Bugera 6260 issue

[Chuck H]

Any suggestions for follow up.

Well I just looked at the schematic more closely and realized I was in error regarding the peripheral circuits. The AC filament winding looks to be connected to the other circuits I mentioned through a single 4.7k resistor (R104). Why, I can't say.

I don't suppose there'a any follow up except that it's obvious that connection became hot enough to discolor. That's a result of excess current. And the filament voltage you report seems low at 6V unloaded/5.7V loaded. That may be normal for that amp. The schematic doesn't say. But at face value you have symptoms of an over loaded filament winding. Follow up for me would be to confirm the voltages you have there, which I can't do and the schematic doesn't specify. And if it's indeed low I would be looking for why. If there is a problem the amp may work for awhile, but on borrowed time.

[Helmholtz]

The AC filament winding looks to be connected to the other circuits I mentioned through a single 4.7k resistor (R104).

That elevates the 6.3V heaters to +24VDC and also means that there can't be a grounded CT for the 6.3V winding (or other ground reference like balancing resistors).

[Chuck H]

Ah! Thank you. That's where I was confused. Because the DCV reference was only to the one side, rather than to the CT. I haven't seen that before. I guessed it was probably an elevation circuit but didn't want to speak out of my depth.

[Helmholtz]

Because the DCV reference was only to the one side, rather than to the CT.

The 6.3V side where the resistor connects to will be at constant +24VDC while the other side will be at +24VDC +/- 6.3VAC, i.e. varying between 15.1V and 32.9V instantaneous voltage.

[DrGonz78]

I remember working on a 6262 where the yellow filament wiring had to be soldered directly to the board due to the fact that the molex connector was not holding up well. Not sure what the connector looks like in this 6260 amp but the OP keeps mentioning it looking burned and cleaning pins got it working again. But how long will those pins hold up if that is the type of connector on the amp. I think we need a picture to confirm what we are dealing with...

[Snibbornairb]

The discoloration was just to a light brown, not nearly as bad as that picture. Could the addition currwnt be tge result of turning on standby switch before tubes warmed up? Not too familiar with tubes and like I said, it was my son who was operating the equipment when we lost the power section.

[Snibbornairb]

It has that same style molex connector

[Snibbornairb]

Do you know what caused the failure in the amp in the picture?

[Chuck H]

Do you know what caused the failure in the amp in the picture?

THAT is the perfect question Although it's possible to diagnose if there's an issue in your amp as well. And that's good because it's not necessarily the same problem.

[g1]

I think in the case shown, the type of connector used is just not a great idea for carrying this type of current. A slight bit of resistance develops across the contacts (oxidization) and you have a lot of heat developing. From there it's just a downward spiral, more heat causes more resistance causes more heat, etc.
Very common for these and similar connectors in heater wiring circuits to have been bypassed by techs, often with no other underlying high current fault.

[Chuck H]

I think in the case shown, the type of connector used is just not a great idea for carrying this type of current. A slight bit of resistance develops across the contacts (oxidization) and you have a lot of heat developing. From there it's just a downward spiral, more heat causes more resistance causes more heat, etc.
Very common for these and similar connectors in heater wiring circuits to have been bypassed by techs, often with no other underlying high current fault.

Agreed, but,..

6V on unloaded winding and 5.7V loaded. Normal? I don't know this amp. I think it should be confirmed that that is the normal voltage for this amp and that there isn't something loading the winding.

[DrGonz78]

If it has that molex connector it needs to be removed and soldered straight to board. As I remember there was a service bulletin from Bugera about fixing that exact issue.

[g1]

Agreed, but,..

6V on unloaded winding and 5.7V loaded. Normal? I don't know this amp. I think it should be confirmed that that is the normal voltage for this amp and that there isn't something loading the winding.

I got the impression that measurement was done at the socket, not at the winding. So I'd expect some drop at the connector when winding loaded.

[Chuck H]

My memory said 5.7V for some reason. It was actually 5.6V. This is what I read:

There is a little burn on the connector at the yellow wire. It reads about 5.6v....I replaced all the tubes with tubes pulled from a working amp...

Then

So it seams it may not just be the connection. When I pulled all the power tubes, I then had the 6v on the traces below.

I interpret this to be read from the board traces without power tubes installed.?. It could be that it was read at the socket and the socket was presenting some resistance before cleaning? Which, BTW, is not usually best done with sandpaper. But since it was done and the amp was working I didn't mention it before.

[g1]

A reading taken right at the winding both loaded and unloaded would help.