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 Post subject: Re: Resistor that replaces the field coil
PostPosted: Apr Thu 08, 2021 8:16 am 
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Joined: Jan Tue 16, 2007 7:02 am
Posts: 4357
Location: Lexington, KY USA
It's too late to try to figure this out tonight.

I do want to say I'm sorry about your scare with the smoke. It is a relief that the set still works!

Ted


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 Post subject: Re: Resistor that replaces the field coil
PostPosted: Apr Thu 08, 2021 2:23 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 292
Location: Ontario Canada
Thanks for the reply and the help Ted ,at first I thought that I had put the extra cap in backwards ,thats how they react when put in the wrong way smoke and all , but I don,t think so , I ran the set for an hour before I put it back in the cabinet and turned it off and on more than a few times , all the original caps were in a large metal rectangle housing and I am sure they were all negative to the chassis , I took out the original metal housing that held the 4 caps and replaced them with modern caps . I will take the chassis apart tonight and check the cap again and also take off the extra cap on the 4 uf and put extra on the i uf caps , please just let me know if it is the 1 uf on the left in the schematic or the one on the right side of the schematic , again thanks so much , I won't change anything until I hear from you , I am in no hurry ,take care Ted all the very best Rick
PS - After the resistor and choke I put in and the place where the wire goes to the 27 tube plate I get 92 volts when I use the wall plug which is 125 volts ,I also use a buck transformer to drop the voltage to the set , I was told less voltage is better on these old sets ,I have a plug box with cord and a switch , the buck coil transformer is not in the radio chassis ,this way I can use the buck coil on any radio I want. The voltage from the buck coil is106 volts and when I use it on the radio I get 86 volts at the plate on the 27 tube .When I measure the voltage on the 27 tube I put one end of the probe on the plate pin of the 27 tube and the other end of the probe on the chassis to get the voltage.


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 Post subject: Re: Resistor that replaces the field coil
PostPosted: Apr Fri 09, 2021 9:58 pm 
Member

Joined: Jan Tue 16, 2007 7:02 am
Posts: 4357
Location: Lexington, KY USA
I don't think I understand the voltages reported above. They seem to be mostly very high.

What i get for voltage at the power strip on spot D & C is 473 volts

473 V is crazy high for what should be around 100V on the B+ line for the signal tubes.

If you have roughly the 80V drop across connector 2352 expected from the voltages on the print, you would have over 540V at the more positive terminal of 2532. And more still at the rectifier. Sounds much too high. Anyway, what is the voltage rating for your filter caps? 630V would be none to high if these voltages are actually present. For sure, you don't want to apply power without the two output tubes.

follow the the wire to the 27 tube I get 130 volts

130 V is probably OK for the 27 plate, given that the 50V value on the print was probably taken with a 1000 ohm per volt meter. But that's still a 343V drop across the driver transformer primary. That's a but much. The print values imply a 50V drop across this winding, and that's with the heavy load from their meter.

I will take off the 2 uf cap I put on the 4 uf capacitor ,,, which 1 uf cap should I add to the one left on the schematic or the one on the right on the schematic

The 4uF filter cap on the schematic, connected right on the rectifier's positive output, is the one that should be increased only with caution. Note that this small value cap still must have a fairly stout ripple current rating.

To replace the B+ filtering lost when the field coil was removed, the value of the filter capacitor immediately after the former field coil connection can be increased. This is across the 1uF capacitor that connects to the left hand side of connector 2352 and to terminal strip 2268-D. This is where you reported measuring 473V.

It would be interesting to know what sort of filter caps you are using.

Ted
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 Post subject: Re: Resistor that replaces the field coil
PostPosted: Apr Fri 09, 2021 11:57 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 292
Location: Ontario Canada
Hello Ted ,when I check the voltage befor and after the 2.5 K 25 watt resistor and the choke I put in I get the same on both ends of the resistor 473 volts , is this because the set is split in half and I am taking the readings without the set being attached to the radio only reading the power supply with no load on it , only have the 80 tube in and the rest of the radio is not in the circuit , because the voltage drops at the plate of the 27 tube ,and that is with all tubes in and both halfs of the radio bolted together at the power strip and running . What I have done is ordered new caps , two Electrolytic 4UF at 600 volt caps to go in the 4UF spot and one more to go in the 2UF spot and two 2 UF 630 volt film caps to go where the 1UF caps are , I am sure the caps I used are too low in voltage ,they are in the set now and in circuit so I can't get a proper test on the one i suspect is now bad ,the bang and the smoke with no damage that I can find on any transformer or coil I am sure that it,s a cap , and I am thinking the extra 2 UF I put on with the 4UF cap is now bad, I used 450 volt caps because I had seen a film on youtube of a fellow repairing a model 31 Eveready radio and he used 450 volt Electrolytic caps , never seen the set working , I should have used 600 volt caps right from the start , the caps I used I got from Justradios all new a 4 UF electrolytic at 450 volts for the 4UF spot and a 2 UF electrolytic at 450 volts for the 2UF spot and two 1 UF 630 volt film cap for the 1 UF spots in the set .When the caps come and I install them I will hook up two alligator clips one to each side of the 2.5K resistor and tape the wires tight so they can't move and short out and one wire to the plate of the 27 tube plate and take the voltage , the name on the Electrolytic caps is MIEC , I will post the voltage I get after I take it , the new caps should be in next week some time , if you think I should do anything else or anything different please let me know , again take care stay safe and THANKYOU all the very best Rick
PS- When you place an order there is a $30.00 min. so I ordered extra caps of the same in case I have to switch them from the way I planned


