I have two ZENITH sets, one is a J-733 & the other is a ZENITH Y-724. I love working on mechanical things & this I ran across. The J-733 is a normal looking ANT. section stator. The inside of the loop goes to the 12AT7 tube & then to the stator sec. of the tuner. The Y-724 has a different set-up. The inside of the loop goes to the 12AT7 tube & then to the stator sec. of the tuner ---- get this ---- through a .047 condenser. Now in checking the part nos. of the tuners of both sets they ARE the same. My friend tells me that when you put two condensers in series the total capacity is less than the smallest one. Is this true? Both sets are AM-FM, both use the same input tube, both have loop antennas, both have the same part nos. on the tuners. So why did ZENITH make this BOO-BOO? The reception on FM on the Y-724 is real good but needs alignment-there are TWO peaks, not the usual low-high-low signal. The AM is litterly piss-poor unless a local station is tuned in. The low end signal gets better as the dial is moved upwards. There are 3 stations from the same town, one is at the extreme low end-one is up a little bit & the other is up a little bit more. Also on the old ZENITHS does the tuner CAM on FM slugs need to be adjusted to make the dial track differently? The FM stations are beyond the markings on the low side on the low end & the high side on the high end. Also can an AM signal generator be used to align up an FM set? My friend DOES NOT have a sweep & marker generator. How good of a job can be done with an AM generator on FM? Can just the IF's be aligned or can the stations be done also? What is a limiter, discriminator & a ratio detector for?. I need some help on this one!! What is a sweep & marker generator??

Recall that the tuning cap has to tune the loop antenna to resonance. It may be that Zenith changed the inductance of the loop antennas from one model to another (by changing the diameter of the loop, number of turns, or wire diameter), and found the easiest way to accommodate this was to insert a fixed capacitor in series with the variable cap to enable achieving resonance across the band.

Often there is a variable padder in series with the main tuning cap to accommodate "manufacturing variability". If the set is built with sufficient precision, this adjustable padder may be unnecessary. Or maybe these were just "el cheapo" sets and Zenith didn't give a hoot that they had poor dial tracking or lacked sensitivity at one end of the band or the other. In a "competitively priced" set, great attention was paid to eliminating superfluous or marginally-useful parts, so the presence/absence of a part between two similar models may reflect either a cost-saving change or an engineering fix to solve a problem.

:Recall that the tuning cap has to tune the loop antenna to resonance. It may be that Zenith changed the inductance of the loop antennas from one model to another (by changing the diameter of the loop, number of turns, or wire diameter), and found the easiest way to accommodate this was to insert a fixed capacitor in series with the variable cap to enable achieving resonance across the band.
:
:Often there is a variable padder in series with the main tuning cap to accommodate "manufacturing variability". If the set is built with sufficient precision, this adjustable padder may be unnecessary. Or maybe these were just "el cheapo" sets and Zenith didn't give a hoot that they had poor dial tracking or lacked sensitivity at one end of the band or the other. In a "competitively priced" set, great attention was paid to eliminating superfluous or marginally-useful parts, so the presence/absence of a part between two similar models may reflect either a cost-saving change or an engineering fix to solve a problem.
: Thanks so very much for responding. I know nothing about electronics but I am learning on this web site. You people could give me an education. My friend knows a LOT more but we don't get together too much. He is ALWAYS busy!

::Recall that the tuning cap has to tune the loop antenna to resonance. It may be that Zenith changed the inductance of the loop antennas from one model to another (by changing the diameter of the loop, number of turns, or wire diameter), and found the easiest way to accommodate this was to insert a fixed capacitor in series with the variable cap to enable achieving resonance across the band.
::
::Often there is a variable padder in series with the main tuning cap to accommodate "manufacturing variability". If the set is built with sufficient precision, this adjustable padder may be unnecessary. Or maybe these were just "el cheapo" sets and Zenith didn't give a hoot that they had poor dial tracking or lacked sensitivity at one end of the band or the other. In a "competitively priced" set, great attention was paid to eliminating superfluous or marginally-useful parts, so the presence/absence of a part between two similar models may reflect either a cost-saving change or an engineering fix to solve a problem.
:: Thanks so very much for responding. I know nothing about electronics but I am learning on this web site. You people could give me an education. My friend knows a LOT more but we don't get together too much. He is ALWAYS busy!
:
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Hi Austin,
I think this was done to keep hot AC off the antenna loop. It was a change in the design, not seen on the earlier T724.

Best regards,

Bill Grimm

........ My friend tells me that when you put two condensers in series the total capacity is less than the smallest one. Is this true?........

Yes but in the case of an 0.047 in series with the tuning cap, the 0.047 is so much larger that the series combination will very close to the tuning cap section alone.

The total capacitance of capitors in series is found by taking the reciprocal of the sum of the reciprocals of the individual capacitances. For two caps in series this works out to the product of the two divided by the sum of the two.