Re: T4XC Meter Problem Setting Bias
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Ferris:
The best way to set the bias is to measure the voltage drop across each cathode resistor after checking the ACTUAL resistance of each of those two resistors (3 in the TR-series transceivers).? Use Ohm's Law to calculate what the current really is in each tube.? The bias?reading is the total of the measured and calculated across each cathode resistor.
The cathode resistors?have probably gone higher than the 15 ohms they were specified?to be.? If they are much above 17 ohms I usually swap them for new 15 ohm resistors, especially if they are more than about 0.2 ohms DIFFERENT.? Then do the above voltage drop test.
As you have?discovered a small magnet can be positioned?to "zero" the meter, then?carefully glued in place, Been there and done that!? if being OFF ZERO bothers you too much.? It might be better, though, to go through the above voltage drop check to set the required 70 mA bias current in a T-4(any) and 100mA in a TR-(any).? Then glue the magnet on to show 70mA? (or 100mA in a transceiver).
73 Peter VE7PS
73 Peter VE7PS
On Sat, Feb 11, 2023 at 3:46 PM Richard Knoppow < 1oldlens1@...> wrote: I would not trust the meter.? Drake used very cheap meters. The pointer may be stuck or the zero may be off.? I don't think these meters have an external zero adjust.??
-------- Original message -------- Date: 2/11/23 3:22 PM (GMT-08:00) Subject: [DRAKE-RADIO] T4XC Meter Problem Setting Bias
The meter needle in my T4XC has a resting stop about a mark or so up from 0. SEE THE ATTACHED PHOTO. This occurs when the rig is both off and on. I have set bias according to the manual; adjusting the pot on the power supply so the needle aligns with the mark above the meter scale. The question: With the meter not resting on 0, is the bias correct if I adjust the power supply pot so the needle is at the mark above the scale, or should I compensate by raising the bias so the needle is on a higher mark on the scale? I tried a little trick by holding a tiny magnet close to the left side of the meter and I can get the needle to 0. Once I remove the magnet, the needle goes back to its place one mark above 0. Not sure if this would be a valid way to set the bias; holding a magnet so the needle is on 0, then adjusting the bias to align with the mark above the scale. 73 Ferris NB6T  .
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