Toob Amplified PC Speakers

On a sunny day (Mon, 02 Dec 2013 12:58:56 -0600) it happened Tim Wescott wrote in :

You are sick man, very sick.

All of my tube amplifiers, starting when I was only 14 years old, were all open-chassis style. Only the preamplifier (Dynaco PAT-1, IIRC) and the tuner, Dynaco FM-3, had cases.

I quit tubes in 1962 and built my first 30W+30W solid state power amplifier using Motorola RF power transistors.

Having played clarinet in high school orchestra, marching band and various Dixieland and dance bands, I was never fond of the toooob "warmth"... and the intermodulation distortion... a good Mozart wood-wind ensemble that includes a French horn will illustrate distortion better than any test instrument. ...Jim Thompson

Just for fun, you might do a single stage class-A stage using a 2A3. I did one when I was a kid, but with 5 in parallel ;-) ...Jim Thompson

Google says there is a "headphone preamp" kit for $60 to $70 that uses

Use toobs that need 5 V, 500 mA or less at the filaments and you can power each filament off of a USB port! Or, ask Antec if they have a PC power supply with DC outputs at +200, +12, +5, +3.3, -5, and -12 V, and an AC output of 6.3 or 12.6 V - Chinese engineers need to laugh too!

Buy a couple of old toob radios at the thrift store and use the best power transformer (get ones that have one), both output toobs, and the chassis to roll your own? Schematics for old radios are pretty easy to find on the interweb.

Matt Roberds

This kit has been around forever and seems to get good reviews:

There's also this little kit from a Chinese seller on Ebay:

which has the output transformers on board - you'd need to supply a power transformer.

You'd have to put them in a chassis if you wanted it, but since they're both mounted on PCBs it shouldn't be too hard: buy an aluminum chassis and punch holes for the tubes, mount the board underneath so the tubes poke through and then mount the transformers underneath or on top as your preference.

Good for you! Nostalgia has its place in our hearts.

Can 12AX7s and such still be ordered?

I have an old 1964 GE Essential Characteristics of tubes data book. If you promise to actually build your amplifier(s) and it will assist you, I will send it to you free of charge.

John

Well, somehow my brain elided the fact that you don't want to scratch build. So, my offer is probably worth nothing. Sorry.

Better yet, a push-pull transformerless design!

Yup. Tubes that are popular with musicians (for guitar amplifiers, etc.) are still in production in a few factories (China and Russia, mostly), and there's still an active trade in "new old stock" and "used and tested" tubes of these types. The 12AX7/12AU7 family are heavily used in guitar amps, and so remain available.

I recently lucked into finding a big batch of tubes of various sorts at a garage/moving sale... got three boxes of used tubes, two emission-type tube testers, and some manuals and tube-data guides, for the "please take this away, I don't want to take it all to Arizona" price of $4. A friend of mine glanced at them, and identified several Telefunken 12AX7 tubes ("These are gold!"). I ended up selling a batch of seven of them (tested good on his fancy tester) on eBay for $145!

Sorta hated to let them go, but none of my audio gear is glassFET-based and I figured that other people could make better use of them than I.

Yes, there are lots of tube types still in current manufacture, and many types are still available new old-stock.

You want to have the Receiving Manual too, so you can check out the full data and curves:

I remember a quasie tube output, that was bad car ma.

It required a safety circuit on the output, not for users but for equipment. The outfit could care less about the user safety! :)

This was a magnetic server that required a broad range of bw. the tube outputs were a pair of 4-400Z. Had dual HV supply because you needed the - rail for the bottom side. each heater had their own transformer with CT to tie off to the common for pinch off biasing.

The top side had some strange method of driving the tube, but it worked

Jamie

How I hate the cross-posting.

PAIA used to sell a tube preamp, or you could have built it from the article in Radio Electronics. I don't know if PAIA still sells it, but the idea was to "give that tube sound", and apparently just a double triode was good enough.

You're not going to find a tube amplifier cheap, the only ones interested are the high end people. Even used tube amplifiers from days gone by likely carry a premium.

Build a starved circuit amplifier.

Or, Popular Electronics once had a tube amplifier that was a cathode output, though I think they used a transformer.

Find something old, and feed the signal into it. People are adding audio input jacks to AA5 radios. I think that TMC GPR-90 I got last year for $20 at a garage sale has audio input connections, it certainly has an IF jack for an SSB converter and I think even audio output jacks, so surely it has audio input jacks.

Michael VE2BVW

'sokay, I appreciate the thought. I have tons of tubes and data, what I lack is decent output transformers and the will to do yet another design project.

I may go that route, particularly now that someone's suggested a kit and I've taken a look at the price (!!!).

Thanks. That's exactly what I was looking for, except that now that I know what a fair price is, I may just buy new speakers :(.

get on of these:

put in a with couple of must impressive looking tubes you have on top and power the filaments ;)

-Lasse

Search for 'Zen Amp' there are some DIY pages out there. Both Tube and Mosfet designs.

Cheers

I think I still have a box of prime used 4-400's around the shop packed away if you'd like? I know I gave away a couple of them in the past, but should still have at least 4 of them. I also have some 3-500Z but you aint getting them!

I'll have to look to refresh my mind!

Jamie

I have various old power tubes, including some VT-4's, if I want POWER tubes. I was thinking more on the lines of a couple of 6V6 single-ended stages.

If you want a respectable, easy to build, low power tube amp kit, look at the Velleman kits. They are well-designed and have good output transformers.

For the most part, when you buy a tube amp, you are buying transformers and engineering. Everything else is of comparatively minimal cost and effect.

--scott