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 Post subject: Re: Westinghouse model 801 grandfather clock radio.
PostPosted: Sep Sun 29, 2019 8:22 pm 
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spsquires wrote:
So you mean a smaller cap with resistor?

Please read what I posted previously.....these questions have all been answered. I was referring to the coupling cap that is required when you no longer have a transformer.

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 Post subject: Re: Westinghouse model 801 grandfather clock radio.
PostPosted: Sep Sun 29, 2019 8:28 pm 
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Not sure what part you are talking about.


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 Post subject: Re: Westinghouse model 801 grandfather clock radio.
PostPosted: Sep Sun 29, 2019 8:53 pm 
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spsquires wrote:
Not sure what part you are talking about.

All of the diagrams that show how to bypass an open transformer winding show a coupling capacitor!! You have read all this material and you stated that you tried at least some of the ideas.

At this point, I think you will need to re-read the whole thread to refresh your memory.

Basics--again: With a transformer, you get coupling between stages---due to the mutual inductance of the transformer. If a winding is open, you no longer have a transformer---therefore no signal can get through.
that is why the coupling capacitor is needed. Again, it is shown on all the circuit diagrams that were posted or referenced.

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 Post subject: Re: Westinghouse model 801 grandfather clock radio.
PostPosted: Sep Sun 29, 2019 8:56 pm 
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In particular, read this again---and tell me which parts you do not understand

pixellany wrote:
Let's review how these things work:
Start with a simple broadband amplifier. The driving tube has a resistor in the plate circuit, and the next stage tube has a resistor in the grid circuit. Both act to set up the DC operating point for the 2 tubes.
The signal is coupled from one stage to the next with a capacitor (from plate of tube #1 to grid of tube #2)

One limitation of this basic circuit is the DC voltage drop in the plate circuit. This means that you can't always get the desired operating point for the tube, and therefore performance is compromised.

The solution is a transformer. Now we can independently set the DC operating point, and have the impedance determined by the transformer ratio and the load presented by the 2nd stage.

But, what if we want the circuit to be tuned? For starters, we can just replace the plate resistor with a tuned coil. The DC resistance (low) allows more freedom in setting up the tube bias, and we can now tune for a specific frequency. In "filter language", we now have a single-pole bandpass filter.

But--how about just tuning that transformer? If the primary and secondary are both tuned, now we have a two-pole bandpass filter. This will have a sharper response than the single-pole version. It can also be "stagger-tuned" to give more control over the bandpass shape.

But---back to the case with the single coil. We CAN put the coil in the grid circuit of the 2nd stage. BUT--now we're stuck with the plate resistor that will reduce the Q of the tuned circuit. You can mitigate this somewhat by using a very small coupling capacitor. This however reduces the overall gain.

This little ramble might convince you to get a working transformer---or maybe to learn the SPICE program, and do some simulations. My guess is that--if you only have one tuned coil--you want it in the plate circuit of the 1st stage.

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 Post subject: Re: Westinghouse model 801 grandfather clock radio.
PostPosted: Sep Sun 29, 2019 10:12 pm 
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So you are saying change the working coil over to the primary and use the resistor on the secondary.


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 Post subject: Re: Westinghouse model 801 grandfather clock radio.
PostPosted: Sep Mon 30, 2019 12:14 am 
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correct, but the resistor might no be required. As a minimum, it will be a different value. After you have read everything, this may become clearer.

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"Measure voltage, but THINK current." --anon.


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 Post subject: Re: Westinghouse model 801 grandfather clock radio.
PostPosted: Sep Mon 30, 2019 12:19 am 
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So the secondary might not even be required.


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 Post subject: Re: Westinghouse model 801 grandfather clock radio.
PostPosted: Sep Mon 30, 2019 12:58 am 
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spsquires wrote:
So the secondary might not even be required.

If you use the secondary winding in the plate circuit, then there NO winding on the "secondary" side. After you read everything, this may be clearer.......

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 Post subject: Re: Westinghouse model 801 grandfather clock radio.
PostPosted: Sep Mon 30, 2019 1:05 am 
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What I meant was the resistor becomes the secondary.


