Forums :: Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives
Support This Site: Contributors :: Advertise


It is currently Jul Sat 20, 2019 2:59 pm


All times are UTC [ DST ]





Post New Topic Post Reply  [ 6 posts ] 
Author Message
 Post subject: Testing Field Coil (RE-45)
PostPosted: Jan Wed 23, 2019 1:13 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 350
Location: Worcester ma, usa
I have a Electrola RE-45 .The field coil is testing open with a DVM, VC tests good. I read that you can get a false open read with a DVM on some coils . The large power resistor in the 245 amp has two open sections so I don't think I test it with the amp. Can I test it with a variac ? This RE45 is looking more like a parts set but I want to be sure. Any suggestions ? thanks


Top
 Profile  
 
 Post subject: Re: Testing Field Coil (RE-45)
PostPosted: Jan Wed 23, 2019 1:54 pm 
Member
User avatar

Joined: Jun Wed 14, 2006 11:49 pm
Posts: 7585
Location: Leo, IN or Zellwood, FL
calman44 wrote:
I have a Electrola RE-45 .The field coil is testing open with a DVM, VC tests good. I read that you can get a false open read with a DVM on some coils . The large power resistor in the 245 amp has two open sections so I don't think I test it with the amp. Can I test it with a variac ? This RE45 is looking more like a parts set but I want to be sure. Any suggestions ? thanks


An open field coil is an open field coil. Sometimes when you check the ohms of some coils if there happens to be an electrolitic capacitor someplace in the circuit the meter will change readings. The DVM applies a very very small voltage to the circuit under test. If you see the meter reading changing then clip lead onto the coil and let it set for a minute or two and it will usually settle out. Then reverse the leads of the DVM and do it again and again sometimes it will take a minute of two to settle out and read a steady number. If the speaker and field coil are completely disconnected from the radio or amplifier then no other parts are involved with your checking of the field. The meter reading should be steady. An Open is an Open. Sometimes it is possible to repair the field coils. Load up about 100 mfd worth of electrolitic capacitor to around 300 to 400 volts. Now discharge it across the field coil. If you get a spark when connecting it them someplace in the field coil that voltage did spark across the open in the field coil. Sometimes it will "Weld" that open spot in the field coil. Many times this is at the location where the somewhat flexible stranded wire is connected inside the field coil to the magnet wire and the connection has corroded and isn't a solid connection. After sparking the field coil a time or so and retesting it then let it set and recheck ohms again after a bit of time. Then install it back into the amp or radio and run it for a while. It either works or else it doesn't work.

as to the power resistors in the RE-45 amp/power supply... so replace them. An open resistor is junk and needs to be replaced. Probably bad leaky capacitors applied an excessive load to the power resistor sections and therefore they burned open. Or else just the nature of how they are built the sections went open. Buy new correctly rated resistors and replace them.

John k9uwa

_________________
http://www.JohnJeanAntiqueRadio.com


Top
 Profile  
 
 Post subject: Re: Testing Field Coil (RE-45)
PostPosted: Jan Wed 23, 2019 8:51 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 350
Location: Worcester ma, usa
My bench power supply is only 60v/5A and it won't charge a cap to 10 volts . It will light a 24v bulb and display the amps its drawing . It should charge a cap ? Its a BK 9110 PS.


Top
 Profile  
 
 Post subject: Re: Testing Field Coil (RE-45)
PostPosted: Jan Wed 23, 2019 9:37 pm 
Member

Joined: Jan Tue 16, 2007 7:02 am
Posts: 2978
Location: Lexington, KY USA
I read that you can get a false open read with a DVM on some coils .

A straight DVM reads voltage only, so can't be used directly to check for open circuit or continuity.

Some DMMs do have a continuity range that won't work, if the resistance of the thing you are checking exceeds some arbitrary threshold determined by the meter's design. So use a resistance range. That gives you a number.

If you set a DMM for 20k ohms full scale, it should work.

What is your meter doing? Is it really a voltmeter-only instrument? Is it set to an ohms range? What reading do you get with the meter probes not touching anything? When the probes are shorted together?

Ted


Top
 Profile  
 
 Post subject: Re: Testing Field Coil (RE-45)
PostPosted: Jan Wed 23, 2019 10:15 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 350
Location: Worcester ma, usa
I used a Fluke 116 and a BK 2831E bench meter. I get OL the meters. The VC tests good at 12R. I was able to reflow the solder joints on the wire junctions on coil .


Top
 Profile  
 
 Post subject: Re: Testing Field Coil (RE-45)
PostPosted: Jan Wed 23, 2019 11:29 pm 
Member
User avatar

Joined: Jun Wed 14, 2006 11:49 pm
Posts: 7585
Location: Leo, IN or Zellwood, FL
calman44 wrote:
My bench power supply is only 60v/5A and it won't charge a cap to 10 volts . It will light a 24v bulb and display the amps its drawing . It should charge a cap ? Its a BK 9110 PS.


Someplace in your collection of old radios you have at least one that has a real power transformer that produces at least 300 volts plus direct off the rectifier tube? so wire up 5 22 mfd 450 volt litics in parallel. load the cap with the radio B+ supply. Discharge it across the field coil. If it sparks when you connect it to the field coil then it also sparked across the open inside the coil someplace. Sometimes it works and sometimes it doesn't work. Your not out much to try it.. since the speaker field is presently open...

John k9uwa

_________________
http://www.JohnJeanAntiqueRadio.com


Top
 Profile  
 
Post New Topic Post Reply  [ 6 posts ]  Moderators: Marcc, Norm Leal

All times are UTC [ DST ]


Who is online

Users browsing this forum: chazz046, chazz99, Exabot [Bot] and 11 guests



Search for:
Jump to:  




























Privacy Policy :: Powered by phpBB