[jmcgill]

    My first restoration, Philco Model 40-165 code 121.  Speaker had been removed so I am going with a PM.  In the schematic, is the 1700 ohms the DCR read as if the choke was disconnected?  I mean it has nothing to do with X sub L?  Also, should there be a couple of fuses?  One in the line and one at the power supply output?

[Radioroslyn]

<  I mean it has nothing to do with X sub L?  Also, should there be a couple of fuses?  One in the line and one at the power supply output?

Correct. Inductance is measured in Henrys.  Resistors have very little inductance (wire wound) which can be a issue at RF but in power supply filtering it's a non issue. With that being said you'll need to increase the value of the three capacitors to 33mfd or so to eliminate 60cy hum. Remove #54 from the circuit.
You can add fuses 1A to the ac line and 150ma to the center tap of the HV winding.

[jmcgill]

Thanks for the info.  So wouldn't I still need a small choke with sufficient current carrying capabilities in series with the resistor to smooth out the hum?  If I did use a small coil, would the caps still need to be changed ?

Jim McGill

[Radioroslyn]

No not necessary, you can filter using just caps and resistor. If you look at more modern set like ac/dc set from the '50s there's no inductance in the filter. Just as a guess if you didn't increase the size of the caps your probably looking at 5-8H to replace the field coil in terms of inductance. The series resistance isn't very critical in this circuit. Where it is critical is when the field coil is connected to the HV center tap back the chassis gnd. In this case the fc or choke does two things filters 60cy hum and develops negative dc voltage used for biasing. The fc dc resistance determens the amount of bias. Circuits wired with the fc or choke in this fashion are known as negative lead filtering.
That's part of the long answer to your question. The short answer is to use a 1700 ohm 25w resistor in place of the fc. Actual dissipation is about 15W but nobody likes a flaming hot  power resistor. Remove the .05mfd that is across the fc it's used to resonate the inductance to the fc to 60cy and will just couple hum across the replacement resistor. Good practice sez to limit the input cap below 40mfd so 33mfd is good and while your ordering go ahead and replace all 3 of them with 33mfd @ 450v.

[jmcgill]

Thanks for taking the time to explain the field coil replacement in detail.  I think it is time to start ordering parts.  One more question; The replacement speaker should be 8 ohms, right?

[morzh]

3.5 Ohm. A 4-ohm speaker will do.

[Radioroslyn]

Just for the heck of it you may want to check the resistance of the primary of the output transformer to be sure it's ok.

[jmcgill]

Guess what...the audio output transformer primary is wide open.  Where can get details on the parts for this 40-165K?  Ohms don't tell the whole story.  I saw some books about philco radios in two volumes.  Will they answer the questions I have about part details?  I want to order the right output transformer.  Although my basic electronics is weak, I have swapped enough boards in digital equipment to know that even a part number suffix can make the difference between working and staying up all night only to find out I needed a C board not and A board.  Thanks for your help.

[Radioroslyn]

Well the long answer is to look up the output tube's specs   http://tubedata.milbert.com/sheets/021/4/41.pdf   and look for load resistance. This is what the plate wants to see as a load. This is different from the dc resistance of the output transformer (530 ohms) or the plate resistance ( abt 68K).

At 180v it's about 9000 ohms for the primary, the secondary needs to match the impedance of the voice coil. The original spkr's vc is about 2 ohms. If you are using a pm spkr then most of those are 4 or 8 ohms.

So the short answer is you need a 9k to 4 or 8 ohm output transformer.

Check ur PM

[jmcgill]

I apologize.  I located the output xformer at tubesandmore.com.  I store my old radio information in a directory called oldradios on my wife's old semi-broken laptop.  At 73 I get a little confused.  Hope you understand.

[morzh]

This is the Push-Pull transformer. You need a Single-Ended (SE) transformer.

125CSE by Hammond is the one you might want. But it is expensive.

Your connections will be primary - only one way and the secondary - BLK to ORG/GRN for 4/8 Ohm

http://www.ebay.com/itm/240012-Tube-Audi...SwRUhY9jyc
http://www.ebay.com/itm/tested-tube-amp-...SwlndZCoDF
(these two do not say if it is P-P or SE type, nor do I think they have documentation with them - you could ask)

http://www.ebay.com/itm/OT10SE-USA-Singl...xy2E1SEY30

http://www.ebay.com/itm/OT8SE-Single-End...SwgNRV8Oov
(my favorite - you have to see if the size fits).

[Radioroslyn]

Hey Jim,
Send me your mailing address via the private message or email and I'll drop you a new Stancor A3822 free. It's a multi match that is designed to match 7000 to 10K

[jmcgill]

I have search the net for a 1700 ohm 25 watt wire wound resistor to replace the field coil.  Can't find anything within 5% tolerance.  How about two resistors between 3300 and 3500 ohms in parallel at 20 watts each?  By my novice calculations that should yield resistance within tolerance.
By the way...I must have done something wrong and deleted my original thread.
Thanks...Jim McGill

[Ron Ramirez]

Jim

You deleted the first post in this thread. Fortunately only we on the mod/admin team can permanently delete posts and threads, so I was able to restore it for you. In addition, I added your last post to this thread since it is on the same subject.

[Radioroslyn]

Yes the two resistor in parallel should work fine.