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The 'hidden' values on tuning dial, e.g. 1630kc

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The 'hidden' values on tuning dial, e.g. 1630kc Empty The 'hidden' values on tuning dial, e.g. 1630kc

Post by Neon27 on Sun Aug 01, 2010 5:33 pm

Good day!

I have a RCA Victor Victrola 65U Radio I'm trying to restore.

It seems as though somebody attempted to restore the poor thing a decade or so ago, and in the process, ruined some of the electrical system and chassis. The Vinyl-player is not the original and the main HV smoothing cap has been replaced affraid

The radio is completely dead - I doubt the power supply is even working. 'Deadness' aside, I'm able to perform the necessary repairs to get it working again, my problem resides in the IF tuning process!

I've managed to tune radios in the past by following the service manual instructions. Unfortunately, the manual I poses has 1. no clear representation of the tuning values on the image of the dial and 2. the radio's tuning dial values were spray-painted over by the person who re-conditioned it last.

I can deduce the location of the 1630kc mark (it's the last one on the dial), and it seems this is the only tuning point required in the tuning process.
The larger issue at hand is distinguishing the exact valve pins to which I need to attach my signal generator (test-oscillator)
In the text it asks for me to: "Connect the oscillator to the I.F. grid" and then "Connect the oscillator to the 1st Detector grid"

The layout and schematic representation of the tubes is as follows, in order from the antenna side:
12SA7: Converter12SK7: I.F. Amplifier
12SQ7: 2nd Detector-AVC-Audio
50L6-GT: Output

In my assumption, the 1st detector would be the Converter tube (12SA7), but which grid should I use? My guess would be the grid connected to the antenna Shocked
Secondly, Which grid should I use in tuning the IF stage? (12SK7) My guess would be grid_1 - connected to the output of the first I.F. transformer.

Any advice would be highly appreciated by myself and the radio!

Best regards!
Eddie
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Post by Neon27 on Mon Aug 02, 2010 11:49 pm

Here's the link to the schematics...

http://www.nostalgiaair.org/Resources/062/M0015062.htm

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Post by Resistance is Futile on Thu Aug 05, 2010 4:53 am

This is from the web:
Some of the older literature refers to converter/mixer tubes as “first detectors” since some type of detection process is required to extract the intermediate frequency
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Post by Neon27 on Thu Aug 05, 2010 12:41 pm

Thanks for confirming
I've ordered a resister/capacitor kit for this radio on Mouser, so I'm just waiting for the parts to arrive.

I'm also restoring a Silvertone 2015, the electrical system is quite similar in design. The only large difference is the incorporation of an RF amplification tube preceding the Converter.
I actually found it scary how similar the Silvertone was to my Victrola! It even uses the same tubes!

I love how easy it is to fix these old AM radio's, it's a relaxing breath of fresh air. Working with surface-mount boards with a 1000-component count is a HUGE contrast haha!
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