On the schematic, the AVC is at the junction of R10 (1 megohm resistor) and the wire from the bottom of the secondary winding of the 1st IF transformer (the wire color possibly may be black or brown). To double check for the right 1 megohm resistorjunction, just measure the resistance from the 6K7 grid cap to the 1 meg resistor. You should measure around 7 Ohms resistance. To measure the AVC with the radio on, use a high impedance VOM from that point to chassis. There should be a minus voltage on the AVC which will vary according to the strength of the signal into the radio.

Radiodoc
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:I've been told by I can measure IF Signal Strength my measuring -voltage on my AVC line. Could someone please help me identify it?

On that digital radio alignment trick you've taught me, will a car radio do? I can't see why not.

:Neal: Radiodoc has identified your test points. The AVC bus runs between your converter, IF Amp and detector circuits. The negative avc voltage is used to bias the converter and i-f tubes. That way when you receive a very strong station, a large negative control bias is placed on the r-f tubes that reduces their gain. When you receive a weak station, the opposite is true. When you align the radio using the avc voltage, you are looking for the most negative voltage (strongest reading), regardless of your speaker volume. If you use your speaker output voltage for alignment purposes and you don't have the volume at max, the AVC circuit is working against you by trying to keep all the signals at the same level and it's more difficult to find peak output (avc is constantly adjusting the gain).
:Steve
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Want to go for it ?..... then initially hook DC metering positive lead to ground and connect the negative metering lead to the most accessible point along primary AVC buss [A] . Tune the receiver across the broadcast band spectrum and take note of the highest voltage peaks that you experience when peaking on each station. Take note of the strongest station reading presented. Peak on top of that station again and then take a jumper lead and short secondary AVC buss [B] to ground and take note of the reading now and then peak on the station again.....-6VDC....-8VDC...-12VDC ? ? ?

What you would want to do then is to interpolate 1/4 of that highest voltage attained and establish that as being a safe level to align to.....stable enough to maintain a precise tracking reading and yet be WELL down the gain curve so as to not be having stages going into any clipping onset / compression. The shunting of the sub AVC line [B] relieved the frontal stages of being controlled and their gain is cranked up in this manner.
You now have that AVC reference level established and now you can go back and hook in your RF signal generator for the 455 Kc alignment and then either use its attenuator to bring the previously metered voltage being to that ~ value again, or decouple the gens RF into the front end by incrementally distancing the unit from the unit and then fine tune in the level with the attenuator. Then you drop the tone modulation and solely use un-modulated RF / CW and then go thru the peaking of each IF adjustment and then repeat it again. By now, your voltage observations should have revealed to you how critical an IF tuning adjustment can be on a precise alignment.
If you were having a 5% tuning error initially...plus 4% in the next stage ...plus 7% in another stage and then a final 8% could result in a cascaded ..stage to stage…gain error of getting a mere 105,000 gain as compared to 135,000 when peaked up optimally with metering of the AVC buss.

Finally, strip off the instrumentation and pull the [B] AVC jumper aand do an off the air reception evaluation.

If there was any question of your accuracy of your generators 455 Kc setting , come back and I will clue you in on a final + / - 50 cycles accuracy sources referenced to 455 Kc, without even using your generator.A real bare bones alignment.


Schematic markup:

