[Boatanchors] Audio Amplifiers (And, no, I'm not an audiophool!)
w_b_morton at hotmail.com
Wed Dec 25 22:44:49 EST 2013
I have a chassis from an old Magnavox hi-fi. (Or hi-fi-ish in its current state. Maybe more 'ish'.)
Don't remember if it is from a phono player only or a radio/phono combination, but I am sure it would take a nominal line level input and amplify it accordingly. Typical 6V6 Push-Pull type of thing. If it was phono-only, it should be a relatively simple task to remove the RIAA compensation stuff.
I know I have the rectifier and 6V6 tubes. Let's assume you would need to source the preamp tubes from somewhere else. (If I have them in from the original set, they are yours.) I know it is not in the design realm of the tubes you have, but it will save you some construction time. At the best, it is plug and play. At the worst, you would have to completely rebuilt the circuitry - but the power and output transformers, sockets, RCA jacks, and chassis are right there.
Just re-cap, maybe test the tubes, mount the thing on a piece of plywood, hook it up and you are off to the races. You could skip the mounting on plywood step if you want to live dangerously.
Yours for the cost of shipping plus a cup of coffee. I would have it professionally packed at the UPS store and shipped the most economical way.
Would this fit the bill?
> From: wh7hg.hi at gmail.com
> To: Boatanchors at puck.nether.net; tetrode at googlegroups.com
> Date: Tue, 24 Dec 2013 21:55:15 -1000
> Subject: [Boatanchors] Audio Amplifiers (And, no, I'm not an audiophool!)
> Okay, here’s the situation. I’m setting up to do some serious work in
> creating animations and other stuff for Noelle, essentially creating a
> digital universe where we can be together. It's kind of like how animated
> movies are made but on a much smaller scale and significantly lower budget.
> The video side I have pretty well covered including creating the animations
> themselves however the audio portion is still seriously lacking. If I had
> my druthers, I’d have something like a tube-type Harmon-Kardon amp and a
> brace of AR-4s (AR-3s wouldn’t fit here.) but I don’t so have to go a
> slightly different path.
> Cruising my local Goodwill & Salvation Army stores netted me no joy which is
> quite different from ten years ago when I did find a pair of ugly AR-4s that
> still were good inside. I should have snared them but I was kinda sorta
> homeless at the time and had nothing to connect them to. And no cash to buy
> them. I guess that counts too. There were also some decent stereo amps and
> receivers but that was ten years ago. Now the only things they have are
> boom boxes and computer speakers which seem popular with others but have all
> the audio response of a … hmmm … I can’t think of anything bad enough. Tin
> can with a slack string?
> Going through one of my tube boxes, I located a small collection of 25L6,
> 35L6 and 50L6 tubes, some 12SL7s or 12SN7s (I don’t recall which) along with
> some others I can’t remember right off. Memory serving the *L6s are all the
> same save the heater voltage so mixing them shouldn’t be an issue if I have
> to do so. For the moment, let’s dismiss the heater issues and concentrate
> on what’s really important – i.e., the audio. I know that computers don’t
> have the greatest audio capabilities in the world but I’d rather the machine
> be the limiting factor than what comes after. The desired end is reasonably
> flat response over the 20-20k cycle range – pretty typical for a decent
> stereo system back in the day – with around 5-10w out per channel. Part of
> the time I’ll be using headphones (mostly during editing) and the rest of
> the time speakers.
> As I remember, and I could easily be wrong, the line out on a computer audio
> system is looking for a 600 ohm load. As a result, the first order of
> business is to get that up to something a tube can handle more or less
> gracefully. After that come the volume controls and tone controls (bass,
> mid and treble) which, last I did anything with audio were supposed to be
> isolated from one another to prevent interaction. After that, a phase
> inverter and push-pull *L6s then out to irritate the neighbors. I may add a
> sub-woofer channel, tapping off each channel just before the tone controls
> and pushing the audio through low pass filters to a mixer and a fairly
> reasonable amp but I doubt I’ll find a sub-woofer like the old days –
> response in the 10-200 cps range*. OTOH, I may add the third channel just
> in case. It certainly can’t hurt.
> * It seems that people are happy with 35-15k cps response and don’t care
> about what they’re missing. Even some audiophools. Even the ones who can
> hear negative frequencies and distortion that can’t be registered on any
> known instruments like scopes and all. Weird.
> From what I can see, I’ll need a brace of 10kohm ct to 4 or 8 ohm output
> transformers and a slew of audio taper pots. I think I have some slide pots
> that will work for that part although I haven’t measured the resistance yet.
> They’re on a reject pot board from an equalizer that I have yet to
> dismantle. (The pot board, not the equalizer. I don’t have it. If I did,
> I wouldn’t need the tone controls.) One thing I don’t know is if metal film
> resistors are good for audio systems. The only input I have on that is from
> the phools who say they sound “metallic.” I have carbon comp resistors
> although I have to dig them out and apply an ohmmeter to see how much
> they’ve wandered off from the shown value but metal films are cheap and
> Anyway … now that I’ve drifted into a stream of consciousness thingie, any
> suggestions would be greatly appreciated.
> Mele Kalikimaka me ka Hau'oli Makahiki Hou!
> Michael, K3MXO, BL01hx15np24 ... or there abouts
> Note to self: Hire new henchmen. Good ones this time. Also start
> interviews for attractive female lab assistant.
> <blocked::blocked::http://wh7hg.blogspot.com/> http://wh7hg.blogspot.com/
> Hiki Nô!
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