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 Post subject: Heathkit FM-4 tuner
PostPosted: Feb Thu 15, 2018 4:46 am 
Member

Joined: Jun Mon 24, 2013 3:00 pm
Posts: 1129
Location: Champaign IL 61822
I got mine today. USPS smashed the package but it was double packed
and the inner package was fine.

I ran it up on a variac and dim bulb and it sounds fine on 2000 ohm
headphones (which is how I frequently used it in high school .)

If this gizmo gets recapped it will need axial electrolytics. Has anyone used the axial
ones from JustRadios? Are they reliable? What do they look like? How big
are they compared to the originals?If too different I might restuff the originals with
the radial caps I stock.


I've got
a good schematic but no manual (for alignment, though except for the tuner
its very generic.) Does anyone have a full manual?
I never found one online.


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 Post subject: Re: Heathkit FM-4 tuner
PostPosted: Feb Thu 15, 2018 3:43 pm 
Member

Joined: May Sat 06, 2006 4:03 am
Posts: 3080
Location: ZIP 23831 South of Richmond, VA 25 miles down the pike.
For comparing you can get size data on electrolytics on tubesandmore site. SAMS link below for alignment if this is what you need.

Bill J.

https://app.box.com/s/z0hbb1sck1y5dh7w2npjlrbl2wc8tbkz


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 Post subject: Re: Heathkit FM-4 tuner
PostPosted: Feb Fri 16, 2018 3:54 am 
Member

Joined: Jun Mon 24, 2013 3:00 pm
Posts: 1129
Location: Champaign IL 61822
I recapped my FM-4 using radial electrolytics and an axial film cap for the
output. All the radials fit under the chassis.

After alignment by the book it worked fine on non-HD stations but
on HD ones was bad. I realigned just the ratio detector can using a scope
on the multiplex output, rocking the tuning knob back and forth. After I aligned
for complete symmetry of the appearance of the HD signal about zero
volts (using both slugs) it works fine on all stations now. By the book this
was very unsymmetrical.

Fidelity and sensitivity is much better than the FM-3. One of my
two favorite classical music stations is HD.

Note that I claim the HD in HD Radio stands for "horrible distortion".


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 Post subject: Re: Heathkit FM-4 tuner
PostPosted: Feb Fri 16, 2018 10:15 pm 
Member

Joined: Jun Mon 24, 2013 3:00 pm
Posts: 1129
Location: Champaign IL 61822
An oddity I noticed last night.

The schematic specifies a 300 antenna. The connection to the tuner is 300
ohm twin lead.

But the schematic says one side is grounded at the tuner!

And a simulator says that the impedance is 100 ohms!

In other words, its a good match for 75 ohm coax!

WHY ... other than that 300 ohm was "expected" back in the day?

Its quite true that the thing will only receive the strongest signals
if a 1/4 wave long wire antenna is connected to the grounded terminal.


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 Post subject: Re: Heathkit FM-4 tuner
PostPosted: Feb Tue 20, 2018 11:21 pm 
Member
User avatar

Joined: Feb Sun 02, 2014 1:58 pm
Posts: 992
Location: Tennessee 38058
dtvmcdonald wrote:
I recapped my FM-4 using radial electrolytics and an axial film cap for the
output. All the radials fit under the chassis.

After alignment by the book it worked fine on non-HD stations but
on HD ones was bad. I realigned just the ratio detector can using a scope
on the multiplex output, rocking the tuning knob back and forth. After I aligned
for complete symmetry of the appearance of the HD signal about zero
volts (using both slugs) it works fine on all stations now. By the book this
was very unsymmetrical.

Fidelity and sensitivity is much better than the FM-3. One of my
two favorite classical music stations is HD.

Note that I claim the HD in HD Radio stands for "horrible distortion".


You are right. So much garbage intentionally added to FM signals these days. I remember the good old "pure signal" days.

_________________
Mike
KN4GGM

"This is the last radio I will ever buy, dear; I promise"


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 Post subject: Re: Heathkit FM-4 tuner
PostPosted: Feb Thu 22, 2018 11:33 pm 
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User avatar

Joined: Nov Fri 10, 2006 12:24 am
Posts: 2076
Location: Thornhill, Ontario
The FM-4 is one of my daily drivers (I have two.) Both have been recapped with Just Radio caps, no problem. I also converted both rectifiers to FW as I hate 1/2 wave on principle! Both were realigned "by the book" with a 10.7 MHz sig.gen. and VTVM, no scope used... results very good, nice tuners.
Good luck,
Cheers,
Roger

_________________
Roger Jones,
Thornhill, Ontario
Ontario Vintage Radio Assoc. http://www.ovra.ca


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 Post subject: Re: Heathkit FM-4 tuner
PostPosted: Feb Thu 22, 2018 11:41 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 23191
Location: Haledon, NJ, usa
dtvmcdonald wrote:

If this gizmo gets recapped it will need axial electrolytics.

..... I might restuff the originals with the radial caps I stock.

Why do say "it will need AXIAL electrolytics"?

You can just use the radials you have in stock. Remember the two leads do not need to connect to the same location as before. Only the positive leads go to the same place but the negative lead can be soldered to the nearest ground point.

_________________
To be a man, Be a non-conformist, Nothing's sacred as the integrity of your own mind.
-Emerson


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