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 Post subject: Vibrator power transformer check...
PostPosted: Nov Fri 09, 2018 3:30 am 
Member

Joined: Jan Wed 07, 2015 10:39 pm
Posts: 157
Location: Jamison PA
Hi Folks

I have been working on my Delco 3203 32v set for quite a while. To cut to the chase, I had taken out some hacks that had bypassed the transformer and vibrator section. It is correct now, all recapped etc as well as a vibrator that works too. I had the radio playing, but had the transformer get mighty hot after a very short period of time. I had posted about it a year ago, and we went through the checks of pulling tubes, measuring draw, and it appeared that it might be partially shorted on the secondary, as the radio did play, but voltage would drop as it got hot...I suspect the trans was bad from the get go, and I did all the work on it before I figured that out. The first time it played, I heard the dreaded sizzle, but no magic smoke. It actually played a few more short times after that. I removed the trans and there it sat.

So here it is nearly winter again, and I did some studying and picked it up off the bench again. I had disconnected it from the chassis. I typically play with these in the colder months....

It has a center tap primary and secondary, for a total of 6 wires. Wire 1 and 5 go to vibrator primary, wire 2 and 4 are vibrator secondary. 32v DC in, specs say 175 at the plates of 6A7, 6B7, 6D6. Screen grids on the 43 outputs are 175.

B+ was not that high, probably 150 and dropped as it got hotter.

Center tap primary to wire 1 is 1.6 ohms, and center to wire 5 is 1.8 ohms. I have continuity between wire 1 and 5..

Center tap secondary to wire 2 is 102.8 ohms. Center tap to wire 4 nothing. No continuity from 2 to 4.


Seems to me there is a break on wire 4 in the secondary winding. I guess the radio worked because there was enough B+ to receive, but the resistance of the break in wire 4 just kept getting it hotter.....


Sound right to you all?


Should I get brave and try to isolate that winding and find the break?.


It seems that rewinding this is not something the trans shops I contacted wanted to do.

Thank you

Mike


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 Post subject: Re: Vibrator power transformer check...
PostPosted: Nov Fri 09, 2018 4:45 am 
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Joined: Nov Tue 14, 2017 5:09 am
Posts: 818
Location: Austin, Texas
Mike,

I think you should be able to use a dual 24V, dual 115V, transformer as a replacement. Are the core dimensions on this one close to your transformer?
Attachment:
Transformer.jpg
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Jay


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 Post subject: Re: Vibrator power transformer check...
PostPosted: Nov Fri 09, 2018 5:48 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 26886
Location: Detroit, MI USA
I think that Heyboer can wind you a brand new one. Need to provide exact specs or possibly send them the old one for a sample. They don't rewind existing stuff but build excellent quality new ones.

_________________
Dennis

Experience is what you gain when the results aren't what you were expecting.


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 Post subject: Re: Vibrator power transformer check...
PostPosted: Nov Fri 09, 2018 7:58 am 
Member

Joined: Jan Tue 16, 2007 7:02 am
Posts: 2614
Location: Lexington, KY USA
Operating the rectifier circuit half wave will definitely stress the transformer. Besides delivering lower B+ voltage, the remaining secondary winding will get hotter.

Try four diodes in a full wave bridge on the surviving half of the secondary.

If you still have a heat problem, increase the bias on the audio output stage to reduce the B+ current, and give the transformer some relief.

Running the output stage at lower current only affects how loud the radio can play when turned-up. Should still be louder than the sets that used 32V directly for B+.

Next radio, check all the coils and windings for continuity before doing anything else.

Ted


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 Post subject: Re: Vibrator power transformer check...
PostPosted: Nov Fri 09, 2018 2:26 pm 
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Joined: Nov Tue 14, 2017 5:09 am
Posts: 818
Location: Austin, Texas
Usually Lurking wrote:
Try four diodes in a full wave bridge on the surviving half of the secondary.

Ted


Ted,

I suggested using SS diodes on another vibrator supply thread. One other person mentioned that he had trouble keeping 1000V diodes alive with the square voltage wave and transients from the vibrator transformer. I haven't looked at the waveforms but fast recovery diodes may be needed for the application. I don't think the transients should be more than 1000V but the buffer caps are usually rated for 1600V or more. Without doing some testing, I don't know what diode specifications are needed for the application but the usual 1N4007 may not be satisfactory.

