Forums :: Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives :: Books
Support This Site: Contributors :: Advertise


It is currently Feb Wed 21, 2018 12:24 pm


All times are UTC [ DST ]





Post New Topic Post Reply  [ 43 posts ]  Go to page Previous  1, 2, 3  Next
Author Message
 Post subject: Re: Upgrading Heathkit FM-3 Tuner to FM-3A?
PostPosted: Feb Sat 10, 2018 12:16 am 
Member
User avatar

Joined: Jul Mon 08, 2013 2:48 pm
Posts: 246
john8750 wrote:
Tube Radio wrote:
Could the drift be caused by ceramic disc caps with the wrong tempco?

If so perhaps replacing them with the right tempco would fix the drift.

AFC is indeed a good thing to add though.

I added AFC to my Magnavox CR-192 FM tuner and it was fairly easy to do and works good.



I am looking at getting an FM4. I believe its an improvement over the FM3/FM3a :?:


Yes, the FM-4 has a better (factory built) front-end and includes an AFC circuit which makes it more or less drift-less.


Top
 Profile  
 
 Post subject: Re: Upgrading Heathkit FM-3 Tuner to FM-3A?
PostPosted: Feb Sat 10, 2018 2:00 am 
Member
User avatar

Joined: Dec Mon 29, 2014 9:39 pm
Posts: 3875
Location: Los Angeles
Good. Looks like it will need some TLC right away.

_________________
John Smith, over and out.
If I did something right, I made a mistake.


Top
 Profile  
 
 Post subject: Re: Upgrading Heathkit FM-3 Tuner to FM-3A?
PostPosted: Feb Sat 10, 2018 8:57 pm 
Member
User avatar

Joined: Dec Mon 29, 2014 9:39 pm
Posts: 3875
Location: Los Angeles
Comparing the FM4 schematic and the FM3, some differences are:
Third stage of power supply filter caps.
Silicone diode rectifier, tube for the FM3.
Switchable AFC circuit.
1.7mh choke between each tube filament, .005mf disc cap at each tube.
Output amp section changed to a6BN8 cathode follower. Also contains the ratio detector, 6AL5 for the FM3.
All different tubes, must be updated with newer selection.
In the FM3 schematic, I see a dashed line with a capacitor. Might be a thought for an AFC circuit.

_________________
John Smith, over and out.
If I did something right, I made a mistake.


Top
 Profile  
 
 Post subject: Re: Upgrading Heathkit FM-3 Tuner to FM-3A?
PostPosted: Feb Sat 10, 2018 9:03 pm 
Member
User avatar

Joined: Dec Mon 29, 2014 9:39 pm
Posts: 3875
Location: Los Angeles
Phil, I noticed something on the FM3 schematic. AFC afterthought?
Attachment:
20180210_115530.jpg
20180210_115530.jpg [ 92.87 KiB | Viewed 181 times ]

_________________
John Smith, over and out.
If I did something right, I made a mistake.


Top
 Profile  
 
 Post subject: Re: Upgrading Heathkit FM-3 Tuner to FM-3A?
PostPosted: Feb Sat 10, 2018 11:15 pm 
Member
User avatar

Joined: Jul Mon 08, 2013 2:48 pm
Posts: 246
john8750 wrote:
Phil, I noticed something on the FM3 schematic. AFC afterthought?
Attachment:
20180210_115530.jpg


No, it's not an AFC "afterthought" . The capacitor shown in dashed line denotes the stray capacitance coupling the local oscillator to the mixer in the 6U8 tube. This capacitor doesn't actually exist as a separate physical part but is made of the internal capacitance of the tube and socket which is enough (a few pF will do) to couple the local osc and mixer within the same tube.
The other (longer) dashed line is there to shown that the sections of the (tuning) capacitors are mechanically linked.


Top
 Profile  
 
 Post subject: Re: Upgrading Heathkit FM-3 Tuner to FM-3A?
PostPosted: Feb Sun 11, 2018 3:42 am 
Member

Joined: Jun Mon 24, 2013 3:00 pm
Posts: 898
Location: Champaign IL 61822
john8750 wrote:


That's not an FM-4. But there were two there on Ebay. I've been looking for one. I had one
in high school and college. I built a transistor stereo adapter for it, my own design.
I bought one of those FM-4s.

