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 Post subject: Philco D-1347 Selenium Replacement Problem
PostPosted: Mar Sun 15, 2020 8:51 pm 
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I hate to admit that I have a problem with this as I have replaced a selenium with a diode before on other
circuits but never done a double(not that it should be twice the problem)
I took pics.....made a hand sketch and when I had it together it didn't work. I turned it on and monitored the
voltage on the plus side of C19A. As it was warming up I noticed the voltage was in negative territory and went past
240, hit 400 then dropped to zero. Still checking things.


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 Post subject: Re: Philco D-1347 Selenium Replacement Problem
PostPosted: Mar Mon 16, 2020 3:53 am 
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Location: Dallas Co. Arkansas
Could you post the entire schematic?

Rob

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 Post subject: Re: Philco D-1347 Selenium Replacement Problem
PostPosted: Mar Mon 16, 2020 5:18 am 
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Image

Where the original caps on bakelite wafers or grounded to the chassis , i think they shouldn't be grounded to the chassis along with the negative end of cr1 . Make R 25 200 ohms at at least 5 watts .

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 Post subject: Re: Philco D-1347 Selenium Replacement Problem
PostPosted: Mar Mon 16, 2020 1:50 pm 
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Caps were grounded to chassis


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 Post subject: Re: Philco D-1347 Selenium Replacement Problem
PostPosted: Mar Mon 16, 2020 5:08 pm 
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I think the caps negative should be connected to a common B- , not the chassis.
The chassis is connected to B- through C4. Don't know how you could have negative
voltage unless diodes were reversed. Might have ruined the electrolytics too.

Rob

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 Post subject: Re: Philco D-1347 Selenium Replacement Problem
PostPosted: Mar Mon 16, 2020 5:28 pm 
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Location: Minneapolis, MN USA
The power supply in that radio is a voltage doubler circuit.
Ensure that all caps and diodes are oriented correctly.


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 Post subject: Re: Philco D-1347 Selenium Replacement Problem
PostPosted: Mar Mon 16, 2020 10:47 pm 
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Which cap is in the picture , and do you have a photo a photo of before you started working on it

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 Post subject: Re: Philco D-1347 Selenium Replacement Problem
PostPosted: Mar Tue 17, 2020 10:39 pm 
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The cap in the pic is the 20 uf
I didn't have a 200 ohm resistor to put in place of the 50 ohm
so I tried a 250 ohm/10 watt and the voltage was about 100 volts to low
thought I had one, looks like I'll have to order one and also looks like it will work


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 Post subject: Re: Philco D-1347 Selenium Replacement Problem
PostPosted: Mar Wed 18, 2020 12:47 am 
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Since there are two 20's in that section of the schematic it would be much more helpful to ID it by description - is it C19B or C20? I assume C20 but assumptions in electronics can get you in a world of trouble.

Larry

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 Post subject: Re: Philco D-1347 Selenium Replacement Problem
PostPosted: Mar Wed 18, 2020 1:56 pm 
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Sorry Larry
The one in pic is C20 which checks ok
after applying power the first time resistor r25 ended up toast
when I installed the new caps C19a, b, c, d, and C20
I automatically connected them to chassis grounds like the originals were.
Was I wrong with this?


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 Post subject: Re: Philco D-1347 Selenium Replacement Problem
PostPosted: Mar Wed 18, 2020 2:18 pm 
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If I have this labeled correctly and if R25 is connected directly to C20 (difficult to see) and only C20, what is the green wire and why is it grounded? If the wire from R25 is connected to the same tab as CR1 that wire needs to be connected directly to C20, nothing else.

Attachment:
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 Post subject: Re: Philco D-1347 Selenium Replacement Problem
PostPosted: Mar Wed 18, 2020 2:42 pm 
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R25 originally went to the negative tab of C20 which was a twist tab connection to chassis ground
The green wire to ground was put there because I read that as the selenium negative ground, which
now looks like a mistake


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 Post subject: Re: Philco D-1347 Selenium Replacement Problem
PostPosted: Mar Wed 18, 2020 3:43 pm 
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Location: Boston, MA USA
B- is not chassis ground on this set. It is "isolated" from ground by C4 (0.1uF). C4 is the ONLY capacitor that is connected to chassis ground. Be aware that one side of the power cord is connected to B- through the power switch. And be sure that C20 (20uF) is NOT connected to either B- or chassis ground.

