westend wrote:Now that is what I wanted to hear. I've been studying a little on tube circuits but that "crack habit" with the associated compulsive scroungophiling behavior sounds like it's right up my alley. I've been on a recent binge on the SS stuff (coke habit?) and at present have five pieces of gear in various states of transit. Your post and the look of Jim's amps have given me some inspiration. I have the efficient speakers-Fostex BLH at 93db. Is there a particular direction to start or one piece of gear to start with? I have SS tuners and amps but no straight preamp other than using a SS receiver. Would a tube amp be the place to start and what circuit is recommended?
Well if your into the Yard/Garage/Thrift Store scrounging thing, it's a good place to start finding vintage tube gear on the cheap.
Ham radio meets are another way to find related gear. Craiglist, eBay.......of course, caveat emptor with eBay......
Don't expect to pay big bucks for the stuff, set a budget. I go as cheap as possible, like free.
Be patient. Unless you absolutely have to have it, the deals will come with time.
If you can get it dirt cheap, grab it whether if works or not. Say if you pick up a non-working tube amp for a couple bucks, the iron and tubes are worth that.......organ amps are also a great source of tubes and iron for projects.
Old vintage tube console stereos can be had for peanuts, but do keep in mind most of them have small output transformers and are a little thin on bass. But if they can be had for a few bucks, why not? You can always make up the difference with a subwoofer if need be. Besides, parts is parts.....
And if you come across test gear for cheap, nab it. A good old school volt/ohm meter is a good thing to have, or a vacuum tube volt meter, or a tube tester....etc......you start working on the circuits, you'll have to measure voltages, do some math, test tubes...etc...
I still need a good volt/ohm meter, but I do have a good bench DMM. It's good to have both.....hell, you can get obsessed with the test gear as well......eventually, you'll want a scope if you don't have one.
You mention you have solid state power amplifiers, maybe build a simple tube linestage and use it before a power amp. Kinda best of both worlds, SS bass grunt with tube flavor.
I see kit linestages for ok prices, and I suppose for ease of build they are ok deals, but I encourage DIY as in scratch build because you can do it for damn near nothing.
Hear is a few links to uncle Ned's tube data page off the website. On page one of the RCA resistance coupling charts, explains how a tube is loaded, the break point frequency between stages, etc...
Look at that diagram no. 1. on page 1. You build a power supply for the tube's plate, a filament winding or transformer for the heaters.
You park a volume pot (100K, usually) in front of the tube feeding the grid. The cathode resistor and bypass cap sets the bias and gain of the tube, with the trick of getting the tube working in it's linear region of it's curves. Grid voltage as well.
The coupling cap from the plate to the next stage can either be another tube stage or a power tube for a single-ended amp, or a phase inverter circuit for a push-pull amp.
Or you can hook the coupling cap to a pair of RCA jacks and make it a linestage.
I think the break point frequency is explained in that link to pg 1.
Linestages and pre-amp circuits can get WAY complicated than that, but that's about as simple as it gets.
I started with a couple Eico HF-12 integrated PP 6BQ5 mono amps to cut my teeth with vacuum tube circuits. A simple tube amp is a fine place to start, it's all a matter of checking parts for tolerance, tubes, voltages. It gets easy over time, just don't get tagged......take heed to the high voltage.
As far as what circuits are recommended, you may like a single-ended tube amp circuit or you may think they suck and prefer a push-pull. You may think push-pull sounds like clean solid state, (not a bad thing) and prefer a bit more colored sound of a single ended directly heated triode amp. It's all a matter of finding out........
Recommended circuits to build? Start off easy. Rebuild a simple console tube amp and get the hang of things, then move on to a scratch built circuit/amp.
What's wrong Jim, a little miffed by the crack habit comment?
You have a pair of 8, 10 watt SET monoblocks with intentions (I think) of building a linestage or pre-amp. You think your just gonna stop after that?
Mod those Forte xovers......trust me.....