Excellent stuff here, much food for thought. For clarity's sake, let me state that I'm not wedded only to SE topology. My focus rather is on building an amp that "sounds good", whatever that may mean, out of junk tubes that nobody wants. It should be obvious that I really don't know a lot about electronics, but that won't stop me from throwing a bunch of parts together! The article you referenced gives technical explanations that are a little over my head, but it's gratifying to know that other people are taking tubes which were designed for use in television sets and designing guitar amps around them.
What got me started in this direction was the realization that a large part of the cost of a guitar amp comes from the tubes and transformers it uses. Just now I received in the mail a ClassicTone #40-18031 that set me back $30-$40. This will go into my first project amp, which will be a Champ clone. Still on order are three very standard tubes (12AX7, 6V6, 5Y3) for which I paid full price. I'm already out $100 or more, and I don't yet have a cabinet or a decent speaker, let alone capacitors, resistors, etc., etc. I don't begrudge the vendors the prices they charge, because I understand their need to make a profit, but I'm acutely aware of how expensive a hobby building guitar amps can be.
For the past few months, in leafing through many data sheets, I've seen that vacuum tubes have output impedances covering a wide range. Yet, based on a cursory examination of many different actual guitar amp schematics, I've made the obvious realization that many, if not most of them, seem to require a center-tapped PT that delivers 150V to 300V per side and an OT with a primary impedance of 5k to 8k in order to drive an 8-Ohm load. So, dumbass cheapskate that I am, I'm asking why it should be so. My junkbox contains a pile of OT's and PT's which won't be useful in any way, and which will likely end their lives in a burning cauldron, because all they are is raw copper with some worthless steel that merely detracts from the minimal scrap value that resides in the copper!
I recently posted a query, which several people (including yourself) were kind enough to read and reply to, regarding a pair of OT's I scavenged from a solid-state jukebox. Knowing from direct observation that big guitar amps use big transformers, I was hoping that I had the basis for a big, ballsy amp. Alas... Then, it hit me that maybe I could still use these hefty hunks of junk if I could find tubes whose output impedances were not the standard 5k to 8k, hence that earlier thread. Believe me: I wouldn't waste my time, let alone that of others, if I didn't think these discussions might benefit somebody else down the line. Word alone cannot convey my gratitude for the valuable free advice I've picked up here. In my own various lines of work over the years, I've given away hundreds, if not thousands, of dollars' worth of my time and expertise, because I know how valuable a person's time can be. And I still haven't given up on those two OT's; maybe if I turned them backwards they will end up finding a use. I refrained from posting a schematic diagram, because in truth they would require surgery because the primaries and secondaries are electrically connected inside and I didn't want to encourage some newbie from messing around with potentially lethal voltages. But, since I've re-opened that topic in a sidelong way, here is a file I found from the service manual to a Rowe CD-100A LaserStar:
Topic: "Oddball" Tubes: Worthy of experimentation? (Read 4704 times)