tube is flashing and glowing very bright!

[pho_boi]

Hello friends,

I've got a Cayin A-50T integrated amplifier, and I'm experiencing some very scary problems.

Out of nowhere, one of the EL34 tubes starts to flicker and glow a lot more than the others. My right speakers starts to make popping sounds too, this is when I switch everything off. It's happened 3 times over the past year or so.

I'm sure that its not the tube, because the first time it happened I changed all four EL34s and it's still occuring in that same tube position. The other three tubes have never had this happen, only happens in that one tube socket.

Any clue what is going on? I really wanna fix this because I don't want to ruin my speakers or the tubes.

Thanks everyone 🙂

 

[karma]

what shape are your tube sockets in? are thay new old?

 

[SHiFTY]

Does the grey metal structure (plate/anode) glow bright red? Or is it more of a sparking in the tube?

If it is glowing red, then you have either a bad coupling capacitor or no bias voltage.

If it's sparking you might have no screen voltage or a faulty connection.

 

[pho_boi]

what shape are your tube sockets in? are thay new old?

It's a pretty new amplifier, the socket are just the regular 8 socket ones for el34s.

Does the grey metal structure (plate/anode) glow bright red? Or is it more of a sparking in the tube?

If it is glowing red, then you have either a bad coupling capacitor or no bias voltage.

If it's sparking you might have no screen voltage or a faulty connection.

It's the filaments (i think), they normally glow like regualr tubes. But that particular tube starts flicker and glowing a lot brighter than the others.

I've checked the bias, and they are all at 0.35v or 35ma.

 

[karma]

ic well shifty covered the rest

cheers😀

 

[pho_boi]

I've found a link with pictures of my amps underside, can someone point out to me which ones are the coupling caps?

http://www.sanyue.net/read.php?tid=11067


Thanks

 

[Alastair E]

coupling caps.....

Not really easy to see in the pics postd, They take ages to load, and you cannot see even then..........

Best get the schematic and check there........

 

[Svein_B]

You can find some excellent photos at store.acousticsounds.com
Select the <large images for high bandwidth users>

I do not have a circuit diagram, but from memory:
Input 12AX7 (both triode halfs in parallel), direct coupled to 12AU7 phase splitter in LTP configuration. Coupling caps are .22uF (RealCap) mounted on bias reg circuit board.

Svein_B

 

[pho_boi]

I'll go get some replacement caps soon.

Would there be anything else that would be causing these symptons?