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

[J Mcvey]

The question is if he "got onto" an actual injection point at pin #4. The manual shows pin #4 as unused.If that's the case, the signal would be injected by stray capacitance , causing severe attenuation as reported.
It's also possible that his description was a typo.The mystery continues...
 

    On Wednesday, September 28, 2016 4:12 PM, AKLDGUY . <neilb0627 at gmail.com> 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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