So are you saying the level of hum reduction depends only on the winding ratio and is independent of the current through the compensation winding? Doesn't seem right....
As an aside, that amp is very quiet as originally configured - great engineering for what was a cheap product back in the day...
Think about it. It's really not that hard. Hint: It's not the DC current, but the hum current that counts.
Best regards!
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There is no significant hum even in a cheap radio amp with low value capacitors that you need to cancel it ... and there are other ways of injecting ripple if you really need that .
Without reading a technical document obout this I would rather think that the winding is for reducing the DC flux in a tiny cheap SE transformer so it can sound louder without nasty saturation distortions . Doing so will reduce costs in iron and copper , this is a good reason for a manufacturer , not that you could hear some little hum .
Without reading a technical document obout this I would rather think that the winding is for reducing the DC flux in a tiny cheap SE transformer so it can sound louder without nasty saturation distortions . Doing so will reduce costs in iron and copper , this is a good reason for a manufacturer , not that you could hear some little hum .
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Yes the DC flux reduction is something I already explained to Zilch on another forum. That will depend on the current in the "compensation" winding.
But surely there will also be some cancellation of ripple because the primary and compensation windings are opposite?
When I have a gap i will bypass those windings and see if there is any difference in hum. When I say that radio is quiet, i mean amazingly quiet from a hum point of view - quieter than my already-quiet EL84 amp with a really good power supply including a big choke
Maybe is doing something cancelling the hum or maybe not . If this is the role why they didn't use it in amplifiers ?
Hum cancellation is as easy as the following: Ripple current is injected into the OPT at the Eb terminal and is divided into two branches: The, let' say, upper one flows through the main primary winding and the tube's internal plate resistance to the cathode which is virtually grounded by the RC combination. The lower one flows through the cancellation winding and the filter resistor to the filter capacitor, which also forms a virtual ground. This part is in opposite phase with the upper one, as the helper winding is wound in the same direction as the main primary. Conclusion: Hum gets cancelled if the ripple current through the tube's resistance times the primary turns number equals the ripple current through the filter resistor times the helper winding turns number.
Isn't it really easy?
Best regards!
Isn't it really easy?
Best regards!
The windings and currents are not the same ... and significantly tilted towards the primary side . The extra windings has few turns and the current is just for G2 and the rest of radio tubes .
The hum cancellation works via the screen grid.
G2 modulation in opposite phase.
Best regards
Philipp
G2 modulation in opposite phase.
Best regards
Philipp
Not convincing at all ... the schematic normally is with that extra winding and a series resistor entering G2 ... but with a filter cap directly on G2 to ground , like in any basic amplifier the G2 is decoupled .
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Remember we're talking about ripple, which is AC.
Anyway, your remark proves that this extra winding doesn't significantly contribute to reduce flux.
Best regards!
If I understand your conclusion correctly, it states that hum gets cancelled if the ripple current through the primary times the primary turns equals the ripple current through the helper winding times the helper winding turns (since the ripple current through the resistance of the tube equals the ripple current through the primary and the ripple current through the filter resistor equals the ripple current through the helper winding).
In post #39 you wrote:
"Instead, the winding ratio of primary and comp must equal the ratio of the tube's internal plate resistance and the filter resistor value."
Your conclusion being as it is, why than do the values and the ratio of the filter resistor and the resistance of the tube matter for the correct working of this anti-hum provision?
Ofcourse the resistance of the tube is there anyway. But I would think that it is possible to achieve a certain amount of ripple current in the anti-hum winding without having to use a filter resistor. So than why does the filter resistor has to be there and why does it have to have a certain value?
The time to edit my post was expired so a new one.
The coin in my machinery drops slowly. By now I start to doubt if it is possible to leave the filter resistor out if the number of turns of the anti-hum winding is relatively low. But I'm still not there completely yet....
I'm happy for Kay that this is really easy for him. Probably this means that many things are really easy for Kay and that because of that he hardly makes mistakes, or?
The coin in my machinery drops slowly. By now I start to doubt if it is possible to leave the filter resistor out if the number of turns of the anti-hum winding is relatively low. But I'm still not there completely yet....
I'm happy for Kay that this is really easy for him. Probably this means that many things are really easy for Kay and that because of that he hardly makes mistakes, or?
I must repeat that this radios have filters like 100uF input then 50uF for G2 and probably another 50uF for small tubes . This is decent even for an amplifier ... of course we are not talking about hi-fi here .
And many radios don't have that winding , there is somebody who claimes that those have a disturbing level of hum ? To claim an effect there must be a cause first .
The resistor ( in Kohm range ) in series with the winding is mandatory , otherwise that winding just sitting between 2 filter caps would be a short for AC audio. The resistor is of course calculated like a RC filter for G2 , like in a normal amplifier .
And many radios don't have that winding , there is somebody who claimes that those have a disturbing level of hum ? To claim an effect there must be a cause first .
The resistor ( in Kohm range ) in series with the winding is mandatory , otherwise that winding just sitting between 2 filter caps would be a short for AC audio. The resistor is of course calculated like a RC filter for G2 , like in a normal amplifier .
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Well, it really isn't my personal issue if your coins are dropping slowly 🙄.
Best fegards!
I agree the filter capacitor doesn´t help regarding this funciton.
However I was referring to this circuit example from a German standard textbook about radio electronics.
In the description it says that even the remaing ripple voltage counteracts via screen grid modulation.
Best regards
Philipp
However I was referring to this circuit example from a German standard textbook about radio electronics.
In the description it says that even the remaing ripple voltage counteracts via screen grid modulation.
Best regards
Philipp
Attachments
Unfortunately your schematics doesn't read the »AÜ«'s (= OPT's) turns numbers. Hence we can't do the math.
Best regards!
Best regards!