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Old 8th Oct 2018, 2:25 pm   #61
Mrgroovy
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Default Re: Need help identifying old capacitor from 1930s radio

Well its probably not connected that way (except in my caveman's schematic). I'm not entirely sure how to draw this, but I think I understand this cannot be right. I'll have another look at it asap.
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Old 8th Oct 2018, 2:26 pm   #62
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Default Re: Need help identifying old capacitor from 1930s radio

Left it too long to edit last post. Suitably refreshed after some fresh air.
Apologies if my last post came over as a bit abrupt - not intended
Mrgroovy, I think the problem might be that you are using a meter of some sort to check continuity to chassis and it cannot distinguish between a direct connection and a connection to a coil whose other end goes to chassis. My suggestion would be to only mark points that you can visibly see a wire or tag to chassis. I think that would make things clearer.
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Old 8th Oct 2018, 2:53 pm   #63
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Default Re: Need help identifying old capacitor from 1930s radio

So far I think that originally the heaters (of the amplifying valves) would have been connected one side to chassis, the bias arrangement for the output valve as it is looks over biased to me as the grid return resistor is connected across the original 500 ohm bias resistor and the added 350 ohm resistance, I think the cathode de-coupling would fall short as well.

The volume/gain pot might be reducing the antenna input while at the same time altering the bias on the RF amp?

Some of the connections on the detector coil look a bit fresher than other connections in the receiver, and what's the switch connection doing for that coil assembly, one contact appears to connect to an HT feed to the coil, how would that switch wave bands for that coil ? Bearing in mind that it appears to be a grid leak detector who's grid circuit one would expect to be tuned.

Lawrence.

Last edited by ms660; 8th Oct 2018 at 3:00 pm.
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Old 8th Oct 2018, 3:10 pm   #64
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Default Re: Need help identifying old capacitor from 1930s radio

Hopefully not adding any further confusion, my understanding of this set is that the original indirectly heated ouput valve has been replaced by a directly heated one- the AZ 1. Looking at the schematics, it looks like some attempt has been made to avoid potential hum problems by adding a resistive centre tap to ground on the AZ 1 filament since the usual centre tapped heater winding used with this type of valve is not present. This may have been done incorrectly.

If the output valve has its own heater winding on the transformer, it should be possible to sort it out fairly easily but if it's commoned with the other valves' heaters and they have one side grounded, they will need to be connected via individual twisted pair wires to the output valve heater pins and not grounded. It might end up easier to fit another indirectly heated valve for the output and go back to something closer to how it may originally have been built!
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Old 8th Oct 2018, 3:42 pm   #65
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Default Re: Need help identifying old capacitor from 1930s radio

Ok, did some small modifications to the schematic. Looks rather messy, sorry for that, and as Buggies pointed out, there was an error with regards to the variable capacitor. Fixed that now. There is a few things though that puzzles me. There is a switch (S4) which is in fact controlled by the same lever as the S2 switch, and I didn't realize that is was a switch until now. The reason for that it that two of the points (I called them 1 and 2 here) that the switch connects/disconnects, already have continuity and I can't seem to find out how and why. The switch is not broken because I de-soldered one of the connectors so see if I could brake the continuity and it works as it should. However, the two soldering points, so to speak, that both have wires that goes into the RF Coil have continuity even if the switch is on or of, so as far as I can see the switch serves no function. Though, I'm sure it does when you tell me why! So just for the sake of explaining what I found I made a line right on top of the 1 and 2 to resemble the continuity I measured between them, and then you have the switch after that.

And lastly I've also drawn in the wires going from the RF coil nr 1 to the top/hat (what ever they are called) of the first E452 tube, and the other one that goes from one of the inductors to the second E452. X markes the spot.

Yes I know that the way I present the tubes, coils etc on my primitive schematics are not by any means correct so please take it for what it is. Until I really know how to read schematics I will have to stick with these caveman's drawings of mine.
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Old 8th Oct 2018, 3:44 pm   #66
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Default Re: Need help identifying old capacitor from 1930s radio

Quote:
Originally Posted by buggies View Post
Left it too long to edit last post. Suitably refreshed after some fresh air.
Apologies if my last post came over as a bit abrupt - not intended
Mrgroovy, I think the problem might be that you are using a meter of some sort to check continuity to chassis and it cannot distinguish between a direct connection and a connection to a coil whose other end goes to chassis. My suggestion would be to only mark points that you can visibly see a wire or tag to chassis. I think that would make things clearer.
No worries mate! You are probably spot on. I'm using a meter with continuity to connect the dots for this schematic. It's the only why I know.

