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 Post subject: GE 250 Questions
PostPosted: Jun Wed 13, 2018 9:16 am 
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Location: Hammond, Ind.
I just found a GE 250 at a local shop for a good price. I am in the process of repairing it. I have some questions about 2 parts.

The Willard 25-2 battery is the subject of my first question. I was wondering if it is possible at all to reuse this battery, as I prefer everything to be as close to original as possible. The two seals, what look like grommets, on the rear of the battery are ineffective. I found that out by filling the battery. They still felt pliable. Are they replaceable? They look like grommets but I don't know if they come out, or how to get them out. I have a PowerSonic 260 as a modern substitute already, but I was just wondering about the original.

My second question is about the bias cell. I have heard it is possible to do something with water to revitalize them? How does that happen? and if that is not possible, what is a good substitute for the 5v bias battery? Is it also correct that the positive end of the battery goes to ground to give off -5 volts? Is there a 1v watch battery in existence that there can be 5 of?

Was also wondering about a knob. one of the knobs has a little chip on it. Is there some sort of filler for the off white plastic available? or does someone have a replacement knob for this radio? it is one off the off white knobs with a red arrow on it.

Finally, are there any other "special" parts of the radio like the bias cell, or other special parts that normally fail? And all of 0.5uf caps with four leads can be replaced with single caps right?


Any information is helpful
Thanks

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 Post subject: Re: GE 250 Questions
PostPosted: Jun Wed 13, 2018 10:53 am 
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Location: Louisville, Ky
doubt you can renew the original Willard cell, but you can replace it with a modern lead-acid sealed battery, 2.1 volts. the bias cell can be replaced by a coin battery. There are posts on this site regarding both issues if you search for them.


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 Post subject: Re: GE 250 Questions
PostPosted: Jun Wed 13, 2018 11:16 am 
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If it's really 5 volts, it will need several coin batteries?? A well-stocked harware store will have a wide range of choices.

The cheap way out? Add a cathode bias resistor. The only downside is some loss in output power.

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 Post subject: Re: GE 250 Questions
PostPosted: Jun Wed 13, 2018 3:17 pm 
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Location: Roslyn,Pa 19001
> special parts that normally fail?
I'd start w/ the batteries, buffer caps, and the vibrator.

GL
Terry


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 Post subject: Re: GE 250 Questions
PostPosted: Jun Wed 13, 2018 7:37 pm 
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Location: Hammond, Ind.
I am replacing all of the paper/electrolytic caps for sure. What is the buffer cap? Is that the HV rated cap? I have a replacement for it.
Also the vibrator has a weird pin layout. I doubt there are many replacements out there. The relay contacts inside are very loose. If you shake the can, you can hear the contact jump from point to point. I have no experience with vibrator type sets. I guess I will open the can?

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 Post subject: Re: GE 250 Questions
PostPosted: Jun Wed 13, 2018 8:27 pm 
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Location: Roslyn,Pa 19001
It's C-31 .003@1.5KV.

>Also the vibrator has a weird pin layout.
That's what makes it special! I doubt you can tell about the contact's condition as the inside of the vibrator the mechanical parts are surrounded in rubber. The rubber deteriorates and can cause the innards to rattle. Typically the contacts on the vibrator get pitted from use and either stick together or won't make good electrical connection. Someone may have designed a s/s replacement.

I'd search the forum under GE 250. The subject has been posted on before. There is also a GE 260 which is very similar but has short wave coverage.

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Terry


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 Post subject: Re: GE 250 Questions
PostPosted: Jun Wed 13, 2018 9:06 pm 
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The buffer capacitor is C31 on the Rider's schematic, it is rated for 1500V and is 0.003uF. I would use a 1600V 0.003uF cap as it is across the secondary of the vibrator transformer and will be exposed to high voltage spikes as the vibrator contacts open and an inductive kick causes a HV spike in the secondary. I know that the capacitance value is critical for proper timing of the contacts in the vibrator, however I do not know what the tolerance is. I used a Sprague 0.003uF 1600V orange drop, I don't know if a modern 0.0033uF cap is close enough in tolerance.

The contacts in the vibrator should move as you describe, when energized the collapsing field in the vibrator coil causes the contacts to move which both "chops up" the 2V from the battery and rectifies the 90V from the transformer secondary.

If you have the original battery it is guaranteed to be bad unless it has never been unsealed or filled. Flooded batteries like the original will rapidly decay if not kept charged as the sulfur in the acid will adhere to the lead plates. The lead will also oxidize if the battery is not filled but is opened and exposed to air. Hopefully you did not get any acid burns filling the original battery with the failed seals.

The Power sonic 260 is a good replacement but does not look original. I went ahead and built a replica Willard 25-2 out of acrylic in which to house a Hawker X 2V 5Ah or Hawker E 2V 8Ah sealed lead acid cell. You can see that here: viewtopic.php?f=1&t=299224

The three and four lead capacitors are used to simplify hookup, the connections on the same end are the same piece of metal (I've broken a couple open). So normal capacitors can be used in conjunction with a terminal strip.

As to the bias cell, this radio cannot use cathode bias because the tubes have no cathodes. Most other portables of the era used a resistor in series with B-, the voltage drop across which biased the output tube. However, GE didn't do this on the 250 or 260 and the design is not easily adaptable.

