[Ron Ramirez]

Mondial, I know that several people have successfully made this LED conversion of their stereo indicators, but there is virtually no info on this available online - or, at least, no info that is easily found in a Bing or Google web search.

I did find a modicum of info on this subject on one site, and it talked about selecting a shunt to match the current of the original bulb - that would make it less than 1000 ohms (actually 395 ohms). Does that make sense, or is that just a load of kaka that is best ignored?

I'll open the 4400 back up tomorrow morning and experiment with a couple different values, starting at 3.3K, and see what happens. Then I'll move on to replacing the remainder of the 440's electrolytics.

[Mondial]

I don't see any reason to exactly duplicate the current drain of the bulb. Back when Fisher designed the circuit, they used a bulb which needed 35 mA, which was about as low as was available. If they were to design the same circuit today they would use a LED and drive it with 10 mA. So there is no real reason to burn off the excess current as heat with a very low value shunt resistor. Even if you exactly matched the current drain, the LED will still behave differently because it turns on at a much lower voltage than the incandescent bulb.

If you reduce the value of C11 the 100 uF cap, it will decrease the delay in the LED turnoff. With the lower drain of the LED, the cap value could be reduced proportionally.

Experiment with the shunt resistor and see how it behaves, but I certainly would not go below 1.5 K or so.

[Ron Ramirez]

Okay!

This morning, I opened the 4400 back up and removed the 10K shunt resistor in the LED Stereo Beacon circuit.

I tried a 2.2K resistor. It helped, but the Beacon was still fading slowly.

I then removed the 2.2K and tried a 1.5K. It made the Beacon respond better, but still faded somewhat slow.

Then, I paralleled that with another 1K (which equaled 600 ohms). More improvement.

Removed those two and installed a 470 ohm resistor. I think this is as good as it is going to get. It now fades away in just over a second when tuned off signal, much quicker than with a 10K, and better than with a higher value resistor. It does not fade as fast as it would with an incandescent bulb, but the fading action is good enough for me.

I think whoever had posted online about matching the current of the original bulb must have had a good point, as the LED works much better with a low value shunt.

Since I haven't soldered the 470 ohm resistor in yet, I might try a 390 ohm resistor (the next smallest size I have) before I button it up. But I don't think the 390 will make that much more of a difference.

[Ron Ramirez]

I did try a 390 ohm resistor, and it made the LED respond *almost* as well as the incandescent. The LED indicator now fades out in one second when I switch the unit from FM Stereo to FM Mono.

However...

I'll have to buy a higher wattage 390 ohm resistor. Calculations show that at 35 mA, the 390 ohm resistor will be dissipating just under 1/2 watt, and the only 390 ohm resistors I have are...1/2 watt units.

So I temporarily soldered an old 430 ohm 1 watt resistor in place (measures 442 ohms), which I will use until my next parts order when I will order some higher wattage 390 ohm resistors.

I think I have that problem solved to my satisfaction. Photos later. I have a 440-T cabinet which I am going to put the 4400 into for the time being until I find another cabinet, and then I will probably put the 440-T in the other thread back into this cabinet since it came out of it to begin with. I had to make a foot for the cabinet, and I have it clamped in place, waiting for the glue to dry.

[Mondial]

Ron, you can achieve the same result without dissipating all that power if you reduce the value of the electrolytic to ground. This cap is what is causing the slow response. What is the value in the 440?

With a smaller value cap, the response time can be made as small as you like, with a higher value resistor that won't consume so much power.

[Ron Ramirez]

That's just it - the 4400 does not have the two electrolytics across the Stereo Beacon that the 440 has. The only cap I can find in the line going to the MPX board is a 0.22 uF cap in the power supply. Remember, I do not have a service manual or circuit diagram for the 4400 since it is such an oddball. I never did call A.G. Tannenbaum to get the manual from him, I got busy and forgot. I guess I really should get that.