Jay


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 Post subject: Re: Vibrator power transformer check...
PostPosted: Nov Fri 09, 2018 2:53 pm 
Member

Joined: Jan Wed 07, 2015 10:39 pm
Posts: 157
Location: Jamison PA
I remember being advised to try the diodes to help with the vibrator grounding timing. That didn't seem to hurt or help, as the real issue was the transformer itself (wasnt sure at the time)

As the vibrator is a synchronous one (self rectifying) basically I am getting half wave rectification as only one side is actually working here?
The vibrator was hot too, as I suppose all the current was on one set of points.

How would this dual 24v transformer work in this application??

Thank you

Mike


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 Post subject: Re: Vibrator power transformer check...
PostPosted: Nov Fri 09, 2018 3:30 pm 
Member

Joined: Nov Tue 14, 2017 5:09 am
Posts: 818
Location: Austin, Texas
Mike,

A dual 24V transformer or 48V center tap transformer with 115/230V input windings will have about the same turns ratio as your vibrator transformer. Note that the peak of 24VAC is 33.6V which is close to the 32VDC input of your radio. If you drive the 24V secondaries from the vibrator, you should get close to the correct B+ voltage on the transformer primary windings. The vibrator frequency will be higher than 60Hz but I don't think the transformer core losses will be any worse than the original transformer. If you want to keep the original appearance, the problem will be finding a new transformer with the same core dimensions.

Jay


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 Post subject: Re: Vibrator power transformer check...
PostPosted: Nov Fri 09, 2018 9:27 pm 
Member

Joined: Jan Wed 07, 2015 10:39 pm
Posts: 157
Location: Jamison PA
Thank fellows, much appreciated.

Jay, I believe size wise would be fine. I guess its a 5:1 so 24V equals 120V and 32V should be 160v? That should work well. How do I source that one?

I would assume that the two center wires are tied on each to make a center tap, then just input and for primary and secondary vibrator connections?

Thank you

Mike


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 Post subject: Re: Vibrator power transformer check...
PostPosted: Nov Sat 10, 2018 6:57 am 
Member

Joined: Nov Tue 14, 2017 5:09 am
Posts: 818
Location: Austin, Texas
Mike,

One choice is this Triad transformer from Mouser:
https://www.mouser.com/ProductDetail/Tr ... %2fv86U%3d
However it is for PC board mounting and would not fit in the original transformer covers.
I'll see if I can locate a similar transformer with wire leads.

Jay


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 Post subject: Re: Vibrator power transformer check...
PostPosted: Nov Sat 10, 2018 2:45 pm 
Member

Joined: Jan Wed 07, 2015 10:39 pm
Posts: 157
Location: Jamison PA
Many thanks :mrgreen:

I'll stay tuned...


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 Post subject: Re: Vibrator power transformer check...
PostPosted: Nov Sat 10, 2018 5:12 pm 
Member

Joined: Jan Tue 16, 2007 7:02 am
Posts: 2614
Location: Lexington, KY USA
Just replacing the vibrator contacts with two diodes will not solve the open transformer winding problem. Using four diodes in a full wave bridge will do a lot more for you.

The TVS diodes mentioned in the other thread will solve the transients kill the diodes problem. Or you can add an MOV across the transformer winding.

If the transformer problem is only the open winding, using the four diode bridge, plus possibly reducing the audio output stage standing current, will definitely make the radio play OK without overheating. This can be a cheap and easy interim solution while you look-into replacing the transformer.

Using a four diode full bridge rectifier would also allow use of a replacement transformer with a single high voltage winding.

Ted


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 Post subject: Re: Vibrator power transformer check...
PostPosted: Nov Sat 10, 2018 5:49 pm 
Member

Joined: Nov Tue 14, 2017 5:09 am
Posts: 818
Location: Austin, Texas
The Triad F-213Z is what I would suggest as a replacement transformer. It would not fit in the original transformer end bells so it would look different than the original.
Attachment:
Triad F-213Z.jpg
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Several places have it for sale. This one seems to have the best price but I only did a quick search.
https://www.arrow.com/en/products/f-213z/triad-magnetics

If you go with one of these, make temporary connections to the ends of the high voltage winding and put something like a 0.1uF, 600V, cap from the center tap to ground (only the cap on the center tap). Check the center tap voltage relative to ground. If it is negative, the end connections will need to be reversed. The voltage may be a lot higher than normal due to the switching transients from the vibrator.

