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Fine tune condenser?
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Author:  radionut [ Dec Fri 21, 2018 4:20 am ]
Post subject:  Fine tune condenser?

Hi Folks, recently acquired a mid 30's Admiral tombstone,made by Continental radio corp.. The tuning condenser is stumping me as to how it works with a set of auxiliary tuning fins. It has a smaller set of fins opposite of the main tuning condenser. Take a look at the pics. The dial has the standard broadcast and short wave ,but has a 10 thru 100 section numbering. I've just not seen this set-up ,but ,I'm sure someone has. Thanks for any info, and how it's supposed to work.

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Author:  JnTX [ Dec Fri 21, 2018 4:28 am ]
Post subject:  Re: Fine tune condenser?

A second set of plates for fine tuning is not uncommon on the communications receivers used by hams. Usually there is only one plate per section in those receivers so the ones in your radio look different then I have seen before. I think they are probably for the same purpose of allowing more precise tuning of short wave stations.

Jay

Author:  radionut [ Dec Fri 21, 2018 4:34 am ]
Post subject:  Re: Fine tune condenser?

it also affects the broadcast band. There was no alignment info in riders so getting it right on is going to be tricky .

Author:  pixellany [ Dec Fri 21, 2018 4:38 am ]
Post subject:  Re: Fine tune condenser?

Tell us what happens mechanically when tuning. For example, is there just one tuning knob, or are there two?

Author:  radionut [ Dec Fri 21, 2018 4:51 am ]
Post subject:  Re: Fine tune condenser?

there are 2. One for each condenser. If your going through the dial towards 1600 and say it's not too sensitive ,if you turn the small set it brings in more stations. If your finding a weak station ,tweaking the small condenser brings the signal in better. Not ever seeing this set-up ,I've just been playing around with it and that is what I have discovered.

Author:  pixellany [ Dec Fri 21, 2018 4:59 am ]
Post subject:  Re: Fine tune condenser?

Model number??

My guess is that the smaller tuners are used to peak up the antenna and RF stages.

Author:  lorenz200w [ Dec Fri 21, 2018 5:05 am ]
Post subject:  Re: Fine tune condenser?

Appears to me to be a shortwave bandspread feature: the main tuning cap is used for gross tuning; the smaller cap rotor is used for fine tuning. The stators of the two caps are in parallel so the capacitance is additive. The 0-100 graduated scale is for logging the position of the fine tuning cap. Similar concept to what is used in the Hallicrafters S-38 entry-level receiver.

Author:  thunderbird281 [ Dec Fri 21, 2018 6:30 am ]
Post subject:  Re: Fine tune condenser?

It's a nice option to have in all bands. If you were to monitor the AVC such as S-meter does you will see you can peak any station to best reception with the fine tuning capacitor.

Author:  radionut [ Dec Fri 21, 2018 11:54 am ]
Post subject:  Re: Fine tune condenser?

model 171x ,riders 6

Author:  pixellany [ Dec Fri 21, 2018 2:20 pm ]
Post subject:  Re: Fine tune condenser?

Well, the schematic is no help.....

Note that there are three circuits tuned by the tuner: BC antenna transformer, RF (affects all bands), and oscillator (also all 3 bands). To understand what the smaller tuners do, we simply need to know which of the three circuit they are part of.

Author:  radionut [ Dec Fri 21, 2018 2:31 pm ]
Post subject:  Re: Fine tune condenser?

Yep,not much info there.No alignment info.Those small company radio manufacturers had very poor schematics.At least thas my experience...

Author:  Wally58 [ Dec Fri 21, 2018 2:32 pm ]
Post subject:  Re: Fine tune condenser?

Is this the receiver?:
http://www.nostalgiaair.org/pagesbymode ... 002957.pdf

Is the 'fine-tune' variable capacitor linked to the dial pointer at all? Or is it possible that it is not a fine-tuning capacitor and is used to maximize, compensate or trim the antenna input (also used in many communications receivers)?

Author:  radionut [ Dec Fri 21, 2018 2:54 pm ]
Post subject:  Re: Fine tune condenser?