Quote:
Originally Posted by ms660 View Post
So far I think that originally the heaters (of the amplifying valves) would have been connected one side to chassis, the bias arrangement for the output valve as it is looks over biased to me as the grid return resistor is connected across the original 500 ohm bias resistor and the added 350 ohm resistance, I think the cathode de-coupling would fall short as well.

The volume/gain pot might be reducing the antenna input while at the same time altering the bias on the RF amp?

Some of the connections on the detector coil look a bit fresher than other connections in the receiver, and what's the switch connection doing for that coil assembly, one contact appears to connect to an HT feed to the coil, how would that switch wave bands for that coil ? Bearing in mind that it appears to be a grid leak detector who's grid circuit one would expect to be tuned.
Not sure where the detector coil is, but I've changed a few molded old wires whose insulation was peeling off. The power cord is all new, switched to a 3-prong cord, not sure if I'd done that by the time I took that picture so it's probably not visible. All the wires going receiver to the output transformer (which by the way is mounted to the speaker) and the wires going to the field coil on the speaker have been changed.
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Old 8th Oct 2018, 3:59 pm   #67
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Default Re: Need help identifying old capacitor from 1930s radio

Latest theory I think it might have been modified for one wave band reception only, the redundant wave band position being selected for gram so that no signal or noise breaks through when using the gram input. This is why I was asking earlier as to how many switch positions there were.

Lawrence.
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Old 8th Oct 2018, 4:02 pm   #68
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Quote:
Originally Posted by Herald1360 View Post
Hopefully not adding any further confusion, my understanding of this set is that the original indirectly heated ouput valve has been replaced by a directly heated one- the AZ 1. Looking at the schematics, it looks like some attempt has been made to avoid potential hum problems by adding a resistive centre tap to ground on the AZ 1 filament since the usual centre tapped heater winding used with this type of valve is not present. This may have been done incorrectly.

If the output valve has its own heater winding on the transformer, it should be possible to sort it out fairly easily but if it's commoned with the other valves' heaters and they have one side grounded, they will need to be connected via individual twisted pair wires to the output valve heater pins and not grounded. It might end up easier to fit another indirectly heated valve for the output and go back to something closer to how it may originally have been built!
It's a thought, and if I should find myself unable to fix this I would definitely consider changing the power tube but as for now I'm very determined on getting it to work the AL1. I'm also pretty sure my poor schematics is not as helpful to you kind folks as they should be. I feel they are improving but there's still some more work to be done until I really get the hang of it. Need to figure out how to represent this in an absolute accurate way. Only then could it be safe to say if it will or will not work with new capacitors. Worst case scenario; I know a well seasoned tube amp repair guy that might have a look at it for me, but I really want to be able to fix this myself, having spent so much time on it already. The help and guidance from all you guys are invaluable, and I feel a bit overwhelmed by all the information and knowledge it takes to fix up a vintage 1930s radio!

Quote:
Originally Posted by ms660 View Post
Latest theory I think it might have been modified for one wave band reception only, the redundant wave band position being selected for gram so that no signal or noise breaks through when using the gram input. This is why I was asking earlier as to how many switch positions there were.
I wish I could confirm that but I can't say I know how to check.

Another theory: It was probably "fixed" by a traitor repair guy during WW2 so that the resistance wouldn't be able to use it. Hence probably why they put in a German Telefunken AL1. Problem solved!

Well, joke aside. I think I'll try take some more close up pictures which might help to see things more clearly.
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Old 8th Oct 2018, 4:34 pm   #69
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Default Re: Need help identifying old capacitor from 1930s radio

Fair enough - that is what I would be doing with an unknown circuit. Problem arises when you have coils or transformers involved which may only have a few turns of wire between the pins - so the meter says they are all joined together. This is true but...
I am guessing that your two switches just short out part of the tuned coil windings on medium wave - perhaps you can confirm - if the switch is marked M/L?
BTW its great to see someone sticking with a job like this - you would be surprised how many give up after one post and ten answers.
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Old 8th Oct 2018, 4:45 pm   #70
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Default Re: Need help identifying old capacitor from 1930s radio

So far as I can make out (photo's 2 & 4 in post number 4) one of the wave band switch contacts that's connected to the detector coil transformer is connected to an HT feed, question is why?

Lawrence.
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Old 8th Oct 2018, 5:02 pm   #71
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Default Re: Need help identifying old capacitor from 1930s radio

Does anyone have radiomuseum membership? Could they try to contact the owner of the AH37, Peter Holst?
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Old 8th Oct 2018, 7:02 pm   #72
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Default Re: Need help identifying old capacitor from 1930s radio

Not sure what you mean by the detector coil transformer? If you mean the large AF choke between the switch and large capacitor block then this is the anode feed for the detector. There are a few capacitors which I assume will be RF filters and a capacitor to the AL1 grid.

