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.
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.
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The Antek should work OK. You could even power the two channels separately if you are highly motivated. 😀
Thanks for the help, folks.
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.
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.
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.
Don't think the 10 GV8 tubes are 6.3 volts for heaters
http://www.radiomuseum.org/tubes/tube_10gv8.html
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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?
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..
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?
Something doesn't make sense.
3oomA should be big enough to run an 8 watt amp. Is it a 300mA transformer? and if so why did it's primary go bust?
3oomA should be big enough to run an 8 watt amp. Is it a 300mA transformer? and if so why did it's primary go bust?
The original transformer is 300mA and it worked great until I forced it to operate in high temperatures.
There may be a thermal fuse in the primary that opened up. I don't believe they are using a doubler here, but not having seen the schematic I can't say for sure, so 300mA would seem to be plenty.
I would love the fault not to be yours, but if you insist....😀
Pictures please of the offending enclosure......😉
Seriously whatever caused the demise of your transformer I would be grateful of someone more knowledgable letting us know whether or not 300mA is overkill.
Brgds Bill
sorry Kevinkr for not checking before posting
Pictures please of the offending enclosure......😉
Seriously whatever caused the demise of your transformer I would be grateful of someone more knowledgable letting us know whether or not 300mA is overkill.
Brgds Bill
sorry Kevinkr for not checking before posting
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Schematic?
Doesn't appear to be a voltage doubler........looks like a full wave bridge and CRC
S-5 Electronics K-12G Tube Amplifier Schematic - DIY Audio Projects Photo Gallery
Doesn't appear to be a voltage doubler........looks like a full wave bridge and CRC
S-5 Electronics K-12G Tube Amplifier Schematic - DIY Audio Projects Photo Gallery
The offending enclosure is little more than a box that surrounds the kit on all sides. On the top I have panels for input connectors, speaker connectors, input selector, and volume. It's sort of a weird design but it makes sense in context, as it's meant to drop in to a top-access compartment in my custom made stereo console.
I cut a big slit over the top of the tubes but didn't think to give the transformers ventilation as well. Huge mistake. When I get a replacement transformer I'm going to drill ventilation holes on the top over the transformers and along the bottoms of all of the sides to allow air to be drawn in.
300mA is enough for sure. That's the current rating of the transformer I'm trying to replace. The proposed replacement is an Edcor that is only rated for 250mA. Therein lies the conundrum. Should I get the Edcor and push my luck? Or should I seek out a replacement transformer elsewhere. I suppose I could get another from S5, but it seems like that wouldn't be any less expensive than buying a higher quality transformer elsewhere.
I cut a big slit over the top of the tubes but didn't think to give the transformers ventilation as well. Huge mistake. When I get a replacement transformer I'm going to drill ventilation holes on the top over the transformers and along the bottoms of all of the sides to allow air to be drawn in.
300mA is enough for sure. That's the current rating of the transformer I'm trying to replace. The proposed replacement is an Edcor that is only rated for 250mA. Therein lies the conundrum. Should I get the Edcor and push my luck? Or should I seek out a replacement transformer elsewhere. I suppose I could get another from S5, but it seems like that wouldn't be any less expensive than buying a higher quality transformer elsewhere.
The Edcor probably has more than sufficient capacity, but don't hold me to that as I have no way of knowing for sure.. 😀 Does it provide 12.6V filament power which you can pad down with a resistor? 6.3V versions of those tubes may be hard to find and expensive.
I think that's as close to a direct replacement as I'm going to get. Filament voltage is only 0.2V more than the kit transformer.
The amp will draw 150 mA DC or less, which requires about 250 mA AC from the transformer (power supply ripple current in addition to the DC load). The Edcor should be just enough - the Antek will be loafing at that load. If you connect the two 6.3V windings in series, you have a center-tapped 12V winding (you may need some resistors to drop the voltage a bit).
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