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Bit of UKWEe
Old 01-15-2018, 07:17 PM   #1
BTaylor
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Default Bit of UKWEe

Recently got another UKWEe.
It is a 1942 model. Internal label was bnz code. This is apparently "SABA". I have another later year radio with "SABA" plainly marked, rather than the code.

Face of the receiver was over-painted gray at some point. I could see that the original color had been a light field gray. It is apparent on the label faces, among other places. The over-painting wasn't badly done, but was doubtless post-war, and I decided to remove the paint and do quality repainting in the original color, or as close as possible. If the original paint were there, even with quite a bit of usage and wear, I would not have done this. In one of my photos, you can see the outline of the over-painted vertical "yellow stripe" near the frequency window.

An earlier owner had replaced the light bulb for the scale with a flashlight style bulb and short soldered leads. He may not have had access to the "festoon" bulbs that were originally used. Already now removed and returned to original condition. Another radio had a very old and original looking blue bulb installed. Any thoughts on that? The blue color doesn't seem very noticeable in use, other than dimming the light some. Blue bulbs are available...

Internally the receiver is very clean and intact, with printed labeling quite undisturbed. (A capacitor has the "bnz" code as well.) Tubes all test good. Preliminary attempt to operate the receiver is puzzling. The anode voltage indicator bulb lights immediately, but rapidly dims and goes out in about the time you would expect tubes to warm. Generator produces proper voltage, but drops to 109V in use. An alternate generator does the same.

BTaylor
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Old 01-15-2018, 07:19 PM   #2
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Old 01-18-2018, 07:26 AM   #3
Funksammler
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I have blue bulbs in some of my tank sets, but most have white lightbulbs. You also sometimes find blue lightbulbs in Luftwaffe radios. I think it was mainly done to dim the light when working in dark environments. Blue light keeps you awake longer, perhaps important when radio operators had to man their radios for hours on end.

When your anode voltage light goes out after the valves warm up there must me something causing excess anode current to flow. Since it only happens after the valves warm up I suspect the fault is not in the anode circuit itself, but in the steering grid circuit of one or more of the valves. Since it probably affects several valves to cause such a significant voltage drop, I would start by looking at the AVC circuit....

regards,

Funksammler
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Old 01-18-2018, 10:59 AM   #4
Val
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BTaylor, thanks for the pictures, nice Ukw.E.e.

I guess the fault is leaking capacitor, starts conducting when
certain voltage threshold is passed...
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Thanks
Old 01-18-2018, 06:05 PM   #5
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I appreciate the input, as always. I will post a photo here when the cosmetic work is completed, and also the outcome of my troubleshooting.
BTaylor
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Troubleshooting
Old 01-22-2018, 12:50 PM   #6
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Default Troubleshooting

Can't expect help walking through every step of a repair process, but the help I have gotten has been amazingly useful.
Perhaps it was unwise, being new to much of this, but I thought I would not install all of the tubes and see if the anode voltage would remain adequate. It seems that would not be destructive? Of course the unit would not receive...

Anyway, if all except the Uberlagererstufe tube are installed, the anode voltage light stays on and the voltage drop doesn't appear.

So I will look at that area for problems. Faulty capacitor(s) perhaps. This seems like progress.

BTaylor
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Old 01-22-2018, 01:06 PM   #7
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Sounds you are on the right track...No problems taking the valves out and a good way of fault finding. Does the light go out if you ONLY install the Überlagerer valve? Looking at the schematic I can't quite see how this circuit would be problematic, unless the control grid is somehow connected to a positive voltage....

regards,

Funksammler
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Old 01-22-2018, 01:09 PM   #8
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Quote:
Originally Posted by BTaylor View Post
Anyway, if all except the Uberlagererstufe tube are installed, the anode voltage light stays on and the voltage drop doesn't appear.
Try to change that tube if you have a spare. It isn't uncommon that tube become conducting or short circuited - air gets inside via some small crack etc...
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Still Testing...
Old 01-23-2018, 09:20 AM   #9
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Default Still Testing...

Thanks to all!
I believe one of my two EUa4 units has "issues". I will have to look at it as well. It may have trouble producing anode voltage for all the tubes. Heater voltage also can act up, it seems.

Using this generator unit, I found that anode voltage was maintained when only the Oberlagerer tube was in place, but adding any (apparently) other two tubes would make the indicator wink out. But I could put all other tubes in place except the Oberlagerer without a problem. So, if nothing else, this seems to show that the current draw by the Oberlagerer tube is higher than most, and my questionable generator can't do it all.

