Help with Shorted Tube [Archive]

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malikarshad

11-06-2005, 01:36 AM

My tube fuse (1/2 amp fast blow) of right channel keeps on blowing. I checked the manual and it says i should check if the red led is not light then that tube is blown.
But the problem is non of the LED is on as there is no bias current because of blown fuse.
Then how do i go about finding which of the tube is shorted.

BTW its a Cary Tube Amp. Its has Quad El-34's for each channel. The left channel is good but there is the a problem with the right channel.
Here is the link to the amp specs http://www.caryaudio.com/products/audio/cad280sa.shtml

I'm very new to tubes so excuse me if i have said anything incorrectly.

What's the best way to find out which tube is shorted so that i don't keep on blowing fuse. So far I have blown 3 fuses.

Please help..........

organ

11-06-2005, 01:49 AM

Does the LED light up after replacing the fuse?

Try swapping the left tubes for the right. If the fuse blows on the same side again, it's most likely the amplifier.

Is it still under warranty? Try to contact Cary Beautiful amp btw. Hope you find the problem soon.

If you know any techies that are good with tubes, bring it to the shop. Trial and error is no fun especially when you have 12 power tubes to deal with(too much $$$).

Maurice

malikarshad

11-06-2005, 01:56 AM

Does the LED light up after replacing the fuse?
Maurice
No the LED's does not light up at all. I have also tried to adjust the bias for the RC but nothing happens. The fuse blows everytime I turn the amp on so I don't get a chance to do anything with the bias.
I think I will try swapping the tubes from LC to RC.
BTW how do i remove the tubes? Just pull it out!!!

organ

11-06-2005, 02:00 AM

The EL34's can be a little tight depending on the tube sockets used.

First, get a good grip on the base of the tube (the hard plastic part). Use your other hand and start wiggling/pulling slowly from the top of the tube. They should come out very easily like this.

organ

11-06-2005, 02:01 AM

Actually, before swapping tubes. Check every tube on your right channel. Make sure none of them have burnt marks or look strange.

malikarshad

11-06-2005, 02:17 AM

Actually, before swapping tubes. Check every tube on your right channel. Make sure none of them have burnt marks or look strange.
Little late but I went ahead a swapped the tubes and again the tube fuse is blown. I don't have any more fuse now. I'll have to wait until morning.

BTW does the burnt marks indicate that the tube is out?

The amp also has 2xEL84s and 2x12BZ7. Could these also cause a problem?

organ

11-06-2005, 02:29 AM

Man, sorry to hear about that.
If the tube was shorted, you're likely to see burnt marks in the glass if there were sparks with high voltage.

It could be the small driver tubes but hell, it could be anything. So far, I'm guessing it's the amp. If it blows again tomorrow, you should get it repaired.

malikarshad

11-06-2005, 02:31 AM

i checked all the tubes and there are no burnt marks or anything unsual from outside. checked all the amp fuses and they are OK.

malikarshad

11-06-2005, 02:24 PM

Anybody any thoughts. I've got this great amp and I cannot use it.
Please guys let me know..... :(

madmax

11-06-2005, 07:25 PM

You could pull all the tubes out and see if the fuse still blows. That would tell you there is something wrong on the inside of the amp. Good place to start.
madmax

malikarshad

11-06-2005, 08:41 PM

You could pull all the tubes out and see if the fuse still blows. That would tell you there is something wrong on the inside of the amp. Good place to start.
madmax
Thanks for the advice. I'll try that. :cool:
Damn these amp has 12xEL34.
Is it necessary to replace all 12 if one is blown. The tubes are EL34 BSTR. What brand is that?

madmax

11-06-2005, 09:09 PM

I don't think so. Each one probably has an adjustment to set the bias so they don't have to be matched. It would be a good idea to get the same brand as it has. If they have a marking on them like "34", "35", any two numbers like that you can order a single of the same value at www.thetubestore.com or other places.

BlueMDPicker

11-06-2005, 09:13 PM

The tubes are EL34 BSTR. What brand is that?

I believe they're Ruby tubes. Popular in guitar amps.

malikarshad

11-06-2005, 09:33 PM

I believe they're Ruby tubes. Popular in guitar amps.
Yes they are Ruby tubes. Do you know where to buy it or can i replace it something similar that will match the rest of the EL34 BSTR's

I don't think so. Each one probably has an adjustment to set the bias so they don't have to be matched. It would be a good idea to get the same brand as it has. If they have a marking on them like "34", "35", any two numbers like that you can order a single of the same value at www.thetubestore.com or other places.
Yes there are no. 31 and 32 on them.

I tried removing all the tubes & turning on the amp. The good news is :) the fuse does not blow.
The bad news is how do i find out which ones of the 12 tubes is shorted? :confused:
Do you think I should put one tube at a time a check if the tube blows? I'm not sure about it. Can somebody tell if I can do that?

BlueMDPicker

11-06-2005, 09:40 PM

You can get the tubes here (http://www.magicparts.com/main.htm) .

Put your tubes in in pairs, one per side, starting at the back. Turn all your bias pots all the way down. Power up with each pair until you encounter the fuse issue. Now you have it down to 1 of 2 tubes.

The amp will probably play with a pair missing at lower power. Order two new ones.

Are you sure you do not have a short at the speaker binding posts?

Edit - Oh yeah, don't forget to re-bias your tubes.

madmax

11-06-2005, 10:17 PM

Actually, do you know how to bias the tubes? Don't take that as a put down if you do, its just that you said you were new to tubes. :)
madmax

malikarshad

11-06-2005, 10:59 PM

Actually, do you know how to bias the tubes? Don't take that as a put down if you do, its just that you said you were new to tubes. :)
madmax
Well I read the manual first. It was when I was setting the bias I ran into the fuse problem. I can set the bias individually for each channel.
I was able to set the bias on one channel but the fuse always blows out even if the bias is turned to the minimum.
But thanks for asking :cool:

malikarshad

11-07-2005, 01:12 AM

The amp will probably play with a pair missing at lower power. Order two new ones.

Man thanks a lot for your advice :) . I was able to find a bad tube. Do I have to buy the same brand or any brand is ok as long as they match
The tubestore.com lists Shuguang EL34B (http://www.thetubestore.com/shuguangel34b.html) as Ruby EL34BSTR.
Thanks all for your valuable advice. It was really an experience troubleshooting the problem.

organ

11-07-2005, 01:15 AM

It might be the bias. Make sure you start with both bias pots on minimum. As you decrease one channel, the other will increase and vice versa. You have to increase one channel a little, check the other channel and increase it. Doing it slowly is the best way.

The EL34BSTR are from Ruby tubes. Ruby purchased from Shuguang which are made in China and put their logo on the tubes. Do they look like these? http://www.thetubestore.com/shuguangel34b.html I have a quad of Shuguang EL34B and they sound like SS to me.

Maurice

malikarshad

11-07-2005, 02:03 AM

organ

11-10-2005, 01:30 AM

Remember to increse the bias slowly over a period of 30 mins or more. Only when the amp is fully warm will the bias stabalize. Also, keep checking it throughout the day/night because it will drift along with your incoming AC from your wall. My amp is made to be biased at 1.56DCV but will drift 0.1V so I like to keep it around 1.46V.

I don't plan to use my Quad of Shuguangs EL34B's again. So if you're interested, PM me.

Maurice