Aga Baltic AH37. Need help identifying old capacitor from 1930s radio
 

Hi. This is my first post here, so let me briefly introduce myself. I just recently found an interest in vintage tube radios and have already started collecting a quite few old pieces. I have two years formal education from vocational school in electronics almost twenty years ago, so my skills are a bit rusty to say the least. I live in Norway.

So then,

I recently bought an old radio from Swedish company Aga Baltic. It is a cathedral type radio with 4 tubes in it. The model is AH37 and according to my research it was manufactured in 1932. I have not found any schematics. I've cleaned it up inside, changed the bad wires and connected a new three prong cord. All 4 tube lights up and there is even sound (albeit weak) coming from it. I also swapped out a 10uF electrolytic cap which was the only electrolytic cap I could positively identify. When powered up there is quite a loud hum coming from the power transformer. I thought that changing the electrolytic cap might eliminate this, but it wasn't all that easy. The 10uF electrolytic is hooked up to what seems like a centre tap (ground right?) from the power supply. Some of the other connections (pardon me for not being absolutely accurate here) from the power transformer goes to what seems to be a multi-sectioned capacitor of unknown brand. There is a logo on it which could be the letters HS or SH? I don't know. There is a total of three of these caps underneath the chassis, all from the same manufacturer, with the largest one directly connected to the power transformer. I suspect it to be bad since both sides of the metal can around it is bulging out. The can is labelled 1+2+4+2 1500V - and 0,1UF 500V - . I guess the straight line (-) after the 1500/500V means DC as opposed to ~/AC?

Can anyone tell me something about this? What type of capacitor is it really? It is easy to find a replacement? I don't mind using single replacement caps; it is probably the only option, but I really don't know what kind of capacitors I should use.

Thanks!

Re: Need help identifying old capacitor from 1930s radio
 

That's a multi-section capacitor, not wholly dissimilar to the one in this post:-

https://www.vintage-radio.net/forum/...99&postcount=8

Your best bet is to "restuff" it by fitting new capacitors inside the can. You may be able to lift the Paxolin lid slightly, snip all the wires off its underside and then dig out the contents of the can. This will save a lot of unsoldering and resoldering of wires.

The figures on the Paxolin show quite clearly which caps go where. Any capacitor of more than 1uF is likely to be of the electrolytic type and therefore polarized. Their negative ends will likely be connected externally to the chassis, possibly by the long bare wire linking several terminals.

Lower value caps are not polarized and can be connected either way round.

Re: Need help identifying old capacitor from 1930s radio
 

I am rebuilding a similar capacitor box from a Columbia that has 10 capacitors inside it. The block in yours contains multiple capacitors that are wired to the tags at the top. You cannot leave the old capacitors in circuit as they leak (behave like resistors) and can overheat or at the very least stop it working properly. It looks like someone has made some recent changes as there is a modern electrolytic in there so it is possible someone has already taken the box apart.

If it were mine, and the fact it is still bulging, I would rebuild the block but be warned that it is messy work as the block looks to be filled with bitumen. Take plenty of pictures before you dismantle it and of course you need to know the value of each capacitor and the tags they are connected to before you start.

Then its a case of extracting the old capacitors and working out a way of fitting replacements back inside. Because you do not want to take it apart again I would use 630V film capacitors and not electrolytics.

PS: Post crossed with Graham, our recommendations are the same but I don't believe you would find any electrolytics in a 1932 capacitor block.

Re: Need help identifying old capacitor from 1930s radio
 

Hi Graham,

Thanks for the reply, and for the suggestion on how to restuff the cans. I think, if I am not mistaken, that only the top right connector on the 0,1UF section is connected to ground. At least there is continuity between the top right connector and the chassis/ground, and not continuity between any of the other connectors and ground. Could always be a short somewhere perhaps? Electrolytic capacitors of 1500V is not really easy to find, and probably not cheap? My best bet would be to couple four 450V in series and match the capacitance and voltage required for each, right? And as for the the 0,1uF, is that most likely an electrolytic as well? These mystery multi-section cans are only the start of this enigmatic radio. There are six other normal looking capacitors inside, all with capacitance values in CM. I read that 1000cm is approximately the same as 1100pF?

I'll attach a few more pictures. The brown electrolytic 10uF is now changed with a modern one.

Re: Need help identifying old capacitor from 1930s radio
 

Hi PJL,

Thanks. The modern electrolytic is actually the one I changed. It was definetly bad cause when I took it out it was all loose inside, sounding like a percussion shaker. As you can see the voltate rating is very high, but it should not be a problem if these are not electrolytic as you now suggests?

Re: Need help identifying old capacitor from 1930s radio
 

"Take plenty of pictures before you dismantle it and of course you need to know the value of each capacitor and the tags they are connected to before you start."
The values are printed into the paxolin plate.