I recently bought and restored an FM-3. Performance of that is OK on really big signals,
poor on weak ones.


Top
 Profile  
 
 Post subject: Re: Upgrading Heathkit FM-3 Tuner to FM-3A?
PostPosted: Feb Sun 11, 2018 3:56 am 
Member
User avatar

Joined: Dec Mon 29, 2014 9:39 pm
Posts: 3875
Location: Los Angeles
dtvmcdonald wrote:
john8750 wrote:


That's not an FM-4. But there were two there on Ebay. I've been looking for one. I had one
in high school and college. I built a transistor stereo adapter for it, my own design.
I bought one of those FM-4s.

I recently bought and restored an FM-3. Performance of that is OK on really big signals,
poor on weak ones.



It sure looks like the FM4. I just bought one.

_________________
John Smith, over and out.
If I did something right, I made a mistake.


Top
 Profile  
 
 Post subject: Re: Upgrading Heathkit FM-3 Tuner to FM-3A?
PostPosted: Feb Sun 11, 2018 4:08 am 
Member

Joined: Jun Mon 24, 2013 3:00 pm
Posts: 898
Location: Champaign IL 61822
I may have been mislead by the word "amplifier". There is a matching amplifier I also
owned in high school, same black cover. But it didn't have a slide rule dial!


Top
 Profile  
 
 Post subject: Re: Upgrading Heathkit FM-3 Tuner to FM-3A?
PostPosted: Feb Sun 11, 2018 6:00 am 
Member
User avatar

Joined: Dec Mon 29, 2014 9:39 pm
Posts: 3875
Location: Los Angeles
dtvmcdonald wrote:
I may have been mislead by the word "amplifier". There is a matching amplifier I also
owned in high school, same black cover. But it didn't have a slide rule dial!



Yeah, it says amplifier, but the further description shows an FM4. I put up an amplified antenna to receive a better signal for my FM3. Works very well, pretty good fidelity. It drifts a bit, not bad after about 10 minutes.
Hoping to get the FM4 working better. I might try to add the multiplexer.

_________________
John Smith, over and out.
If I did something right, I made a mistake.


Top
 Profile  
 
 Post subject: Re: Upgrading Heathkit FM-3 Tuner to FM-3A?
PostPosted: Feb Sun 11, 2018 6:01 am 
Member
User avatar

Joined: Dec Mon 29, 2014 9:39 pm
Posts: 3875
Location: Los Angeles
Tubologic wrote:
john8750 wrote:
Phil, I noticed something on the FM3 schematic. AFC afterthought?
Attachment:
20180210_115530.jpg


No, it's not an AFC "afterthought" . The capacitor shown in dashed line denotes the stray capacitance coupling the local oscillator to the mixer in the 6U8 tube. This capacitor doesn't actually exist as a separate physical part but is made of the internal capacitance of the tube and socket which is enough (a few pF will do) to couple the local osc and mixer within the same tube.
The other (longer) dashed line is there to shown that the sections of the (tuning) capacitors are mechanically linked.



That figures. I thought I cracked a secret code.

_________________
John Smith, over and out.
If I did something right, I made a mistake.


Top
 Profile  
 
 Post subject: Re: Upgrading Heathkit FM-3 Tuner to FM-3A?
PostPosted: Feb Sun 11, 2018 6:10 am 
Member

Joined: Apr Thu 14, 2016 8:25 pm
Posts: 300
Location: pensacola fl
Hi all. If you want a super tuner get a heathkit PT1 the fm has 5 if stages and afc. You can get the diagram on line free and look it over.


Top
 Profile  
 
 Post subject: Re: Upgrading Heathkit FM-3 Tuner to FM-3A?
PostPosted: Feb Sun 11, 2018 6:36 am 
Member
User avatar

Joined: Dec Mon 29, 2014 9:39 pm
Posts: 3875
Location: Los Angeles
Audioman wrote:
Hi all. If you want a super tuner get a heathkit PT1 the fm has 5 if stages and afc. You can get the diagram on line free and look it over.



