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Post by acbaker123 Thu Mar 11, 2021 6:06 pm

I just got an atwater kent model 33 that is in great shape, except, I do not know how to power it. the schematics are not that helpful. of the 6 conductors i can't tell what is what and they do not label the voltage on each one. if someone can tell me what voltages go where according to the schematic that would be great, both are hard to see and not descriptive, or tell me where I can find this info. i tried radiomuseum.org.

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Post by acbaker123 Fri Mar 12, 2021 10:25 am

I found a schematic that is very useful and lists the battery pinouts and voltages, but now I do not know what to replace them with, new batteries? modern dc power supplies?

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Post by acbaker123 Fri Mar 12, 2021 3:15 pm

I have a couple of transformers that get close to the required voltages, can I just rectify these and use them instead?

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Post by Chas Sat Mar 13, 2021 2:16 pm

One can waste a lot of time trying to save money building a DC power supply for a 20's era radio...

I have many 20's radios and never built a power supply. I have used a combination of 6 volt lead acid auto battery, and a Majestic "B" supply along with a "C" battery of AA cells. another combination of 6 volt auto and all dry cells made up of a "replica" "B" batteries. Three pairs of these were built. One pair was a re-furbished French "B" battery, another was a triplet of 45 volt "B" batteries, one tapped for detector built into metal lunch boxes. The last pair of 45 volt "B" batteries was built into a pair of plastic food storage containers.

This was done some time ago, long before modern commercial power supplies were built. Though all the batteries exist they have expired from age...

I operated for several years in the late 60's a Grebe Syncrophase powered from a Kokomo B lead auto battery and some dry cell "C" I also had a filament relay that would transfer the power to the B supply to a trickle charger when the set was turned off. I liked the clear audio the Grebe had...

I now use an ARBE-III it provides all the required voltages.

The most difficult part of the power supply is the "A" battery to deliver pure DC. Home made "A" supplies will hum, unless much time and money are spend in an adequate design and build...

My preference is to pay up front, forgetting a couple of steak dinners and opt for Spaghetti "O's" and getting a complete, warranted unit I do not have to tinker with or even repair if it fails.

GL  chas
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Post by acbaker123 Sat Mar 13, 2021 5:08 pm

ok, i will still try to build my own for now, time is not as much concern as money for me, I have had that ARBE-III come up several times now and it looks like it would be very handy but I dint want to fork out $170 for one right now, being a college student and all. as always thanks for the advice.

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Post by Chas Sat Mar 13, 2021 7:43 pm

Tutor those who need help in the areas where your an expert, for cash...
---------------------------------------------------------------------------------------
I suppose building  a power supply is a learning curve. If you are major or minor in electronics. The effort is worth more than the power supply but the knowledge that can be applied to the courses...

ARBE-III has no competition for a unit that is an equal. There are more light weight power supply designs for 20's battery radios.

Even the ARBE-III cannot power a 3 tube radio from 1922 that is OEM equipped with 1 amp tubes. Though there are few of those radios around and good 1 amp tubes are both hard to find and expensive. Setting a goal to answer to the ARBE not having certain flexibility could be a graduate project. Do all the logistics and creating such a power supply for less than an ARBE-III by using off shore assembly and components, would be interesting... One does have to provide for a distributor mark-up..

Good Luck with your studies...  chas
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Post by acbaker123 Sat Mar 13, 2021 10:06 pm

one more thing. I got the radio at an antique store. there was however an Atwater kent horn speaker from the same era. they had it listed for $150. it was in unknown functional condition, but decent cosmetic shape, how likely is it that the speaker would not work?. and can I use any more modern two-wire speaker?. from what I have seen $150 is not a bad price, but again it is hard to justify for an amateur like me.

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Post by Chas Sat Mar 13, 2021 10:45 pm

Atwater-Kent horns, FWIK, are all pot metal drivers with the exception of model "M". To be sure, do this bring a small battery, 1-1/2 volts and connect the battery across the tips on the cord to the speaker. if it clicks generally, the speaker driver coils are good. Turn over the horn and be careful that the driver base does not separate from the horn. The cap that covers the driver should be dark brown Bakelite molded cap. There should be a coarse molded knurling on the edge of this large cap. You should be able to turn this cap within the steel body staying in place. This the diaphragm adjustment.

If the cover over the driver is what looks like die cast metal and may be warped, chips broken out it, it is pot metal. If so, set the speaker down you do not want that speaker...

In the good A-K horn model with the Bakelite cover, it is possible for the gaskets that one each side of the steel diaphragm to be broken or gone hard. That can make the speaker rattle as well as the diaphragm adjustment cap be stuck with the diaphragm too tight.

The Bakelite driver cover can be freed up. When that is done the works are carefully taken out to access the diaphragm and those gaskets. Making new gaskets and cleaning the threads on both the cover and the body. Re-assemble with a little bees wax on the threads.

The purpose of diaphragm adjustment on a horn speaker is to change the sensitivity to loud signals. Loud signals require the diaphragm to be more distant from the pole pieces. For weak station DX the diaphragm needs to be very close almost striking the pole piece.

A horn speaker is polarized. The identified wire or the (+) connection goes to the Amp "B" battery, the negative goes to the last audio tube plate connection..

What happens is the DC flow attracts the diaphragm and also re-enforces the internal magnet in the speaker.

FWIK almost all cone speakers use a bi-polar driver. Because they are bi-polar they are not polarized and do not have a user adjustable driver adjustment.

You radio would sound better with a cone speaker. The cones were available at the time the 33 was made...

BTW have you done a triage on the 33? What is important is to check the resistance of the audio transformers, if they have gone open the set will have to be repaired by replacing the transformers in some way...

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Post by acbaker123 Sat Mar 13, 2021 10:49 pm

I have checked everything but the transformers, so I will look into it thanks

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Post by acbaker123 Sun Mar 14, 2021 9:51 am

I have questions about powering this radio, I am confused about how the -6v works. I understand the -4.5 but to me, it looks like the -6 should be positive. and also, do I need a high impedance speaker because of the 90 volts, or does the tube deal with it? I am also wondering if I can hook up the power inputs exactly as they would with a battery, or if it would be different because obviously, transformers are not batteries.

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Post by acbaker123 Sun Mar 14, 2021 9:57 am

Atwater Kent model 33 Captur10



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Post by Chas Sun Mar 14, 2021 2:40 pm

acbaker123 wrote:I have questions about powering this radio, I am confused about how the -6v works. I understand the -4.5 but to me, it looks like the -6 should be positive. and also, do I need a high impedance speaker because of the 90 volts, or does the tube deal with it? I am also wondering if I can hook up the power inputs exactly as they would with a battery, or if it would be different because obviously, transformers are not batteries.
Forgive my "Frankness".

It appears that interpreting the schematic and understanding how the radio is powered are confusing. You can bet it was for me when I first encountered a 20's era battery radio at 16y.o.

Almost all vacuum tubes of the 20's require three power sources. The origin of the convention "A", "B" & "C" for notations of these sources came about from the first scribbled hookups when tubes were made in light bulb factories.

> Ignore this, there were radios built that required a "D" battery in reference but not necessarily the "D" cell (battery) we know today...

Your notation "-6" is in fact "negative 6 volts". There should be on the schematic a "+6+.

If the "A" battery p[polarity is reversed the radio will work poorly or not at all.

All of the power sources are related to each other and have common connections, if not in the radio, at the batteries.

In the 33 the "-B" is connected to the "A+" this provides an additional positive voltage to the plate circuits of all the tubes even though it is not clearly defined. There should be at least two other B+ connections. The detector tube is at "+22-1/2", the amp tubes are at "+90".  The "B" battery is all the same battery with a tap at +22-1/2...

The "C" battery has its positive connected to the "-A", this too is additive. There is but one "-C" and the schematic shows it to be connected to the last audio tube to provide bias for the grid of that tube.

The spacing's of the grid wire in the two different tubes requires bias to keep the tube operating in its characteristic curve. The larger grid spacing of the 112 provides for both greater power handling capacity in the plate circuit but the bias must be made more negative.

The "A" battery circuit lights the filaments of the tubes, it must be from a power source of low impedance and can deliver current. So, powering the "A" circuit with "D" flashlight batteries is doomed to soon fail in that the filament circuit requires a total of 1-1/2 amps. FYI the normal "A" source was a 6-volt, 60 to 120 amp hour lead/acid battery.

The radio will work with a lead/acid 6 volt battery of about 20 amp hours but reduced operating times and more frequent charging.

Do not be misled by the fact that the tubes have 5 volt filaments. The panel rheostats have three purposes; 1- Drop the 6 volts to what ever is needed in the radio in response of the user. 2-The voltage drop provides bias. 3-The ability to vary the brightness of the filaments controls the amount of electrons thus volume is controlled, in very simple receivers the filament rheostat also control the amount of regeneration, this radio is NOT a regenerative radio...

Do not set the power source for the "A" to 5 volts, it must 6 volts up to 6.6 volts... The "A" source must be robust. Building to 1-1/2 amps does not account for voltage drop in hookup and power leads.

This radio uses thoriated filament vacuum tubes, they can be re-rejuvenated if need be when emission falls off, exception it the 112 which is an oxide tube, when it no longer has emission it is done... The 112 can be replaced with the 201a...

