What Did I Fry?

[blown240]

I was putting new electrolytic caps in my organ tonight and I ran into a snag...

I got them all in and bundled nice and cleanly and I went to turn it on.  A split second before my 3amp slow blow fuse went out there was "lightning" in my rectifier tube. (shouldnt have used a slow blow)

Come to find out I installed the caps backwards.  I thought the crimp was in the negative end and the stripe was on teh negative end of caps with both leads on the same end.

So I reversed all the caps and tried to fire it up again.  I guess I must have fried the rectifier tube because 2 of the 680ohm resistors started smoking.

Does this make sense, or am I missing something?  and just to clarify, what lead is the negative and positive on electrolytics?  I guess I am looking at a new rectifier tube and a couple new resistors.

[Platefire]

usually a rectifier tube is working or no. So if it is producing enough voltage to make the resistors smoke, it's probably fine. On the celectrolytics caps the positive end is marked with a "+" and negative "-". On a guitar amp I would normally pull the tubes to take the load off and turn it on to check voltage output of rectifier, but with all the tubes in some organs it may be a problem to do. Something you changed is still amiss! Look closely. Platefire

[blown240]

I am going to take the rectifier tube to my amp guy to test tomorrow.  And get the replacement resistors.  The caps I got are not marked with a + or -.  The either have a crimp, or a silver stripe depending on the way the leads come out.

[bigsbybender]

BUILD A LIGHTBULB CURRENT LIMITER!

$9 in parts have saved me thousands of dollars over the years. I didn't use one last year when restoring a 1935 Hammond Tone Cabinet, and the damage cost me over $450 in a new Power Transformer, rectifier, caps, rare power switch, and 2A3 tubes. Had I used it, I would have found that there was a shorted rectifier tube which was a $15-20 part with no damage done.


j.

[LooseChange]

+1 on the limiter.
Let's see a picture of the ecaps you are using.

[sluckey]

Look at the black and blue caps. They are marked the same but using different colors. Radial lead caps should be marked similarly...

[RicharD]

+2 on the lamp limiter.

[blown240]

I will build a lamp limiter today and redo all of this.  I hope I didn't fry anything else, but it seems to be limited to the power rail.

[jjasilli]

Also, if you have spare parts on hand you can temporally bypass the rectifier tube socket with a pair of SS diodes.  (Add a power resistor, say 100R 25W if you want to keep B+ down).  That should give ballpark correct, unloaded & loaded voltages, maybe save another rectifier tube at start-up.  And the project can go forward without waiting for the tube.

[blown240]

Looks like I fixed it!

I built a lamp limiter ($10.01)
Got another new set of Electrolytics installed
Borrowed a 5U4 from another amp

Them I fired it up with the lamp limiter. It took about 20 seconds before it really dimmed down, but I figured with all the circuitry and caps in this organ that may be about right.  So I unhooked the limiter and now the organ sounds FANTASTIC!  Its amazing what $20 in new caps will do!

[Tom_Hull]

hi


nice to hear,,,, that its working for you.... mine is still a head ach ..lol

BUILD A LIGHTBULB CURRENT LIMITER!

$9 in parts have saved me thousands of dollars over the years. I didn't use one last year when restoring a 1935 Hammond Tone Cabinet, and the damage cost me over $450 in a new Power Transformer, rectifier, caps, rare power switch, and 2A3 tubes. Had I used it, I would have found that there was a shorted rectifier tube which was a $15-20 part with no damage done.


j.

thanks.........  i' ll need to buy 75 and 100 watt lights now,,,,,, if there are any ,,,,, . its going to be against the law here lol,,,... the terrible 75 watt and 100 watt  light bulb,

if there are no light bulbs at the store  ,, what should i do ...

use christmas lights ,,lol ...thanks

[firemedic]

FYI if the e-lytic cap has no + or - markings, the arrow/chevron on the stripe will point towards the negative side.

[HotBluePlates]

Another tip: the crimp is "always" the positive end.

"Always" is in quotes because you will sometimes run into bipolar caps, which have no real + or - end. However, on these caps, both ends are crimped.

[birt]

hi


nice to hear,,,, that its working for you.... mine is still a head ach ..lol

BUILD A LIGHTBULB CURRENT LIMITER!

$9 in parts have saved me thousands of dollars over the years. I didn't use one last year when restoring a 1935 Hammond Tone Cabinet, and the damage cost me over $450 in a new Power Transformer, rectifier, caps, rare power switch, and 2A3 tubes. Had I used it, I would have found that there was a shorted rectifier tube which was a $15-20 part with no damage done.


j.

thanks.........  i' ll need to buy 75 and 100 watt lights now,,,,,, if there are any ,,,,, . its going to be against the law here lol,,,... the terrible 75 watt and 100 watt  light bulb,

if there are no light bulbs at the store  ,, what should i do ...

use christmas lights ,,lol ...thanks

if you really can't find a normal incandescent, go halogen. those are still available in the 100W to 2KW range ;-)

[blown240]

What difference is there between using a 75 watt or a 100/200 watt bulb?   Seems to me that the higher the wattage the more it will bring the power down.   So maybe the bigger the better?

[sluckey]

Think about it in terms of bulb resistance. A higher wattage bulb must have a lower resistance than a low wattage bulb. R = E²/P

A 25W bulb measures 45 ohms. A 60W bulb measures 17 ohms. A 90W bulb measures 13 ohms. (cold readings)

So, using a higher wattage bulb (lower resistance) in series with the amp will allow more current to flow thru the amp.

[blown240]

OK  that makes sense.  Its basically what I thought, just exactly backwards.  THANKS!

[sluckey]

Another way to think about it is to consider the worst case scenario. The amp is a dead short (just like a light switch). In this case the 25W bulb would draw 25/120 = 0.21 amps, the 60W bulb would draw 60/120 = 0.5 amps, and the 90W bulb would draw 90/120 = .75 amps. These are the maximum currents that the bulbs could draw and each would be at it's brightest. IOW, you could say, current would be limited to these maximum values. Higher wattage bulbs have a higher limited current.

Now hopefully your amp is not a dead short and the bulbs will glow at a reduced brilliance.