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 Post subject: Re: Westinghouse model 801 grandfather clock radio.
PostPosted: Sep Mon 30, 2019 12:20 pm 
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spsquires wrote:
What I meant was the resistor becomes the secondary.

That does not make sense....with just one winding, there is no longer a transformer, so you no longer have a primary or secondary. If you try my suggestion you put the good winding in the plate circuit, and then you add a coupling capacitor to the next stage. Assuming there is already a bias resistor, then there is no need to add a resistor.

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 Post subject: Re: Westinghouse model 801 grandfather clock radio.
PostPosted: Sep Mon 30, 2019 7:52 pm 
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So connect the two wires from bad winding to good winding and the two wires from good winding to bad winding and add a capacitor between these two wires.


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 Post subject: Re: Westinghouse model 801 grandfather clock radio.
PostPosted: Sep Mon 30, 2019 9:32 pm 
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Connect the good winding in the plate circuit---as shown in the various diagrams in this thread.

Connect the plate through a small** coupling cap to either the grid of the following stage or the anode of a diode if the stage is the 2nd detector. in the case of the 2nd detector, also connect whatever WAS connected to the bottom of the IF secondary. (this is the nodes that feeds the audio stages and the AGC bus.

**I can't tell you the right value---earlier I suggested that 200pF might be too large. You simply have to find what works.

Another thought: I think this solution may be better when it is not driving the 2nd detector---ie it may work better in a postition that just drives a tube.

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 Post subject: Re: Westinghouse model 801 grandfather clock radio.
PostPosted: Oct Tue 01, 2019 12:44 am 
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I will try and get back at radio in a day or so.


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 Post subject: Re: Westinghouse model 801 grandfather clock radio.
PostPosted: Oct Mon 07, 2019 5:34 pm 
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I connected the good winding to the primary side of IF can but not sure where to connect cap has I tried the radio without and nothing.


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 Post subject: Re: Westinghouse model 801 grandfather clock radio.
PostPosted: Oct Mon 07, 2019 7:49 pm 
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pixellany wrote:
Connect the good winding in the plate circuit---as shown in the various diagrams in this thread.

Connect the plate through a small** coupling cap to either the grid of the following stage or the anode of a diode if the stage is the 2nd detector. in the case of the 2nd detector, also connect whatever WAS connected to the bottom of the IF secondary. (this is the nodes that feeds the audio stages and the AGC bus.

**I can't tell you the right value---earlier I suggested that 200pF might be too large. You simply have to find what works.

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"Measure voltage, but THINK current." --anon.


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 Post subject: Re: Westinghouse model 801 grandfather clock radio.
PostPosted: Oct Mon 07, 2019 8:07 pm 
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Got it hooked up but would not work without resistor. I got so so volume but noticed the volume control is only making any volume on the last quarter turn of control. First 3/4 of volume has no affect at all.


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 Post subject: Re: Westinghouse model 801 grandfather clock radio.
PostPosted: Oct Mon 07, 2019 9:14 pm 
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Also the volume control is supposed to be 6000 ohms . So to test it properly it has three wipers so you measure across the outside two to get reading but does it be done with volume high or low and does it have to be disconnected from circuit?


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 Post subject: Re: Westinghouse model 801 grandfather clock radio.
PostPosted: Oct Mon 07, 2019 9:41 pm 
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Please post a drawing or schematic markup to show how you have the transformer windings and capacitor wired.

Volume control: measure resistance between the 2 ends, and then from one end to the wiper. Verify that it changes smoothly as you turn the control

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"Measure voltage, but THINK current." --anon.


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 Post subject: Re: Westinghouse model 801 grandfather clock radio.
PostPosted: Oct Mon 07, 2019 10:16 pm 
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The volume is good and the if is wired like sketch on page 5


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 Post subject: Re: Westinghouse model 801 grandfather clock radio.
PostPosted: Oct Mon 07, 2019 10:29 pm 
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That does not match what we have discussed. if the good winding is on the primary side, you do not use the resistor.
Also, you would only have one winding connected..
I also want to see exactly how it is connected on the output side--including the grid bias resistor for the next tube.

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"Measure voltage, but THINK current." --anon.


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