This circuit is called a half-wave voltage doubler. It has the advantage of twice the B+ voltage normally available from a transformer-less power supply which allows much more amplifier power output, while still allowing B- to be connected directly to incoming AC power, rather than through one of the rectifiers as in the more common full-wave voltage doubler.

-David


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 Post subject: Re: Philco D-1347 Selenium Replacement Problem
PostPosted: Mar Wed 18, 2020 7:37 pm 
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Joined: Apr Wed 03, 2013 2:38 pm
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I guess I don't understand the difference between all the electrolytic cans neg being connected to chassis ground
but when replaced with new caps the neg is not connected to chassis ground


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 Post subject: Re: Philco D-1347 Selenium Replacement Problem
PostPosted: Mar Wed 18, 2020 8:36 pm 
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The reason Most AA5's and other line operated sets don't ground the B+ to the metal chassis is that if the AC line is flipped t becomes a shock hazard .
If all the metal components are covered y plastic or wood it is somewhat safer but not good practice , that is why i wanted to see a picture of the chassis before you stared working on it .

Can you take another photo of the two diodes and the cap , from another angle , it looks like the center point of the two diodes is grounded , but i believe it isn't .

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 Post subject: Re: Philco D-1347 Selenium Replacement Problem
PostPosted: Mar Wed 18, 2020 9:44 pm 
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stratozen wrote:
I guess I don't understand the difference between all the electrolytic cans neg being connected to chassis ground
but when replaced with new caps the neg is not connected to chassis ground

The original electrolytic capacitor negative cans were never connected to chassis ground. They must not be connected to chassis ground now.

-David


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 Post subject: Re: Philco D-1347 Selenium Replacement Problem
PostPosted: Mar Thu 19, 2020 5:52 pm 
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Joined: Apr Wed 03, 2013 2:38 pm
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Here is (I hope) a better pic of the diode connection
The wire that's connected to the plus and minus of CR1 and CR2 is
connected only to the plus side of C20 and not to ground.
I believe the mistake was connecting the neg sides of C20, C19a, b, c, and d to chassis ground
The original can ground connections were the tabs that secured the can to the chassis and the wires
were soldered to the tabs


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 Post subject: Re: Philco D-1347 Selenium Replacement Problem
PostPosted: Mar Thu 19, 2020 8:21 pm 
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Let some of the more estute guys jump in and correct me if I'm reading that schematic wrong but shouldn't the green wire I drew above be connected to pin 5 of the 12AT7 and not to ground?

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Diode.jpg
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Larry

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 Post subject: Re: Philco D-1347 Selenium Replacement Problem
PostPosted: Mar Thu 19, 2020 8:59 pm 
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rocketeer wrote:
Let some of the more astute guys jump in and correct me if I'm reading that schematic wrong but shouldn't the green wire I drew above be connected to pin 5 of the 12AT7 and not to ground?

Attachment:
Diode.jpg

Larry


Pin 5 of the 12AT7 is one side of the AC line , R25 connects to the other side of the AC line which is going to ground .

If the cans were soldered to the chassis , they were grounded to which is very unusual for a line operated set .
Could someone been in there before you that replaced the cans in the past If the bad caps haven't been disposed of can you post at photo of them and the markings on the side .

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Last edited by battradio@ on Mar Thu 19, 2020 9:10 pm, edited 1 time in total.

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 Post subject: Re: Philco D-1347 Selenium Replacement Problem
PostPosted: Mar Thu 19, 2020 9:07 pm 
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battradio@ wrote:
rocketeer wrote:
Let some of the more astute guys jump in and correct me if I'm reading that schematic wrong but shouldn't the green wire I drew above be connected to pin 5 of the 12AT7 and not to ground?

Attachment:
Diode.jpg

Larry


Pin 5 of the 12AT7 is one side of the AC line , R25 connects to the other side of the AC line .

Understood but that doesn't answer the question, is the drawing correct or not?

Larry

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