Tube Line pre-amp smoked, pictures

[ymarko]

This is my 1st post in Tube Forum.

I got beautiful-looking, but non-working tube line pre-amp for free.
Owner said he got it about 8 years ago and it worked great, until one day smoke came from the right side.

I know next to nothing about electronics; this is Chinese clone and no schematic is available.

I opened the unit and here are my findings:

a) Fuse is 2A and it’s blown. I don’t believe this unit should run on 2A fuse, probably it should be something like 0.5A. I’m thinking that maybe fuse is the reason for the smoke, so when some part failed, 2A fuse did not protect the unit.

b) Black wire that goes from transformer to capacitors cut in half (picture). Cut is clean, not melted, not sure why.

c) Yellow part that sits on top of 2 large capacitors looks melted (picture). Part says PME2602HB622. I searched online and it’s capacitor, but I don’t found any specs. Could you maybe direct me to a replacement part?

Tubes seem fine. Two 6DJ8 tubes and one reads (not very legible read) like 6V6GT tube.

 

[gadget73]

Hm, not sure what purpose they are trying to serve with a capacitor across a voltage dropping resistor. I thought that went to ground initially, but no. Honestly, I'd chop it out of there and call it a day. it serves no useful purpose other than to sit way too close to a high wattage resistor that is chugging out heat. If you feel compelled to replace it, a 0.01uf 630v film cap of some sort mounted far enough away from that hot resistor to not melt again would do the trick.

 

[vinylkid58]

Two 6DJ8 tubes and one reads (not very legible read) like 6V6GT tube.

The tall tube isn't a 6V6. Looks more like a 6N6P.

jeff

 

[ymarko]

Here is close picture of this tube.
It reads: 6 (space, maybe something missing) 6 (kind of dash "-", possibly part of "G") T.
I tried different versions and came up with 6V6GT.

Still have 2 questions:
- Is 2A fuse seems fine, or I should go with a smaller one?

- What is PME2602HB622 ? What would be a replacement part?
I appreciate your input to eliminate it altogether, but before I do this, I would like to know what it is.

 

[mrwood200]

First tube forum post & you got a project!

I would recommend trying to learn as much as you can about the unit/circuit prior to fuses, etc. How about some pictures of the faceplate? back? Any label, model number, etc?? So far, looks like a nice unit certainly worth a project!

I don't think that is a 6V6GT; the ones I have seen have alignment keys in the base.

 

[Pio1980]

6J6 equiv if 7 pin, mebbe.
True 6J6 is a common cathode frame grid dual triode.

Sent from my SM-N900V using Tapatalk

 

[peterh]

6V6GT is an octal socket tube. So it's not a 6V6

About the "rifa cap" ; just remove it. It obviously toast.
It is in parallel with a 12 ohm resistor , thus a .22 uF cap won't do much of a difference.

To be sure one has to reconstruct the schematics.

 

[ymarko]

This tube has 9 pins, and a space between pin 1 and 9. Has Chinese Star logo.

There's no sticker on the back panel.
There's a label next to detachable power cord and fuse compartment, it says 220V. That was my question to owner, but he said pre-amp worked just fine in US with this fuse. I still believe 2A is too much for a pre-amp.

 

[vinylkid58]

This tube has 9 pins, and a space between pin 1 and 9. Has Chinese Star logo.

So it's a Chinese 6N6P then.

There's no sticker on the back panel.
There's a label next to detachable power cord and fuse compartment, it says 220V. That was my question to owner, but he said pre-amp worked just fine in US with this fuse. I still believe 2A is too much for a pre-amp.

It's not going to work "just fine" if it's got a 220V primary transformer.

jeff

 

[ymarko]

Preamp worked for many years in US in this configuration. First with original owner (for years), then with second owner (for years), and only then smoke.

I'm not sure how official 220V sticker is, but common sense tells me that unit should not smoke because of under-voltage. Probably some other reason.

 

[gadget73]

If it was running at half voltage, it probably just wouldn't work. Most probably it can be used on either 110 or 220 with some internal wiring change. Thats possibly part of what that cut wire is about.

 

[derekva]

If it was running at half voltage, it probably just wouldn't work. Most probably it can be used on either 110 or 220 with some internal wiring change. Thats possibly part of what that cut wire is about.

That's what I was thinking as well.

-D

 

[denny3249]

The RIFA-style suppression safety cap that went up in smoke looks identical to the ones Yamaha used in their X power supplies found in several amps. Some time ago, a service bulletin was issued by Yamaha to replace them with a newer X rated suppression cap as they had a tendency to go up in smoke or catch fire...for no reason other than being faulty. If you want to put a replacement in it's place, they are available at Mouser. A schematic would be handy to understand why it's located where it is....

 

[vinylkid58]

Preamp worked for many years in US in this configuration. First with original owner (for years), then with second owner (for years), and only then smoke.

I'm not sure how official 220V sticker is, but common sense tells me that unit should not smoke because of under-voltage. Probably some other reason.

You really need to hook it up to a variac and test some voltages. Otherwise you're just guessing, and so are we.

Thats possibly part of what that cut wire is about.

Cutting a wire on the secondary side doesn't make sense IMHO.

jeff

 

[jaymanaa]

The RIFA-style suppression safety cap that went up in smoke looks identical to the ones Yamaha used in their X power supplies found in several amps. Some time ago, a service bulletin was issued by Yamaha to replace them with a newer X rated suppression cap as they had a tendency to go up in smoke or catch fire...for no reason other than being faulty. If you want to put a replacement in it's place, they are available at Mouser. A schematic would be handy to understand why it's located where it is....

I remember that. It gave Rifa a pretty bad black eye for awhile. I've used the PHE (blue case) series with very good results though.

FWIW, I just looked at a bunch of Rifa caps and none of them sported that big "F" logo? Could there be two different companies here?

 

[vinylkid58]

I had a look on the Digikey site, and you can still get the PME series caps, but they are listed under "Kemet" as the manufacturer.

jeff

 

[ymarko]

If you want to put a replacement in it's place, they are available at Mouser. A schematic would be handy to understand why it's located where it is....

There's no schematic.
Could someone knowledgeable please identify this faulty capacitor and direct me which one to buy?

 

[denny3249]

Remove the cap and look on the backside for any identifying marks... I'm taking a WAG that it's .22uF because of the .22 at the end of the part number... As far as voltage rating, maybe there's something on the other side, but I would imagine anything 275v or higher would be ok.... Do a search on Mouser for 'safety film capacitors'.

 

[ymarko]

Remove the cap and look on the backside for any identifying marks... I'm taking a WAG that it's .22uF because of the .22 at the end of the part number... As far as voltage rating, maybe there's something on the other side, but I would imagine anything 275v or higher would be ok.... Do a search on Mouser for 'safety film capacitors'.

You are Da man.

Indeed, everything is printed on the back side and edge. 0.22uF and 250V.
I also read online that these caps fail without reasons.

Could you please save me 2 weeks of confusing Mouser work and give me a link to the replacement cap?

 

[jaymanaa]

Could someone knowledgeable

That just eliminated 99% of the people on AK. ara: