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 Post subject: AK Model 46 voltages...
PostPosted: Feb Mon 26, 2018 6:34 am 
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I have seen many previous threads ref: AK Model 46 and mention of a "schematic" that has the voltages and resistance on it. All the ones I have found in the usual locations do not. I need the values to troubleshoot the (4) 26 tubes that are only getting .5 VDC. Any help would be appreciated.

Rudy


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 Post subject: Re: AK Model 46 voltages...
PostPosted: Feb Mon 26, 2018 6:37 am 
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Here's the modern schematic, with voltages.
http://atwaterkent.info/TechData/Drawin ... 100sch.pdf

- Leigh

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 Post subject: Re: AK Model 46 voltages...
PostPosted: Feb Mon 26, 2018 6:39 am 
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Thanks Leigh, this is going to help.

Rudy


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 Post subject: Re: AK Model 46 voltages...
PostPosted: Feb Mon 26, 2018 6:40 am 
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Hi Rudy

Here is the schematic from Leigh's site:

http://www.atwaterkent.info/TechData/Dr ... 100sch.pdf

Filament for #26 tubes come from the power transformer. It goes through a connecting board. When voltage is low nuts on the connecting board aren't making good enough contact. Tighten the nuts. You may need to clean up connections first.

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 Post subject: Re: AK Model 46 voltages...
PostPosted: Feb Mon 26, 2018 7:27 am 
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Hi Norm,

Thanks for the quick reply. I am worried about what is going on under the connector board. Is there a trick to getting that sucker out so I can see bottom and check resistors?

Thanks,

Rudy


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 Post subject: Re: AK Model 46 voltages...
PostPosted: Feb Mon 26, 2018 1:58 pm 
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Rudy18D wrote:
Hi Norm,

Thanks for the quick reply. I am worried about what is going on under the connector board. Is there a trick to getting that sucker out so I can see bottom and check resistors?

Thanks,

Rudy


It comes apart in layers.

The first connector attached to the receiver cable has 12 or so nuts holding it down. Remove the nuts and it lifts clear.

The second connector with the resistors underneath is wired to the power supply with short leads. It attaches to the power supply with 2 nuts that are in the center of the connector.
Once the two nuts are removed, the inner board lifts off, but the short leads limit its motion. You will need to unsolder a few of the wires on one side to have enough clearance to lift it off and flip it over to examine the resistors underneath. Usually I just unsolder them all so I can remove it completely. Make sure to label any wires you disconnect so you can reconnect them properly.

Like Norm says, the nuts and screws are responsible for the electrical connection through the connector. They need to be clean and tight. The two inner nuts and screws are the ground connection between the radio and the power supply.

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 Post subject: Re: AK Model 46 voltages...
PostPosted: Feb Mon 26, 2018 3:17 pm 
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Good stuff. I will tackle tonight.

Thanks Paul.

Rudy


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 Post subject: Re: AK Model 46 voltages...
PostPosted: Feb Wed 28, 2018 12:00 am 
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I now have the control board out of the AK46. Can anyone help me identify the resistors on the underside of this board? Terminals 11 and 12 have a replacement black dog bone resistor and terminals 9 and 10 have a replacement Black and Red dog bone resistor. The others between 1 and 2, 5 and 6, and 7 and 8...I have no clue about them either.
Thanks


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 Post subject: Re: AK Model 46 voltages...
PostPosted: Feb Wed 28, 2018 12:16 am 
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The resistors are all identified on the modern schematic.

- Leigh

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 Post subject: Re: AK Model 46 voltages...
PostPosted: Feb Wed 28, 2018 2:47 am 
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Rudy18D wrote:
I now have the control board out of the AK46. Can anyone help me identify the resistors on the underside of this board? Terminals 11 and 12 have a replacement black dog bone resistor and terminals 9 and 10 have a replacement Black and Red dog bone resistor. The others between 1 and 2, 5 and 6, and 7 and 8...I have no clue about them either.
Thanks


From your photo, going left to right:The three wire wound resistors are all 20 ohm and center tapped. They often will have intermittent connections where the resistor wire is riveted to the center tap connection. They can sometimes be fixed by staking the rivet with a suitable punch. If they are open you can replace them with two modern 10 ohm resistors connected in series. Also, loose screw terminals can affect the connection to these wire wound resistors.

The fourth resistor from the right is 12.5 K. ohms. The fifth one is 65K ohms. On those two, originals would often drift high in value. They look like they may have been replaced long ago.

Is there also a wire wound resistor on the top side of the board?

