Triode st70 trouble.
- Thread starter dmag
- Start date
Pio1980
AK Member
It was a "floating heater" arrangement with capacitor bypass, to allow the heater lines to self-elevate.
I havent run a signal through this. I can if desired.
When i received it i checked wire for wire of the old one. Everything matched color wise.
Is it possible the wire colors were done wrong, as in a green and brown were mistakenly used for the green/yellow and brown/ yellow and vice versa? Would the thing still work at all?
Heres a pic of what may be center taps(?) to the cap board. They run thru a .022 cap to the ground connection.
And gadget, outer of the input to pin 3- ef86 gives me 7 meg on the right and open on the left channel. With tubes and shorting plugs in. With tubes out- open.
And by the way, thanks for sticking with me on this.
When i received it i checked wire for wire of the old one. Everything matched color wise.
Is it possible the wire colors were done wrong, as in a green and brown were mistakenly used for the green/yellow and brown/ yellow and vice versa? Would the thing still work at all?
Heres a pic of what may be center taps(?) to the cap board. They run thru a .022 cap to the ground connection.
And gadget, outer of the input to pin 3- ef86 gives me 7 meg on the right and open on the left channel. With tubes and shorting plugs in. With tubes out- open.
And by the way, thanks for sticking with me on this.
Attachments
Maybe, need a bit more solder on those 0.022mfd leads?
Is whatever is under the green wire touching the board? Is it supposed to?
Sounds like an open on the signal ground to circuit board. Looks like a pair of wires from the board to each Jack. On the board the signal ground goes to circuit ground through a 10 ohm. Think I'd have a look at the jack wiring
Sounds like an open on the signal ground to circuit board. Looks like a pair of wires from the board to each Jack. On the board the signal ground goes to circuit ground through a 10 ohm. Think I'd have a look at the jack wiring
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That is one of four standoffs that the board is attached to. I suppose wires touch it when it is attached. But it would be no fifferent from them touchkng tje chassis. In the pic the board is not attached. Ive even run the amp with it lifted from the chassis.
The FCT wires were soldered from the bottom, but I have already resoldered them.
The FCT wires were soldered from the bottom, but I have already resoldered them.
Gadget these suggestions were the key. I ohmed the input jack wiring and it was good. I looked at the board layout diagram to find the ground resistors and one had a little chip in it. Checked them both and they rang at 16 and 30 megs! Replaced them and voila!!! Hum gone.
Voltages are below. There are differences from Triode’s spec. Small tubes pins 4,5 and 9. They forgot about the heaters i guess.
One other question, the layout calls for 10 ohm , 1/4 watt for these resistors. They had supplied 1/2 watt. I have 1/2 in there now. Why the smaller size, and is it necessary? Could that have contributed to the fried transformer? Or a result?
Ill go through the thing soon, since its pretty messy after all this.
I cant thank you and Mr Bochie enough. I saw a quote somewhere that experience is what you get when things dont go as planned.
Steve
Attachments
It's not carrying any significant current or voltage, can use any wattage you have with no issues.
The only time that would ever carry current is if it was using an un grounded cord and there was a short from the ac mains side to chassis *and* you had something plugged in to the input Jack's that was grounded. Current would flow from chassis through that resistor to ground. Absent that, truly NFC.
Glad you got it worked out.
The only time that would ever carry current is if it was using an un grounded cord and there was a short from the ac mains side to chassis *and* you had something plugged in to the input Jack's that was grounded. Current would flow from chassis through that resistor to ground. Absent that, truly NFC.
Glad you got it worked out.
