SP600 LED light replacements.. NOW this is odd!

[ke7trp]

I read the article in ER about using LED plug in #47 bulbs.   I ordered some white, Green and Blue ones. 

The SP600 uses 4 #47s.  Since one was out, today, I put two of the LED Bulbs in on the right side of the radio.. Neat looking. Lit right up.  Matches my two stacked O scopes in a nice cool green. 

Turned on the RXER and noticed that the BC station I normaly listen to is now comming in at 85DB over!  Normaly about 50.  The Static between stations is now up at 0 on the Scale.. WAY more noise.

This is NOT the S meter. Its RX gain. The reason I know this is I normaly use the RF gain control about 5 and not full up.  Anything past 5 never made any difference.

Now, I have a smooth RF gain from low to high.  It no longer peaks at 5 on the dial.

Stunned by this, I put two new standard 47sback in.  The RXer went back to being normal.. RF gain at 5 and nothing past it helps.

If I turn AVC OFF.  The Reciever overloads around 2 on the dial with the LEDs in place and 6 on the dial with the Standard bulbs. 

I guess some schematic study is in order here.. I guess I am changing this line to DC since these are Light emitting diodes?

I am not suggesting this as a performance gain.. I am just real curious as to how changing the bulbs to LEDs is producing this behavior.


Clark

[ke7trp]

Well thats nice..   The 600 just died.  Massive HUM out speaker.. Then Total overload of Reciever on all stations. Audio tube is no longer glowing a slight blue.  Even with the Standard bulbs back in place.

Gotta rip it out of the rack and start checking tubes and Caps!  There goes the rest of my day!

Great.. BIG thanks to the guy that wrote that article and to Ray for printing it!

Clark

[ke7trp]

Got it out on the bench.  Started going through it with my Cap checker. Bad caps.  Filters are Fried.  WTF? 


Clark

[ke7trp]

Need some help with this one guys. 

Sat down and put three new filters in the Rig.  Clean DC now..  Major hum. Overloading IF stage. Cant hear anything but hum and overloaded audio.  Checked caps for 20 minutes. I dont see anything bad.

Any ideas?

C

[W1GFH]

Wow, I'll be interested to see how this one turns out. Not familiar with troubleshooting the SP600, but it sounds like the dial lamps were somehow in line with the supply voltage to one or more detector and AVC tubes?

[ke7trp]

The act of me inserting the bulbs or the LED bulbs themselves must have shorted something.  I cant seem to figure this one out.  I have checked all the easy stuff.  Next up is the Voltages throughout the rig. Not an easy task on one of theses beasts.

Clark

[flintstone mop]

The dial lamps would probably come off the filament line.
Let's look at this that it was a strange coincidence.
Sounds like the receiver was in need of service time with the P.S. caps needing replacement.

Keep us posted on the progress.

Fred

[ke7trp]

Figured out it.. I think.

All of the "vitamin" metal can caps in the audio stages are bad. Some go to the tube pin then to ground. Most are .022's. Not sure what the hell happend. I did not disturb ANYTHING this morning. I simply reached in with two fingers, Popped the bulbs out and put the new ones in.  Turned it on and bam. The LED's are diodes.  They have a resistor. Maybe I got a bad one and it shorted this to ground?

So there are about 10 of these damn things..  ONE of them tests right around .020 on the tester. The rest wont test.  I have to go by what the checker is telling me and replace them.

What should I buy to replace them?  Orange Drops? 

Clark

[W1GFH]

If you're going to buy new caps, the yellow axial polys fit into tight spaces better than Orange Drops.

[ke7trp]

Yeah.. They are bad.. The HUM is from the audio stage. We isolated it by pulling tubes.  Bias is there. -50 volts. All voltages seem there.  It must be those coupling caps and or some of those Vitamin Q's.  The DC supply is clean. Its not a low 60HZ. Its the tone you get in an audio system when you have a Ground loop.

What a mess...  I will never understand how inserting some LED's caused this.

C

[WD5JKO]

Clark,

On anorther post you said:
"Today while waiting for my Dog to get out of surgery.  I Decided to try to run HI FI audio out of the SP600. I was told by three hams that you cannot do this like you can with the R390A."

 Is it possible that your hum and your recent activity with a Hi-Fi hooked to the detector output could be connected?

Jim
WD5JKO

[ke7trp]

Its possible that it loaded the circuit down and blew a cap out.  The HUM is on HiFi, headphones and on the 600 ohm out.

The very first thing I did was to remove that tap on the Diode terminal. 

If I pull the Audio Driver tube it doubles in volume. So it must be in the audio stage.  Those LED lamps have Resistors inside. I wonder if it loaded it down or it just decided to go when I turned it back on that ONE time.

I will have to go back to a Halli.. My R390A hears the 50Kw disney channel all over the bands.  The R390 is in the cleaning stages, The Northern 159 has a broken S meter and now my Beloved Sp600 is dead.  Not a good week for the boat anchors..  I also lost the blower on the King.  Lucky for me, I have the week off at home so I can fix all this junk!

