How about a Variac?

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colcolt

Part of the Furniture Now
Jun 11, 2012
856
0
I have an old tube radio, an Atwater Kent Model 42 I'm going to be working on soon and since it has a transformer and not the needed batteries older ones had, I'm curious if I shouldn't get a Variac to feed it since after measuring my outlets where I'd be using it measure 135-139v I thought that the addition of a Variac might be necessary as I feel sure back in the day these radios were in use home voltages weren't as high as mine. In fact, I think that's a little high for modern appliances and think I'll call the utilities tomorrow and have them check.
I didn't want to fry that old transformer with close to 140v so thought the addition of the Variac and set it for 110 may prolong the life of the transformer. Anyone have thoughts on this if you're electrically/electronically minded?

 

colcolt

Part of the Furniture Now
Jun 11, 2012
856
0
The Variac is just a single stage transformer with the capability of varying AC voltage from the line. In my case it's a bit high. I could use the Variac to lower it to 115-120 instead of the 135 volts or so I'm currently getting. Old transformer radios from the late 20's and 30's may not like that much voltage induced into the primary side.

 

photoman13

Lifer
Mar 30, 2012
2,825
2
Still don't know what you're talking about. Wish I did. I have an old radio (maybe 40s or 50s) that I put computer speakers in and can hook an ipod up to. I even got the volume on the radio to work with it. That is about my extent of knowledge.

 

johncorosz

Can't Leave
Sep 15, 2012
366
0
You should be fine doing that colcolt. I would really consider cruising the forums online that are dedicated to old radio restoration. They can line you up with the exact, proven methods for bring those back to life.

 

colcolt

Part of the Furniture Now
Jun 11, 2012
856
0
Back in the mid 80's old tube radio restoration was a hobby. I just got interested in it again lately. I always wanted an Atwater Kent as they were the Lexus of radios in the day. I found two on ebay I bought. One has the battery system and the other a transformer. I'm not concerned with the battery operated one as I can put a battery eliminator circuit to that one and get it going again after replacing old paper capacitors and open resistors. It was the one with the transformer I was concerned about with the high voltage I have available at the outlets. Atwater Kent designed and set up their radios to 120 volts...not the 135 or more I'm getting.
I think I need to call the utilities tomorrow and have them check on the neutral line and maybe the meter. Could be some corrosion in the breaker box.
This is one I bought with the battery operated circuit.
Model30.jpg


Model30AtwaterKent.jpg


 

colcolt

Part of the Furniture Now
Jun 11, 2012
856
0
This is what you need, photoman. I'm getting one myself. You hook our ipod up to it with songs stored on the ipod and find an empty place on the AM dial(harder to find an empty area on FM) and you can get it to play on that station on any radio you have in the house...upstairs or down stairs or in another room. Tune it in to that frequency and you're set. I'm getting one so I can upload old radio programs to an mp3 player, like the ipod and hear programs like The Whistler or Johnny Dollar and be able to listen to them through the very radios that once played them.
http://www.sstran.com/pages/AMT3000/overview.html

 

colcolt

Part of the Furniture Now
Jun 11, 2012
856
0
I've done my fair share of electrical work, happyjacks. Replaced nearly every switch in the house, receptacles, wired up new dining room light with a dimmer, etc. I've worked on old tube radios where you can have up to 750v DC on those old transformers, big enough to choke a horse but, I'm not wild about dealing with 240 much. I've been bitten more than once with 120 and DC voltages with the old radios so, not a complete stranger to it all. The voltmeter is a man's best friend! I do nothing until I ascertain there is no voltage there, hot to neutral or hot to ground.
I too think the variac is a good idea with the transformer radio and for sure I'm giving the utilities board a call about the line voltage.Too much voltage and you can blow every one of those expensive tubes.

 

colcolt

Part of the Furniture Now
Jun 11, 2012
856
0
I'll be happy to let them, too. I need to find out what's going on. I suspected the neutral but want them to check it all. The breaker box and breakers are old and it may not hurt to replace the main at a minimum.

