[OldRestorer]

Well I am glad I didn't try to re-cap this little sucker.

Way above my pay grade

Kirk

[Eliot Ness]

I checked my Rider, Beitman, and Gernsback service manuals last night but could not find any of the following sets:

Acratone 25B
Simplex 4Z
Zephyr 4Z

I did see a partial ad for the Acratone 25B and it looks like the Century (first radio listed):

http://www.wa2ise.com/radios/acratone.html

And in the fine print for the Acratone 25B ad that I linked to on RadioMuseum they mention that the 76 is used as the rectifier.

You just need to get rid of that line cord. Personally I'd use a diode and then a capacitor or resistor to drop the voltage. The diode will get you down to about 85 volts. The following site (near the end) gives you the formula to calculate the size capacitor you'd need. As Tom mentioned, you'd use a non-polarized cap.

http://www.vintage-radio.com/repair-rest...calcs.html

[morzh]

I calculated I need a 7uF cap to present about 380 Ohm of reactance to make the current 300mA when serialized with the 4 tubes (25V at 300mA) and one Candohm and pilot light (7 Ohm).
Will need to buy that one, needs to be a film or non-pol electrolytic 200V or so.
With a diode that can be a twice the value cap.

Yes using the cord is a hazard.....but I never saw those before, this is the first one; I only heard of'em.

The asbestos does not seem to be flaky though.

[morzh]

Today did full recap.
Also electrolytics.
And even that 6nF tubular cap inside the antenna coil

I have to get me a nice 10uF cap to use with a diode to cut te voltage to filaments.
Thing is, none of my lytics is 300mA rated.

So I have an old large tubular Mallory from possibly 40s or 50s which says 10uF and - !!! measures as much.

I am reforming it as I am writing this and the eage is large....not sure whether it will reform. But if it will it should be able to work with an amp or so. Judging by size.

Will see.

[OldRestorer]

Confusing but Good work anyway!

Remember, you can only try your best so if it doesn't work out I will just keep the 20 cabinet.

[morzh]

Although I did not risk leaving the cap on while away at work, I left it overnight and it formed nicely down to 40uA leakage on 100V voltage. I upped it to 200V this morning and it started going down rapidly which is a good sign - yesterday it was going down sooooo sloooow...I had my doubts.

Tonight will proceed, hopefully giving it up to 300V overnight.

[morzh]

http://www.nostalgiaair.org/PagesByModel...004064.pdf

The sch on the right is fairly close.

[Eliot Ness]

A reformed cap would be fine to test the radio with, but I'd be hesitant to send it to the owner with a reformed cap in it. Odds are it will eventually sit on a shelf for months between uses. New caps are pretty cheap insurance and AES has some nice Solen 10µf metalized polypropylene film caps for $6.75:

http://www.tubesandmore.com/products/C-FS-630

[morzh]

Yep, this is what'll have to go in there. Regular electrolytics will not take the current.
If it works I will order one from AES or from Parts Express.

[morzh]

Have just realized the cap/diode in series won't work...it will just charge the cap and that will be that.
Nope. I just need a cap alone. No diodes. Otherwise it becomes complicated.
The cap should be 7uF to give me 300mA with the load in this radio.

I have two 3.3uF 100V caps in parallel just to see if it is as predicted, then will buy a really good one, with adequate voltage rating etc.

[morzh]

The calculation seems correct, the voltage acoss the tubes filaments and the pilot s 28V (I am not sure what the pilot across the Candohm is but cold it gave me 6 Ohm that would make it 2V) sonI expected 27.2V which is close. Ultimately will measure current, it is the better criterion, should be 300 mA.


Update 10 minutes later....

I fully expected it to work, but nooooo....
No life in the speaker.
I looked at the B+.... 0V.

Cecked the 76 tube...dead. The filament is good, but the tube is fully dead otherwise.
I think, it is a broken wire - three of them have loose bases.

Anyways, Kirk - do you have a 76 toob?

[OldRestorer]

I have 13 of them, lol
Want me to mail it to you?

Kirk

[morzh]

Yes, if you don't want to first order the cap and then mail them together.
Then I could test the radio for working and install the cap later.

Then I could move to the next chassis.

[Arran]

Mike;
I was not sure what you were planning when you mentioned using a diode and a capacitor, which is why I didn't say anything. In terms of line droppers I have heard of three main ways, to do it, with a big wire wound resistor, with a large value capacitor, or a diode, you can use a combination of a resistor and a capacitor, or a resistor and a diode, but not a capacitor and a diode.
In truth there is also a forth way, you could use the winding of a transformer or choke in series with the tube filaments, but I've never seen anyone do this. I have heard of people rebuilding resistive line cords, but it seems like a fruitless effort unless the radio is really, really compact.
Bob Andersen has carried out a lot of experiments with various alternatives to resistive line droppers for his series string TVs. One thing that he found was that the capacitive line dropper gave the softest start, With the diode dropper a current limiter was a good idea to add in addition to any extra resistors needed to get the voltage right. Speaking of high value film capacitors, there are some Panasonic or Nichicon ones on Mouser's site, 2.5 or 3 uf at 450 volts, under $2 a piece, I think that they are polyethylene or polypropylene, they are red with radial leads.
I thought that this Century radio may have been another example of the imfamous "Plant A" radios, but those typically use a proper rectifier tube like a 25Z5/25Z6, and a 43/25A5/25L6 power output. The only sets I have heard of using a diode connected triode, like a 76, as a rectifier were home made sets based on plans in Popular Science, Radio Craft, or similar magazines in the 1930s, not something built commercially.
Regards
Arran

[morzh]

The Detrola I gave the link to above did exactly the same, and the radio is fairly close schematic-wise.

As for the droppers.....I need 6.2-6.5uF cap. I found that 6.2uF cap, metallized poly, and if I need to adjust a bit I add caps in parallel.

A diode and a resistor - the resistor will still have to dissipate 1/2 of the wattage of the heater cord which is about 15W, which is still a lot.

A capacitor and a diode can be used together but then you have to parallel the cap with a resistor and the RC has to be much shorter than the 16ms which is only possible if you need to drop a whole lot so your cap is small, or your resistor will dissipate a lot and it will defeat the purpose.

Anyways, I measured the current yesterday, with 6.6uF it gave me about 312mA which is pretty good, so 6.2uF will bring me to just about 300mA, and I did not see any spikes in current or voltage.