[ARC5] Brian's deaf set. Has a 12SK7.

[AKLDGUY .]

Pin #4 is not unused. It is the Grid 1 pin. We are talking about the
BC-454, which uses a 12SK7 at the second IF amp, not the AN/ARC-5 which
uses the 12SF7.

73 de Neil ZL1ANM


On Thu, Sep 29, 2016 at 10:15 AM, Leslie Smith <vk2bcu at operamail.com> wrote:

>   Hello Neil,
>   Looks good to me!  The problem appears to be AFTER G1 of the second IF
> tube (or in the PSU supplying the set).
>
>
>    73 de Les Smith
>    vk2bcu at operamail.com
>
>
>
> On Thu, Sep 29, 2016, at 06:11, AKLDGUY . wrote:
>
> I was under the impression that the problem was determined to be between
> the grid of the second IF amp and the audio output, because Brian said this:
>
> "For instance, when I apply 1 V of 1415 kHz 30% modulated by 400 Hz to pin
> 4 of the 2nd IF amplifier, I get 4.6 mW AF output; the op and maintenance
> manual says that 110 mV should give 10 mW AF out. So, attenuation is 10 log
> 10 / 4.6 + 20 log 1000 / 110 = 3.37 + 19.17 = 22.5 dB down."
>
> In that case, I question the need to remove the RF cover and check the
> front end tuning. Or have I misinterpreted something? The method of
> calculation of 22.5 dB looks correct to me, although I haven't checked the
> actual figure.
>
> Brian, have you retained the 15 uF bypass capacitor at the 12A6 cathode,
> or have you replaced it?
>
> 73 de Neil ZL1ANM
>
>
> On Thu, Sep 29, 2016 at 3:21 AM, Bill Cromwell <wrcromwell at gmail.com>
> wrote:
>
> Hi,
>
> The question about the tuning is still going begging. If you haven't
> looked at the tuning caps you do not know if the tuning peak is achieved at
> the limit of the cap's range. It may be this is okay but what if it would
> peak higher except there is no further adjustment available from the cap.
> If the cap is at maximum position further adjustment makes the detector
> voltage recede again - just like normal, 'good' tuning. The same applies to
> the minimum position. The cap is good but the tuned circuit overall is not.
>
> The devil is always in the details.
>
> good luck and 73,
>
> Bill  KU8H
>
>
> On 09/28/2016 05:04 AM, Brian wrote:
>
> Hello folks,
> I am most grateful for all the suggestions you have been putting forth.
> As Les has divined, I am rather busy at present - so I can't do much till
> the weekend.
> Some clarification seems to be required. This is a bog-standard BC-454-B.
> All the tubes are warm. All the base Voltages are what I would expect. I
> did feed signals to pin 4 of the IF amplifier tubes, 12SK7s.
> As all the IFTs peak up, then the trimmer caps are OK, as I suspect are
> the coils in the IFTs. I have yet to remove the cover over the variable
> tuning capacitor. But as the padders and trimmers there all have the
> required effect, I don't think the problem is there.
> I hope to do some serious signal injection - but over the weekend.
> In the meantime, keep your suggestions flowing.
> 73 de Brian, VK2GCE.
>
> On Wednesday, September 28, 2016 9:51 AM , you said:
>
> Hello All
> I had an (off-group) reply from Brian a few days ago.
> I intended ringing him; but it seems (from what he said privately) -
> he's up to his ears with work and other private matters at the moment.
> Sometimes life gets so busy that radio drops into the background.
>
> 73 de Les Smith
> vk2bcu at operamail.com
>
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