Coronado dial off

Post by Kurt Draper
Just to check, on AM, I tuned it to a local station at 900 KHz.
I found the local oscillator on a digital radio at 1350 KHz.
I don’t know what it’s supposed to be.

That's a consistent problem with some radios. Not ALL of them are
455 KHz IFs. That would explain the tracking issues. If the IF is
set wrong, that's the result.

I found your post on the antique radio forum with the tube line up.
That's sounds like a late enough model however, to not have some
goofy non-standard IF frequency.

--
"I am a river to my people."
Jeff-1.0
WA6FWi
http:foxsmercantile.com

Michael Terrell

2020-03-01 20:07:58 UTC

Post by Kurt Draper
I posted about this radio last week. A gentleman named Michael answered me. The radio is a Coronado 46 RA 85762A. The other numbers on the chassis are 6A85 113145. The dial is way off. 840 comes in at910 & 96.9 comes in at 95. He asked me about a damaged oscillator coil. It doesn’t show any signs of physical or heat damage. The trimmer on the tuning capacitor are within 1/2 turn of tight. Just to check, on AM, I tuned it to a local station at 900 KHz. I found the local oscillator on a digital radio at 1350 KHz. I don’t know what it’s supposed to be. Thanks for getting back to me so fast. Best Regards, Kurt

That would be a 450KHz IF, if the counter isn't loading down the oscillator with its input capacitance. Some things to check:

Can you measure the L.O at both ends of the band? This will give more information about the error.

Is there a slug in the L.O. coil? If so, is it adjustable?

Fox's Mercantile

2020-03-01 20:55:56 UTC

Post by Michael Terrell
That would be a 450KHz IF, if the counter isn't loading
down the oscillator with its input capacitance.

That's the problem.
Realign the IF to 455 KHz.

--
"I am a river to my people."
Jeff-1.0
WA6FWi
http:foxsmercantile.com

Michael Terrell

2020-03-01 21:15:33 UTC

Post by Michael Terrell
That would be a 450KHz IF, if the counter isn't loading
down the oscillator with its input capacitance.

That's the problem.
Realign the IF to 455 KHz.

That won't cause the dial to be of by 70KHz at that frequency.

Fox's Mercantile

2020-03-01 21:24:54 UTC

Post by Michael Terrell
That would be a 450KHz IF, if the counter isn't loading
down the oscillator with its input capacitance.

That's the problem.
Realign the IF to 455 KHz.

That won't cause the dial to be of by 70KHz at that frequency.

It will if you have to pad the LO to work 50 KHz off frequency at
the low end. The resulting LC ratio fucks up the tracking at the
high end.

He mentioned that the padders are both almost closed all the way.
(maximum capacitance).

The minimum to maximum values of the local oscillator tuning
capacitor is dependent on the IF frequency being correct.

--
"I am a river to my people."
Jeff-1.0
WA6FWi
http:foxsmercantile.com

Michael Terrell

2020-03-02 00:22:18 UTC

Post by Michael Terrell
That would be a 450KHz IF, if the counter isn't loading
down the oscillator with its input capacitance.

That's the problem.
Realign the IF to 455 KHz.

That won't cause the dial to be of by 70KHz at that frequency.

It will if you have to pad the LO to work 50 KHz off frequency at
the low end. The resulting LC ratio fucks up the tracking at the
high end.
He mentioned that the padders are both almost closed all the way.
(maximum capacitance).
The minimum to maximum values of the local oscillator tuning
capacitor is dependent on the IF frequency being correct.

1350KHz
-900KHz
-------
=450KHz not 400KHz

Fox's Mercantile

2020-03-02 02:12:37 UTC

Post by Michael Terrell
That would be a 450KHz IF, if the counter isn't loading
down the oscillator with its input capacitance.

That's the problem.
Realign the IF to 455 KHz.

That won't cause the dial to be of by 70KHz at that frequency.

It will if you have to pad the LO to work 50 KHz off frequency at
the low end. The resulting LC ratio fucks up the tracking at the
high end.
He mentioned that the padders are both almost closed all the way.
(maximum capacitance).
The minimum to maximum values of the local oscillator tuning
capacitor is dependent on the IF frequency being correct.

1350KHz
-900KHz
-------
=450KHz not 400KHz

Good for you, you can count.

The assertion is still the same.
If the IF is off frequency (5 KHz) it will STILL affect the tracking.

--
"I am a river to my people."
Jeff-1.0
WA6FWi
http:foxsmercantile.com

Jay Hennigan

2020-08-31 00:32:16 UTC

Post by Michael Terrell
That would be a 450KHz IF, if the counter isn't loading
down the oscillator with its input capacitance.

That's the problem.
Realign the IF to 455 KHz.

That won't cause the dial to be of by 70KHz at that frequency.

Correct.

Post by Fox's Mercantile
It will if you have to pad the LO to work 50 KHz off frequency at
the low end. The resulting LC ratio fucks up the tracking at the
high end.

455 - 450 = 5 KHz difference, not 50. It won't really make a significant
difference. Some early sets used 450 KHz IF, but 455 became the standard
to reduce birdies.

Jim Mueller

2020-03-02 03:41:17 UTC

Post by Kurt Draper
I posted about this radio last week. A gentleman named Michael answered
me. The radio is a Coronado 46 RA 85762A. The other numbers on the
chassis are 6A85 113145. The dial is way off. 840 comes in at910 & 96.9
comes in at 95. He asked me about a damaged oscillator coil. It doesn’t
show any signs of physical or heat damage. The trimmer on the tuning
capacitor are within 1/2 turn of tight. Just to check, on AM, I tuned it
to a local station at 900 KHz. I found the local oscillator on a digital
radio at 1350 KHz. I don’t know what it’s supposed to be. Thanks for
getting back to me so fast. Best Regards, Kurt
Sent from my iPad

You mention that both the AM and FM dials were off. Are the pointer
positions off by the same physical distance (inches) on the dial? If so,
the problem is highly likely to be mechanical.

--
Jim Mueller ***@nospam.com

To get my real email address, replace wrongname with eggmen.
Then replace nospam with expressmail. Lastly, replace com with dk.

Heriberto

2020-08-17 17:53:31 UTC