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 Post subject: Heathkit FM4
PostPosted: Mar Mon 19, 2018 9:51 pm 
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I have a Heathkit FM4 to restore. First thing to do is re-cap. Then examine resistors, tighten up screws, retouch some solder joints. Man, 50 year old solder has a certain smell. Reminds me of the time I built several Heathkits.
I will order about five E-Caps and one coupling capacitor right away.
Here is some cool information about the FM3 and FM3A conversion.
viewtopic.php?f=13&t=335331

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 Post subject: Re: Heathkit FM4
PostPosted: Mar Mon 19, 2018 10:03 pm 
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Here are some photos and schematic.
Attachment:
FM41.jpg
FM41.jpg [ 136.13 KiB | Viewed 2457 times ]

Attachment:
FM42.jpg
FM42.jpg [ 110.49 KiB | Viewed 2457 times ]

Attachment:
FM43.jpg
FM43.jpg [ 144.15 KiB | Viewed 2457 times ]

Attachment:
fm-4.pdf [193.16 KiB]
Downloaded 45 times


Attachments:
FM43.jpg
FM43.jpg [ 144.15 KiB | Viewed 2457 times ]

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 Post subject: Re: Heathkit FM4
PostPosted: Mar Mon 19, 2018 10:05 pm 
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Attachment:
fm-4.pdf [193.16 KiB]
Downloaded 54 times

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 Post subject: Re: Heathkit FM4
PostPosted: Mar Mon 19, 2018 10:07 pm 
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Looks easy enough. Mostly disc ceramic capacitors (should be still good) and just a few electrolytic and/or tubular capacitors. Let us know how it goes.

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 Post subject: Re: Heathkit FM4
PostPosted: Mar Mon 19, 2018 10:45 pm 
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Don Cavey wrote:
Looks easy enough. Mostly disc ceramic capacitors (should be still good) and just a few electrolytic and/or tubular capacitors. Let us know how it goes.



Of course I will Don. Looks like fun.
I have the FM3 that works fine. Just a bit of station drift. I did the same re-cap to it.
The FM4 should have better selectivity.

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 Post subject: Re: Heathkit FM4
PostPosted: Mar Thu 22, 2018 3:28 am 
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Location: Thornhill, Ontario, Canada
I have two of these, both restored... very nice tuners. I changed both power rectifiers to FW (using salvaged FW assemblies from scrapped PC power supplies) because I just don't like 1/2 wave... it's a religious thing!
Cheers,
Roger

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 Post subject: Re: Heathkit FM4
PostPosted: Mar Thu 22, 2018 3:58 am 
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engineer wrote:
I have two of these, both restored... very nice tuners. I changed both power rectifiers to FW (using salvaged FW assemblies from scrapped PC power supplies) because I just don't like 1/2 wave... it's a religious thing!
Cheers,
Roger

Pardon my ignorance but what is an FW Assembly?
Full wave bridge?

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 Post subject: Re: Heathkit FM4
PostPosted: Mar Thu 22, 2018 6:38 am 
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engineer wrote:
I have two of these, both restored... very nice tuners. I changed both power rectifiers to FW (using salvaged FW assemblies from scrapped PC power supplies) because I just don't like 1/2 wave... it's a religious thing!
Cheers,
Roger



Thanks Roger. I respect your Religion but want to keep it as stock as possible. Half wave will be fine, for me. Plus that is a pretty neat looking diode.

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 Post subject: Re: Heathkit FM4
PostPosted: Mar Thu 22, 2018 6:42 am 
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Pbpix wrote:
engineer wrote:
I have two of these, both restored... very nice tuners. I changed both power rectifiers to FW (using salvaged FW assemblies from scrapped PC power supplies) because I just don't like 1/2 wave... it's a religious thing!
Cheers,
Roger

Pardon my ignorance but what is an FW Assembly?
Full wave bridge?



I am guessing 'full wave' It has a single diode in the power supply. And I guess that would be a bridge rectifier.

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 Post subject: Re: Heathkit FM4
PostPosted: Mar Thu 22, 2018 5:34 pm 
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Hi all. Changing to a full wave bridge has two advantages. First the hum level will be easier to filter given the same size capacitors and secondly the power transformer will run cooler.




Bob


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 Post subject: Re: Heathkit FM4
PostPosted: Mar Thu 22, 2018 9:34 pm 
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Audioman wrote:
Hi all. Changing to a full wave bridge has two advantages. First the hum level will be easier to filter given the same size capacitors and secondly the power transformer will run cooler.




Bob



Well, that is something to consider. Guess I will have a look at that.
Thanks Men.

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 Post subject: Re: Heathkit FM4
PostPosted: Mar Sat 24, 2018 11:28 am 
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These are the full wave bridges from PC power supplies (circled in red)

I use them often as well.


