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Old 6th Oct 2018, 6:02 pm   #21
Mrgroovy
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Default Re: Need help identifying old capacitor from 1930s radio

I have attached a really crude schematic/wiring diagram, or more like a crossover between those two. Hopefully some of you will understand. Especially the power transformer part is very unaccurate, so sorry about that. It's all just a bit new to me and I've forgotten all about these things over the last 20 years. Trying to catch up, so thank you for your patience!

So on the picture you'll see the powertransformer, the rectifier tube 506 (that is what it is right?) and the power output tube AL1 and how they both are connected with the multi-section capacitor, the field-coil on the speaker and the output transformer before the speaker as well as a few resistors and the by now infamous electrolytic.
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Old 6th Oct 2018, 6:08 pm   #22
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Default Re: Need help identifying old capacitor from 1930s radio

I used 630V for the reservoir and smoothing and 400V for all other capacitors. Mine has a triode output so does not need the capacitor across the output transformer. I got some of the cheap dark red PCB mounting types from ebay that are OK for putting in the box.
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Old 6th Oct 2018, 6:41 pm   #23
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Default Re: Need help identifying old capacitor from 1930s radio

Found a mistake, (probably plenty more), but forgot one of the wires going to ground, from the top right connector on the multi-section capacitor. See new attachment.
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Old 6th Oct 2018, 7:01 pm   #24
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Default Re: Need help identifying old capacitor from 1930s radio

No worries, It's not a bad first attempt, according to what I reckon so far the original bias method was the second method I described earlier, the bias voltage being developed across the 500 ohm resistor, one end of which is connected to chassis, the HT windings centre tap being connected to the junction of the 500 ohm and the 0.33 megohm resistors, when the valve type was changed to the AL1 the centre tap was connected to chassis in order to suit the cathode bias arrangement that was adopted for the AL1.

Lawrence.
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Old 6th Oct 2018, 7:21 pm   #25
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Default Re: Need help identifying old capacitor from 1930s radio

Thanks Lawrence, you seem to know a whole lot about this. As of now, it is a bit technical for me to understand, but I'll appreciate you trying to explain this anyway. I will get the hang of this sooner or later!

Is it possible, with what you see here, to determin if perhaps if I could use some electrolytic capacitors in place of some of the multi-section ones? I guess that would call for some rewiring as well? I definitely don't have the skills yet to do any of these mods without help from you guys, so feel free to enlighten me! And by the way; thanks to all of you for taking your time helping me out with this! Much appreciated!
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Old 6th Oct 2018, 8:25 pm   #26
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Default Re: Need help identifying old capacitor from 1930s radio

I don't know a whole lot about this receiver, I'm just making a few assumptions as the photo's and details unfold.

You can replace the 1uF, 2uF and 4 uF in the capacitor block with electrolytics if you want to, the 0.1uF should be replaced with a modern polyester or polypropylene type, just keep in mind that electrolytics are polarity sensitive, really important to be aware of that in HT circuits otherwise things can go splat in a violent way.

I've no idea what the HT voltage is in this receiver, but normally 450 volt electrolytics will do for most receivers, if in doubt use polyester or propylene types as these are available in voltages greater 450 volts.

So far as the working voltage of capacitors is concerned you have to realize what voltage the HT can increase to under a no load condition (sometimes caused by a fault) That voltage can equal the peak of the AC voltage being supplied to the rectifier eg: Peak voltage = AC (RMS) multiplied by 1.414, for instance 300 volts AC into the rectifier would result in an unloaded voltage at the reservoir capacitor of 424 volts DC.

When replacing capacitors the old ones must be disconnected from the circuit

Lawrence.
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Old 6th Oct 2018, 9:23 pm   #27
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Default Re: Need help identifying old capacitor from 1930s radio

I wouldn't go to electrolytics- you can get 630V 4.7uF polyester types for a few pounds and they're not overly large. The smoothing choke in the HT supply will compensate for the low C values and pentode output valves are tolerant of a fair amount of ripple on the anode supply. In your circuit it looks like the 1100pF (1000cm?) capacitor is the one that should be 1600V- 1000pF will be fine and easier to get, though you could use a couple of 2200pF 630V caps in series if you're keen on the 1100pF bit.
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Old 6th Oct 2018, 9:26 pm   #28
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Originally Posted by ms660 View Post
I don't know a whole lot about this receiver, I'm just making a few assumptions as the photo's and details unfold.

