Tube AMp repair tech

Hi guys,

Managed to let the magic smoke out from my Cary 805 SE mono last night. Any idea who is able to make a competent repair in Malaysia ?

Regards,
Joe Ling

Try him. He is one of the best known hifi repair man. Another is Mr Yap based at Taman Megah Petaling Jaya.

Oh no!! The same thing happened to me in December. How did it happen?

In my case - I mis-mounted the 845 tube in one of the sockets, probably causing a short. It took out a resistor, bias pot, and a fuse. Cost of parts = AUD$20. Cost of repair (total) = AUD$100. The annoying thing is that the parts were not readily available - Cary uses very high tolerance parts. Make sure that your repairer does not use generic parts for repair.

It is quite easy to open up your amp to inspect it BTW. Remove all the tubes, then turn it upside down. Remove every screw that you can see. The bottom plate should just lift off.

Hi Doc,

Thanks for the quick reply. Already contacted Mr. Oh.

WongKK. I went away for a week & when I came back, decided to mount the newly purchased pair of EMT 300B. The first tube was ok. Managed to adjust the bias & got it working. When I mounted the second tube, I noticed the bias current shooting up & before I could adjust, smoke started to appear from the chassis seeping up from the OT. Immediately switched off unit.

I tried the EMT tube in the other working unit, Again, current shooting. Quickly disconnected before I see smoke.

Also I noticed that one of the NOS 6SN7 has a rattling sound on the unit that gave up the smoke. Not sure this problem was before the smoke incident or after.

Regards,
Joe Ling

Hi Joe, sorry to hear that. You probably have a faulty 300B. Can you get a refund?

I suggest you take a look in your amp just to make sure that you know for yourself which part has been damaged. I would look at the 300B socket - there should be a couple of resistors leading up to it.

Here is a picture of my Cary 211AE when it blew. If you look closely, you will see a blown resistor. It is in the 9 o'clock position in the bottom 845 socket. If you look at the same resistor at the top 845 socket, you will see it is brown coloured and pristine - this is a Vishay branded resistor.



If you look at your "good" amplifier, you should be able to read the value of the resistor. Make sure your repairer orders the exact same part and does not substitute it for some 1-sen resistor.

There is also a strong likelihood that the bias pot is blown. Cary themselves can supply the replacement, but they are somewhat slow at responding to emails. If you want, I can call my repairer and ask him where he sourced his parts from. From memory, they came from Canada, and took about 5 business days to arrive. The parts are very cheap.

I suggest that you change resistor, bias pot on the other "good amp" as well since it may have overheated and sustained damaged to some extend.

after all the parts are cheap, so do it just as a precaution.

SET circuit quite simple, if you have multimeter and and familiar with the use of solder gun , i think u can trouble shoot by yourself.

what's the wattage of the chatode resistor?

since it it cause by high current draw, u may need to check or replace item below:

1) cathode bias resistor
2) cathode bias capacitor
3） hum pot
4) plate resistor
5) bias pot.

for the part like resistor, other than searching for original resistor , u can always take this chance to replace with "better resistor" like duelund, kiwame & so on.