I performed a complete restoration on this set about 4 years ago. All components are that old. It's been working great until recently.
I removed all the tubes and they all test good. I powered the set up with no tubes in it and all the transformer output voltages look good. I see no fried components. The person said they saw a little smoke coming from the power transformer and the radio just had a hum to it that the volume control had no affect on.
That's all I've done today after a 6 hour drive and there's more testing to be done of course.
I'm wondering if anyone has had a transformer that acted like this. The transformer makes no audible noise but placing my hand on it, it feels like a vibration coming from it. It doesn't get warm but again, it's under no load at this time. The humming from the speaker may tell me a filter cap has gone bad on me but I don't recall a transformer having this vibration.
Any preliminary ideas would be appreciated. I'll be doing more testing in the morning.
Thanks,
Perreroni (Johnny)
Johnny, I would guess you had an e-cap that is heading South. If the transformer is not heating under no load I would not immediately suspect it. The vibration may be due to some loose screws on the laminations or perhaps mounting to the chassis. Perhaps a fiber washer under the mounting screws to dampen? I know Scott used some rubber tape of some type to isolate the transformer they used for powering up the 800B. It was running even when the radio was turned off. Gave off a little vibration noise if not isolated. But what do I know?
Jerry
Jerry
Agree, sounds like a recap is needed. When transformers heat up a lot, sometimes the tar comes out and the the winding pack vibrates freely. If there is not a short in the windings, you can take the bells off, and repack. I've used Elmers followed with electrical tape on the outside of the winding pack to firm things up a bit more against the bells. Make sure all screws are tight as well.
I went back to an old basic first with these Loctal tubes. I cleaned all the pins again. I'm picking up a few AM stations but weak. If I remember, I need the copper wire loop antenna out of the cabinet to make this AM work. Please correct me if I'm wrong.
I get lousy FM here but I do pick up a few stations. I'm getting nothing on the FM band using my dipole in the attic.
Transformer is running warm when powered up now and tubes installed. But all voltages are solid and steady. I did re-secure the transformer to the chassis and that vibration in minimal now. There is no real hum as was explained to me but there is a static and crackly sound coming from the set.
The Ecaps test good isolated and I could throw new ones in. But I don't believe that's my problem now. Have to agree with Jerry. "But what do I know".
I also cleaned the bandswitch again. No change so still pluggin' away.
Please let me know on that copper rod loop antenna that's in the cabinet. I don't have it and if my memory serves me well at all any more, I think I need it for the AM.
Johnny
Need a dipole upstairs or on roof for FM.
Thanks codefox but this one has always worked well enough where it's at. I don't do much FM work.
I remember having trouble with this radio when I built it and the biggest problem was the Loctal tube pins and sockets. I can't find anything else wrong at this time so I cleaned all the tube pins again and even used a torch tip cleaner to clean the sockets. I'm still just getting static. What AM stations I was getting are gone. Nothing but static now.
Still waiting for an answer on the copper loop cabinet antenna.
Johnny
Yes, you need the cabinet loop antenna for proper AM reception. It is part of the input tuned circuit, so without it AM reception will be weak.
That said, it appears you have additional problems causing the crackling and related symptoms. Might have a bad tube or failing carbon resistor somewhere in the circuit.
Started working my way through it last night. Nothing yet. I replaced all the tubes one at a time and no change. Still looking.
EDIT: I put the signal generator on it and found that (on the Chuck Schwark Philco 46-480 paperwork) R308 1K 1/2 watt was fried. Buried under a mica cap. So through the process of elimination I narrowed it down to a problem in the RF section of this radio. If you've ever taken the bandswitch out of a 46-480 you know it's not fun.
I checked every component I could get to and all looks good but there's a ton of stuff buried in there that you just cant get to without disassembling the whole RF section. This will be the 2nd time I've done one on a 46-480. 1st time was when I built this set in 2009. And I wouldn't have taken it apart then but I could visibly see fried caps and resistors buried in there.
So the fun begins.
Johnny
Well here's what I've done thus far.
I completely overhauled the bandswitch along with the whole RF section. Seperated all the wafers from the bandswitch and thoroughly cleaned each one of them. Replaced all original caps and resistors with new components. I replaced all mica caps with silver micas. I installed new tube sockets for the 7F8 and 7H7 along with all new wiring. I replaced one of the chokes on the 7F8 filament. Didn't like the way it looked even though it did read less then 1 ohm. And I'm not really sure what those chokes do.
I went through all three of the IF cans and replaced all the mica caps along with any resistors I found. Installed all new wiring from the cans to their connection points in the radio.
Now my 1K resistor doesn't get hot any more but I still have problems that I haven't been able to isolate even with the signal generator or DVMM. All my voltages are within tolerance and a set of NOS tubes installed although all the tubes that were in it test good. All Loctal pins scraped until nice and shiny. I replaced a few of the caps in the main chassis but everyone I took out was good. Figured I was wasting my time and came here. I did install new E-caps.
The radio is motorboating only when I turn the volume and tone controls up. I still have no reception on any bands and the motorboating is there on all bands with no change.
Any ideas would not only be helpful but greatly appreciated.
Johnny
This one sounds like a real, well you know what Johnny. As it motorboats on all bands including the FM, I would think a problem in the AF section. Did you try pulling tubes (assuming it's not an AC/DC radio) one at a time to see when it stops? I would try the second detectors to try to isolate the front end from the AF section. Just sounds like the problem is in the audio section. Then again, what do I know?
Jerry
Jerry I started at the front end of the radio. When I got to the 6SQ7 1st audio the motorboating went away. Sounds like I have a new starting point to start troubleshooting from. Keep you posted.
Thanks,
Johnny
Great Johnny, you know where to look. Last time (only time) I had that was on a Scott 800 and it was my mistake a rewire error in the amp section. Check out all your work closely.
Jerry
Thanks Jerry! The radio was completely rewired and all new components installed just 4 years ago and has been working until recently when this problem arose. So I don't see it being a mis-wiring problem. I'll be looking for a bad component or something. Audio transformer checks good as far as resistances labeled on the schematic. But I have work to do on it so I'll let ya know what I find.
Johnny
Well so far I'm finding nothing in the audio circuit that's bad. No caps, resistors etc. The audio transformer resistance readings are per the Philco paperwork. I've never seen a speaker that was bad except for needing a recone but I'll check that too.
I did go back to page one of the Philco troubleshooting guide for this radio. This is the paperwork from Chuck Schwark.
Supposed to have a minimum of 50Kohms from B+ to chassis gnd. I have 22K. Paperwork says to check three capacitors for shorts or leakage. The E-caps and one bypass cap. The old ones were good. Four years old but I installed all new ones anyway. Still 22K from B+ to gnd.
Still pluggin' away.
Johnny
I'm no further then I was 3 weeks ago except the 1K resistor doesn't fry any more after going through the RF section.
I've gone through the audio section with a fine tooth comb and using the troubleshooting procedures laid out in the paperwork. Most of the checks are on caps so I had to isolate them and because of that I just replaced all the caps in this radio.
Speaker voice coil, field and bucking coil are good. All the voltages are good. So I'm stumped on this one. Don't know where to go next. Bad volume control? Bad tone control? Had the volume control out and it appears to be operating properly. Tone control changes the tone of the motorboating. Like I said... STUMPED!
Johnny