Using the better generator, this seems to go away, or it did on my last testing. EUa4 also does fine with another 1945 receiver of mine.

I do have a remaining problem, I think with the volume switch, which is mostly silent, but when shaken and turned some will make radio-reception sounds. This I have not yet examined, but perhaps something is loose or dirty. Imagine that on a 70 year old radio! I have not had my antennae plugged in while testing. In the past, I have picked up portions of transmissions on these receivers from several hundred miles away.

Paint for the face of this receiver has been shipped. It is semi-gloss RAL 2007 "moss grey" enamel. I would have preferred lacquer. So it should look pretty nice.

BTaylor
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Old 01-23-2018, 10:21 AM   #10
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Maybe clean the collector of the E.U.a. Normally when they are faulty (due to capacitor leakage) the output voltage is low already under no load. If it gives full voltage at no load but does not supply sufficient current is a sign of resistance in the circuit.

The switches are often a problem. It is typically a potentiometer with a switch riveted on top of it it, to get to the potentiometer probably requires you to take the switch part off first. Taking the on/off switch out of the radio usually requires the modules to be separated from the chassis, I can't exactly remember what it involves on the Ukw.E.e. I will be looking at a Ukw.E.e over the next few days so I guess we will both find out....

regards,

Funksammler
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Old 01-23-2018, 01:58 PM   #11
Yuri D.
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Quote:
Originally Posted by Funksammler View Post
Maybe clean the collector of the E.U.a. Normally when they are faulty (due to capacitor leakage) the output voltage is low already under no load. If it gives full voltage at no load but does not supply sufficient current is a sign of resistance in the circuit.

The switches are often a problem. It is typically a potentiometer with a switch riveted on top of it it, to get to the potentiometer probably requires you to take the switch part off first. Taking the on/off switch out of the radio usually requires the modules to be separated from the chassis, I can't exactly remember what it involves on the Ukw.E.e. I will be looking at a Ukw.E.e over the next few days so I guess we will both find out....

regards,

Funksammler
I had to restore that switch before. Here are some details:

https://kriegsfunker.com/restoration...estoration.php
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Switch plus
Old 01-24-2018, 09:09 AM   #12
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Default Switch plus

Thanks Yury D. Photos and text are useful.
Now I am wondering if I shouldn't be looking at all these capacitors. If, as your photos and Funksammler suggest, it is necessary to separate the module containing the switch for its removal, at the very least I should check and replace any capacitors exposed in the process.
The switching action appears fine on mine, but the potentiometer element may be oxidized inside, or the moving portion lacking in sufficient contact pressure, or both. Switch reassembly with false rivets and a drop of glue should work. I should have time for this soon.
Paint for the radio face arrived. Looks like it should be great. It seems many earlier radios were not the usual "ordnance gray" of later units.
Attending a large "Battle of the Bulge" event at the end of the month. Sort of a "cowboys and Indians" affair, but large in scope, with many vehicles (occasionally some armor, but never original German). The militaria flea market is always large, with some potential for communications gear.
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Old 01-24-2018, 10:02 AM   #13
Yuri D.
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The switch is a disposable type. Bakelite housing held together by hollow rivets. I drilled the rivets out to open the switch, and secured them back with two screws. Now the switch is serviceable.
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Troubleshooting Still
Old 01-25-2018, 07:31 AM   #14
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Default Troubleshooting Still

Thanks again all.
I think some of my problems have been due to low EUA4 output. A simple cleaning produced what seemed like higher rpm and smoother running. It may have also virtually eliminated the low anode voltage problems.
A thorough disassembly, cleaning and regreasing of the motor bearings and probable capacitor replacement seems like the way to go. Another project, I guess.

I am still thinking that the potentiometer side of the radio switch is not right. It is possible to remove the switch, at least on this version of the UKW.E.e, without separating that module from the rest of the radio. Before I break into the switch, I plan to temporarily connect another potentiometer of the correct value into the circuit to confirm the issue.
BTaylor
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Old 01-25-2018, 07:58 AM   #15
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Before doing anything drastic to the potentiometer, just exercise it. If possible try to get some contact cleaner into the potentiometer. After years of sitting on a damp shelf somewhere, contacts get dirty and corroded, this goes for potentiometers as well as the tuning capacitors and any other switching contacts. Give the Fern/Nah switch and the contact behind the "z. Sender" socket some attention as well. A good exercise usually cleans them up again....

regards,

Funksammler
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