Marks resistor wattage video ?

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audiofanman
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Joined: Wed Feb 24, 2021 11:19 pm
Location: Suffolk County - Long Island, NY

Marks resistor wattage video ?

Post by audiofanman »

I have been (Like Many) digesting Marks videos for months now.
I think I remember one where he is walking trough a schematic, but starting talking about wattage ratings on resistors in schematics...
Does anyone know which one that was ??

Im piecing together a BOM for an upgrade on my Yaqin MC-200B. Posts on the I-way and schematics show the 12AT7 Cathode resistor R3 (pin 3) was upped from 510 Ohm's to 560 on the MC-300C model (newer and most say better).
Also the Data sheet at https://frank.pocnet.net/sheets/093/1/12AT7.pdf
shows typical cathode bias resistor at 570 ohms...

My problem is Im not 100% sure of how much heat may be there.
My guess (Trying my ee legs on for the first time lol)
1 is its a cathode bias resistor (to be sure!) at .5 watt.
2 it looks to me as its elevating the cathode above ground
What I listen with.... Elsinore's, Yaquin MC-13S / EL34 - MS-300B, My pile of schitt :lol: Mani, Loki, Modi Multibit. Audio-Technica AT-LPW40WN/AT-VM95SH/H, R PiCore/LMS + Digi
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mgalusha
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Re: Marks resistor wattage video ?

Post by mgalusha »

I don't know which video it is but you can use a little math to figure it out pretty easily if you know the B+ voltage and plate resistor. If say, you had 300V and a 30k plate resistor with a 570R cathode resistor, assume the tube is passing 100% of the current, it won't of course but it makes it easier if we assume this. The total current through the circuit would be 9.8mA (I = 300/30570) and the calculating the voltage at the junction of the two resistors (vout = vin(r2/r1 + r2)) you get 5.59V, so the bottom resistor is dissipating .055W, almost zero heat. HTH.
audiofanman
Posts: 24
Joined: Wed Feb 24, 2021 11:19 pm
Location: Suffolk County - Long Island, NY

Re: Marks resistor wattage video ?

Post by audiofanman »

Thanks!
I think I got it...
My B+ was much more, but adding the resistors in series before the plate resistor and your run through
got me close enough to place my order....
What I listen with.... Elsinore's, Yaquin MC-13S / EL34 - MS-300B, My pile of schitt :lol: Mani, Loki, Modi Multibit. Audio-Technica AT-LPW40WN/AT-VM95SH/H, R PiCore/LMS + Digi
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