power supply to convert from 32 volt DC - Printable Version
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+--- Thread: power supply to convert from 32 volt DC (/showthread.php?tid=15152)
RE: power supply to convert from 32 volt DC - NostalgiaRadioTime - 08-17-2016
Good idea, Terry. Just tried that...took it up to 32.1 VDC with the variac and set on. Unfortunately, it made no difference in the buzz. It's still there. So, figuring if nothing else I can eliminate that possibility, one by one, I tried swapping tubes with known good one's. This too made no difference in the buzz. I'm at a loss as to what the cause could be. I would think if it were some sort of interference from the transformer itself the buzz would manifest itself steady across the dial. Not drop off after 1100. Any ideas on what to try or check next?
The buzz does get louder when the antenna is connected verses when not. If I hold both the antenna wire and ground wire in one hand....with neither wires touching or connected to anything else...and then touch the shielded cable going to the power supply cylinder, the buzzing gets a bit quieter.
Couple of other questions....could the transformer itself that I'm using in my power supply be causing the buzz? It's not a signal transformer, as I'm still waiting on the one I ordered that got lost (it was found in California and is en route again) but just a standard 120V / 24V step down transformer that is probably less than 50VA.
Also, I replaced the caps in the power supply with the values of the original caps inside. I know they were the original caps, as they match the style and size of the caps under the chassis and showed no signs of ever being replaced. I went by the values on the caps themselves (.1 and .25 's). On the schematic, it shows double the value that were in the power supply.... .25 and .5 's. Could that have anything to do with the buzz?
Sorry for all of the questions. I'm stumped on this...never dealt with a 32 volt radio before or with a vibrator power supply. I can't thank you enough for all of your help and continued patience.
RE: power supply to convert from 32 volt DC - NostalgiaRadioTime - 08-17-2016
As you can see, it's a busy workbench!
RE: power supply to convert from 32 volt DC - David - 08-17-2016
If there is shielding around the vibrator make sure that it is grounded. Proud owner of a MGB I know gives me something to do in retirement. Started picking up engine noise in the radio on AM. My MG has a set of points! Connected a wire from the Bonnet(hood) to the frame problem solved. Me thinks you are picking up RF noise from the vibrator think spark gap transmitter. David
RE: power supply to convert from 32 volt DC - NostalgiaRadioTime - 08-18-2016
Well once again the simplest things...and dumbest mistakes...can cause the biggest headaches. That annoying buzz was driving me crazy on the radio, as I could not pinpoint what was causing it. Nothing helped. Even with the more beefy 175 VA transformer there still was no improvement. I found a couple of small caps I missed and replaced those. Still buzzing. So then I got to fiddling around with the ground wire... again. I had clipped it on to everything metal I could find, and it made no difference. Then it happened. I touched it to the metal plate surrounding the wall socket where I had the power supply plugged in. Eureka! The radio quieted down, and I could get a bunch of stations up and down the dial loud and clear. That was it...so now I know I need to use a 3 prong plug when I hard wire the cord into the power supply. I tried a 3 prong plug cord, just gator wiring it on to the two connections on the transformer and the prong wire onto the ground wire of the radio and it worked fine.
So I want to thank all of you who chimed in and offered advice, suggestions, and help. Especially Terry. Without his help and guidance, I never could have brought this old Coronado farm set back to life. What a kind and generous man...he even PM'ed me his phone number (and I was THIS close to giving him a call too if I hadn't had my AH-HA moment)
When I get it all back together and mounted in the cabinet I'll post some pics of it. That's my weekend project....I have off of work tomorrow so have an extra day to button it up. With temps in the 90's and a 70% dew point, the nice cool basement is a good place to be (as opposed to an already hot factory with no A/C)
RE: power supply to convert from 32 volt DC - NostalgiaRadioTime - 08-20-2016
Well here it is, all back together and playing sweetly:
The small cabinet with it's beautiful burled wood, rippled trim and black accents are what really drew me to this radio, along with the neat dial featuring two pinwheels that rotate when you turn the volume and tone controls:
Here's the back showing the 32 volt vibrator power supply in the metal cylinder (it was originally suspended under the chassis shelf with some kind of rubber straps but that being long gone, and with no picture of what it originally looked like, I improvised with zip ties). You can also see the "black box", the power supply I built to convert the 120V AC to 32V DC mounted on the bottom side of the chassis shelf:
Once again my thanks to all....especially Terry....for helping me revive this 1935 Coronado that, judging by the thickness of the dust completely covering the tuning capacitor, hadn't been played in at least 60 years.
RE: power supply to convert from 32 volt DC - sam - 08-20-2016
nice well done love the dial
sam
RE: power supply to convert from 32 volt DC - Radioroslyn - 08-20-2016
+1!
Your welcome! Glad you got sorted and it's working well. It's very satisfying to give a few bits of advice and see the working finished product. I also enjoy taking some of the mystery out of radio circuits by way of explanation.
My Pleasure!
RE: power supply to convert from 32 volt DC - Paul Philco322 - 08-20-2016
I do not see many Coranados around New England, I love that warm yellowish glow. Be a nice one to sit by on a cold Wisconsin nite, with a toddy, and a good program, like Nostalgia Radio Time on 1420 the Breeze!
Well done.
Paul
RE: power supply to convert from 32 volt DC - kiwi_steve - 08-21-2016
Thats a really nice looking radio - good work getting it running again!
Cheers
Steve
RE: power supply to convert from 32 volt DC - Arran - 08-21-2016
That chassis has a Wells Gardner look about it, very similar to some Ward's Airline sets, be careful about the length of the dial lamps by the way. With regard to the M.I.A rubber straps for that can containing the vibrator supply, maybe you could make some out of some lengths of old bicycle inner tube? Coronado was sold by Gamble-Skogmo I believe, Coronado sets are usually listed under G-S in the Rider Manuals.
Regards
Arran
RE: power supply to convert from 32 volt DC - NostalgiaRadioTime - 08-21-2016
Yes, that's where I found the schematic on Nostalgia Air, under Wells-Gardner. You're right that most Coronado's are listed under Gamble-Skogmo...which is why I had such a hard time finding a schematic. One thing I liked about the chassis is the tube numbers are listed on the tube sockets themselves in white lettering. Ditto for the speaker and power supply sockets. I thought about using an old inner tube for suspending the original power supply cylinder but I wanted it to hang and also be secure enough so that it couldn't slide out of the sides of the straps should the set be moved. With the two sets of zip ties it can't move. I'm guessing the only reason it was suspended / rubber mounted was to squelch the vibration sound. If it had been mounted solid against the wood shelf or cabinet, it would be very noisy. Incidentally it indicated on the schematic that the shielded cable coming from the cylinder should hang down for some reason. There's actually a paper label on the end of the cylinder with an arrow pointing up, indicating how it should hang. I didn't do anything with the dial lamps, so they are as they were set up from the factory. The chassis 'floats' on rubber mounts (which I replaced), and there's a piece of sheet metal mounted on the wood riser where the chassis sits with a wire soldered on to the plate. This wire attaches to the back of the chassis acting as some sort of ground or shield. The chassis doesn't sit directly on the sheet metal plate however.
RE: power supply to convert from 32 volt DC - David - 08-21-2016
Well done, nice looking radio. Alone with the windmill to make 32 volts Dc, farmers could also use a Delco light plant .