zenith 5-R-236 help please - Printable Version
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zenith 5-R-236 help please - KCMike - 12-30-2015
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
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/982/M0024982.pdf
Any help with this would be greatly appreciated.
RE: zenith 5-R-236 help please - morzh - 12-30-2015
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.
RE: zenith 5-R-236 help please - KCMike - 12-30-2015
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?
RE: zenith 5-R-236 help please - Radioroslyn - 12-30-2015
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
RE: zenith 5-R-236 help please - KCMike - 12-30-2015
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
RE: zenith 5-R-236 help please - Radioroslyn - 12-30-2015
> 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
RE: zenith 5-R-236 help please - KCMike - 12-30-2015
That makes sense now. I will resume work on it tomorrow and see what I find out. Thanks
RE: zenith 5-R-236 help please - morzh - 12-30-2015
Why are we complicating things....why not just measure ohms between the filament and cassis? Obviously wit power FF and caps discharged.
RE: zenith 5-R-236 help please - KCMike - 01-01-2016
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.