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You need a high impedance speaker because the plate load for the last audio tube requires sufficient resistance to operate correctly and to extract the varying audio voltage from the plate current.. An output transformer salvaged from a AA5 tube radio will suffice if you want to use a low impedance speaker.

It is possible to use one of those A-K speakers with a bad driver and hide in the base a 3" modern speaker and a tiny output transformer. Will probably sound better than the metal diaphragm. However, such a defective speaker should not be more than $20..

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There is a LOT going on in a 20's radio, but one needs not be an engineer to know how to operate it. When it comes to powering it the power source must be adequate.

A-K designed the radio with few controls, simple...

There is a bronze belt drive for the tuning condensers. In some models of this A-K design the pulleys were made of pot metal, this metal suffers from impurities and develops inter-granular corrosion., The pulleys will swell so much that the bands get broken.

Other models of this design used brass pulleys so they are fine...

There are grid swamping resistors in the RF stages of this radio. These are wire wound and fail from rust. The radio will not work if the resistor(s) are bad. They can be replaced with carbon 1/4 watt resistor. At the value specified.

There is one bypass capacitor across the "B" circuit, as the batteries age, their internal resistance rises. This cause the radio to oscillate via the common "B" connections. This condenser can leak excessively and if on batteries, kill a set of "B" batteries in a weeks time... This condenser is often take apart and the windings removed/replaced with a new condenser so appearance is not changed.

There is a cartridge glass resistor that looks like a fuse, this is the grid leak. It purpose is to remove high negative charge from the detector. It fails by going very high in resistance thus cutting off the detector, stopping operation. The assigned value is 2 meg-ohms, but the detector will work up to 8 meg ohms. The grid lead is made accessible because it failed often and users often experimented and changed the value of the leak. A high grid leak value is more sensitive but less volume, a low or normal grid leak value is low sensitivity and good volume.

Beware of using a digital ohmmeter to measure the resistance of transformers and other coils with an iron core. The reactance of the coils will give a false resistance reading. I highly recommend the use of an analog ohmmeter for all battery radio repair... 

Yes, the radio is connected to a power supply as if it were batteries, but it must be a DC supply that is adequate for the job, yes transformers are the power source for a power supply which would have rectifiers, filters and regulating circuits.

A power transformer is an AC device it cannot be directly connected to the A-K radio.

Poorly designed power supplies will have some value of AC impressed on the DC such a defect will cause hum to appear in the radio speaker. Because of the directly heated tube filaments in a 20's battery radio hum in a power supply must be as low as possible....  chas
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Post by acbaker123 Sun Mar 14, 2021 3:00 pm

extremely helpful, thank you, and for your patience in me just starting out. this forum and the people on it have been the most useful resource in learning about this stuff.

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Post by acbaker123 Sun Mar 14, 2021 6:23 pm

this thing is on one of the tubes in my AK 33, What is it?
Atwater Kent model 33 20210310
Atwater Kent model 33 20210311

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Post by acbaker123 Mon Mar 15, 2021 12:24 pm

I also need a bit of clarification on how the input voltages work, on the schematic if I were to measure between red and blue, would I get 4.5 or 10.5 volts. just trying to fully understand this before I build a power supply.

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Post by Chas Tue Mar 16, 2021 9:21 pm

That heavy nickle plated "dome" is to be placed on any tube that is sensitive to vibration. It prevents microphonics. That is a term given when a tube is sensitive to vibration. It usually goes on top of the detector tube... If you use it be sure the felt pads are in good condition and that the metal does not rest on the glass.

I do not understand connections to red & blue?

Please be more specific.

The schematic you have published is a recent re-draw from the late Leigh Bassett.

In the lower area of the drawing is how the batteries and their voltages are arranged.

Further, the old battery cable will have very faded colors. Where the wires go and their actual colors should be confirmed as the battery cable may have been changed out early in its life and may not be A-K OEM.  You can make tape flags to identify the correct wires...  chas
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Post by acbaker123 Wed Mar 17, 2021 10:36 am

by red and blue, I mean the ones labeled on the schematic. the positive of the A-battery and the negative of the C-battery

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Post by Chas Wed Mar 17, 2021 1:34 pm

acbaker123 wrote:by red and blue, I mean the ones labeled on the schematic. the positive of the A-battery and the negative of the C-battery
A measurement across those two "terminals' will be the sum of the "A" battery at 6 volts and the "C" battery at 4-1/2 volts for a total of 10-1/2 volts.

Leighs schematic is missing the label for C+ but the connections are as described in the lower portion of the schematic diagramming the batteries..
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Post by acbaker123 Wed Mar 17, 2021 1:38 pm

It just clicked, I understand it much better now. thanks a lot for your help and patience.