You can replace the 1uF, 2uF and 4 uF in the capacitor block with electrolytics if you wanted too, the 0.1uF should be replaced with a modern polyester or polypropylene type, just keep in mind that electrolytics are polarity sensitive, really important to be aware of that in HT circuits otherwise things can go splat in a violent way.

I've no idea what the HT voltage is in this receiver, but normally 450 volt electrolytics will do for most receivers, if in doubt use polyester or propylene types as these are available in voltages greater 450 volts.

So far as the working voltage of capacitors is concerned you have to realize what voltage the HT can increase to under a no load condition (sometimes caused by a fault) That voltage can equal the peak of the AC voltage being supplied to the rectifier eg: Peak voltage = AC (RMS) multiplied by 1.414, for instance 300 volts AC into the rectifier would result in an unloaded voltage at the reservoir capacitor of 424 volts DC.

When replacing capacitors the old ones must be disconnected from the circuit

Lawrence.
Thanks for info! I know that electrolytics are polarized and if I haven't got it all wrong the negative side always needs to go to ground, right? I may have missed something obvious, but I don't see how I should go about connecting any of the caps in the block to an electrolytic since neither the 1,2,4 or 2uF are connected to ground. The only cap in the block that is connected to ground as of now is the top right connector of the 0.1uF cap as seen in the schematic I made.
If I connect say all the wirings that goes to one of the two solder lugs on the 1uF capacitor in the block to the anode of a 1uF electrolytic and then connect its cathode to ground, then where does the wirings that goes to the remaining solder lug go? Do I connect them to the same anode or do I use two electrolytics for each one? Sorry if this is a stupid question! It may all well be easier than I think it is; or even more difficult for that matter. I have the greatest respect for these things so don't worry I won't try anything stupid until I know what to expect.
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Old 6th Oct 2018, 9:34 pm   #29
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I wouldn't go to electrolytics- you can get 630V 4.7uF polyester types for a few pounds and they're not overly large. The smoothing choke in the HT supply will compensate for the low C values and pentode output valves are tolerant of a fair amount of ripple on the anode supply. In your circuit it looks like the 1100pF (1000cm?) capacitor is the one that should be 1600V- 1000pF will be fine and easier to get, though you could use a couple of 2200pF 630V caps in series if you're keen on the 1100pF bit.
Yes, you are right. 1000cm=1100pF - or so Google told me. Appreciating all your inputs. I was hoping to use some electrolytics because they are easier to get, but if you think that I can use 630V polyester types for the most part and make sure that I have at leat one 1600V/1000pF to replace the 1000cm/1500V cap I may be able to repair this without too much headache and without breaking the bank.
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Old 6th Oct 2018, 10:24 pm   #30
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Default Re: Need help identifying old capacitor from 1930s radio

From your drawing, the common negative for the two 2uF, the 4uF and the 0.1uF is the three centre tags down one side and the single terminal on the other. So they are all connected to the 500R which connects to chassis. The only capacitor which does not connect to this common rail is the 1uF across the field coil.
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Old 6th Oct 2018, 10:32 pm   #31
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Originally Posted by Mrgroovy View Post
Thanks for info! I know that electrolytics are polarized and if I haven't got it all wrong the negative side always needs to go to ground, right? I may have missed something obvious, but I don't see how I should go about connecting any of the caps in the block to an electrolytic since neither the 1,2,4 or 2uF are connected to ground. The only cap in the block that is connected to ground as of now is the top right connector of the 0.1uF cap as seen in the schematic I made.
If I connect say all the wirings that goes to one of the two solder lugs on the 1uF capacitor in the block to the anode of a 1uF electrolytic and then connect its cathode to ground, then where does the wirings that goes to the remaining solder lug go? Do I connect them to the same anode or do I use two electrolytics for each one? Sorry if this is a stupid question! It may all well be easier than I think it is; or even more difficult for that matter. I have the greatest respect for these things so don't worry I won't try anything stupid until I know what to expect.
The -ve side of an electrolytic capacitor doesn't always connect directly to ground, chassis or HT -ve, it depends on it's function and the circuit, what matters is that the voltage on its +ve terminal is +ve with respect to its -ve terminal.

Best not to use the words anode and cathode for the terminals of an electrolytic capacitor it just confuses things, stick to positive and negative or +ve and -ve.

If I was doing this job I would be inclined to re-stuff the capacitor block with polyester/polypropylene types if possible.