The original bias cells were four UFO shaped discs in an orange cardboard tube. The suggested method to restore them is to drop the cells into a cup of boiling water and let it cool, where water would be drawn into the cells restoring their function. I tried this and only succeed with one cell which died again a day later. I would suggest using a pair of 3V lithium coin cells as their long shelf life (10 year) is advantageous, and the 1V difference between them and the original bias cells will not be noticeable in the output of the radio. Zinc air cells would be closer in voltage to the original at 1.25V per cell but have a very short life once in use (couple months). And yes positive goes to ground.

If one knob is broken, then either a replacement or fixing the original would be in order. eBay often has parts radios for often inexpensive prices. The other option would be to fix the knob with some kind of epoxy then paint it. JB weld would work but it is grey.

The only other special parts in the radio are the two cooper oxide rectifier discs used for battery charging but they rarely fail.

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 Post subject: Re: GE 250 Questions
PostPosted: Jun Wed 13, 2018 9:16 pm 
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http://www.nostalgiaair.org/pagesbymode ... 007630.pdf

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 Post subject: Re: GE 250 Questions
PostPosted: Jun Thu 14, 2018 6:20 am 
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Location: Hammond, Ind.
When filling the battery I used excessive baking powder for cleaning up and luckily did not get burned by the acid. Thank you for the information regarding the battery. Will only one of these PowerSonic 260 batteries be good enough? should I add more to increase the overall capacity? I had seen that thread about the recreated battery. That is quite a well made replacement. Did you repaint the exterior? That radio is like new. Also, when this battery is being charged in the radio, does the charger automatically turn off like a golf cart charger or do I have to check it every hour or so with a VOM?

I will try revitalizing the bias cell with the water method. I hope it will work. Cant the radio be operated with a dead cell too?


My replacement for the buffer is
https://www.ebay.com/itm/3-pcs-003uf-0- ... 2749.l2649
Is this a suitable replacement?


Thanks for all of the information.

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 Post subject: Re: GE 250 Questions
PostPosted: Jun Thu 14, 2018 2:30 pm 
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jimjimmunster wrote:

I will try revitalizing the bias cell with the water method. I hope it will work. Cant the radio be operated with a dead cell too?
.

No. The tube in question requires a negative bias to operate correctly. Without it, it will draw too much current and possibly overheat.

There are a few exceptions but...as a general rule...you can not simply delete a part and have the equipment still work

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 Post subject: Re: GE 250 Questions
PostPosted: Jun Thu 14, 2018 4:28 pm 
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jimjimmunster wrote:
My replacement for the buffer is
https://www.ebay.com/itm/3-pcs-003uf-0- ... 2749.l2649
Is this a suitable replacement?


From an electrical standpoint that would probably work fine, however as I recall there was limited space available in the compartment where this capacitor is housed and a 3000V part may be difficult to work with in that space. A 1500V or 1600V part would be sufficient also.

I would not operate the radio without the bias battery, I don't think this radio could supply enough current to make a 3Q5 redplate however it could damage something in the vibrator supply.

My radio did get repainted, I used Rustoleum silver hammertone.

Your power sonic 260 battery will work fine, but will not last as long as the original. More batteries in parallel will increase run time.

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 Post subject: Re: GE 250 Questions
PostPosted: Jun Thu 14, 2018 9:29 pm 
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I will probably add more PowerSonic batteries.

I will most likely use watch batteries to get 4.5v as the bias cell substitute.

The replacement buffer is quite compact and fits well.

Thank you for all of the information.

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 Post subject: Re: GE 250 Questions
PostPosted: Jun Fri 15, 2018 2:54 am 
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I should add that the 250 uses a constant current charging system. It will continue to charge the battery and will not stop when it is fully charged so overcharging is possible.

If it is fully discharged you can simply divide the battery capacity by the charging current and get the number of hours to charge the battery, adding a little bit additional for charging inefficiencies. Another way would be to watch the voltage until it gets to about 2.15V which would be near 100% for a nominally 2V lead acid cell.

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 Post subject: Re: GE 250 Questions
PostPosted: Jun Fri 15, 2018 1:11 pm 
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I have the model 260 which is pretty much the same radio except for added shortwave bands and an extra IF amplifier tube. I tried the bias cell rejuvenation, also without much in the way of results like stated above. It's pretty easy to use pieces of one of the bias cells and modern watch batteries to restuff the bias cell paper tube. I doubt as well that the 3Q5 is going to redplate without bias, but I would guess tube life would be reduced in any event, and that's the one tube I see replaced a lot in battery portables like this.

I used a Cyclon 5AH cell placed inside the hollowed out case of the original battery. The battery needs to be in the circuit even when running on AC as it acts like a giant filter capacitor in the power supply. Yes, it's about a fifth the capacity of the original, but the radio is still good for a couple of hours of run time.

I thought of trying to make a solid state replacement for the vibrator, but the big challenges are the low voltage which rules out MOSFETs (at least without some way of stepping up voltage in the vibrator replacement) and the need to provide synchronous rectification inside the box, which uses more devices and introduces more voltage drops in an already critical circuit due to the low voltage used.

One last thing: The audio quality, at least on the radio I have, isn't that great. Looks like either the detector or first audio stage has excessive distortion for some reason I can't find at this time. The power amplifier stage uses negative feedback which is unusual in a battery tube radio like this.


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