Attachments:
FWB (PC-PS).jpg
FWB (PC-PS).jpg [ 49.46 KiB | Viewed 2324 times ]

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 Post subject: Re: Heathkit FM4
PostPosted: Mar Sat 24, 2018 6:36 pm 
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Rocco53 wrote:
These are the full wave bridges from PC power supplies (circled in red)

I use them often as well.



Thanks for the suggestion.
OK. I will change to F/W. Might use 1n4007 rectifiers. I believe that the bridge package looks too modern.
I don't know yet.
Still waiting for the replacement caps to arrive. Wont be long.
Of course the caps are modern, but cant help that.

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 Post subject: Re: Heathkit FM4
PostPosted: Mar Sat 24, 2018 8:20 pm 
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john8750 wrote:
Rocco53 wrote:
These are the full wave bridges from PC power supplies (circled in red)

I use them often as well.



Thanks for the suggestion.
OK. I will change to F/W. Might use 1n4007 rectifiers. I believe that the bridge package looks too modern.
I don't know yet.
Still waiting for the replacement caps to arrive. Wont be long.
Of course the caps are modern, but cant help that.

I'll bet that none of the cockroaches hiding in anyone's old radio will ever care if the parts are new-style or old.
( or the rest of the masses of human kind out there in the world who will never look under or understand what they see will ever care for that matter.)

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 Post subject: Re: Heathkit FM4
PostPosted: Mar Sun 25, 2018 12:10 am 
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Pbpix wrote:
john8750 wrote:
Rocco53 wrote:
These are the full wave bridges from PC power supplies (circled in red)

I use them often as well.



Thanks for the suggestion.
OK. I will change to F/W. Might use 1n4007 rectifiers. I believe that the bridge package looks too modern.
I don't know yet.
Still waiting for the replacement caps to arrive. Wont be long.
Of course the caps are modern, but cant help that.

I'll bet that none of the cockroaches hiding in anyone's old radio will ever care if the parts are new-style or old.
( or the rest of the masses of human kind out there in the world who will never look under or understand what they see will ever care for that matter.)



You got me on that one Peter. Most of my friends are dumber than me, and that's pretty dumb.

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 Post subject: Re: Heathkit FM4
PostPosted: Mar Mon 26, 2018 11:19 pm 
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The caps have arrived. So its time to rearrange the work bench and get to work.

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 Post subject: Re: Heathkit FM4
PostPosted: Mar Tue 27, 2018 6:52 pm 
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Here are the capacitors for the upgrade.
Attachment:
20180327_104025.jpg
20180327_104025.jpg [ 108.91 KiB | Viewed 2224 times ]

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 Post subject: Re: Heathkit FM4
PostPosted: Mar Tue 27, 2018 9:06 pm 
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john8750 wrote:
Here are the capacitors for the upgrade.
Attachment:
20180327_104025.jpg

Hi John:
Why 500volt?
I don't see anything under your chassis like that.
If you really need 500v you can often save money other ways.
I'll bet you paid a lot more for that 22uf 500v cap than the others at only 350v.
500v caps are usually costly.
To save some dough on high voltage caps like that you can always just put two 40uf or 47uf caps at 350v in series and have a 20-24uf@700v?

Radial style caps are a lot cheaper than axials too, and help to make for a neater-looking job.

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 Post subject: Re: Heathkit FM4
PostPosted: Mar Tue 27, 2018 9:39 pm 
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Pbpix wrote:
john8750 wrote:
Here are the capacitors for the upgrade.
Attachment:
20180327_104025.jpg

Hi John:
Why 500volt?
I don't see anything under your chassis like that.
If you really need 500v you can often save money other ways.
I'll bet you paid a lot more for that 22uf 500v cap than the others at only 350v.
500v caps are usually costly.
To save some dough on high voltage caps like that you can always just put two 40uf or 47uf caps at 350v in series and have a 20-24uf@700v?

Radial style caps are a lot cheaper than axials too, and help to make for a neater-looking job.



Easy answers to your questions.
I was $1 short of the minimum order of 20 bucks. The higher voltage has a bigger size. All caps on the FM4 are radial. Axials would look weird in a place where radials were meant to be.

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 Post subject: Re: Heathkit FM4
PostPosted: Mar Tue 27, 2018 11:04 pm 
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john8750 wrote:


Easy answers to your questions.
I was $1 short of the minimum order of 20 bucks. The higher voltage has a bigger size. All caps on the FM4 are radial. Axials would look weird in a place where radials were meant to be.

I only saw axials under there with a bunch of ceramic discs... no radial e-caps.
I don't think radial e-caps were even invented back then.

"look funny" to whom?
Is it going into a museum where the visitors get to unscrew the bottom. And are these people old enough to realize that only axial caps were available back then?... and would these museum visitors really care?
Even if it stays in your home, who's going to tear off the bottom and tell you your caps are not period-correct? lol

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