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power switch on the volume control

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schmitt trigger

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Check the note that I've outlined in yellow in the attached schematic.

However, as a youngster, I remember that most, if not all the power switches were indeed integrated into the volume control.

For you old timers: is that how you remember things too?

Anyways, a little trivia; I built almost an identical circuit as shown. But I couldn't get a hold of 35C5 tubes, whereas the 50C5 were fairly common.
Therefore i used the 50C5 and removed the 35W4 rectifier, and substituted it with a selenium rectifier.
That way the total filament voltage matched the household voltage.
 

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BradtheRad

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I remember practically all volume knobs had the on-off switch. It was a contraption sitting inside the metal cover on the potentiometer.
Transistor radios, desk radios, tv's, phonographs.
 

retrogear

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I serviced hundreds of the good old 5 tube AM radios. I can still remember the tubes: 50C5,35W4,12BA6,12BE6,12AV6.
The power switch was always on the volume control. I remember buying controls as a kit that had the option to snap on a power switch on the back.
Maybe the circuit design such as input impedance determines if it would be sensitive to hum ?

Larry G
 

FvM

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"SW should not be mounted on the back of R1" sounds kind of useless for an amplifier with direct mains supply and series connected heaters. With this antique power supply technique, we would also need a "safety" series capacitor in the audio input ground line which further increases hum.
 

retrogear

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Yea with that circuit you'd have to watch the polarity of the AC in or it would have a "tingle" to it. Probably the best would be to have the signal in ground on the chassis and tied to the ground of a three prong AC plug for safety?
 

Orson Cart

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the AC switch on the back of the pot would not meet today's safety standards....!
 

schmitt trigger

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Yea with that circuit you'd have to watch the polarity of the AC in or it would have a "tingle" to it. Probably the best would be to have the signal in ground on the chassis and tied to the ground of a three prong AC plug for safety?
I remember that my grandfather had one of those "table" radios, in a bakelite cabinet with (I guess) bakelite knobs.

Bakelite would break easily, and the volume control had its shaft partially exposed.
I distinctly remember, over 50 years ago, getting zapped by the thing. My grandfather just laughed and told me that I should reverse the plug.
Those days were before polarized plugs.

No consumer safety agencies back then.
 

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it's the metal shaft and can of the pot that make it not met standards these days, you're lucky to have only 115Vac or so, 230-240Vac here...
 

retrogear

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I learned respect when as a young kid I added an external antenna to the clip provided on the back of the radio then tried to adjust it for the best reception while barefoot on a damp basement floor. It knocked me to the ground. Good thing I had a young heart.
 

schmitt trigger

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it's the metal shaft and can of the pot that make it not met standards these days, you're lucky to have only 115Vac or so, 230-240Vac here...
That would be my next question:
I know that transformerless, hot-chassis radios were common in North America.

But what about other parts of the world?
 

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The power switch on the volume pot was almost a necessity as it would force the volume down to 0 before removing power. Certain amplifier configurations, back in the day, would produce a loud thump upon removing power. This "hid" the thump from the user.
 

retrogear

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I thought AC/DC sets would run DC with two 45V batteries giving 90V for plate voltage.
Larry G
 

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