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 Post subject: Re: Westinghouse model 801 grandfather clock radio.
PostPosted: Sep Tue 17, 2019 1:49 pm 
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spsquires wrote:
OK I looked at thread and not sure what size resistor and where to place capacitor.

It's all there....the resistor goes across the open winding, and the capacitor goes between the 2 windings. There are some diagrams, and there is a lot of discussion about how NOT to do it.

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 Post subject: Re: Westinghouse model 801 grandfather clock radio.
PostPosted: Sep Tue 17, 2019 1:52 pm 
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I know the resistor replaces the winding but what value? But do not understand cap placement.


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 Post subject: Re: Westinghouse model 801 grandfather clock radio.
PostPosted: Sep Tue 17, 2019 1:59 pm 
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spsquires wrote:
I know the resistor replaces the winding but what value? But do not understand cap placement.

Read the whole thread.....including my suggestions about part values and comments about how well this might work.

The capacitor connects between the primary and secondary--at the "signal end" **. It replaces the coupling normally provided by the transformer mutual inductance.


** In the typical IF transformer, each winding is referenced to AC ground at one end. The signal is applied to the end of the primary opposite the one that is grounded, and the coupled signal appears at the corresponding point on the secondary.

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 Post subject: Re: Westinghouse model 801 grandfather clock radio.
PostPosted: Sep Tue 17, 2019 2:15 pm 
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Should pin 3 of tube 3 224 be one point for cap?


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 Post subject: Re: Westinghouse model 801 grandfather clock radio.
PostPosted: Sep Tue 17, 2019 2:19 pm 
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spsquires wrote:
Should pin 3 of tube 3 224 be one point for cap?

Consider a very common configuration:
Primary winding is in the plate circuit of a tube.
Secondary winding is in the grid circuit of the next tube.
the coupling cap would go from the plate of the first tube to the grid of the second....

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 Post subject: Re: Westinghouse model 801 grandfather clock radio.
PostPosted: Sep Tue 17, 2019 2:34 pm 
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So cap should be pin 3 of tube 3 224 and pin 2 tube 4 235


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 Post subject: Re: Westinghouse model 801 grandfather clock radio.
PostPosted: Sep Tue 17, 2019 4:04 pm 
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In the thread I linked, see my comments about the size of that cap.

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 Post subject: Re: Westinghouse model 801 grandfather clock radio.
PostPosted: Sep Tue 17, 2019 5:22 pm 
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So I assume my post is correct. So can I use a .1 cap and 10 k 1/2 watt resistor?


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 Post subject: Re: Westinghouse model 801 grandfather clock radio.
PostPosted: Sep Tue 17, 2019 6:21 pm 
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pixellany wrote:
In the thread I linked, see my comments about the size of that cap.

0.1uF would be WAY too high

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 Post subject: Re: Westinghouse model 801 grandfather clock radio.
PostPosted: Sep Tue 17, 2019 6:23 pm 
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So what could I use since I have only normal stock caps . Also is the resistor good?


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 Post subject: Re: Westinghouse model 801 grandfather clock radio.
PostPosted: Sep Tue 17, 2019 9:12 pm 
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Capacitor and resistor would go here:
Attachment:
Untitled-06.jpg
Untitled-06.jpg [ 34.73 KiB | Viewed 902 times ]

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 Post subject: Re: Westinghouse model 801 grandfather clock radio.
PostPosted: Sep Tue 17, 2019 9:42 pm 
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Two things were discussed in the other thread:
1. The resistor that bypasses the IF primary cannot be too large or there will be too large a drop in plate voltage. I think we discussed using an RF choke instead, but I'm not sure,
2. The coupling capacitor cannot be too large or it will totally detune the secondary. I was leaning towards 10s of pF--several orders of magnitude away from your 0.1uF

Another option which I THINK was discussed is swapping the primary and secondary---putting the good winding on the primary side. With an open secondary you can have a much larger bypass resistor.

My hunch is that bypassing 1/2 of an IF like this is a pretty big performance hit, and I'd probably opt for rewinding or replacing the transformer. BUT--if you read the whole thread, you'll also see Peter Balazsy's clever solution:
viewtopic.php?f=6&t=362832&p=3063793#p3063793

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 Post subject: Re: Westinghouse model 801 grandfather clock radio.
PostPosted: Sep Tue 17, 2019 9:54 pm 
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I saw the other device but do not have things to make it. So what resistor do you suggest and would a .0015 cap be close enough?


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 Post subject: Re: Westinghouse model 801 grandfather clock radio.
PostPosted: Sep Tue 17, 2019 10:34 pm 
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You really need to read all of the posts....I said that I was leaning towards 10s of pF. The nominal value that someone suggested in the other thread was 200pF. 1500pF is too high.

For the resistor, look at the other thread. The whole point is to get a workable plate voltage. That depends on what the tube is.

Did you understand the point about swapping primary and secondary? I actually think that may be the better solution.

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 Post subject: Re: Westinghouse model 801 grandfather clock radio.
PostPosted: Sep Tue 17, 2019 10:46 pm 
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I do not understand changing out primary and secondary. But would like to use resistor cap combination.


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 Post subject: Re: Westinghouse model 801 grandfather clock radio.
PostPosted: Sep Tue 17, 2019 11:09 pm 
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spsquires wrote:
I do not understand changing out primary and secondary.

The idea is simply that....if you only have one good winding...use that for the primary.

Quote:
But would like to use resistor cap combination.
great---go for it!!

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 Post subject: Re: Westinghouse model 801 grandfather clock radio.
PostPosted: Sep Tue 17, 2019 11:30 pm 
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Yes but if you eliminate secondary wont that change the radio? If it does not need to be used why install it in the beginning


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 Post subject: Re: Westinghouse model 801 grandfather clock radio.
PostPosted: Sep Wed 18, 2019 12:41 am 
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spsquires wrote:
Yes but if you eliminate secondary wont that change the radio? If it does not need to be used why install it in the beginning

An IF transformer is approximately 1:1. That means that either winding can be the primary or secondary.

You have one winding open, so the radio is already changed. If you want the radio original, you need to replace the transformer.

What you have been asking about is often called a "workaround"---this is something that gets around a problem so that things still work to some degree.

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 Post subject: Re: Westinghouse model 801 grandfather clock radio.
PostPosted: Sep Wed 18, 2019 12:47 am 
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Yes but IF the radio will not work with primary open how will it work with secondary not in place.


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 Post subject: Re: Westinghouse model 801 grandfather clock radio.
PostPosted: Sep Wed 18, 2019 12:53 am 
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spsquires wrote:
Yes but IF the radio will not work with primary open how will it work with secondary not in place.

We have been discussing bypassing the primary. You can also bypass the secondary.

In either case, you no longer have a transformer---you simply have one tuned circuit and capacitive coupling between stages.

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