Yes,thats it.It has its own pointer.Good thought there .May be an antenna trim.

Author:  lorenz200w [ Dec Fri 21, 2018 4:15 pm ]
Post subject:  Re: Fine tune condenser?

radionut wrote:
Yes,thats it.It has its own pointer.Good thought there .May be an antenna trim.

It wouldn't be an antenna trimmer if it operates on both the oscillator and antenna sections of the tuning cap.

Author:  radiotechnician [ Dec Fri 21, 2018 5:42 pm ]
Post subject:  Re: Fine tune condenser?

The police and aviation bands are set by a trimmer according to the instructions,
with a 3500 kHz signal. Given that they are in the 49 meter band, it could be
the extra pointer is a band spread logging dial.

Other bands on the short wave dial are received by tuning within their shaded
section.

That makes it difficult to dial in a station, that the user may need to monitor.

A way of doing it on radios with band spread, is to set the main pointer to the lower
edge of the band shaded block, with the single pointer set to "0" Then the single
pointer is tuned up until the station wanted is heard. Whatever number the pointer is
set to is then logged. Later once the wanted station is heard, the user can two-hand
the dials until the logged station is found at the number it should be, and the main dial
is sweetened to rest exactly at the start of the band block.

That is how I used my band spread pre digital.


'""""

Author:  radionut [ Dec Fri 21, 2018 5:57 pm ]
Post subject:  Re: Fine tune condenser?

Wow,thanks for that info!! Quite a little rig here.When I got this radio someone had robbed the transformer and cut out all the speaker leads so it has been a little work to get this going.

Author:  pixellany [ Dec Fri 21, 2018 6:21 pm ]
Post subject:  Re: Fine tune condenser?

with regard to the tuning question, can you check which part of the tuner is what?
pixellany wrote:
.....

Note that there are three circuits tuned by the tuner: BC antenna transformer, RF (affects all bands), and oscillator (also all 3 bands). To understand what the smaller tuners do, we simply need to know which of the three circuit they are part of.

Author:  radiotechnician [ Dec Sat 22, 2018 10:08 am ]
Post subject:  Re: Fine tune condenser?

Looking at the photo of the chassis, and reading the alignment instructions
I concluded that the extra mesh gangs did adjust the oscillator. The wording
seems to mean the rear gang is the oscillator, however touching the gang
with a station playing will show this.(or the wiring could
be traced.)

If I were an Admiral collector, that set would one I would want to have.

Admiral TV sets were one of my favorite brands, in the TV service days.

A more detailed picture of how the rotors of the main and fine tuning gangs
meshed with the stators would be nice.


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Author:  azenithnut [ Dec Sat 22, 2018 3:29 pm ]
Post subject:  Re: Fine tune condenser?

Very interesting radio. Unusual to have a bandspread feature in a tombstone.

Though I do have this tuning capacitor assembly which has the same feature.
I have NO idea what radio it came out of.

The brand is "DeJong" De Adco Products --- Chicago, U. S. A.

Hard to make out the script... or maybe De Long?

Anyhow, it also has the bandspread outboard variable capacitors on the back of the main tuning capacitors.

-Steve

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Author:  majoco [ Dec Sun 23, 2018 11:56 pm ]
Post subject:  Re: Fine tune condenser?

When the "Fine Tune" pointer is set to zero, what is the capacitor position? Totally meshed or fully open? On the highest frequency band it may not be possible to get the proper alignment if the capacitance of the "Fine Tuner" is too much - it may have to "guess and hope"! Set the "Fine Tune" to the other end of the scale and try again.

I have a Heathkit "Mohican" receiver where they specifically say "Set the Bandspread control to fully meshed" when setting the alignment - but even so it is very easy to get it wrong. The frequency range of the oscillator trimmer is so great that it is possible to get the oscillator on the wrong side injection. The best test is to use a digital radio to find the oscillator frequency and make sure of it's frequency - it's usually above the signal frequency. If you find that the band is deaf in the middle then you've got it wrong!

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