Come to think of it, I have an RME45 and a 75 A4 in there. Maybe I will LUG one of those in the radio room.


Clark

[N4LTA]

One thing you might think about is that LEDs are not rectifiers and have only about a 4-5 volt PRV. If you hook them up with more reverse voltage than that, they can short. That is something I learned the hard way using them in an AC circuit.

In even a 6.3 volt filament circuit - you get more than 9 volts peak reverse voltage. You can't just stick them in there with a dropping resistor  - because in reverse - there is no current flow and no voltage drop in the resistor. The LED sees the full reverse voltage.

Pat
N4LTA

[ke7trp]

These are #47 LED bulb replacement with 12 volt written right ON THEM.  The data sheet says 3 to 14 volts.

Clark

[Opcom]

sounds like the revenge of the #47's..

[ke7trp]

Yeah.  Thats what it was.. At least it kept me busy today.

All voltages checked now.. Bias and B+ on tubes.  All correct.  No ripple.  Must be a cap in the audio stage.

Clark

[N4LTA]

If they are rated for AC - then they should work.

Pat
N4LTA

[ke7trp]

Of course they will work on AC.

C

[N4LTA]

Not necessarily.

LEDs as stated above will not work on AC with a standard dropping resistor like they work on DC. It isn't a given.

Why would you say "of course they will work on AC"?

This one taken from a Google search ( first one that popped up) is DC only

Flexible Voltage Smart BulbsBright Bipolar 9mm Bayonet Single-LED Bulb
   

   B320   6-to-48Vdc 1-LED Bipolar 9mm Bayonet Bulb


I find that almost all of the cheap ones are DC only.



Pat
N4LTA

[ke7trp]

Mine are AC and DC.  The bulbs lit up fine. Nice and Bright. But something shorted caps in this RXer. The moment I put these things in.  I have tested the bulbs outside the radio on DC and AC up to 14 volts and down to 3.. Very little difference in Brightness and all of them come on. 

[N4LTA]

I just mentioned it on a whim. I have seen several instances where DC only LED lamp replacements have been used on AC. At first it seems like it should work fine but it doesn't. It was brought to my attention by a member of the Antique Radio forum. You were having a weird problem that seems to have no explanation.

I did it on a power supply indicator lamp using a  lampholder with a dropping resistor and high brightness blue LED. I hooked it to the 6.3 volt AC heater winding. It failed after a week or so.

After the likely problem was mentioned, I looked at the specs on the LED and was surprised to find that most LEDs have max reverse ratings of 5 volts or less. The 6.3 volt AC voltage approaches 9 volts  and it is enough to break down the diode on the non conducting side of the cycle.

The bottom line is that you can't really treat a LED as a typical diode.

Pat
N4LTA

[N0WVA]

OUT, DEMONS!!!

[w3jn]

Sounds like you might have an issue with the bias supply, or associated circuit.  You say you have -51V there, but how's the ripple?

Get in there with a scope, and read some voltages.  Figure out where the hum is coming from.  THose Vitamin Q caps are the best ever made, and would be my absolute last suspect.  In any event, bad bypass caps in the IF aren't going to cause hum anywhere.

[WB6NVH]

I don't want to sound mean, but this doesn't make much sense to me, if any.  Problems on a filament line are not going to "blow" capacitors.

Vitamin Q caps are really reliable and unless you are pulling one leg up and checking them for leakage, as well as capacity, you can't tell if they are bad. They shouldn't be responsible for hum in any case.  Are you sure they are Vitamin Q's?  Most SP-600's are full of those blasted bumblebees instead, except for the couple contracts which had ceramic discs.  But...I haven't seen every SP-600 contract.

I am too lazy to pull my SP-600 service manuals at the moment but the pilot lamps should just be on a filament supply line in parallel.  Whatever goes on in that filament circuit isn't going to affect anything else, if I remember correctly.

Those LED lamps are sold to replace 12 Volt auto lamps, but they will usually work as a # 47 replacement in radios as they have a limiting resistor built into the base and the PRV is accounted for as well.  I noticed that there are some sold as AC/DC and some just DC.  Frankly, # 47's aren't exactly unobtainium and they last a long time in this sort of application.  If you like colors, I would be inclined to just color the lamps with craft store stained glass coloring paint.

And...here's the main thing about radio improvement projects to remember: No good deed goes unpunished.  

[WD5JKO]

I have been following this thread wondering if the LED replacement was connected to the introduction of hum, or was this just a strange coincidence? Since I am not a big believer in coincidences, I have a theory. Maybe the lamp socket(s) have a problem. If the filament supply has the CT grounded, and either side gets shorted to chassis through a wire stand, then significant 60hz chassis current will flow. This current flow through the chassis would cause a ground loop, and could be picked up in the AF audio stages.

If the HUM is 60Hz then something with the filaments is likely going on. If the HUM is 120 Hz then my idea is all wet.

I bet the cap issue was there long before the LED lights were installed.

Jim
WD5JKO