Re: Need help identifying old capacitor from 1930s radio
 

The SH logo is for Siemens & Halske

Re: Need help identifying old capacitor from 1930s radio
 

I've never seen an electrolytic capacitor with a value of less than 1uF. The 0.1uF capacitor won't be an electrolytic and can be replaced with a polypropylene or similar type.

If you decide to use electrolytic capacitors they'll need to be connected the correct way round, Given that some of the electrolytics will be smoothers it's strange that one side is not grounded. I suggest a bit of reverse engineering,

Re: Need help identifying old capacitor from 1930s radio
 

Thanks, you saved me hours searching in blind for this!

Pretty satisfied with this purchase. I only paid 100NOK for the radio, thats less that 10 quid! (9.3 to be excact) It has a field coil speaker as well that looks to be in near mint condition! It is a very well preserved piece of gear considering its age.

Re: Need help identifying old capacitor from 1930s radio
 

A couple of semiconductor diodes made in 1932?

Re: Need help identifying old capacitor from 1930s radio
 

Has the sound output valve been changed from the original to a side contact type? The valve holder looks different to the others, looks like nut and bolt fixing as opposed to rivets and there's a bright patch on the chassis in the shape of the old square valve holder.

Lawrence.

Re: Need help identifying old capacitor from 1930s radio
 

Wow, you must be right. Well spotted! I really didn't notice the bright spot and that the tubesocket must have been replaced. I guess this has been a mod done way back since the radio didn't show any sign of being worked on in the last 70 years as far as I'm concerned. The tube in question is actually a Telefunken AL1. According to radiomuseum.org the original tube is a E 453. The E 453 and AL1 seem to have similar properties, to my limited knowledge at least? The other three tubes are identical to the ones spesified on this page here: https://www.radiomuseum.org/r/agabaltic_ah37_ah_3.html

Re: Need help identifying old capacitor from 1930s radio
 

Which are you refering to?

Re: Need help identifying old capacitor from 1930s radio
 

The E453 is an indirectly heated cathode valve, the AL1 is a directly heated cathode valve, hence the centre tapped resistance across that valves heater and the bias resistor and bypass capacitor from the centre tap to chassis.....So far as I can make out.

Lawrence.

Re: Need help identifying old capacitor from 1930s radio
 

Interesting. Does that mean that the one 10uF electrolytic capacitor (the brown-reddish one I have swapped out with a modern type by now) was probably not there in the first place? And if so, were there really no electrolytic capacitors originally installed in this radio?

I'm also having a hard time finding replacement capacitors for this radio. Non-electrolytic 4uF 1500V+ capacitors aren't really common values these days. The ones I have found that come closest in value are way to expensive to justify spending on a radio, in my opinion at least.

I found some high voltage film caps (1600v) on justradios.com which can probably work on most but the largest caps. The largest caps being the 1uF, 2uF, and 4UF/1500V) and smallest caps being the 0.22nF to 0.55nF/1500V. I figured that 200CM which is the smallest value capacitor I found in this radio equals 220pf=0.22nF. Please correct me if I'm wrong. You can see one of these small black capacitors in one of the pictures above. Is that what is called a molded paper capacitor? As I said, they are high voltage 1500V~ with capacitance values in CM and manufactured by ERO. Was unable to find any info on them on the web.

Re: Need help identifying old capacitor from 1930s radio
 

I would question the need for 1600V capacitors. They were probably used because they were available. 450V electrolytics should be fine.

I think you need to draw out the circuit for the PSU and output stage to see what mods have been done.

Re: Need help identifying old capacitor from 1930s radio
 

Sorry my mistake, I will get my eyes refurbished.

Re: Need help identifying old capacitor from 1930s radio
 

Thanks. I'll try that and see if I can post it here. As for the 450V caps, do you think that the other small (molded paper?) caps, there are 6 of those in total, would suffice with a 450V rating as well even though they too are rated 1500V?

Re: Need help identifying old capacitor from 1930s radio
 

There's a good chance that the old 10uf was an original fitment, possibly performing the same circuit function as its replacement is doing now, there were two common methods of implementing an arrangement for obtaining the bias voltage for the valve in mains operated receivers, one way was the use of a resistor (usually bypassed with an electrolytic capacitor) connected in series between the cathode and chassis, the other way was by connecting the cathode directly to chassis and connecting the chassis to the centre tap of the mains transformers HT winding via a low (ish) value resistor, the -ve voltage (with respect to chassis) developed across that resistor would then be used as source for the grid bias voltage.

Lawrence.

Re: Need help identifying old capacitor from 1930s radio
 

630V easier to find in non electrolytic than 450V. Depending on the set's HT voltage, 400V might well do, except for any across the output transformer primary (or op valve anode to ground) where 1600V would be more suited.

