Need some help with my Yamaha lamps

[bobbyrae]

Bought this intgrated amp and it sounds great, but the power meter lamps are burned out.

So I got the service manual. Guess what? The schematic says NOTHING about the voltage or current draw of those lamps!! GRRR

So I looked at the supply - it's 85 volts for 4 lamps in series, meaning they are drawing about 22 volts each. Trouble is, they only seem to make these in 14v and 28v. My initial guess was 24v.

The next problem was figuring out the current. Since they all appeared burned out, I was clueless. But then, close examination showed that ONE was still good! So I hooked it up to a power supply that would put out 20v. The current at that point was 100mA.

So what should I conclude about the ratings? Initially I thought 24v, 120mA. But if it was a 28v, then the current would be 140mA.

This is looking kinda hopeless because I just can't find anything even close. See attached photo. I think the shape and size classifies them as T 1-1/4.

And dwojo? He doesn't seem have anything like that.

 

[avionic]

What amplifier model are you refering to?

 

[merrylander]

The voltage and current ratings are usually on the schematic where the lamps are drawn, I would bet on 14V 85mA.

 

[bobbyrae]

The model is CA-810. As I said, the schematic DOES NOT give the ratings for the lamps.

One thing I just found out: after installing some 28v lamps as a test, I measured the voltage drop across each to be 18v. This is because there is a resistor in the loop. So MAYBE 14v, 80mA? Seems like they would burn out quick that way.

 

[jdurbin1]

The CA-1010 used 12V/60mA but there are 5 of them rather than 4... the service manual will list them in the parts section if you can find a copy, as you said the schematic doesn't provide that on this model though they do on others.

Found you an 18V part, but it's only 40mA... T1-3/4 also:

http://www.eiko-ltd.com/Products.aspx?ProductIndex=2102

John

 

[bobbyrae]

Here's another update

I was looking real hard at the lamp board and realized that it IS NOT quite the same as shown on the schematic! There are actually TWO resistors in the loop (not one) plus the four lamps, so if we divide 85 volts 6 ways, then we get to about 14v, which seems more reasonable.

 

[ymarko]

I'm pretty sure they are 14V because the lamp looks like ordinary Yamaha 14V lamp.

I'm not sure why do you need these lamps? Install LEDs, especially if all original lamps burned. You have a perfect Amp to start LED conversion.

 

[bobbyrae]

if I knew how

I'm pretty sure they are 14V because the lamp looks like ordinary Yamaha 14V lamp.

I'm not sure why do you need these lamps? Install LEDs, especially if all original lamps burned. You have a perfect Amp to start LED conversion.

The resistance and light output of LEDs is different from bulbs and I don't know how to pick LED's that are equivalent. Can you point me in the right direction?

 

[bobbyrae]

Here's the answer

Initially, I measured the voltage drop to the light connections (which are inside two resistors), but because there was no load, that voltage drop was incorrect. After accounting for the resistors in the circuit, installing some other lamps that were in the ballpark, and doing some calculations, I concluded that the original bulbs were 12v 100mA. This is a bit more than other Yamaha units at that time, but I believe the higher current is needed for the blue filter the CA-810 uses, which doesn't seem to be present on other models in the same line.

I installed some 80mA bulbs because that was all I could find and they seem to be adequate, but slightly dim.

 

[rpampt]

The resistance and light output of LEDs is different from bulbs and I don't know how to pick LED's that are equivalent. Can you point me in the right direction?

Check with AK's own whsh93a. He has led conversion kits with prewired for proper resistance LED's. Will plug or wire right in depending on necessity. I've gotten a couple kits from him.

 

[vega2k]

Recently I upgraded my CA-810 meter lamps to LEDs and found out that the lamps are 18V. At first my good old LED source assumed that they were 14V, but after frying a couple of LEDs, it turned out they are in fact 18V. As far as the current, I can gladly PM you my source contact so you can find out. Good luck!

 

[dgwojo]

14v/100ma/4.12mm are also available, they're over 50% brighter than the 14v/80ma/4.12mm.

 

[whsh93a]

Yes - the CA-810 definitely uses 18V to drive each lamp - if using LED replacements. My personal notes on that unit say, "The correct lamps are all wired in series and are 18VDC each. They are also wired fuse lamps. The supply voltage is 72VDC for the (4) lamps." This is important information if replacing the originals with LEDs.

I'm guessing that it was originally designed for 14V lamps, though, because the big 560 Ohm series resistor would drop around 24V at 40 mA to get the lamp voltage down to about 12V each. Using LEDs the resistor would not drop anywhere close to the 24V but the whole circuit would run far cooler.

I've attached a photo of the lamp board that was kindly sent to me when having the same discussion with another AK member.

The second photo shows the important parts of the lamp circuit. It shows +- 36V as the lamp supply to the (4) series connected lamps.

DH

Recently I upgraded my CA-810 meter lamps to LEDs and found out that the lamps are 18V. At first my good old LED source assumed that they were 14V, but after frying a couple of LEDs, it turned out they are in fact 18V. As far as the current, I can gladly PM you my source contact so you can find out. Good luck!