Search found 1241 matches
- Mon May 20, 2024 11:19 pm
- Forum: Technical Discussion
- Topic: Common Mode Filtering - A slightly impractical approach to reducing heater induced noise
- Replies: 9
- Views: 244
Re: Common Mode Filtering - A slightly impractical approach to reducing heater induced noise
The only thing I could come up with for 60Hz modulated 30-50kHz is the pulse modulation generated by a power factor correction circuit trying to modify the power taken from the AC mains on an instant-by-instant basis for a high power switching power supply. Maaaayyybe... I considered but didn't ment...
- Mon May 20, 2024 2:30 pm
- Forum: Technical Discussion
- Topic: Common Mode Filtering - A slightly impractical approach to reducing heater induced noise
- Replies: 9
- Views: 244
Re: Common Mode Filtering - A slightly impractical approach to reducing heater induced noise
First off, good investigative work! AC power line noise is commoner than people think; some buildings have "sick" AC supplies. Your post started me on some random thoughts. - You see the noise on the hot and neutral to ground. Do you get the same result on the AC socket itself? If yes, this indicate...
- Mon May 20, 2024 2:40 am
- Forum: Technical Discussion
- Topic: Princeton Reverb tremolo squeal
- Replies: 5
- Views: 129
Re: Princeton Reverb tremolo squeal
Any substantial rebuild would profit from a (re)reading of The Remaking of a Champ from Glass Audio.
- Wed May 08, 2024 7:48 pm
- Forum: Technical Discussion
- Topic: Bad power?
- Replies: 10
- Views: 306
Re: Bad power?
You're right Max. Poor or downright bad AC power lines are common in remote/rural locations. I interpreted "cabin" as rural/remote too. @ OP: You don't mention the vintage of your Princetons (or I just missed it 8-) ) so I can't readily tell if you have old amps designed for 110Vac or more modern on...
- Sun May 05, 2024 6:26 pm
- Forum: Technical Discussion
- Topic: JJ E34L (brand new) emitting a white light - has anyone seen this before?
- Replies: 5
- Views: 202
Re: JJ E34L (brand new) emitting a white light - has anyone seen this before?
Very unlikely to be a spot of contamination on the cathode/plate/etc. The white color of the light indicates a temperature over 5000K of the source. There's no reactive gasses in there to speak of to support a reaction that vigorous if it passes audio at all. It's very, very, very likely to be an ar...
- Wed May 01, 2024 11:52 pm
- Forum: Technical Discussion
- Topic: Can I use 6v6's in a 69 Super Reverb ?
- Replies: 16
- Views: 499
Re: Can I use 6v6's in a 69 Super Reverb ?
"Can I use them?" is not the question. Of course you can.
The question is how long they'll last.
The question is how long they'll last.
- Sat Apr 27, 2024 4:12 pm
- Forum: Technical Discussion
- Topic: Add an HT Fuse?
- Replies: 10
- Views: 689
Re: Add an HT Fuse?
I'd be interested in commentary regarding fusing the rectified DC line vs. both HT legs of the secondary (AC). It goes back to that "what are you trying to protect?" thing. A fuse in the rectified DC line can only stop current flow between the rectifiers and whatever is after them, presumably both ...
- Fri Apr 26, 2024 8:15 pm
- Forum: Technical Discussion
- Topic: Add an HT Fuse?
- Replies: 10
- Views: 689
Re: Add an HT Fuse?
Why do a lot of guitars amp circuits do not have an HT fuse, while others do have them? I believe that it's an economic decision based on trading off the cost of a fuse, holder, and wiring plus some number of warranty calls on the fuse setup, versus the warranty savings of the small percent of amps...
- Sat Apr 13, 2024 7:20 pm
- Forum: Technical Discussion
- Topic: Regarding the B+mosfet reducer and power ground
- Replies: 10
- Views: 611
Re: Regarding the B+mosfet reducer and power ground
That's a clearer explanation of what I was worried about. If the bias is a tap, not a separate winding then the whole bias generation rectifier/filter/is pulled down by the zener setup. The bias voltage is shifted. I - think - what I wrote is consistent with that, at least from the perspective of to...
- Sat Apr 13, 2024 2:28 pm
- Forum: Technical Discussion
- Topic: Regarding the B+mosfet reducer and power ground
- Replies: 10
- Views: 611
Re: Regarding the B+mosfet reducer and power ground
I ... think... that moving only the PT high voltage center tap was the right thing to do for everything except possibly the bias. How is your bias voltage generated? Is the output stage cathode biased? Is it fixed bias? If fixed bias, does the bias voltage come from a tap on the high voltage winding...
- Thu Apr 11, 2024 10:32 pm
- Forum: Technical Discussion
- Topic: Regarding the B+mosfet reducer and power ground
- Replies: 10
- Views: 611
Re: Regarding the B+mosfet reducer and power ground
I'm having some trouble visualizing exactly how you have it hooked up. Can you post even a quickie, crude sketch so I don't mis-visualize it? If I'm visualizing correctly, the MOSFET reducer installed in the ground-to-PT/CT should have no effect on the circuit at all - as long as you tie nothing but...
- Mon Apr 08, 2024 7:11 pm
- Forum: Technical Discussion
- Topic: Paging RG Keen/UL700 pcb/wiring question.
- Replies: 13
- Views: 5573
Re: Paging RG Keen/UL700 pcb/wiring question.
Got it, replied.
- Fri Apr 05, 2024 8:45 pm
- Forum: Technical Discussion
- Topic: New design humming - help requested
- Replies: 20
- Views: 931
Re: New design humming - help requested
I believe it's the best practice, yes. Star grounding is not the only way to get a hum-free setup. It's just the only way that is known to work ahead of building and trying. I like the term I heard here - "constellation grounding". This is a handier way to wire grounds with very, very, very nearly t...
- Fri Apr 05, 2024 1:35 pm
- Forum: Technical Discussion
- Topic: New design humming - help requested
- Replies: 20
- Views: 931
Re: New design humming - help requested
Yep, PCB grounding scheme is the most likely culprit. It may be the PCB combined with how your connections to chassis ground is done. I can't figure it out from the diagrams either (no part designators shown), but one possible issue might be grounding the tremolo depth pot (and in fact the whole tre...
- Thu Apr 04, 2024 11:24 pm
- Forum: Technical Discussion
- Topic: Testing power supply before completion
- Replies: 14
- Views: 685
Re: Testing power supply before completion
Don't forget to drain those filter caps! Even better, permanently install a 220K 3W resistor across the first filter cap to always drain whenever the amp is off. + 1 on the drain-down resistor. The life you save could be your own. I like to put an LED in series with the 220k to have a glowing indic...