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.

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.

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.

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.

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!

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.

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.

Re: Need help identifying old capacitor from 1930s radio
 

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.

Re: Need help identifying old capacitor from 1930s radio
 

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.

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.

Re: Need help identifying old capacitor from 1930s radio
 

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.

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.

Re: Need help identifying old capacitor from 1930s radio
 

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.

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.

Re: Need help identifying old capacitor from 1930s radio
 

Welcome, Mrgroovy!
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.
An admirable approach. It may seem daunting at first, but you seem like a determined chap, so your efforts should be rewarded.
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?

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:)).

Re: Need help identifying old capacitor from 1930s radio
 

C6 looks the right way round to me.

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

Re: Need help identifying old capacitor from 1930s radio
 

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.

Re: Need help identifying old capacitor from 1930s radio
 

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.

Re: Need help identifying old capacitor from 1930s radio
 

Sorry for my dumb question, but to measure the resistance across, does that simply mean to measure the 500ohm resistor in a normal manner? The terminology is still a bit new too me. If I understood what you asked I measured the resistance which is 527ohm.

Re: Need help identifying old capacitor from 1930s radio
 

I meant measure the resistance across the 500 ohm resistor without disconnecting the resistor from the solder tags, in other words the resistor remains connected as per your photos then measure the resistance between the two solder tags that the resistor is attached to. It's to get an idea of the actual bias arrangement that's configured in your receiver with the AL1 fitted.

On a separate note I wonder if the switch near the inductor that's fitted to the rear of the chassis is a tone switch, the inductor that's bolted to the chassis rear and the capacitors next to it being part of it? Could do with the control grid (g1) of the AL1 tracing back to get an idea what route the signal from the detector takes to get to the grid, I wonder if the other choke that's fixed to the underside of the chassis is part of the HT filtering or an anode load for the detector? Or if the inductor fixed to the back of the chassis is?

Just bunging a few ideas in.

Lawrence.

Re: Need help identifying old capacitor from 1930s radio
 

Then it is definitely 527ohm. As for the inductor near the rear with the switch; I made a quick scetch of the lead coming from the AL1 going to the capacitors and the inductor. Probably not the right symbol for inductor in my scetch but maybe you can make something out of it nonetheless.

Re: Need help identifying old capacitor from 1930s radio
 

Cheers for that latest drawing, that appears to sort the PU/gram input and detector grid leak out so far as I can make out.

Lawrence.

Re: Need help identifying old capacitor from 1930s radio
 

There is no assurance that the AL1 modification ever worked properly. If we could find a circuit diagram we could at least see what has been changed but it seems this is very unlikely. It would be helpful to see how the other valves are wired.

Based on the circuit by George, I would say it is wired incorrectly. The reservoir and smoothing capacitors should go to chassis and the centre tap should go to the 500 ohms. A resistor and capacitor smoothing would then be taken off the centre tap to provide the grid bias. The wiring for the other valves may give a further clue as they may also have -ve grid bias.

Re: Need help identifying old capacitor from 1930s radio
 

Do you mean that the centre tap should not go to ground? Did you have a look at the second scetch that I made? It is far from complete but maybe enough to tell if there are any obvious errors. The 500 ohm resistor is placed in parallel between the 0.1uF capacitor in the block and ground.

Re: Need help identifying old capacitor from 1930s radio
 

Lets wait for input from Lawrence.

One of your connections to the mains transformer is probably a screen. This is a foil placed between the primary and secondary that is wired to chassis to reduce noise coming from the mains.

Keep up the good work with the circuit drawing...

Re: Need help identifying old capacitor from 1930s radio
 

Is there a position on the band selector switch for gram input (GR) or are there only the two positions, one for the medium wave band and one for the long wave band ?

Lawrence.

Re: Need help identifying old capacitor from 1930s radio
 

I am getting the impression that changing the output valve to an indirectly heated type has left the bias circuit floating on the heater supply.
It might well be an abandoned repair job that has never worked after the output valve was replaced.

Re: Need help identifying old capacitor from 1930s radio
 

Hi Lawrence,

I'm not sure if I am entirely qualified to answer that question. As far as I can see there are three switches on this unit: One switch that cuts or connects the mains to the power transformer. This switch is actually controlled by the 1000K volume pot in that there is a "metal tag" at the far end of the potentiometer that opens or closes a toggle switch that goes to the mains/OT. Clever little device. I just left it out of the "caveman's schematics" to simplify things. Above the volume pot/power switch, there is another toggle switch, that connects something-something to one of the (I would presume) RF coils? From my overly primitive sketches, it seems like the switch simply connects one of the leads from the coil to ground, if that makes sense. The last and third switch is the one on rear end that you saw in my previous drawing. I'll try make a schematics for the entire receiver as soon as I'm able to.