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DAV output transformer




 
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KA3EKH
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« on: March 25, 2018, 05:59:40 PM »

Ok, so I have a DAV transceiver on the bench that appears to have a failed primary on the audio output transformer. The secondary is good but the primary has gone open. Its in the plate side of a 3S4 and has a +135 volt buss that feeds it. Use to work but now its dead. The big issue is that the transformer is in a sealed metal can (T101A) that also has the modulation reactor and the microphone input transformer.
Anyone have any experience dealing with opening up the can and whatís inside? Options at this time include installing a new transformer somewhere else in the radio, installing a plate load resistor and a decoupling capacitor and using high impedance headphones or perhaps getting rid of the 3S4 completely and building a solid state output amplifier around something like a 741 op amp and using that to drive the headphones?
That transformer can has a flock of wires that go in and out that none are going to be easy to deal with. Wonder if the can may be disassembled on the chassis without having to deal with all the other stuff for the modulator? Another option would be finding the radio section from another DAV or MAB transceiver and moving the crystals and tubes to that. Before anyone says anything I know there are some differences between the MAB and the DAV but converting a MAB to a DAV is just addition of a couple parts right on top the chassis and way easier then this output transformer problem.
Any suggestions welcome.
Just a short not on what a DAV is, itís a WW2 HF AM transceiver that develops about .25 watts of AM using all one volt tubes that are contained within an removable chassis. Itís powered by 135, 67 and -6 volts for bias along with a 1.5 volt battery for the filaments. Used this set several years out in Dayton for the 3885 AM military net and sold it a couple years back but now that it has failed it came back home for repairs.
The DAV was the larger radio that also includes DF circuits for direction finding with its evil twin sister being the MAB that was smaller and radio only.

Ray F/KA3EKH


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KL7OF
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« Reply #1 on: March 25, 2018, 07:46:35 PM »

Picture of your DAV and T101-A please.......UPDATE;..TNX for the pictures, I thought I might have what you need but sorry, No Joy..Steve
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PA0NVD
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« Reply #2 on: March 25, 2018, 09:08:21 PM »

Don't know the DAV, but many of these sealed transformers are potted with a tar-like substance an non;repairable. I should go for an option to mount a small output transformer somewhere else
If you go for an IC amp,
At Aliexpress and alike, you can buy very small amps for approx 1$50. Complete, Just power with DC and they can drive a LS. Look up the IC used, you can easily change gain. A small gain pot is included at the tiny PCB. Absolutely not worth making yourself
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KA3EKH
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« Reply #3 on: March 25, 2018, 09:25:23 PM »

Pictures.


* IMG_3134.JPG (1012.13 KB, 1591x1193 - viewed 84 times.)

* IMG_3135.JPG (892.45 KB, 1818x1364 - viewed 78 times.)
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KA3EKH
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« Reply #4 on: March 25, 2018, 09:33:33 PM »

schematic.

Lot of the collectors are in love with the BC-611 "Handitalkie" but i always thought they were dogs in comparison to the simple easy design of the DAV/MAB with simple switching between receive and transmit. Had three or four of thees over the years and other then leaky capacitors a fairly reliable radio.


* sch.jpg (1613.37 KB, 2024x1642 - viewed 78 times.)
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PA0NVD
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« Reply #5 on: March 25, 2018, 11:49:19 PM »

WOW, what a nice little set!! Didn't know it, It looks so simple. Love to own one and play with it!!
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WZ1M
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« Reply #6 on: March 26, 2018, 03:29:18 AM »

Don't know the DAV, but many of these sealed transformers are potted with a tar-like substance an non;repairable. I should go for an option to mount a small output transformer somewhere else
If you go for an IC amp,
At Aliexpress and alike, you can buy very small amps for approx 1$50. Complete, Just power with DC and they can drive a LS. Look up the IC used, you can easily change gain. A small gain pot is included at the tiny PCB. Absolutely not worth making yourself

Potted transformers are very reapairable, I do them all the time.
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PA0NVD
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« Reply #7 on: March 26, 2018, 09:53:48 AM »

Please give me details how you do that, I am struggling cleaning in order to de-mount the core and wind again. Never succeeded
Still have a 1920 radio with a bad transformer and various interstage transformers of those years with tar that needs repair
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w1vtp
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« Reply #8 on: March 30, 2018, 01:17:16 PM »

Pictures.

Very nice resolution pics.  I have a Bendix TA12 (with dyno / modulator) and an ART 13. I'll have to do a photo shoot

a
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KA3EKH
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« Reply #9 on: March 30, 2018, 01:25:05 PM »

A picture is worth a thousand words!

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