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Post by Chas Wed Mar 17, 2021 2:43 pm

acbaker123 wrote:It just clicked, I understand it much better now. thanks a lot for your help and patience.
Oh, I'm so glad, I used just about all my Elmer tricks Very Happy
As you have noticed, this board is rather quiet. Helps in a way. But others may be able to get across a concept in a different way. Sort of like I have a library of 20's era radio books. All actually say the same thing but so differently.

I don't have the time to enlarge this post at the moment, later this evening I'll try to post a number of reference sites that may help in your understanding.

I do suggest you get an analog ohmmeter, most big box stores have on for less than $20. They do not lie like a DVM can some situations...

Gloat, I just got a used ARBE-III it has some blown zeners and I have to work up schematic. I got lucky the one-way screws that sealed the box were loose Smile

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Post by acbaker123 Wed Mar 17, 2021 2:49 pm

I have considered getting a small analog meter, I do have a little RCA Senior VoltOhmyst vtvm that works fine, I just need to get used to using it.

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Post by Chas Wed Mar 17, 2021 6:03 pm

acbaker123 wrote:I have considered getting a small analog meter, I do have a little RCA Senior VoltOhmyst vtvm that works fine, I just need to get used to using it.
Bookmark these sites:

https://bama.edebris.com/manuals/rca/wv98c/

If that is not your exact RCA VTVM drill down for the model variations.

http://www.atwaterkent.info/

This site originally written by Leigh Bassett (passed) is now hosted and possibly edited by Dan Dane:

Dan's site:

https://roaringtwentiesantiqueradiomuseum.com/



Download the chapters for this handbook:


http://antiqueradios.com/archives/ElementsOfRadioServicingCh1-4.pdf


http://antiqueradios.com/archives/ElementsOfRadioServicingCh5-8.pdf


http://antiqueradios.com/archives/ElementsOfRadioServicingCh9-12.pdf


http://antiqueradios.com/archives/ElementsOfRadioServicingCh13-16.pdf


http://antiqueradios.com/archives/ElementsOfRadioServicingCh17-20.pdf


http://antiqueradios.com/archives/ElementsOfRadioServicingCh21-24.pdf



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Your RCA meter will be fine, DO check the battery and replace it if it has not been replaced in the past three years.



If you have the hand book for the RCA try the re-calibration procedure. FWIR the VTVM has an input resistance of 1 megohm or better so for all measurements except the grid of the detector it is fine. Be aware the the metal cabinet is connected to the black "ground" lead. For isolated measurements use an isolation transformer if the meter case might have potential.



The input resistance of a DVM is always 1 megohm.


For a VOM the input resistance can be from 1kohms/volt to as much as 25k ohms/volt. That means the meter draws current to take the reading. Certain circuits will measure lower than published values or higher depending on the load of the meter. Most vintage schematics will have a legend that notes what the resistance of the meter that was used to publish the vales. If there is no legend then the readings were generally taken with a 5k ohm/volt. This is important to know as taking a reading that seems that is incorrect could lead to an incorrect conclusion as to what the problem is when no problem exists at all...


You can use the VTVM to measure the resistance of the two audio transformer in the AK-33. I do not have exact values but the resistance of any of the windings will not be over 10k/ohms and can be as low as 2k/ohms. A reading of near infinity is an open winding. The transformer will have to be replaced.


If the audio transformers are bad, that, is a show-stopper. Correct replacements should be used, if not correct the radio may still play but the volume may be both low and distorted...



There are also grid resistors in the RF amp. There purpose is to desensitize the RF stage(s) to stop oscillate. They are wire would and often the resistance wire rusts and the resistor goes open.. These have 'eye;et" construction so a tiny 1/10 watt carbon resistor can be soldered via the eyelets and paint black. The radio does not care if the resistor is wire or carbon...  chas
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Post by acbaker123 Wed Mar 17, 2021 6:10 pm

my radio has been well kept and there is no rust anywhere, I have measured the resistance and capacitance of all the components and they seem to be in spec. although I have not yet done a leakage test on the bypass capacitor.

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Post by acbaker123 Wed Mar 17, 2021 6:15 pm

on the RCA wv-98c, I do not have the original probe, was there anything special about it, or was it just straight through?.

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Post by Chas Thu Mar 18, 2021 11:22 pm

acbaker123 wrote:on the RCA wv-98c, I do not have the original probe, was there anything special about it, or was it just straight through?.
https://bama.edebris.com/manuals/rca/wv98c/

Download the PDF file. The schematic is on page 25. It indicates the "normal" probes has a resistor that is shunted by  switch. There is NO direct connection probe.

The probe is a WG-299D

Go to these postings to learn more about the probe.

https://antiqueradios.com/forums/viewtopic.php?t=363921

Steve shows you how to make a replacement probe...

https://www.antiqueradios.com/forums/viewtopic.php?p=3069827#p3069827
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