Adding a resistor from the output transformer into the second stage preamp of a single ended amp could potentially lower unwanted noises and bring tone forward even in the cheapest of amp builds. Improving your budget amp build is worth it. You just need a soldering iron and a $0.10 resistor.
My first amp heads were all built with used transformers and low cost everything. The featured photo is an 11 watt guitar amp head made mostly from parts found in a barn.
It sounded fine. Wasn’t noisy or staticky sounding, and it had tons of gain. I realized quickly after the joy of completing the project wore off that the tone wasn’t what it could be. That is when I decided to research sound quality for the first time.
The only schooling I had for electronics was Highschool level, so I did what any vacuum tube enthusiast does, and started reading from the book featured in this photo. Here is a link where you can read it for yourself for free. http://tubebooks.org/Books/Atwood/Langham%201950%20High-Fidelity%20Techniques.pdf
Turns out that the mediocre tone was easily turned into a flavorful tonal punch by simply adding inverse feedback by following simple instructions on Pg. 55 of (High-Fidelity Techniques by Langham 1950). The sound improvement from adding a resistor blew me away. I added a port into the second stage of the amp to see if my music devises would sound good thru it. Also amazing!
Not all amps sound better with a feedback resistor added (really like 6L6 with no feedback), but I find most are improved for both guitar and musical applications. If you’re interest in trying it out for yourself you can either, read the literature linked in this post, search on the innerwebs, or go here https://www.facebook.com/groups/485856047509004 and use an excel calculator I made to figure out that resistor value. I like using this on single ended amps, so here is a schematic of where to feed the resistor into.
I hope this helps with Improving your budget amp build. FYI I am still riding the struggle bus on my way to that level, but I’ll get there eventually.
Build a kit. That’s how I learned, and I continue to have interest in kits. https://crunchytubeamps.com/product-category/guitar-amp-kits/