I have a 3201 in my collection. No vibrator problems since it uses 48s in the output with 32V on the plates. Also not much output power.

Jay


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 Post subject: Re: Vibrator power transformer check...
PostPosted: Nov Sat 10, 2018 8:36 pm 
Member

Joined: Jan Wed 07, 2015 10:39 pm
Posts: 157
Location: Jamison PA
Thanks again for all the suggestions and help. I removed the transformer bells to take a better look and now the secondary has no continuity at all. Its crispy looking in there......I may take it apart carefully to see how the secondary is wound. Lets say for example, if I was able to unwind and find a break, do you splice and resolder, or do you unwrap the whole thing and start over with fresh magnet wire?

I will try the other transformer, and that you for that, much appreciated!!


I too have the 3201, plus a 3205 (restored) and 3206 plus the early 4049 (restored) made by crosley. The 3201 and 3206 are completely original, as I did remove the chassis from each to see what I had. They both play, and the 3206 is quite loud with 4 48 output tubes in it. The 4049 is the only other transformer verison for B+ I know of, save the that early one that uses a dynamotor....


Will report back....


Mike


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 Post subject: Re: Vibrator power transformer check...
PostPosted: Nov Sat 10, 2018 9:21 pm 
Member

Joined: Nov Tue 14, 2017 5:09 am
Posts: 818
Location: Austin, Texas
Mike,

You may be lucky and the windings are broken where they connect to to the bigger wires. You can unwind some turns from the outside winding without causing a problems. Often the lead from the inner winding is broken off too short to make a connection. You may also find that the insulation is crumbling on the windings. In that case, you need to either rewind the whole thing or get a replacement.

Rewinding is a major task since it will probably be several thousand turns of small wire. If you want the radio to work far into the future, I would recommend replacing the transformer rather than trying to rewind it.

Jay


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 Post subject: Re: Vibrator power transformer, working!!
PostPosted: Nov Fri 16, 2018 2:04 am 
Member

Joined: Jan Wed 07, 2015 10:39 pm
Posts: 157
Location: Jamison PA
I received the dual in and out transformer. 24-0-24, 115-0-115.

I carefully used all my alligator leads to connect the transformer backwards, ie the 120/240 v input was the output now.

I got the polarity correct on my first try. I am using a 32v 2.6 amp power supply. You can see I am running at about 123 volts B+ with this setup. I think once dressing the wiring, resoldering and installing, it might get a little better. Before, when I tried to fire up the radio with the suspect transformer, the power supply would kick off, then reset itself once the tubes had warmed up a little. In retrospect, that should have been a flag right there. Transformer seemed cool, as well as the vibrator. It turned on immediately with no issue. The radio pulled in our local burner 1210 no problem, even up with its guts hanging out. Although I thought the B+ should be higher, it has a loud volume and seems to be acting correctly. Maybe its a good thing running about 50v low (specs say 175v on the tubes), I couldn't tell what the difference would be.

I wanted to share this, as the suggestion of this transformer baled this radio out. I had a NOS 32v vibrator that had a minor difference in how it was powered. I had to rewire a different socket to make it work. Finding the correct one was impossible. This radio had been hacked, to take out the transformer and vibrator out of the circuit (probably because the transformer was partially toast, in my zeal to get it going, I conveniently looked that fact over, lesson learned). This radio uses a seperate line in through dropping candohms to power the filaments and lights. There was a direct wire into the B+ choke that was supposed to go to a 150v DC outside power supply. I got rid of all the hacks and started over to get as close to the schematic as possible.

The real test of course is once its all installed, to go through and carefully check all the voltages and address any issues I find. I recapped the whole set as part of this restoration.

Thank you Jay, and all who responded. It was very helpful and an interesting learning experience.

Sincerely

Mike


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 Post subject: Re: Vibrator power transformer check...
PostPosted: Nov Fri 16, 2018 2:56 am 
Member

Joined: Nov Tue 14, 2017 5:09 am
Posts: 818
Location: Austin, Texas
Mike,

It looks like we are in good shape on the power supply now and can recommend that transformer for other collectors. I don't think you will have a significant change in performance with the lower B+ voltage. Let us know what it is after you get everything mounted on the chassis.

Jay


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