The partial schematic I posted in the 440 thread shows two 100 uF caps, but my 440 actually uses two 200 uF caps. But this is not relevant to the 4400 since I do not see any electrolytics in the equivalent circuit for the 4400.

[Mondial]

Ahh, I forgot you didn't have a schematic for the 4400. I guess I am confusing the 440 and the 4400 since you have been going back and forth between them.

There still must be some large value cap in the indicator circuit somewhere though, otherwise lowering the shunt resistor would not make such a difference in the response time. It will be interesting to check when you find a schematic.

[Ron Ramirez]

Sorry for the confusion...I could see it was getting confusing, so I moved a few posts from the 440-T thread to the 4400 thread this morning.

The 4400 has been playing for over an hour and the 430 ohm resistor is just barely generating any heat - I can *just* feel the very slightest warmth when touching the resistor. Now I need to go turn it off, move it from the bench, and resume working on the 440-T.

[Ron Ramirez]

Photos, dimly lit room with no flash:

[Image: http://www.philcoradio.com/images/phorum...0001-5.jpg]

[Image: http://www.philcoradio.com/images/phorum...0002-4.jpg]

[Image: http://www.philcoradio.com/images/phorum...0003-1.jpg]

and two with flash:

[Image: http://www.philcoradio.com/images/phorum...e00004.jpg]

[Image: http://www.philcoradio.com/images/phorum...e00005.jpg]

I know Arran probably will not approve ...but I really like how the blue LEDs look in this receiver. In my opinion, they really make the dial look great! This is the only late 1960s Fisher receiver I have seen so far that uses a blue Stereo Beacon and a blue tuning meter.

[Arran]

The blue LEDs look fine in the Fisher 4400, since they were used with some discretion with the stereo indicator and the tuning meter. It was with reference to the 2200 series Marantz receivers from the mid to late 70s where I didn't like the look of the blue LEDs. The blue LEDs in a Marantz, on top of a dial and meters that are already blue, is just too over the top.
Regards
Arran

[Ron Ramirez]

This afternoon, I decided to try an experiment on my 4400.

You may remember that the Stereo Beacon circuit had no electrolytic capacitor, as follows:

[Image: http://www.philcoradio.com/images/phorum.../led03.jpg]

However, the other Fishers I have worked on recently have Stereo Beacons with at least one electrolytic, like this:

[Image: http://www.philcoradio.com/images/phorum.../led02.jpg]

So...I added the 200 uF electrolytic. I don't know if it was never present in my 4400, or if someone removed it along the way for whatever reason...but after I added this capacitor, the Stereo Beacon LED became much more responsive and acts more like an incandescent lamp now in terms of response time - when you tune off station, it goes out like it should, with very little delay.

I am now very pleased with the LED Stereo Beacon conversion.

[Ron Ramirez]

Okay...one more and then this thread will have run its course.

A semi-formal portrait - the 4400 with its "new" clothes, a refinished cabinet:

[Image: http://www.philcoradio.com/images/phorum...0003-2.jpg]

The 4400 has become my "daily driver."

I will try to touch up the flaws in the lacquer on the left front edge when warm weather returns.

My 440-T cabinet (which this 4400 resided in until this past weekend) needs a screen like the gold-colored one on top of this cabinet. I found a source that makes repros at a reasonable price; they also make reproduction knob caps, so I'll be getting a cap to replace the missing one on my 4400, as well as a screen for my 440-T cabinet.

[Mondial]

Hey Ron, I need one of those top screens for my 400 cabinet. Please let me know where you got it. Thanks!

[Ron Ramirez]

Sure: JTNS Products in NJ. They advertise on eBay as "bizcoup" but you can contact them direct. If they do not have the screen you want in stock, they will custom make one for you (which is what I am going to have them to do for my 440-T cabinet).

http://cgi.ebay.com/261421359286

Send me a PM and I'll give you the gentleman's email address.