Also, while the type of voltmeter used can radically affect voltage readings, due to the loading effects of low resistance meters, differing ohmmeters should read relatively closely, whether they are VOM, VTVM, DMM etc. as long as they are in calibration. Good DMM¡¯s can offer capability of reading very high and very low resistances not possible with older types of meters, but should still read the same values for given resistances within the range of any given meter type, albeit with fewer significant figures.
Gary?
W0DVN
toggle quoted message
Show quoted text
On Apr 15, 2025, at 6:33?PM, n4buq <n4buq@...> wrote:
?
I wasn¡¯t trying to track down a specific problem. ?I just wanted to perform some cursory checks to see if anything was off-kilter that I might not be aware of and this particular reading puzzled me. ?I¡¯m reasonably certain it¡¯s a mistake in the manual.?
On Apr 15, 2025, at 7:08 PM, Gary Follett via groups.io <xntrick1948@...> wrote:
?
Drake manuals were not free of mistakes, especially in the voltage/resistance charts.
What problem are you having with this radio?
Gary?
W0DVN
On Apr 15, 2025, at 8:54?AM, Bill Leonard N0CU via groups.io <billincolo73@...> wrote:
?
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:
>>
>> ?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
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>
>>>>
>>>>
>>>>
>>
>>
>>
>>
>>
>
>
>
>