73's de Edd

gratefully,
Neal
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:I say there Sir Morris:
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:Isn't this the same set that got the filter(s) capac-a-tittors wired in backwards and they were JUST a couple of silly milliseconds from sounding like a bottle rocket taking off ?
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:I have your sets AVC bust......errr...BUSS....reference marked up on the schema provided below.
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:This sets AVC voltage (-negative ) derivation is from the low side of the second IF transformer circuit, and it is then passed down thru a Pi RF and hi freq AF shunt circuit and then exits as the blue green marked [A] buss and it then passes off its audio component just below, to the volume control circuit, and then takes a turn to the left to the R10 AVC resistor which establishes the quiescent designed AVC level to the front end RF tubes and along with its companion AVC filter capacitor, establishes the attack and decay characteristics of the AVC control voltage.
:I haven't kept up with the stages of progress, but if you initially used a tone modulated signal generator and were depenent upon aural dead reckoning peaking up, I see that you then stepped up an echelon by the monitoring of the audio at the speaker.
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:Soooooooo, I guess that the next thing now might be to refine the state of alignment to the effective degree that you can differentiate between a 1/32---64th of a turn of a trimmer adjustments error.
:IF alignment in this manner will require the use of an analog metering mode, as a DVM's multi sampling and its digit bobbling, just doesn't cut it in this procedure. SO, if you don't have such as..... ultimately.... a VTVM, TVM or FET VM..you might also utilize a VOM , hopefully in the 20K per volt DC sensitivity, but I have seen as low as 1K per volt used in old Riders procedures. However, it really does load down the effectively high impedance AVC line and pulls down the available voltage level that you will be reading as a reference, in order to peak at its max negative voltage level possible.
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:Want to go for it ?..... then initially hook DC metering positive lead to ground and connect the negative metering lead to the most accessible point along primary AVC buss [A] . Tune the receiver across the broadcast band spectrum and take note of the highest voltage peaks that you experience when peaking on each station. Take note of the strongest station reading presented. Peak on top of that station again and then take a jumper lead and short secondary AVC buss [B] to ground and take note of the reading now and then peak on the station again.....-6VDC....-8VDC...-12VDC ? ? ?
:
:What you would want to do then is to interpolate 1/4 of that highest voltage attained and establish that as being a safe level to align to.....stable enough to maintain a precise tracking reading and yet be WELL down the gain curve so as to not be having stages going into any clipping onset / compression. The shunting of the sub AVC line [B] relieved the frontal stages of being controlled and their gain is cranked up in this manner.
:You now have that AVC reference level established and now you can go back and hook in your RF signal generator for the 455 Kc alignment and then either use its attenuator to bring the previously metered voltage being to that ~ value again, or decouple the gens RF into the front end by incrementally distancing the unit from the unit and then fine tune in the level with the attenuator. Then you drop the tone modulation and solely use un-modulated RF / CW and then go thru the peaking of each IF adjustment and then repeat it again. By now, your voltage observations should have revealed to you how critical an IF tuning adjustment can be on a precise alignment.
: If you were having a 5% tuning error initially...plus 4% in the next stage ...plus 7% in another stage and then a final 8% could result in a cascaded ..stage to stage…gain error of getting a mere 105,000 gain as compared to 135,000 when peaked up optimally with metering of the AVC buss.
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:Finally, strip off the instrumentation and pull the [B] AVC jumper aand do an off the air reception evaluation.
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:If there was any question of your accuracy of your generators 455 Kc setting , come back and I will clue you in on a final + / - 50 cycles accuracy sources referenced to 455 Kc, without even using your generator.A real bare bones alignment.
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:Schematic markup:
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:73's de Edd
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Feedback pls…..on that old Warhorse….what type of DC metering did you finally use and what was the highest AVC voltage you experienced on your strongest signal in the initial evaluatory metering that I had mentioned? And IF you still remember , its increased value when you shunted the tail of the AVC buss to ground ? I am definitely more likely to know those specs for newer receivers than that one.

73's de Edd

I used a Fluke 117 (VOM) and the highest negative voltage I remember on the AVC line was -58vdc. I haven't gone through the steps you outlined but I am going to align it one more time after I get the last few paper caps replaced and bad wire replaced. I'll use your proceedure as best as I can understand it and give you more feedback at that time.

I used a 2nd harmonic on 910kc to nail down my IF frequency by rocking my signal generator and finding the 'zero-beat'. A proceedure Steve outlined for me. Right now it sounds really good and my SW is lined up great. There is a little room for improvement on BC and I hope to achieve that when I align it next time. Like I say, more feedback after I work my way through the proceedure you gave me.
Neal
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:Feedback pls…..on that old Warhorse….what type of DC metering did you finally use and what was the highest AVC voltage you experienced on your strongest signal in the initial evaluatory metering that I had mentioned? And IF you still remember , its increased value when you shunted the tail of the AVC buss to ground ? I am definitely more likely to know those specs for newer receivers than that one.
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:73's de Edd
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Ahhhh soooo…so it also WAS, well up in the threshold that I am used to seeing on GT and miniature tubed versions of
receivers . That shunting off of the frontal end of the AVC loop such that it will be ill affected by corrective voltage feedback
certainly solves half the problem along with the initial evaluation of the max AVC to be expected and THEN the setting of working alignment input signal level well down the sensitivity curve that I mentioned.


When everyone else is working with those typical 3-6-9-….or run up the flag if you reach 12v……AVC alignment levels, you can be well up from working with a small level ….such that my oft time mentioned 1/32 of a turn of an alignment adjustment can be seen.


With the Fluke “Electricians” 117’s utilization …that’s still an end “digit bobbler”….. versus an analog, but the Flukes minimal invasive loading, along with the higher AVC level present should minimize that metering inconvenience….Me, I’m still a dyed in the wool analog metering freak for tuning procedures. However, for the reading out or setting to 4.9999---5.0001 VDC, gimme the Fluke….. Duke! ...BUT…who has to set voltages to those exacting extremes, unless it would be a calibration lab ?



73's de Edd