I kinda sorta burned up my K12-G power transformer

[RevMen]

Last year I put together the famous K-12G kit as my first step into the world of tube hi-fi. I liked it a lot. I built an enclosure for it that had ventilation for the tubes but not so much for the transformers. oops. I listened to it for about 4 hours and got really hot and then it stopped working. No glow on the tubes, no voltage on the board, nothing. The fuse is fine, I double, triple checked it and put a meter across it to make sure it's not open.

I'm about 95% sure the power transformer overheated and busted. I can't see any voltage on any of the secondaries, and I'm reasonably sure there's voltage being applied to the primary. I'll finish testing it out tonight to be completely sure.

The wires on the secondary side are like so:

Red - 170 V
Red - 170 V

Green - 5.9 V
Yellow - 0 V
Green - 5.9 V

So there's a center tap for the heater leads but not for the high voltage side.

Would I be able to replace it with this transformer from Antek? Would tying two of the 6.3 V leads together give me 6.3V with a CT? Or would that be 12.6 V? Or none of the above?

This Edcor looks like a direct replacement and not too bad at $40, but I'd like to mess with the Antek if it'll work.

[boywonder]

Do you know how much B+ current the power transformer needs to provide? and heater current?

You can make a psuedo-center tap for the heaters by putting two 100 ohm resistors in series across the 6.3V winding. The center tap is then between the resistors.

[kevinkr]

The Antek should work OK. You could even power the two channels separately if you are highly motivated.

[RevMen]

Thanks for the help, folks.

Originally Posted by boywonder

Do you know how much B+ current the power transformer needs to provide? and heater current?

Just going on memory, I think the markings on the transformer said the 170V current is 0.25A and the 6V current is 3A. But I might be way off. I'll verify tonight.

I suspect swapping the output transformers out for some beefy ones would improve the sound of this amplifier noticeably. I might look into doing that while I'm already ordering a transformer.

[kevinkr]

Upgrading the OPTs isn't a bad idea and Edcor probably makes something suitable. Antek power transformers are very good IMLE, but some have expressed concerns over how their OPTs are wound, and hence their performance.

[Soonerorlater]

Would tying two of the 6.3 V leads together give me 6.3V with a CT? Or would that be 12.6 V? Or none of the above?

Don't think the 10 GV8 tubes are 6.3 volts for heaters


http://www.radiomuseum.org/tubes/tube_10gv8.html

[RevMen]

I went home at lunch, uninstalled the power transformer, and confirmed that there is no voltage on any of the secondaries when there is voltage on the primary. So I guess I burned up the primary.

Here are the markings on the transformer:

MODEL: K-8G
INPUT: 120VAC 60Hz (BLK-BLK)
OUTPUT: 170VAC 300mA(RED-RED)
5.9-0-5.9VAC 2A(GRN - YEL - GRN)

And thanks for the link to the tube data. 10GV8 needs 11.6V and 0.45A for filaments. The kit transformer provides 11.8V and 2A (0.5A per filament) to the heaters, which is just above what's required.

So now I worry that the Edcor's 250 mA rating means it will not provide sufficient current, since the K-8G transformer seems to be spec'd at just enough to get the job done. What do you think? Is the Edcor up to the task, even if its output current rating is 50 mA less than the K-8G?

[kevinkr]

Originally Posted by RevMen

I went home at lunch, uninstalled the power transformer, and confirmed that there is no voltage on any of the secondaries when there is voltage on the primary. So I guess I burned up the primary.

Here are the markings on the transformer:

MODEL: K-8G
INPUT: 120VAC 60Hz (BLK-BLK)
OUTPUT: 170VAC 300mA(RED-RED)
5.9-0-5.9VAC 2A(GRN - YEL - GRN)

And thanks for the link to the tube data. 10GV8 needs 11.6V and 0.45A for filaments. The kit transformer provides 11.8V and 2A (0.5A per filament) to the heaters, which is just above what's required.

So now I worry that the Edcor's 250 mA rating means it will not provide sufficient current, since the K-8G transformer seems to be spec'd at just enough to get the job done. What do you think? Is the Edcor up to the task, even if its output current rating is 50 mA less than the K-8G?

I would say it was very dodgy, but they will make you exactly what you need, although you will have to pay a set up charge in addition to the per piece charge. Depends on how much you are willing to pay..

In terms of padding down 12.6V for the filaments (4 in parallel) something like 0.43 - 0.47 ohms (5W wire wound) in series would do that..

[Soonerorlater]

OUTPUT: 170VAC 300mA(RED-RED)

IMHO 200mA would be ok, it's not like S5 to overspec unless it's from one of their other kits.

[RevMen]

I don't follow you. If S5 is not likely to overspec, then wouldn't I want a replacement transformer that at least matches the S5 transformer?