The AL1 conversion looks wrong and there is no knowing what other changes have been made. A set like this normally uses regeneration and has an associated control?
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Old 8th Oct 2018, 7:48 pm   #73
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Default Re: Need help identifying old capacitor from 1930s radio

It's the transformer that has the detector coil in it, the one that's coupled to the detector, normally an untuned primary connected in the anode circuit of the RF amp and often with a tapped (for band change) secondary (tuneable) It's the one in the photo that has a 220pF coming from it that goes to the grid of the detector valve, It can also be seen in the 3rd photo in post#4.

The thing that concerns me about the AL1 conversion is that the output transformer might not be the optimum load and that the total external "cathode" resistance is at least 850 ohms and is not fully bypassed frequency wise, the manufactures valve data gives 350 ohms for the usual typical HT etc:

https://frank.pocnet.net/sheets/030/a/AL1.pdf

Lawrence.

Last edited by ms660; 8th Oct 2018 at 8:05 pm. Reason: removal/addition etc
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Old 8th Oct 2018, 10:45 pm   #74
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Default Re: Need help identifying old capacitor from 1930s radio

Ok, new discovery. I've been an idiot but for some reason I thought, when I first cast glance on the tubes, that the rectifier tube was a 506, probably because I googled and I found that it was supposed to be that tube and the shape and appearance was identical to that of the 506. However, now when I tried to study the 4 tubes to see if perhaps I could make a more accurate schematics, it turns out that the rectifier in fact is a R0437 https://www.radiomuseum.org/tubes/tube_r0437.html Luckily, according to radiomuseum it is "normally replaceable, slightly different" with among other the 506 tube. Shouldn't be a problem then?
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Old 9th Oct 2018, 7:12 am   #75
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Default Re: Need help identifying old capacitor from 1930s radio

Thought I'd share my latest investigation before I run off to work. Found the schematics for an Aga Baltic AH34 last night. By appearance they don't look similar at all. It seems to be made one year before my AH37, at least according to the date on the schematics. It is not the same radio, but perhaps you guys can make something useful out of it see if there are any similarities with my AH37?

Have a look at the link below and scroll to down find the link to the aga_ah34pdf

http://www.radiohistoriska.se/forum/...=1871&start=15

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Old 9th Oct 2018, 8:44 am   #76
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Default Re: Need help identifying old capacitor from 1930s radio

The AH34 circuit is very helpful. The power supply arrangement is identical and confirms the 500 ohm/0.1uF is wired correctly which I am now thinking is hum-bucking. It also uses a directly heated output valve like the AL1.
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Old 9th Oct 2018, 9:40 am   #77
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Default Re: Aga Baltic AH37. Need help identifying old capacitor from 1930s radio

The blueprint is a help to me to understand the hardware in the pictures.
Couple of component identification questions on the 4th picture in post #4 .
Am I correct that the inductor on the sidewall is the smoothing choke, the one centre-chassis the LF choke and the black cylinder on the rear wall the RFC?
The 1k variable looks to me like a reaction control?
I can't work out the cathode connections to the first two valves.
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Old 9th Oct 2018, 10:03 am   #78
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Default Re: Aga Baltic AH37. Need help identifying old capacitor from 1930s radio

So far as I can make out and going by normal valve numbering convention, V1 has cathode bias, V2 has no cathode bias because it's cathode is connected to chassis.

Lawrence.
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Old 9th Oct 2018, 11:00 am   #79
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Default Re: Aga Baltic AH37. Need help identifying old capacitor from 1930s radio

That AH34 circuit is as commented, very useful. If the heater wiring in your set is redone to be the same, that part of the set will be fine. It looks like the same as I described earlier as a possible way to go.

The low resistance pot across the heaters is known as a "humdinger" and is simply adjusted for minimum hum. Normally its setting would be near central, balancing the heaters to ground, but a useful side effect is that some hum from other sources than the heaters may be cancelled out by offsetting it slightly. On your set , just two fixed reisistors have been used which may not be quite optimum but may have been all that was available when the mods were done. Perhaps the modifier was just an AGA engineer working under difficult circumstances who tried to fix it by using an earlier design to suit parts on hand.


(Aside) Found this interesting site: http://www.aga-museum.nl/page/aga-radio
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Old 9th Oct 2018, 11:43 am   #80
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Default Re: Aga Baltic AH37. Need help identifying old capacitor from 1930s radio

I have updated my circuit but still a few loose ends round V1 area.
I think there is enough information now to say it might work subject to the paper caps being tested/replaced?
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