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 Post subject: Re: Resistor that replaces the field coil
PostPosted: Apr Tue 13, 2021 1:43 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 292
Location: Ontario Canada
Hello ,looks like we got it now ,befor with only the 80 tube in and the set split in half I got 475 volts DC with a 2.5K power resistor and a choke that is 370 ohms to take the place of the field coil, the same voltage before and after the resistor and choke that was taking the place of the field coil 475 volts.Now I have changed the caps again ,this time using 600 volt electrolytic caps at 4 UF ,one in the 4 UF spot and one in the 2 UF spot and in the 1 UF spots I used 630 volt film caps at 2UF, here is the voltage I got with all tubes in and the set attached together and running ,at the 27 tube using the buck coil to run it at 106 volts I got 80 volts DC at the plate of the 27 tube and with the wall plug at 125 volts I got 91 volts DC at the 27 tube plate , now with all tubes in and the set running befor the 2.5K resistor and the 370 ohm choke that takes the place of the field coil, with the buck coil giving me 106 volts I got 212 volts DC and with the wall plug that gives me 125 volts I got 248 volts DC , with the wall plug giving me 125 volts and testing after the resistor I get 122 volts DC and with the buck coil giving me 106 volts after the resistor I get 105 volts DC , I think the voltage I was getting was high because the only tube I had in well checking was the 80 tube and the set was split in half ,I think . The set has no hum at all now even when off station , Ted and the other fellows thanks so much for the help , and also Ted looks like it was that extra 2 UF cap that I put on with the 4 UF cap that blew and smoked , only thing it is not swollen or the end blown out ? , but I tested it and it is dead now , it was put in the right way and I ran the set for over an hour before it happened , I can,t say for sure what took care of the hum ,the extra cap size or the 370 coke I used in series with the 2.5K resistor ,anyway thanks again fellows take care and be safe all the very best Rick


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 Post subject: Re: Resistor that replaces the field coil
PostPosted: Apr Tue 13, 2021 10:14 pm 
Member

Joined: Jan Tue 16, 2007 7:02 am
Posts: 4357
Location: Lexington, KY USA
Glad you have good results. Especially the low hum level.

And thank you for bringing us up to date.

Here are a couple of suggestions for future work.

When voltage measurements are taken to post on the forum for use in diagnosis, they need to be made in a consistent way. They need to make sense taken together. Usually it is best to set up the radio so it is complete and operational, and to duplicate the setup listed on the service print. That way, the other forum members may get something they can work with.

In any case, it is often hard to make remote bench work be effective to solve a problem.

Sometimes, operating the B+ supply without the normal load can cause the voltage to soar so high that things arc over or blow up. That may be what got your capacitor. Applying power while part of the radio is disconnected, or with some tubes pulled out, can be a risky business.

Ted


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 Post subject: Re: Resistor that replaces the field coil
PostPosted: Apr Wed 14, 2021 12:05 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 292
Location: Ontario Canada
I got it Ted, I learn as I go and should be as clear as possible so you fellows have a good look at what I am doing so you fellows have a chance to help me out , I had no idea that the set had to be together with all tubes in and running to get the proper voltages, worst thing I did was watch that youtube video , the fellow there had only the 80 tube in and the radio split in half when he took his voltage readings, and I followed him and got the 450 volt caps when I should have got the 600 volt ones right at the start ,sorry if I caused any problems , I know better for the next time now, by the way I never seen that fellow on youtube get his set working , that should have told me some thing , anyway thanks so much fellows for the help ,the set is working just fine now and has been on and running for the last three hours without any problems or hum at all ,thanks again stay safe and take care all the very best Rick :lol:


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