Changing Frequency Of Belar RFA-1 FM RF Amplifier

FM does it with frequency!
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Audio0702
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Changing Frequency Of Belar RFA-1 FM RF Amplifier

Post by Audio0702 » Tue Jun 04, 2019 7:34 am

Is it as simple as replacing the cyrstal for a new frequency?
Or is their some tuning adjustment that have to be made?
I have never done this however I have access to a local electronics technican who has bench testing equipment to do so.
Thank You in advance for your response!!!!!

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Deep Thought
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Re: Changing Frequency Of Belar RFA-1 FM RF Amplifier

Post by Deep Thought » Tue Jun 04, 2019 3:15 pm

The crystal runs at +10.7 MHz of the desired carrier frequency in overtone mode. You'll also have to tune the 'front end' of the RF Preamp board, and will probably have to tweak the output board tuning too. It is a pretty simple circuit that any experienced radio service guy should be able to figure out.

Here's the manual...
http://www.belar.com/Documents/RFA-1_Comp.pdf
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Bill DeFelice
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Re: Changing Frequency Of Belar RFA-1 FM RF Amplifier

Post by Bill DeFelice » Tue Jun 04, 2019 4:00 pm

The question will be can you get the crystals now that ICM has gone belly-up. I have the formula on retuning inside one of the amps I retuned - I can see if the amp with the info is still in the office.

Depending on how far you're moving it you'll need a new front end coil set, too.

Gee, I would have loved to have seen a tunable AM RF amp like their RFA-4 amp for the FM series.
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Deep Thought
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Re: Changing Frequency Of Belar RFA-1 FM RF Amplifier

Post by Deep Thought » Tue Jun 04, 2019 7:51 pm

Bill DeFelice wrote:
Tue Jun 04, 2019 4:00 pm
Depending on how far you're moving it you'll need a new front end coil set, too.
Does the FM have that? I know the AM version does.
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Bill DeFelice
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Re: Changing Frequency Of Belar RFA-1 FM RF Amplifier

Post by Bill DeFelice » Wed Jun 05, 2019 5:07 am

Deep Thought wrote:
Tue Jun 04, 2019 7:51 pm
Bill DeFelice wrote:
Tue Jun 04, 2019 4:00 pm
Depending on how far you're moving it you'll need a new front end coil set, too.
Does the FM have that? I know the AM version does.
Not sure. I just noticed the thread was about the FM band amp and I'm use to retuning the AM amps. I'd have to look for my crib notes as I've only dealt with one fixed frequency FM amp before moving to the frequency agile RFA-4's.
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Re: Changing Frequency Of Belar RFA-1 FM RF Amplifier

Post by kcbooboo » Thu Jun 06, 2019 5:14 am

A quick look at the manual didn't show any frequency-dependent components other than the crystal.

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Re: Changing Frequency Of Belar RFA-1 FM RF Amplifier

Post by DaveSt » Thu Jun 06, 2019 5:35 am

I would have thought the front end and LO coils would have the range for the whole of the FM band. As Deep Thought said, it is a simple circuit and retuning should not be a challenge for any one with a little experience.

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