[R-1051] Obscure Spectrum Generator alignment question: A1L2 - 500kc input peaking

[Dennis McLaughlin]

On 08/24/2012 02:27 PM, David Wise wrote:
> [The question is at the bottom.]
>
> My radio's a little hard of hearing at some frequencies.
> I ran it without the RF Amp module, to gain access to the RF Translator,
> so I could measure the "LO" injection levels.  The first mixer (fed by the 1MC
> synthesizer) was fine, but the second and third (fed by the 100kc and 1/10 respectively)
> were low, especially at X.000xMHz.  These synthesizers depend on the Spectrum
> Generator.  Therefore, since it looked easy, even without test fixtures, I decided to evaluate it.
>
> I did have to make one cable: BNC male to Hybrid-D Size 8 Coax Pin Contact.
> Other than that, I used only standard test equipment:
>    Spectrum Analyzer (HP 141T/8553B),
>    Active Probe (HP 1120A),
>    Tracking Generator (HP 8443A),
>    Signal Generator (HP 8640B),
>    Oscilloscope (Tektronix 545 oscilloscope with Type K plugin), and
>    20V power supply, 0.5A or up.
>
> I just put the six-pack on the bench, hooked up +20V and 500kHz, and started probing around.
>
> Since the radio basically worked, I expected to see valid combs at all outputs, and I did.
> However, the bandpass filters had drifted enough to put at least one tooth past -3dB.
>
> After reading old posts by Cecil Acuff, I was worried about damaging the slugs, but
> I had no trouble freeing them; I just kept them wet with Acetone from a dropper for
> a couple minutes and they came loose easily.  I guess they used nail polish.  YMMV.
>
> If my spec-an had an accurate center frequency readout, I'd only need the tracking generator
> to align the 100kc strip, as the three slugs interact.  In my case, the TG furnishes the readout,
> so I'd be using it regardless.
>
> My question is about A2A6A5A1L2, the 500kc input autotransformer on the 100kc strip.
> The manual* says to peak it, but I don't see a peak.  Looking at the schematic, there's no
> cap to resonate against.  Early Frequency Standards had a capacitive output impedance,
> which would reflect over to L2, but all the later ones swamp it with a low-value resistor.
> I'm wondering if this adjustment became obsolete after the early Frequency Standard
> was superseded.
>
> * NAVSHIPS 0967-034-2000, "2N Module Repair".  This is the only procedure I have,
> but it was written when the early Frequency Standard was the only kind out there,
> so the peaking procedure might not be relevant to later assemblies.  There's no information
> in NAVSHIPS 94841A, NAVSHIPS 0967-970-9010, or NAVELEX 0967-LP-970-9010,
> and the R-1051H doesn't have a Spectrum Generator.  Can someone check another manual,
> like maybe the D?
>
> Thanks,
> Dave Wise
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Dave,

Could L2 series resonate with C3 and the lump sum value of the Q1 
trigger amplifier?  C3 looks like it is to big to do this.
I checked mine a while ago.  I had 0.6 v p-p at A1J3 and the signal was 
OK at TP1 so I didn't try to adjust the slug. I will remember the 
acetone trick.  Good one.  I adjusted C301 in the frequency standard 
while the radio was fully assembled with the frequency standard cover 
off.  If I remember right the adjustment was broad and could be adjusted 
with the standard removed from the radio.  The cable and module 
capacitance would not detune T302 (500 khz).  Maybe L2 is the same way.
The 10 mhz adjustment C307 in the frequency standard is quite sensitive 
and could easily be misadjusted.  I made that adjustment with the radio 
fully assembled with the frequency standard cover off.