2204 to Dirty Shirley conversion?

  • Thread starter Thread starter ledvedder
  • Start date Start date
At some point in troubleshooting I'll just measure the AC voltage as I progress thru the amp starting at the input jack. You'll need some way to input a constant signal like a loop pedal just looping one note or a delay on infinite delay or something.

For example, measure the input AC voltage at the input jack, then the first grid, then the first plate, then the first gain control hot lug, then the wiper, then next grid, etc. Just follow the signal thru the amp. If you need some sort of ballpark reference for what AC voltages you should expect, measure another amp of yours. It sounds like its in the early preamp because you don't have much distortion so you should get to it pretty quickly.
 
SpiderWars said:
At some point in troubleshooting I'll just measure the AC voltage as I progress thru the amp starting at the input jack. You'll need some way to input a constant signal like a loop pedal just looping one note or a delay on infinite delay or something.

For example, measure the input AC voltage at the input jack, then the first grid, then the first plate, then the first gain control hot lug, then the wiper, then next grid, etc. Just follow the signal thru the amp. If you need some sort of ballpark reference for what AC voltages you should expect, measure another amp of yours. It sounds like its in the early preamp because you don't have much distortion so you should get to it pretty quickly.
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I actually bit the bullet and ordered an oscilloscope w/ signal generator last night. I figured it's a good investment, since I'm really enjoying amp building and modding.
 
ledvedder said:
I actually bit the bullet and ordered an oscilloscope w/ signal generator last night. I figured it's a good investment, since I'm really enjoying amp building and modding.
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You need to know that you should also invest in a good bench isolation transformer where ground on the primary is not tied to neutral on the secondary. When using oscilloscopes and test equipment that isn’t battery powered, you should float either the test equipment or the DUT but never both, and rules of thumb normally point to floating the DUT over your wall powered test equipment. The reason is due to ground loops so you don’t cook your test equipment and also for your own safety working on equipment faults. There are a lot of people that don’t do this and they’re dancing on the dangerous side not knowing that when you start plugging test equipment into the same house electrical panel as your DUT, that they are now electrically connected and a short is simply one bad o-scope probe ground clip connection away. It’s especially important to isolate the DUT when you start clipping your probe reference point to some other potential than ground.

Also please don’t take this the wrong way - also look into buying a rosin flux pen, do some more research on soldering techniques, and let us know more about your soldering gear/temp settings/current solder. You’ve also got to get some practice in with soldering. Those joints need to look shiny and domed.
 
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glpg80 said:
You need to know that you should also invest in a good bench isolation transformer where ground on the primary is not tied to neutral on the secondary. When using oscilloscopes and test equipment that isn’t battery powered, you should float either the test equipment or the DUT but never both, and rules of thumb normally point to floating the DUT over your wall powered test equipment. The reason is due to ground loops so you don’t cook your test equipment and also for your own safety working on equipment faults. There are a lot of people that don’t do this and they’re dancing on the dangerous side not knowing that when you start plugging test equipment into the same house electrical panel as your DUT, that they are now electrically connected and a short is simply one bad o-scope probe ground clip connection away. It’s especially important to isolate the DUT when you start clipping your probe reference point to some other potential than ground.

Also please don’t take this the wrong way - also look into buying a rosin flux pen, do some more research on soldering techniques, and let us know more about your soldering gear/temp settings/current solder. You’ve also got to get some practice in with soldering. Those joints need to look shiny and domed.
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I'm looking into this transformer, Jameco Valuepro ITR300 Power Transformer, Isolation, 120VAC, 300Va, 3.2" W x 4.6" D x 4.2" H https://a.co/d/aWY38F7.

I have gotten better with my soldering on the other turret builds I've done. Definitely not perfect, but better. For this Origin, I've been at 340 degrees C, but it's so difficult getting into some of those tight spots. Here's my soldering station.

20221212_100908.jpg
 
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300VA is too small for tube amps. Many tube amps are in the 400-500VA range especially 100 watters. You’ll possibly eventually venture into other equipment too down the road so it’s better to buy it once especially since they’re heavy and bulky.

I bought mine ages ago, and I only use it when I start bringing out wall powered test equipment, but I use a medical grade isolation transformer. I took it apart and physically verified the ground on primary only grounds the chassis and the transformer core, but not the switched neutral on the secondary. They’re normally held to higher standards with better grade components/switches, are less noisy, and built to tighter tolerances.

You need to double your soldering temperature. I use no less than 650 deg F. They make special pencil tips for sharp corners and just know you likely need to get comfortable with lifting the entire board out of the amp instead of top side soldering.
 
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glpg80 said:
You need to double your soldering temperature. I use no less than 650 deg F. They make special pencil tips for sharp corners and just know you likely need to get comfortable with lifting the entire board out of the amp instead of top side soldering.
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In Jason's videos, he specifically mentions not to go much higher than 340 C when working with the Origin pcb. I did remove the boards from the chassis, but that was also after the 1st time I did Jason's plexi mod to it.
 
ledvedder said:
In Jason's videos, he specifically mentions not to go much higher than 340 C when working with the Origin pcb. I did remove the boards from the chassis, but that was also after the 1st time I did Jason's plexi mod to it.
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340C is not 340F
 
Here's a short video I did of the signal trace from v2 back. Let me know if my assumptions of an issue at v1 are correct?
 
ledvedder said:
Here's a short video I did of the signal trace from v2 back. Let me know if my assumptions of an issue at v1 are correct?
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It probably is early in the pre since it's not very distorted. The voltages don't look off. You probably just have something routed wrong, bad connection, or maybe an inadvertent ground somewhere.
 
I pulled the boards out again today. Traced the signal again. Re-did some solder joints. After putting it all back together, I'm still having the same issue. Ok, here's an interesting thing I found. If I jumper the 10k cathode resistor on v1b with alligator clips, the volume and gain increases. It still doesn't sound right, but I thought it was something interesting. I did the same on the cathode resistors on v1a and v2b, but those both dropped the volume much lower.
 
I think you may have an oscillation.

Check the wiring to the first grid and check the shield is grounded if it’s shielded.

Also have you chopsticked the amp yet?
 
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glpg80 said:
I think you may have an oscillation.

Check the wiring to the first grid and check the shield is grounded if it’s shielded.

Also have you chopsticked the amp yet?
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Yep, I've chopsticked it. The wiring to the 1st grid is this shielded cable. I've tested it.
Screenshot_20221212_231229_Gallery.jpg
 
Using your signal generator you should be able to put a tone into the input of the amp and then trace the AC voltage as it goes through the amp with your multimeter. Just stick your negative probe on the chassis and probe with the positive. Follow it from input to output not output to input. (Grid to plate, follow the voltage dividers, and check mathematically the voltage dividers are working).
 
glpg80 said:
Using your signal generator you should be able to put a tone into the input of the amp and then trace the AC voltage as it goes through the amp with your multimeter. Just stick your negative probe on the chassis and probe with the positive. Follow it from input to output not output to input. (Grid to plate, follow the voltage dividers, and check mathematically the voltage dividers are working).
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What can I use as a signal generator temporarily? My oscilloscope won't be delivered for a few more days.
 
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