All, I've got a generic Philco radio question. I've worked on some radios that had schematics with warnings not to turn on the radio without the speaker attached. I'm now working on a 40-165 and I'm wondering if I can power it up safely without the speaker. Since the filter caps and many film caps had been replaced I thought I'd power it up but I only get a ticking sound. I've got the speaker installed in the cabinet and the radio is way too big to move and it's a pain to remove the speaker. I'm hoping it's safe to power up on my bench without the speaker. Also, are tube pin resistance and voltage tables available for Philco's? I hate to split up threads, the radio I'm working on is here Philco Radiobar Zephyr .
Thanks,
Keith
It's not a good idea to power a radio up without a speaker connected. The B+ will go high and possibly damage the filter capacitors. Also, the screen grid in the output tube will draw a large current and get red hot.
Please do not power up without a speaker or something to handle the load. The audio output tubes could be fried in short order the power has to go someplace. This would be like running a transmitter without a ant. load the output finals would go up in smoke. David
In the first place, even if one forgets about potential damage, why run a radio with no speaker with all tubes populated? To me the single reason to have no speaker is when the tubes are out and you want to check the power transformer output; after that if you powe up - you want to hear it play.
OK, I get the point but can I wire in a 1700 ohm resistor in place of the 1700 ohm field coil? And if yes, what wattage do I need? I have two problems at the moment. First the radio cabinet is extremely heavy and is on the second floor of my house and the radio chassis is in my basement shop. The second problem is I just rebuilt a crushed antenna shield and installed it in the cabinet. I can't get the speaker out without removing the antenna and I'm worried that I'll break it when I try to get it out. I can do an alignment upstairs but I'm just not set up for soldering outside of my shop. The radio cabinet is huge and can be seen here Zephyr .
thanks,
Keith
NOT A GOOD IDEA. Believe me I once was working on a radio. I accidentally did power up a radio with the speaker unplugged. I had not sound and I looked in the cabinet and saw tubes glowing cherry red. I was lucky, I immediately powered down the radio and reconnected the speaker. All was okay with the radio but I always insure that the speaker IS connected when powering up a radio
If your radio doesn't have the output transformer mounted on the speaker you can use a high wattage 1700 ohm resistor in place of the field coil and a regular PM speaker on the voice coil leads.
You need some type of speaker arrangement. You want to be able to listen to the radio and you will want the chassis out of the cabinet to do an alignment.
(This post was last modified: 12-27-2014, 04:57 AM by thirtiesradio.)
Yes, I definitely need some sort of temporary speaker set up. At the moment I get a loud ticking sound on AM and a hum on shortwave. I need to get this onto my bench for trouble shooting. If I use a PM speaker what kind of wattage do I need for the resistor to replace the 1700 ohm field coil?
Thanks,
Keith
http://www.nostalgiaair.org/PagesByModel...013334.pdf
Well lets see the schematic shows 300v ahead of the coil and 215v after. So that leaves 85v across the coil probably less and a rough figure of 100MA current (it's probably more) comes out to about 8.5watts then double that. I would say 20watts would work. You could start with a 10watt resistor and see how fast it gets hot. Be sure to watch the voltages and adjust accordingly.
Personally I would make up some adaptors for a 100ft extetension cord and hook up the speaker. Thats if there are only three wires. I don't think the radio will care much about the long wires. If you have a baby monitor you could use that to listen the speaker from the other location.
Desperate times call for desperate measures
Good luck
!!!!!!!!!!!!!!!!!!!RESISTANCE IS FUTILE!!!!!!!!!!!!!!!!!!!!!!
/\/\/\/\/\/\/\/\/\
Quote:I can do an alignment upstairs but I'm just not set up for soldering outside of my shop.
I'm wondering, usually the soldering part would be virtually done before you put power to it so I would do everything I need to do to it that I can see, then take it upstairs and hook up to the speaker to check voltages and do the alignment. Also, if you need to do a simple solder, you cant bring up a soldering iron and mat to make a small change if needed?
I'm wondering, usually the soldering part would be virtually done before you put power to it so I would do everything I need to do to it that I can see, then take it upstairs and hook up to the speaker to check voltages and do the alignment. Also, if you need to do a simple solder, you cant bring up a soldering iron and mat to make a small change if needed?
The previous owner had changed the electrolytics and about half of the paper capacitors so I figured it was safe to power it up. All i could hear was a load clicking noise so I completely recapped the radio and replaced all the wires with bad insulation. It still sounds exactly the same. I do have a disconnected wire that I can't find on the schematic. The previous owner labeled it "GR" which to me could me ground or green (it appears to be a white wire with a green tracer). Here's a photo of my mystery wire.
Could this be my problem? I know my LO isn't working as well since I couldn't hear it on a nearby radio. I confess I still have two micromolds I haven't replaced yet one is a 5300pf and the other is a 3300pf that I can't find on the schematic. I have another wire that I can't trace and that's the one that's between the red and black antenna wires (third screw from the left) it's unconnected as well.
Thanks,
Keith
I decided I needed to pull the speaker out of the cabinet for further testing. Fortunately, I managed to do this without damaging my antenna. I now have it on my bench attached to the radio minus the antenna. I then discovered that I've got a 7G7 tube installed where I should have a 7B7 tube. Is the 7G7 a proper substitute or could this be my problem? I also just noticed that the nut is missing on an IF can (visible in above photo) so someone been in there before
Thanks,
Keith
