My St-70 is alive. After exorcising a couple of bugs, I've got it up and running. I had two PT leads crossed due to poor labeling or assembly on my part and with the faded leads, you can't tell. I also had one missed solder joint on a resistor. Other than that, no fuss, no muss.
I'm surprised at how strong it is and the few tunes I played through the CD player sounded really good. I'm tired and going to bed. I'll post pics when I get caught up. Yellow_Light_Colorz_PDT_09
It's Alive!!!!
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It's Alive!!!!
by rockable » Mon May 12, 2008 8:30 pm
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rockable - Posts: 49
- Joined: Thu Apr 10, 2008 7:02 pm
- Location: Greensboro, NC
by rockable » Tue May 13, 2008 5:34 pm
Aargh! Yellow_Light_Colorz_PDT_21
The left channel has a raspy distortion in it on the beat of the music at high volume. There is also a turn on transient thump in that channel when I power up. I also noticed that the left OT gets warm while the other is cool to the touch.
I've eliminated bad tubes, input signal and speakers. I've got the tubes biased at about 70ma/450v each pair. I've double checked my wiring and remelted a bunch of solder joints.
Ideas?
The left channel has a raspy distortion in it on the beat of the music at high volume. There is also a turn on transient thump in that channel when I power up. I also noticed that the left OT gets warm while the other is cool to the touch.
I've eliminated bad tubes, input signal and speakers. I've got the tubes biased at about 70ma/450v each pair. I've double checked my wiring and remelted a bunch of solder joints.
Ideas?
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rockable - Posts: 49
- Joined: Thu Apr 10, 2008 7:02 pm
- Location: Greensboro, NC
by rockable » Tue May 13, 2008 6:49 pm
Got it. The wire from pin 11 apparently cares whether you connect it to V2 rather than V3. Yellow_Light_Colorz_PDT_06
I am now turning electricity into heat and squeezing the music out it with my ST-70!
I am now turning electricity into heat and squeezing the music out it with my ST-70!
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rockable - Posts: 49
- Joined: Thu Apr 10, 2008 7:02 pm
- Location: Greensboro, NC
by burnedfingers » Wed May 14, 2008 4:40 am
When in doubt of the correct leads you can always take the end bells off the output transformers and check the wiring there and then re-label the wires. Mine were so faded and or missing that the only option was a visable check followed by a check of the output transformer wire positions inside.
You have to realize also that the stereo 70 is only 35 watts a channel and the power can be used up rather quickly with speakers of questionable efficiency. Crank up a bunch of bass and treble and your on your way to clipping in a hurry.
If you have a scope ,signal generator, and dummy load inject a signal and look at the waveform on the scope. Most will clip at around 15-17 volts into a 8 ohm load per channel. I personally run the bias at 50mA per tube.
In all the stereo 70 is so simple a 10 year old could put one together thus the reason for the 70's sales in great numbers.
You have to realize also that the stereo 70 is only 35 watts a channel and the power can be used up rather quickly with speakers of questionable efficiency. Crank up a bunch of bass and treble and your on your way to clipping in a hurry.
If you have a scope ,signal generator, and dummy load inject a signal and look at the waveform on the scope. Most will clip at around 15-17 volts into a 8 ohm load per channel. I personally run the bias at 50mA per tube.
In all the stereo 70 is so simple a 10 year old could put one together thus the reason for the 70's sales in great numbers.
- burnedfingers
- KT88
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- Joined: Mon Sep 05, 2005 6:38 am
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