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 Post subject: Re: AK Model 46 voltages...
PostPosted: Feb Wed 28, 2018 3:34 am 
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Yes Paul, there is there also a wire wound resistor on the top side of the board, wires seem a bit loose on it too. Can you tell me about that one too?


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 Post subject: Re: AK Model 46 voltages...
PostPosted: Feb Wed 28, 2018 6:00 am 
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Last question on this AK. This resistor is on top and looks to have some winding issues. Can anyone help figure out a replacement for this one as well?
Thanks


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 Post subject: Re: AK Model 46 voltages...
PostPosted: Feb Wed 28, 2018 7:03 am 
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Rudy

Resistor in question is 16A (625 ohms) and 16B (1000 ohms). They are used for biasing 26 tubes and 71As. Check them with an ohm meter. Since originals were flat you won't have much room for replacements. Could be relocated?

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 Post subject: Re: AK Model 46 voltages...
PostPosted: Feb Wed 28, 2018 7:54 am 
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Hi Norm,

16A tests at 650 and 16B at 1260. A little off from base. Not sure if that enough of a delta to try and relocate with new resistors. Ideas?


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 Post subject: Re: AK Model 46 voltages...
PostPosted: Feb Wed 28, 2018 7:57 am 
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With that said however...it was the 26's I was having issues with initially.


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 Post subject: Re: AK Model 46 voltages...
PostPosted: Feb Wed 28, 2018 12:21 pm 
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Your resistance measurement on 16a and 16b are probably ok, in spite of the outward appearance. This resistor also has rivets that make the connection between the resistance wire and solder tabs.
Connect your ohmmeter to the resistor and apply pressure to the rivets with an insulated tool. You may note a change in resistance. If the reading changes much, the rivet may be a little loose.
When that is the case, I use a punch to lightly/gently reset these rivets for a better connection.

I don't think your 26 tube filament voltage issue is related to any of this though. In this radio usually the cause of low filament voltage at the tube will be a high resistance connection somewhere in the filament supply circuit.

This could be because of loose screws, 5 and 6, at the power supply connector, a bad solder joint or oxidation on the tube socket connectors themselves. The tube sockets are somewhat prone to oxidation, and I usually detail clean them with deoxit and pipe cleaners.

The filament current is normally fairly high, but at a low voltage, only 1.5 volts. It doesn't take much circuit resistance at any connection point to result in a voltage drop in this circuit.

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 Post subject: Re: AK Model 46 voltages...
PostPosted: Mar Sat 03, 2018 3:15 am 
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UPDATE: Thanks to the help of this group the AK46 is now up an functioning...almost.

Volume is low at about a 1/3 of what the max volume should be.
The voltages from Leigh's modern schematic were slightly low when I finished redoing the resistors on the control board. For example on the control board terminals 1 and 2 should read 5.0V and I was getting 4.4. Terminals 5 and 6 should have been 1.5V and I was getting 1.2V. And terminals 7 and 8 should have read 2.5V and I was getting 2.2. Would this possibly cause the low volume output? If not, there are a couple of other variables. I did not replace the metal capacitor box on the under side of the chassis. It looked to be in good shape and no rust on it at all and still sealed. Another variable is that I don't have a tube tester that can test the 26's, 27 or 71A tubes. I suppose if any of the tubes were weak it could cause the lower than expected audio output. And yet another variable could be the volume POT. It acts like it grounds out if you turn the volume all the up to stop or all the way down to stop but has good control as you move it from up to down??

Ideas that might cause the low audio issue?
Thanks,
Rudy


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 Post subject: Re: AK Model 46 voltages...
PostPosted: Mar Sat 03, 2018 3:27 am 
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This radio has several wax paper capacitor in the power supply.
They are frequently leaky and can load down voltages like you are experiencing.
Pull the rectifier tube and measure the filament voltages again and let us know if they come up.

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 Post subject: Re: AK Model 46 voltages...
PostPosted: Mar Sat 03, 2018 3:49 am 
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processhead wrote:
This radio has several wax paper capacitor in the power supply.

Those capacitors should ALWAYS be replaced before power is ever applied to the set.

- Leigh

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Click "Grebe Stuff" for Synchrophase info


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 Post subject: Re: AK Model 46 voltages...
PostPosted: Mar Sat 03, 2018 8:20 am 
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Hi Paul,
I pulled to rectifier and the voltages increased very little .1 across the board.

Leigh,
What should I replace that flat set of capacitors with? And how have you mounted the new capacitors? Underneath?

Thank you both.

Rudy


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