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General Vintage Technology Discussions For general discussions about vintage radio and other vintage electronics etc. |
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12th Feb 2021, 1:31 pm | #41 | ||
Hexode
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Re: Vintage tube mixer input impedance
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12th Feb 2021, 1:46 pm | #42 | |
Dekatron
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Location: Cornwall, UK.
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Re: Vintage tube mixer input impedance
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The energy in the reservoir capacitor is what keeps the stages working when the rectifier isn't conducting, the rectifier only conducts for a fraction of the +ve half cycle of its supply voltage. Lawrence. |
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12th Feb 2021, 2:24 pm | #43 | ||
Hexode
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Re: Vintage tube mixer input impedance
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12th Feb 2021, 2:29 pm | #44 |
Dekatron
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Re: Vintage tube mixer input impedance
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12th Feb 2021, 2:36 pm | #45 |
Hexode
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Re: Vintage tube mixer input impedance
ok... i am really confused... i donno anymore
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12th Feb 2021, 2:54 pm | #46 |
Dekatron
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Re: Vintage tube mixer input impedance
Often (but not always) with a filter resistor connected to the cathode and the reservoir capacitor that junction would be used to feed a power output stage, not a stage that would feed into another stage of amplification, that's because of the relatively high level of ripple voltage present across the reservoir capacitor.
Lawrence. |
12th Feb 2021, 3:03 pm | #47 | |
Hexode
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Re: Vintage tube mixer input impedance
Quote:
This I understand... but that capacitor pin which is only connected to the cathode of the 6x4 and nothing else... that is where I am lost at and getting confused which pin of the cap is the reservoir cap is it that one? but that is not connected to the 4k resistor here at all.. i am really sorry i think I do your head in with this... ...the reservoir cap is only used here to store energy straight from the rectifier and nothing else... ? Last edited by Levente; 12th Feb 2021 at 3:17 pm. |
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12th Feb 2021, 3:26 pm | #48 | |
Dekatron
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Re: Vintage tube mixer input impedance
Quote:
Again it looks to me that circuit wise the 4k resistor is connected between two of the capacitors in the can, one of those capacitors being connected to a 4.7k resistor and a circuit feed and the other capacitor being connected to the cathode of the rectifier. The reservoir capacitor is the one that's connected to the cathode, the 4k (as connected) is a filter resistor and the other capacitor it's connected to is a filter capacitor. Lawrence. |
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12th Feb 2021, 3:44 pm | #49 | ||
Hexode
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Re: Vintage tube mixer input impedance
Quote:
the 4 k resistor is only connected to the triangle pin and the rectifier the "-" pin of the cap is only connected to the rectifier (same where the 4k is) the triangle pin is connected to the OT and the 4,7k resistor and then the rest i did not display as it is not important for now... |
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12th Feb 2021, 3:50 pm | #50 | |
Dekatron
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Re: Vintage tube mixer input impedance
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Plenty of tutorials etc on the internet about this. Lawrence. |
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12th Feb 2021, 4:14 pm | #51 | ||
Hexode
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Re: Vintage tube mixer input impedance
Quote:
Thank you, understood, also looking at it on line of course. Considering the above explained, in my mixer, the reservoir cap is not connected properly, left out of the circuit right? according to the drawing i made earlier... Levente |
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12th Feb 2021, 4:27 pm | #52 | |
Dekatron
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Re: Vintage tube mixer input impedance
Quote:
In your layout connection sketch and photos the cathode of the rectifier is connected to a capacitor, that capacitor is the reservoir capacitor. Lawrence. |
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12th Feb 2021, 4:30 pm | #53 | ||
Hexode
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Re: Vintage tube mixer input impedance
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Levente |
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12th Feb 2021, 4:35 pm | #54 | |
Dekatron
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Re: Vintage tube mixer input impedance
Quote:
Lawrence. |
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17th Feb 2021, 5:28 pm | #55 | ||
Hexode
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Re: Vintage tube mixer input impedance
Quote:
Finally I did manage to measure the mystery component pictured earlier: Measuring only 7.4 Ohms and just out of curiosity measured the capacitance and reads about 92uF. I wonder what this could be? A capacitor or a resistor... Surprisingly there are only a few out of spec's parts found... that very first burning 4k reads 5.4k, the second filter can capacitor (20uf+20uf) is dead. No capacitance can be measured. There is also one resistor, the plate resistor of 12au7, which supposed to be 50k according to the color code but measures only 36k. Can a resistor drift downwards and not upwards? I attached a pic from that resistor in question. Thanks a lot again for your input and great help as always I simply can not thank enough for this forum and you... |
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17th Feb 2021, 5:35 pm | #56 |
Dekatron
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Re: Vintage tube mixer input impedance
The grid should have a DC path to ground, my 1st guess would be that the mystery component is an inductor.
A 50k resistor going down to 36k would be unusual in my experience, did you measure it out of circuit? Lawrence. |
17th Feb 2021, 6:02 pm | #57 | |
Hexode
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Re: Vintage tube mixer input impedance
Quote:
With regards the resistor, i removed it from circuit and measuring 36 kOhm on the dot. Not sure... the color coding calls for 50k unless mislabeled in the factory (?). |
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17th Feb 2021, 6:07 pm | #58 |
Dekatron
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Re: Vintage tube mixer input impedance
That's a possibility.
Usually resistors of that kind of value go high rather than low. Lawrence. |
17th Feb 2021, 6:18 pm | #59 |
Hexode
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Re: Vintage tube mixer input impedance
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17th Feb 2021, 6:25 pm | #60 | |
Dekatron
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Re: Vintage tube mixer input impedance
Quote:
If you have the time try and reverse engineer a schematic for your mixer. Lawrence. |
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