[Hallicrafters] R-274 Sensitivity Testing

[Thomas Hoyer]

Using a Hickok 209A which is surprisingly accurate for its age. My Fluke DVM definitly loads the readings a bit.


I'll see if I can run the tests you suggest tonight.


Thanks, 
Tom



-----Original Message-----
From: Richard Knoppow <1oldlens1 at ix.netcom.com>
To: hallicrafters <hallicrafters at mailman.qth.net>
Sent: Wed, Feb 28, 2018 10:11 am
Subject: Re: [Hallicrafters] R-274 Sensitivity Testing

What are you using to measure stage gain, the meter may be 
loading the stages differently than the one used by Hallicrafters.
     Also, make an old fashioned overall gain measurement, this 
is where you put a specified modulated signal into the antenna 
terminals and measure the audio output.
    Also measure the signal to noise using the old fashioned 
method of a 30% modulated signal. I didn't look at  my copy of 
the handbook but there should be specifications there for this 
test. It will give you a value for a S/N ratio of something like 
10db, the values vary with the receiver. If these come out about 
right there is nothing much wrong.
     The mica caps should be at least as good as the ceramics.

On 2/28/2018 5:11 AM, Thomas Hoyer wrote:
> 
> I have my 274 up and running on all bands now. A couple tube swaps (good for good but one works better the the other....) and a couple capacitor changes.
> 
> 
> In checking the sensitivity I find that while it seems to receive well, the sensitivity is somewhat lacking. A quick check based on the RF stage gain chart in the manual confirmed my suspicions. For example, I need 12uV input to get 10 (-10v actually) across R107 on band 1. This is after alignment per the manual. Walking through the other section confirms that each stage needs more input then shown to get the -10v specified.
> 
> 
> So I decided to back up and check the other sections per the manual. I found just the opposite when checking the 2nd and first 455 IF stage gaines in that I needed less, much less, input to get the specified output.
> 
> 
> Normal Broad, V10-1, calls for 30,000uV to get -10V. I only need to input 12,500uV to get -10v
> V9-1 calls for  3200uV and I input 1100uV to get -10v
> V3-7 calls for 700uV and I only need 260uV.
> 
> 
> These values seem to be way off..... Too much stage gain?
> 
> 
> 
> 
> Going through the second mixer starts to show a possible issue:
> 
> 
> T26-7 calls for 1500uV, but 500uV will get me to -10v
> V6-1 calls for 170uV, but 120uV will get me to -10v
> 
> 
> V3-7 calls for 120uV but I need 220uV to get to -10v. So it looks like this stage has some issue. I went over all of the resistance and voltage checks around V3 and all are well within spec. Most all of the resistors have been replaced through the entire radio as have the capacitors except for the ceramic ones and a couple of the micas that seem to measure fine.
> 
> 
> There are a couple things I'm wondering about (as I bounce around subject areas here), I did replace a couple of the 33pf coupling capacitors between stages. I used mica caps vs the ceramic called for in the parts list. Should I go back to a ceramic? Maybe the mica is messing with the coupling between circuits?
> 
> 
> I did verify that the output of my HP signal generator is correct at the various frequencies and voltages levels specified using my spectrum analyzer.
> 
> 
> Looking for some clues.......
> 
> 
> Tom
> W3TA
> 
> 
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-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL
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