Re: TR-4 Resistance Chart
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Can a 10 Meg input impedance HP DVM be used to measure these resistances? That input impedance spec is the same as what I have seen listed for some VTVMs but I have experienced a number of resistance values be way off from what is in the Drake chart. Some are high and some are low. I assume that most of the high values are from component drift, some differences are obvious errors in the chart, but some I just can't explain. Bill N0CU
Yes, it's 330K (orange, orange, yellow).
Thanks,
Barry - N4BUQ
> Can you read the value on the resistor itself?
>
> Gary
>
> W0DVN
>> On Apr 14, 2025, at 8:18?AM, n4buq <n4buq@...> wrote:
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>> ?I discharged C145B by shorting the end of R125 that's connected to it (the +245
>> ?rail) to ground.? With V7 in or out, I get the same value of about 355K at Pin
>> ?7.
>>
>> Thanks,
>> Barry - N4BUQ
>>
>>> Yes, I'm measuring from V7 pin 7 to ground.? I'll fully discharge C145B and
>>> check again.? I think I measured it with and without the tube.? I'm not sure I
>>> see how having the tube in or out would make a difference but I'll make sure to
>>> measure it both ways and report back.
>>>
>>> Thanks,
>>> Barry - N4BUQ
>>>
>>>> Are you measuring from V7 pin 7 to ground? The other end of R115 goes to the 245
>>>> volt line. That can complicate the measurement if the supply capacitor is not
>>>> fully discharged. Also, try the measurement with V7 removed.
>>>>
>>>> Gary
>>>>
>>>> W0DVN
>>>>>> On Apr 13, 2025, at 12:59?PM, n4buq <n4buq@...> wrote:
>>>>>>
>>>>>> ?I started checking the resistance values in my TR-4 and found that Pin 7 of V2
>>>>>> ?is around 355K.? The value in the chart is 246K and I'm wondering how that's
>>>>>> ?possible.? Pin 7 has a 330K and a .005uF connected to it so I can't see how
>>>>>> ?that can be 246K.? Is that a typo and should've been 346K?
>>>>>>
>>>>>> I know the values aren't meant to be taken as exact but, unless R125 is under
>>>>>> it's designated value, I can't see how it could be less than 330K but perhaps
>>>>>> I'm missing something about this circuit.
>>>>>>
>>>>>> Thanks,
>>>>>> Barry - N4BUQ
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