing now and hope to finish it up by tomorrow.
Thank for the help.




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