Thanks. I will check it out. Is that an AM/FM with amplifier?

_________________
John Smith, over and out.
If I did something right, I made a mistake.


Top
 Profile  
 
 Post subject: Re: Upgrading Heathkit FM-3 Tuner to FM-3A?
PostPosted: Feb Sun 11, 2018 10:34 pm 
Member
User avatar

Joined: Jul Mon 08, 2013 2:48 pm
Posts: 246
john8750 wrote:
Audioman wrote:
Hi all. If you want a super tuner get a heathkit PT1 the fm has 5 if stages and afc. You can get the diagram on line free and look it over.



Thanks. I will check it out. Is that an AM/FM with amplifier?


It's only a AM/FM (mono/binaural/simulcast) tuner, without amp. The PT-1 is also the best performer in the early series Heathkit mono tube tuners (before the later AJ series), actually much better than a FM-3/FM-4 .


Top
 Profile  
 
 Post subject: Re: Upgrading Heathkit FM-3 Tuner to FM-3A?
PostPosted: Feb Sun 11, 2018 11:08 pm 
Member
User avatar

Joined: Dec Mon 29, 2014 9:39 pm
Posts: 3875
Location: Los Angeles
Tubologic wrote:
john8750 wrote:
Audioman wrote:
Hi all. If you want a super tuner get a heathkit PT1 the fm has 5 if stages and afc. You can get the diagram on line free and look it over.



Thanks. I will check it out. Is that an AM/FM with amplifier?


It's only a AM/FM (mono/binaural/simulcast) tuner, without amp. The PT-1 is also the best performer in the early series Heathkit mono tube tuners (before the later AJ series), actually much better than a FM-3/FM-4 .




I like it. My FM3 works very well. Not stereo and wont hold still till after 10 mins. Wow would it be great to build a Heathkit today. I built several kits around 1977. Nothing with tubes. AM/FM Stereo tuner amp, AR1515, I think. And 1304 audio processor, worked very well together. The 27" color TV. A single trace O Scope. A dual channel power supply. Experimenter's test bread board, still use it today. I have seen those still new in kits, but cost way more than their worth.
The old days are gone.

_________________
John Smith, over and out.
If I did something right, I made a mistake.


Top
 Profile  
 
 Post subject: Re: Upgrading Heathkit FM-3 Tuner to FM-3A?
PostPosted: Feb Tue 13, 2018 6:50 am 
Member

Joined: Apr Thu 14, 2016 8:25 pm
Posts: 300
Location: pensacola fl
Hi all. The heathkit aj30 is the same circuits as the pt1 with a different look but otherwise the same tuner just more modern look. They can be had on ebay. The fm stereo version is the aj41 but the am is not as good. You can always plug an mpx decoder for fm stereo. They can be had tube or solid state. Tube versions from heathkit and eico show up on ebay.


Top
 Profile  
 
 Post subject: Re: Upgrading Heathkit FM-3 Tuner to FM-3A?
PostPosted: Feb Tue 13, 2018 7:05 am 
Member
User avatar

Joined: Dec Mon 29, 2014 9:39 pm
Posts: 3875
Location: Los Angeles
Audioman wrote:
Hi all. The heathkit aj30 is the same circuits as the pt1 with a different look but otherwise the same tuner just more modern look. They can be had on ebay. The fm stereo version is the aj41 but the am is not as good. You can always plug an mpx decoder for fm stereo. They can be had tube or solid state. Tube versions from heathkit and eico show up on ebay.



Cool, and thanks. Do you happen to know the kit no. for the Heathkit MPX'er?

_________________
John Smith, over and out.
If I did something right, I made a mistake.


Top
 Profile  
 
 Post subject: Re: Upgrading Heathkit FM-3 Tuner to FM-3A?
PostPosted: Feb Tue 13, 2018 7:13 am 
Member
User avatar

Joined: Dec Mon 29, 2014 9:39 pm
Posts: 3875
Location: Los Angeles
I found it. AC11. Two are on ebay right now.