Lawrence.
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Old 7th Oct 2018, 12:40 am   #32
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Default Re: Need help identifying old capacitor from 1930s radio

I suggest we get the full circuit drawn out before starting to replace capacitors. I agree with lawrence that the 500 ohm resistor looks as though it was in the negative path and used to create the bias voltage for the valves. This is very typical of radios from early 1930's. However, the 0.1uF capacitor across it would not be enough to remove 100Hz ripple so it must have been after the smoothing capacitors.

I am also not sure if the 500 ohms resistor is still passing current or if it is shorted out by the other wire that goes to the transformer?

The field coil is across HT and not used as a choke as it is on later 1930 radios and a separate choke is provided. This is the same as the Columbia 356 I am working on which is also from 1932.
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Old 7th Oct 2018, 8:26 am   #33
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Ok guys, I think I will have to spent some more time reading up on this stuff. I agree that a full schematics would have been really helpful, and I will do my best to try lay out the whole circuit but as of now I don't have the skills to do so. I mean, I can barely read schematics as it is. This is a steep learing curve indeed, but in the long run I'm probably better off knowing not only how to but why I do whatever mods necessary to get this unit up and running again. I will also try to re-stuff the capacitor as it will definately look better. I even think I'll change the electroltic I put in with an axial and put it inside the shell of the old brown, just for the looks.
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Old 7th Oct 2018, 12:17 pm   #34
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Default Re: Need help identifying old capacitor from 1930s radio

So far as I can make out the 0.1uF across the 500 ohm resistor is for RF bypass, main ripple current doesn't flow through the 500 ohm resistor.

Lawrence.
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Old 7th Oct 2018, 1:54 pm   #35
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Thumbs up Re: Need help identifying old capacitor from 1930s radio

Quote:
Originally Posted by Mrgroovy View Post
Hi. This is my first post here…
Welcome, Mrgroovy!
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Originally Posted by Mrgroovy View Post
This is a steep learning curve indeed…
You are right. Radio sets from the 1930's often have rather idiosyncratic arrangements in their power supplies (and for applying grid bias) so they are probably not the best ones to start with.
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…but in the long run I'm probably better off knowing not only how to but why I do whatever mods necessary to get this unit up and running again.
An admirable approach. It may seem daunting at first, but you seem like a determined chap, so your efforts should be rewarded.
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Ok guys, I think I will have to spent some more time reading up on this stuff.
There is a useful resource here. There is a lot of information, but don't let that put you off. There are sections on 'Power Supplies' and 'capacitors' which might be the most relevant to you at this stage.

The lack of a schematic makes things more difficult for you. It's certainly worth trying to get hold of one. The 'search' function on this forum works well, and may lead to useful sites:

https://www.vintage-radio.net/forum/...ad.php?t=62752
http://www.johansoldradios.se/
http://www.nrhf.no/index.php
http://www.aga-museum.nl/page/voorpagina
http://wordpress.radiomuseet.se/

Is this your radio here: https://www.radiomuseum.org/r/agabaltic_ah37_ah_3.html?
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Old 7th Oct 2018, 3:32 pm   #36
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Default Re: Need help identifying old capacitor from 1930s radio

I have done a rough circuit from your sketch. Apologies for poor valve components. Open to corrections of course (especially the polarity of C6).
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Old 7th Oct 2018, 3:57 pm   #37
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Default Re: Need help identifying old capacitor from 1930s radio

C6 looks the right way round to me.
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Old 7th Oct 2018, 4:12 pm   #38
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Default Re: Need help identifying old capacitor from 1930s radio

To help verify the bias arrangement maybe the OP can measure the resistance across the 500 ohm resistor without disconnecting anything.

Lawrence
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Old 7th Oct 2018, 6:22 pm   #39
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I have done a rough circuit from your sketch. Apologies for poor valve components. Open to corrections of course (especially the polarity of C6).
Hi, can't believe you actually took your time doing this. Thanks, much appreciated! In fact, I was working with a schematic myself this evening but it takes a lot of time and not really knowing how to do it I had to give up at one point. Looking at my new attempt it is not too different from yours. I'll post it here so you all can have a look.
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Old 7th Oct 2018, 6:29 pm   #40
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Hi Wellington,

Thank you, I will look into those sites.
Yes, it is the same radio at the one you found, except mine has a different power tube. I have really tried to find the schematics for this, searching both English and Swedish websites but no luck so far. I think you guys will be able to help me out though, so I wouldn't be too worried about not having the schematics at this point.
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