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 Post subject: AC/DC Vibrator
PostPosted: May Mon 28, 2012 7:43 pm 
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Joined: May Thu 10, 2012 10:05 pm
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For an AC/DC set having a power supply that includes a rect tube and vibrator...

Does the vibrator have impact on the heaters when the set is switched to ac voltage?

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 Post subject: Re: AC/DC Vibrator
PostPosted: May Mon 28, 2012 9:23 pm 
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Location: Lexington, KY USA
Sudsy,

Depends on the radio. The vibrator must work in order for the heaters ( well, filaments ) to get power when operating an AN/GRR-5 from AC power.

I suspect that few civilian radios have vibrators in the A supply.

The AN/GRR-5 is a mobile receiver ( think tanks, or APCs ) that provides regulated DC for the signal tube filaments, except when running off dry batteries. This is for sure an AC / DC set, in that it works from dry batteries, 6/12/24VDC and 117VAC.

What is commonly called an AC/DC radio has only one power input connection, and no vibrator. What sort of radio do you have here?

Ted


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 Post subject: Re: AC/DC Vibrator
PostPosted: May Mon 28, 2012 10:50 pm 
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Thank you for your reply Usually Lurking.

The set is a Zenith 5J217. In a/c mode, have all of the voltages near spec except for the filaments. Seemed to have narrowed down to vibrator as potential. Research keeps pointing to deficiencies in B voltage potentially pointing back to a vibrator problem. Haven't located anything pointing to filament problems pointing to vibrator. It does not vibrate in a/c mode, not sure if it is intended to. Haven't performed a vibrator dim-bulb test on it yet.

Just not sure if chasing the wrong rabbit at this point.

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 Post subject: Re: AC/DC Vibrator
PostPosted: May Mon 28, 2012 11:36 pm 
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Here is the schematic from Nostalgiaair http://www.nostalgiaair.org/PagesByMode ... 024961.pdf

The transformer has a 120 volt primary and a vibrator primary, a 6 volt AC and high voltage secondary.

There is an AC-Battery transfer switch which puts the heaters on the transformer for AC but on the battery for DC. If the switch is dirty or damaged, this would affect the heater voltage as low voltage and high current is affected by any resistance in the switch contacts.

The vibrator is only used for driving the power transformer to create high voltage on battery operation.

Don

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 Post subject: Re: AC/DC Vibrator
PostPosted: May Tue 29, 2012 12:13 am 
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Joined: May Thu 10, 2012 10:05 pm
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Thank you Don.

That is the knowledge I was hoping for.

Looking at the schem, is there detail that indicates this that I can pick on or is this more of an experienced
knowledge?

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 Post subject: Re: AC/DC Vibrator
PostPosted: May Tue 29, 2012 7:27 am 
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Location: Lexington, KY USA
Sudsy,

Don is exactly correct. The vibrator has no function when operating on AC. The schematic ( thanks for the link, Don!) even has a note suggesting that the vibrator be removed when using AC power.

As to how to figure out what's going on in the power supply for this set, after looking at a lot of radio circuits over the years, you will notice that this radio has everything required for both a normal transformer operated AC set, and also for a typical car radio of the era. The change-over switch connects the parts to be one or the other. You can see schematics for both sorts of set in the back of a 40s or 50s tube manual.

You might try drawing the power supply circuit without the switch, making two versions of the drawing. Once the switch is out of the picture, the circuit is easier to understand. First draw the 6VDC circuit, then the 115VAC version.

Check the AC voltage at the heater winding on the transformer and see if it is correct. This winding is shown on the schematic as the top winding on the right hand side of the transformer.

Ted


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 Post subject: Re: AC/DC Vibrator
PostPosted: May Wed 30, 2012 4:58 pm 
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Thank you for your reply Usually Lurking. And thank you Don for the link to the schem. I can read the vibrator note on yours!

That was a very good exercise to go through. I believe I understand the schem now having broken the two apart like you recommended.

I don't know if I have correctly done what you recommended in checking the voltage. It was very difficult and time consuming to identify which was the winding for the heaters. I don't think my methodology was the best but hopefully the end result is correct at least.

I see the winding as top right as you pointed out on the schem. Then I went to the actual switch (to avoid having to disconnect the 7 wires to take off the power supply) and the connector tabs on the switch do not line up like the schem tabs line up so I didn't trust the positioning relative to the schem to identify. Thus traced the wires from pin 2 & 7 of rect tube. Found the two taps on the switch, disconnected the one going to the transformer and measured the voltage.

I have thoughts that I needed to disconnect ground from the transformer as well to get the voltage, but not sure.

The voltage measured 3.5v.
Heater voltage is at 2.9v.

If I did this wrong or using a poor method, please tell me.

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 Post subject: Re: AC/DC Vibrator
PostPosted: May Thu 31, 2012 4:59 am 
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Sudsy, The center tap of the heater winding is grounded, so if you are measuring from one leg of the transformer to the chassis, you will measure half the voltage, so 3.5 volts AC would be good. You would have to measure from one end to the other of the heater winding to see the full 6 to 7 volts AC. They ground the center tap of the heater winding to reduce hum.

The confusion factor is that when the set runs from battery, you read 6 volts from the tube to the chassis. That is why both wires go through the switch.

By the way, if the pilot lamps are bayonet style, #1490 is the closest match
Don

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 Post subject: Re: AC/DC Vibrator
PostPosted: May Thu 31, 2012 3:27 pm 
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Joined: May Thu 10, 2012 10:05 pm
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Have been looking for the cause of the low heater voltage and it has been ok all along. Measured heater voltage pin to pin and shows 6.3v on AC setting! Thank you!
Man, the learning curve can be frustrating.

That is good news then as far as the transformer and heater circuit.

U have esp? Set did not have pilots in it. Grabbed some 1490's and good to go. Thank you again.

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 Post subject: Re: AC/DC Vibrator
PostPosted: Jun Fri 01, 2012 12:25 am 
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I had a hunch you would need pilot lamps. By the way, the original lamps were 2.9 volts each with R11 in series to run on 6.3 volts. The 1490 lamps are 3.2 volts each, 6.4 volts for two, so you can jumper out R11 (a 15 ohm wirewound resistor) to make the lamps brighter.
Don

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Diode Don, all problems rectified.

Someone with less knowledge than I had been in there before ....


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 Post subject: Re: AC/DC Vibrator
PostPosted: Jun Fri 01, 2012 2:37 am 
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Joined: May Thu 10, 2012 10:05 pm
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Thats great advice Don! Thank you very much! :P

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Sudsy


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