_________________
John Smith, over and out.
If I did something right, I made a mistake.


Top
 Profile  
 
 Post subject: Re: Upgrading Heathkit FM-3 Tuner to FM-3A?
PostPosted: Feb Tue 13, 2018 5:52 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 5193
Location: Woodinville, WA USA
Back to the FM-3. Thanks to John, who sent me a copy of the complete FM-3 manual. I have ordered a few caps to do a basic recap of the tuner.

Meanwhile, the plot thickens. Now that I can compare both manuals to my set, it looks like my "FM-3" is not an entirely stock FM-3. Nor is it a stock FM-3A.

For one thing, the power supply for both the FM-3 and FM-3A has a pair of 20-mfd electrolytics separated by a 1K/2W resistor. But in my set, the 1K/2W resistor has been replaced by a part resembling a transformer (note the arrows in the next two photos). I'm guessing this is a choke, serving the same purpose as the 1K/2W resistor:

Image

Image

The space where the choke is installed is just a big blank spot in both the FM-3 and FM-3A assembly diagrams, so whoever installed this part wasn't following either of those manuals.

Another addition is an eight-lug terminal strip containing a network of a dozen capacitors and resistors, including a trimmer capacitor, and mounted directly above the tuning capacitor:

Image

I wonder if this strip is part of the mysterious C-FM-3 upgrade kit? The article describing the C-FM-3 upgrade kit (page 89, http://americanradiohistory.com/Archive ... 957-12.pdf) mentions "numerous capacitors and resistors" and it shows a diagram of soldering on the "new oscillator trimmer capacitor."

If you compare the FM-3 and FM-3A schematics, you won't find any strip with a dozen components including an oscillator trimmer capacitor. So, if this is indeed a C-FM-3 component, did the upgrade add more than what's shown in the stock FM-3A schematic?

Whoever made these mods didn't have the complete C-FM-3 upgrade kit, which also included a new tuner drive, edge-lit dial glass, and an extra pilot lamp, according to the article previously cited. So possibly someone used only part of the kit . . . or was clever enough to devise these mods on his own?

The C-FM-3 upgrade manual would answer these questions, but I haven't been able to find that manual yet.

In the meantime, I'll go ahead with a basic recap, and possibly look into adding AFC as described in the January, 1957 Radio Electronics article. (Note: the C-FM-3 upgrade is different from adding AFC.)

Phil Nelson
Phil's Old Radios
https://antiqueradio.org/index.html
Phil Nelson
Phil's Old Radios
https://antiqueradio.org/index.html


Top
 Profile  
 
 Post subject: Re: Upgrading Heathkit FM-3 Tuner to FM-3A?
PostPosted: Feb Fri 16, 2018 12:29 am 
Member
User avatar

Joined: Dec Mon 29, 2014 9:39 pm
Posts: 3875
Location: Los Angeles
Phil- looks like your unit was kit-bashed. And some real nice work. My FM3 was very well built. It was dusty inside, and come to me with the outsides removed. But it was un-retouched. So after a normal recap, including the output couplers, it works very well.
I just received my FM4. Need to replace 5 electrolytics and a diode. It too looks well built and should operate well.
Thanks for the you know what Phil, wasn't necessary.

_________________
John Smith, over and out.
If I did something right, I made a mistake.


Top
 Profile  
 
 Post subject: Re: Upgrading Heathkit FM-3 Tuner to FM-3A?
PostPosted: Feb Fri 16, 2018 12:55 pm 
Member
User avatar

Joined: Jul Mon 08, 2013 2:48 pm
Posts: 246
Looks like some "un-official" upgrade to me. Filter resistor has been replaced by a choke and the extra tag strip with parts might be an AFC circuit. Trying to follow the blue wire (last tag at the right) could give you a clue: if it goes to the ratio detector (6AL5) stage it is very likely an AFC circuit.


Top
 Profile  
 
Post New Topic Post Reply  [ 43 posts ]  Go to page Previous  1, 2, 3  Next

All times are UTC [ DST ]


Who is online

Users browsing this forum: Ron Ramirez and 5 guests



Search for:
Jump to:  






















Privacy Policy :: Powered by phpBB