 

radio807

Can't Leave
Nov 26, 2011
444
7
New Jersey
Definitely use a Variac, not only because of the higher than normal voltage coming into your home, but also because of the danger of blowing the power supply electrolytic capacitors like Happy Jack said. Blown caps are very messy and have the potential to do more damage to the power transformer than your high mains voltage.
I restore old shortwave receivers and transmitters, and I would recommend that you do the following:
First, safely rig up a fuse in the AC line unless the radio is already fused, which is unlikely. A catastrophic failure that could damage the power transformer might take out the fuse before it's too late. Not a guarantee, but a reasonable precautionary measure. I never operate equipment that isn't fused. You should try 5 Amps, no more.
Second, I recommend grounding the chassis before you plug the radio in. I'm not familiar with the AK Model 42, so before grounding the chassis you should first check the schematic to ensure that neither leg of the AC line is connected to the chassis like some old radios were (since this one has a power transformer it's not likely to be the case here, but check the print first; I think that design technique came years later). The ground wire will protect you from a short in the primary of the power transformer, a shorted AC bypass capacitor if you radio has them, and a host of other evils.
Third, do a close visual inspection of the top and bottom of the chassis and look for anything out of the ordinary like burned components, tar or any other unusual discharge from the power transformer. Also look at the electrolytic cans: it was commonplace in the day to use liquid-filled caps and if your radio still has them you'll likely find that they have leaked (dried light-colored powder evident where the wires exit the bottom of the can). If you find that, don' even think about powering up the radio, Variac or no, until you replace the caps.
Also regarding the capacitors, if they are the originals or replacements of the same type as originals (liquid-filled, with wires coming out the bottom though a crimped rubber seal) again, don't power it up until you replace them. It would be miraculous if the originals are good, or even safe to apply power to.
Next, make sure that the speaker is connected; many of the old sets had a voice coil in the speaker that was also part of the power supply filter circuit.
When you apply power, bring it up slowly from zero, gradually bringing it up to around 50 VAC and let it hang there for several minutes while you use all of your senses except taste to monitor what's happening. Be alert for smoke, unusual smells, arcs, popping or sizzling sounds, etc. Use your hand (top of the chassis only and far away from exposed connections) to feel if anything is getting warm throughout the process of bringing up the voltage. Pay particular attention to the power transformer and electrolytics; there's no way they should be getting warm at this point, or at any time during the power up sequence on the Variac. If things start to heat up, unplug immediately.
If all seems OK at this point, you can slowly bring up the voltage in 25 Volt increments and repeat the above process over the course of several minutes each time until you get up to 110 VAC, and go no higher. If any any point you hear a loud hum coming from the speaker that doesn't go away by turning down the volume control you might as well stop right there are replace the power supply electrolytics before you go any further.
Best of luck. Let us know how you make out.
Jim

 

lonestar

Lifer
Mar 22, 2011
2,854
161
Edgewood Texas
Facinating conversation. (Even though its mostly over my head :rofl: )

Good luck with your radio Colcolt, its beautiful. I see the knobs are Bakelite, what is the body made of ?

 

colcolt

Part of the Furniture Now
Jun 11, 2012
856
0
Well, I feel a little like Edith Bunker. Had the guys come out and check the service panel and the line coming in to the house and all was well. There was 121 volts on one leg and 121.3 on the other under load so no problem there. I'm thinking...maybe it's my meter? I pulled the 9v battery out and replaced it with a new one. I went back to check the same receptacle that measured 143v and now it checked out 121.1. :oops: It pays to check the simple things first. The old battery read out at 5.6v-much too low for a 9v battery and that was why I was getting erroneous readings.
radio807-I think your synopsis is superb and the first thing I plan on is NOT to plug the radio in to see if it works...wrong way to check if you like your radio. I'll replace all capacitors, especially the electrolytics and check resisters for open condition. I'm just hoping the transformer is good. I hate melting out all that tar!!
lonestar-the cabinet is some type of metal with a "crinkly" finish. The model 30 that's coming tomorrow is a lot different than the model 42 in that it's battery operated and has no transformer per se and has some strange voltage requirements. The cabinet is made of mahogany.

 

colcolt

Part of the Furniture Now
Jun 11, 2012
856
0
Here's a schematic for the Model 42 Atwater Kent. This really comes in handy when it's time for trouble shooting and checking component values. If you think that looks complicated check out the schematic for a transistor radio from the 60's.
http://www.atwaterkent.info/TechData/Drawings/Images/AK09800sch.pdf

 

colcolt

Part of the Furniture Now
Jun 11, 2012
856
0
Just in case anyone may be curious/interested, I received the Model 30 Atwater Kent yesterday and took the chassis out to access what may have to be done to get it playing once more A 1926 radio that looks good for it's age. Some wiring will need replacing and a couple resistors I've checked are open so, those will need replacing. RF transformers tested good but not sure about the tubes yet until I get another wiring harness to replace the ratty one that's original. This will be a winter project and something not done in a couple weeks.
Here's a few pics of the inside and what it looks like. It's not your Daddy's radio...but, your Grand Daddy's! :) I took the tubes out so they wouldn't get in the way of taking the chassis out. There's six altogether...4 01A tubes and one 112A.
_DEF4618a.jpg


_DEF4617a.jpg


_DEF4611a.jpg


_DEF4612a.jpg


 
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