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Hey, I totally believe you, and that's what got me thinking - and how I realized that I didn't understand something that's relevant and useful. Hopefully Chuck or others can point me in the right direction, otherwise I may need to simulate some circuits in LTspice, and play with parameters.

Right. I believe the two main underlying factors are (1) cost, and (2) physical size. Polarized electrolytics that meet the tube amp requirements that @GAStan describes are cheaper and smaller than could be achieved by a nonpolar capacitor. So those factors really shrink the addressable...

Yes, I believe you're right. There do exist nonpolar electrolytic caps on the market, but they are definitely much less common than polar electrolytics. And while I believe that it would be possible to make a polarized MLCC, all the commercial MLCCs that I am aware of are nonpolar...

I'm seconding @giovanni here, and adding an additional point. The capacitance of some MLCC's are very sensitive to DC voltage, so (1) check your circuit regarding the DC voltage that any capacitor may face, and then (2) check the datasheet for your capacitor of choice. Here's just one example...

So let me return to this old thread for a question. On this and several other threads, I've read @HamishR state that using lower gain transistors (e.g., 2N3904 instead of BC239) alters the sound, making it smoother with less harshness. So that makes me intrigued. But after some reflection...

I largely agree with the 2 comments above, but my one concern would be for power supply caps. In principle if there's a lot of ac current running through it (e.g., from a noisy power supply) and the ESR is appreciable, then the cap can get warm - and then the heat shrink could elevate it's...

Here's what Reuters says regarding 'de minimis' shipments (i.e., less than $800) from China (April 3, 2025 article): Trump signed an executive order on Wednesday that closes a trade loophole known as "de minimis" that has allowed low-value packages from China and Hong Kong to enter the United...

@Grazza - lol, no worries, just wait until you get old like me - then you'll discover a whole new world of typos. So keep your sense of humor, it will serve you well in years to come! Cheers!

Yes, I used a 1N4678 1.8V Zener Diode, it's rated as a 500 milliwatt Zener. Hence the "1v8" marking on the PCB, it's similar notation to 4k7 for a 4.7 kiloohm resistor.

Well, all countries besides China still have 10% tariffs, plus higher tariffs on certain things from Mexico and Canada. I have read through all the announcements put out by the White House, and honestly they are confusing. Even the White House later admitted they'd forgotten about an additional...

And one directory higher (https://www.rsp-italy.it/Electronics/Databooks/) lists ~100 companies, with multiple databooks under each company. Very useful!

Nice link to an extensive set of Fairchild data books! Thanks!

DHL, package is still w/ Tayda in Bangkok. The package and paperwork were given to DHL, who took the package to the airport, and then it was returned to Tayda. Sounds like some additional tariff paperwork was required. Right now, I notice that the Tayda website is offline, I wonder if /...

My Tayda package was just returned to Bangkok - "The shipment has been returned per shipper's or consignee's instructions or according to our standard procedure", whatever THAT means. Crap, this whole situation smells like it could be a real big mess...

I'm sure the shipping services aren't thrilled either, it definitely isn't good for them. If I was a customer service person for UPS/FEDEX/DHL, I'd get ahead of the curve and quit right now. I expect delays all around as a result...

Make America Groan Again...

I would suggest that you do an internet search for the service manual for that HP pulse generator, and then look them up

I'd rather pay more than have you bow out of making PCBs. Do what you have to do to stay in business, we love your PCBs. Life itself is expensive!

Just make sure that it's a DUAL opamp, and the pin designations (in, out, V+, etc) match that of the JRC4558 (which is the same as an RC4558). Note added: In that circuit, I don't think the opamp itself makes a huge difference, the distortion is primarily coming from the diodes in the feedback...

@ac30irons - wonderful, enjoy the new stompbox!