[ARC5] BC-453 drift test

[Tom Lee]

That sounds like great advice, Bill. Operating at the lowest practical 
B+ would cut the temperature rise, and that should reduce both the time 
to stabilize, and the total drift.

Tom

-- 
Prof. Thomas H. Lee
Allen Bldg., CIS-205
420 Via Palou Mall
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu
650-725-3383 (public fax; no confidential information, please)

On 1/10/2018 8:01 PM, Bill Cromwell wrote:
> Hi J,
>
> I think you said you are running the receivers on something over 200 
> volts B+. Reducing that will help with the receivers stabilizing a 
> little sooner and maybe reducing the 'drift' a little bit more. It 
> will certainly reduce power consumption. I would recommend dropping B+ 
> to no more than 180 volts. I run mine at about 90 volts. When I get 
> down tp 45 volts the performance starts dropping off noticeably. It 
> would probably work on much lower B+ *IF* circuit adjustments were 
> made. Further reduction of 'drift' is probably not much of an issue if 
> you are already able to 'decode' WSPR.
>
> Enjoy your radio.
>
> 73,
>
> Bill  KU8H
>
> On 01/10/2018 09:23 PM, J Mcvey via ARC5 wrote:
>> No, most of those tank caps are mica. Generally they are usually OK.
>> They don't leak but when they are  bad, they will either be intermittent
>> ( silver migration), or shorted.
>> The standard operating procedure is to change all of the paper and
>> electrolytic caps in the "cans" . I cut them open with a pipe cutter,
>> gut the contents and replace with either mylar or ceramics. The
>> electrolytic cans get 105 degree types inside. Then I solder the can
>> back together. looks like it never happened except for the thin band of
>> solder.
>> Hot air soldering makes the band almost disappear.
>> Those bypass caps that I replaced are ALWAYS leaky and will mess with
>> the tube biases, etc
>>
>>
>> On Wednesday, January 10, 2018 8:59 PM, Tom Lee <tomlee at ee.stanford.edu>
>> wrote:
>>
>>
>> Yes, WSPR is definitely more challenging!
>>
>> The capacitors you changed -- I assume that a couple were part of the LO
>> tank (say, C-8 and C-10 in the schematics I have). Is that right, or did
>> changing others reduce the drift? I'm curious...
>>
>> Tom
>>
>> -- 
>> Prof. Thomas H. Lee
>> Allen Bldg., CIS-205
>> 420 Via Palou Mall
>> Stanford University
>> Stanford, CA 94305-4070
>> http://www-smirc.stanford.edu <http://www-smirc.stanford.edu/>
>> 650-725-3383 (public fax; no confidential information, please)
>>
>> On 1/10/2018 5:24 PM, J Mcvey wrote:
>>> The test was done at a more or less arbitrary frequency. The LO
>>> started at 540Khz and ended up at 539.300Khz give or take a few hz.
>>> So, yes that would be about 0.13%.  However 700Hz and 1Hz/second  is a
>>> big deal with WSPR! Once it settles down, I can decode WSPR, though.
>>> The radio stabilizes faster now that the caps were all replaced. It
>>> used to take twice as long to get there. Going to give a try again
>>> tonight.
>>>
>>>
>>>
>>>
>>> On Wednesday, January 10, 2018 7:48 PM, Tom Lee
>>> <tomlee at ee.stanford.edu> <mailto:tomlee at ee.stanford.edu> wrote:
>>>
>>>
>>> Without knowing the LO frequency it's hard to give a precise answer,
>>> but that warmup drift represents roughly a couple tenths of a percent
>>> at midband. That sounds reasonable, as does the warmed-up drift. The
>>> dropping in frequency during warmup is consistent with the inductor
>>> and capacitor expanding as it heats up (L and C both increase under a
>>> linear expansion), so it makes sense.
>>> -- 
>>> Prof. Thomas H. Lee
>>> Allen Bldg., CIS-205
>>> 420 Via Palou Mall
>>> Stanford University
>>> Stanford, CA 94305-4070
>>> http://www-smirc.stanford.edu <http://www-smirc.stanford.edu/>
>>> 650-725-3383 (public fax; no confidential information, please)
>>> On 1/10/2018 3:45 PM, J Mcvey via ARC5 wrote:
>>>> I recapped this radio and tested the LO drift afterwards.
>>>> Coupling the plate via 7pf cap and a x10 scope probe to a frequency
>>>> counter, the results were as follows:
>>>> The LO dropped in frequency at a rate of about 1 HZ / second upon
>>>> power up.
>>>> The drop rate slowed until it more or less stabilized an hour later
>>>> 700 Hz lower than the start up
>>>> measurement.
>>>> Once at the bottom of the descent, it would sit and go up and down a
>>>> couple of Hz in a very slow undulation.
>>>>
>>>> I guess this a normal warmup scenario? What say you?
>>>>
>>>>
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>>
>>
>>
>>
>>
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