Model 89 Cathedral - Printable Version
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RE: Model 89 Cathedral - Mondial - 03-10-2014
That's great. I'm glad you found the problem and got it going.
After all that work though, it would be a shame not to align it a bit. At least peak the IF and adjust the RF and ant trimmers (labeled 1st detector and RF on diagram) on the variable cap at 1400kHz. It will make a big difference in performance.
RE: Model 89 Cathedral - NostalgiaRadioTime - 03-11-2014
Thanks Mondial. If I get brave enough I may give alignment a try. Right now I want to make sure it keeps playing before I try tweaking it. When something causes so much trouble I always get nervous trying to make it better. Sometimes you're best off to leave well enough alone. At least until its proven itself as being stable and reliable. Test number one comes after work tonight to see if it still comes to life a day later!
RE: Model 89 Cathedral - NostalgiaRadioTime - 03-11-2014
I did a little tweaking tonight on the trimmers. Nothing extreme for now, but did make a bit of an improvement. I'm happy with it anyhow. It's now back together and on display in my home. I know this isn't the place to post photos of restored radios, but since you have all been so helpful, I figured I'd borrow the Model 89 thread to show mine. Go easy on me.... I know it's not a 100 point or factory / period correct, but I like it just the same
Here you can see the reproduction cabinet labels that really look nice
RE: Model 89 Cathedral - gregb - 03-11-2014
Looks fantastic Greg, be proud of a job well done! What did you use on the tube shields, they looks good.
Gregb
RE: Model 89 Cathedral - Mondial - 03-11-2014
Chassis looks great. Did you paint it or is it the original plating?
Am a bit confused by the label saying to adjust this screw... That is the IF trimmer so I hope no one tries to "adjust" it. Actually one of the hole plugs should be over that adjustment hole because the screw has 250 V on it. The center IF adjustment hole had no plug because it had no HV on the screw, only AVC voltage.
Label looks like should be for the regeneration control of the Model 80 instead.
RE: Model 89 Cathedral - NostalgiaRadioTime - 03-11-2014
Thanks Mondial. No, the chassis is just naval jellied.
Good to know about that little label... I really wasn't sure where that was for. I may take it back off. And move the hole plug.
Thanks, Gregb as well. I actually used some chrome spray paint on the tube shields
RE: Model 89 Cathedral - skyscraper - 03-11-2014
Absolutely beautiful looking radio! Congrats again!
Mine certainly doesn't look a tenth as good on the outside, but at least I have you beat for originality underneath
I pulled the coil again. Unwound it and peeled off the plastic, now I just have to wait for the spool of 38 wire. I'm very hopeful my chassis will be singing again this weekend.
One bit of a problem though, one that's gotten me before. I failed to take into account how much faster the 80 tube heats than the rest, because of the direct cathode. The primary B+ line spikes to about 480v before settling almost a hundred volts less than that a few seconds later. The supposed voltages are nowhere near the maximums. My filter caps are only rated for 450v, and they're all I could find. They were actually recommended. Is a 7% spike for a short time dangerous for them? I've gotten very mixed messages about this from other sites.
RE: Model 89 Cathedral - NostalgiaRadioTime - 03-12-2014
Thanks Will. I couldn't have done it without your help.
Oh no doubt your under chassis is more correct. I didn't bother to open that large square metal cap box. I just soldered the caps on to where they went and to various ground points externally.
Interesting about the 450 volt caps. Do you mean the two can caps on top of the chassis? I didn't notice a 480 volt spike in mine. But that's not to say there isn't one I overlooked. Keep us posted what you find. Good luck with the 38 gauge wire. Practice threading a needle while you wait for it to arrive!
RE: Model 89 Cathedral - Mondial - 03-12-2014
The voltage spike on warmup is typical of any radio with a filament type rectifier and remaining tubes of the heater cathode type.
I normally use 500V rated electrolytics, especially for the first cap after the rectifier. You are probably ok with the 450V rated ones as they usually have a higher short term "surge" rating, but if you can find higher rated ones its preferable.
I have tested 450V rated caps on a tester at up to 550V or so on a cap leakage tester and they seem ok, but you definitely don't want to expose them to overvoltage for long periods.
RE: Model 89 Cathedral - skyscraper - 03-12-2014
Perfect, thank you.
I got the spool of red baby hair today, and tried to wind the coil with teflon tape. The stuff is really hard to work with, and once you lay down a turn, it sinks in and won't move again. Once again, I ended up with some tiny gaps and maybe one overlap that I couldn't fix. I soldered it in, and it seemed to sort of work, I got a station at 560kc, but I had to leave shortly after. Came back, and it's the exact same thing. Stops working at 1100 or so.
I was hoping to be celebrating with Greg tonight
Oh well. Next plan, redo it again with the polyethylene plastic to insure there are no irregularities whatsoever, and maybe add a turn or two. Edit - I got it to oscillate. I pulled the 42 audio tube to try to see what is causing the 'thunder' noise, when I put it back in it worked fine across the dial... Heard Atlanta, New York, Chicago and Nashville. It worked for 5 mins or so, then died again. What a terrible headache of a radio. At least I know that coil seems to be responsible, it didn't do this before.
RE: Model 89 Cathedral - Mondial - 03-12-2014
How much DC voltage do you have on the screen grid and plate of the 36?
I am wondering because when you removed the 42 the supply was unloaded and the B+ rose higher. With the higher voltages the osc started working correctly, so maybe your screen voltage is marginally low?
RE: Model 89 Cathedral - NostalgiaRadioTime - 03-12-2014
One thing on that "baby hair" wire is scratching off the red enamel coating so you can get a good solder connection to the lug. You have to do a thorough job or when you solder you won't get continuity. Do too good of a job, and you'll break off the end of the wire. It's even harder to do the end after you've done the windings. I wound up putting a piece of scotch tape around the winding until it was soldered to hold it in place.
I got mine pretty close but there were a couple of tiny gaps in my windings too. It didn't seem to matter a great deal. I think the number of windings is more critical.
RE: Model 89 Cathedral - skyscraper - 03-12-2014
Relative to K, 237v for the plate and 91v for the screen. Specs call for 230 and 90, so that's fine.
It occurred to me to change the tube. With a different 36, it's oscillating fine now, and has been for half an hour. It's very fragile though, even messing with the shields can stop it.
I'm torn now between declaring victory and rewinding that coil once again.. Unless it will positively affect performance, I'll probably leave it.
In which case, the final problem is the noise. It sounds like low rolling, constant thunder with the volume down, and adjusting volume doesn't seem to change it. If you disconnect the 75 detector, it goes away.
As always, thank you so much for your help.
Greg, no scratching something I can barely even see.. I got Temco Solderon RED for my wire. It's very convenient and a great product. Cheap on ebay.
RE: Model 89 Cathedral - Mondial - 03-12-2014
Noise sounds like a bad 75 tube. Had the same problem and replacing the 75 corrected it. Could also be a bad resistor in the 75 plate circuit but I would try the 75 first.
RE: Model 89 Cathedral - NostalgiaRadioTime - 03-12-2014
Oh I wish I would've found that wire, Will. Would've made life so much easier!
Thanks for the tip. Congrats on getting it to play for an extended time. I bet with Mondial's suggestion of a different #75 tube, the thunder will stop rolling and the sun will come out!