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Thread: First question on my build

  1. #141
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    from the photo in #134 looks like your using crimp ring connectors. maybe thats ok but there are i counted at least 6 or 7 wires connected to that bolt. not really optimal IMO, also you really should be using solderable toothed ring connectors to give some bite into the metal if not already.

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  2. #142
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    Quote Originally Posted by J Luth View Post
    Originally that wire was running down the side of the amp along with a the 6.3v from the PT to the pilot light and the power switches. It then connects to a terminal board along with the standby switch and then a wire to the filter cap. I moved the wire yesterday figuring it may be interacting with the 6.3v and pulled it up away from everything I could. It was late and had to stop before I could see if it did anything.
    Did moving that wire have any effect on the 120Hz hum? It looks like it's running in in a long loop.

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  3. #143
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    Thanks Chuck

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  4. #144
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    That's all been changed. All of those crimp connectors were soldered also. Still trying different grounding.

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  5. #145
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    I moved the rectifier down by the filter caps, the wire from the rectifier to the cap is now only about 3" long but the wire from the standby switch is still long.
    What I have done has had a small effect on the hum but I really haven't had a chance to check it much. The past couple of days has been hectic here doing quick in and out jobs for people. That's what I get for doing 1 day or same day turnaround's.

    I'll be using it tomorrow, well actually tonight. That will be a real world test.

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  6. #146
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    Quote Originally Posted by J Luth View Post
    I'll be using it tomorrow, well actually tonight. That will be a real world test.
    We'll expect a full report

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  7. #147
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    Did a bit more cleaning up inside the amp but I didn't get a chance to try the amp other than turning it on and making sure it worked before I had to head out tonight.

    Well the full report would be, I took it to the gig tonight, no mushroom cloud, I didn't let the smoke out, the other members said the amp sounded better than it did and they liked it before all this and dare I say it, not a peep out of it, no hum, no buzz no nuttin just tons of volume and tone. The only issue with it is it now has a ton of gain, Have to pay close attention to the volume knob. It was a small club didn't need the volume up much, probably in the area of a little more than 1/2 way between off and 1/4 and it was considerably louder than it would have been before at that same setting.

    I have a couple of more coming up in a week or so only time will tell.

    So if it is all set, time will tell, I would like to thank all that have helped with this.

    Now to figure out the output watts.

    So here's another question or two.
    Is putting a signal into the amp, taking an ACV reading at the output jack, squaring that number and dividing it by the OHM load a close to accurate way to get the output? If so what would be the best tone to use. I have the small oscillator that can generate the tone and has an amplitude knob but not sure which tone to one use and what to set the amplitude of the oscillator to. Or is there a better way to get the output with what I have for equipment which includes an oscilloscope.

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  8. #148
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    The trick to measuring the power out is knowing when the amp distorts. Once the amp hits full power and starts clipping, the output power measured will increase fast. But you are really interested in clean power.
    Since you have an o-scope, it's easy to see. Set the amp volume to 1/3rd or 1/2, tone controls mid way. Bring the test tone amplitude up from zero til you see the sine wave start to flatten out on top and bottom. Back off till the flattening is just barely starting. Now measure the AC volts at the load and do your calculation. My preferred test tone frequency is 400Hz, many use 1Khz.

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    "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey

  9. #149
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    Thanks g1 just saw this.

    I was messing with it today with the scope and meter and was doing it close to what you wrote. I started with 1Khz and also tried a few others other difference was I set the oscillator amplitude to about 1/4 tone controls in the center and turned the amp volume knob up until the peaks of the wave started to flatten. Then fine tuned the volume knob until it was just before the wave flattened.
    Wasn't sure what tone to use or volume settings. I definitely need to mount the small dummy load to a heat sink or get a 100 - 200 watt dummy load, gets hot quickly.

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    Last edited by J Luth; 04-02-2018 at 03:44 AM.

  10. #150
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    So what kind of power output did you get?

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  11. #151
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    Quote Originally Posted by J Luth View Post
    Wasn't sure what tone to use or volume settings. I definitely need to mount the small dummy load to a heat sink or get a 100 - 200 watt dummy load, gets hot quickly.
    400Hz is fine. I set the oscillator output to 100mV and then use the volume control on the amp. 100mV will drive the amp to full power without overdriving the input stage. The dummy load will get hot. I'd use 200W or more for a 100W amp.

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  12. #152
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    Tested today although I don't trust my VM that much. Some day I'll get a better one. A Fluke would be nice but too expensive. Have see if there is a good one for less than a Fluke.

    Set the oscillator to 420Hz and as close to 100mV as I can with the meter, brought it up on the scope to where it just stats to show distortion.

    Usable is 85 to 87 watts before it distorts, if I push it all the way just to see what happens it's 135W.

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  13. #153
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    Planing on getting a 200W dummy load soon.

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  14. #154
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    Used the amp again and all is good.

    Thanks to everyone for the help.

    Have another question but that will be in a different thread.

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