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Mod parent up 'Informative'. Great stuff.

AES (http://www.tubesandmore.com/) is an excellent resource; one of my favorite parts vendors for tube amp builds/mods. No relationship, just a happy customer.

Time for new filter caps?

Likely so.. Getting a good filter cap that's gong to work at 800 Volts is going to be fun though. Electrolytic's don't like over voltage about as much as reverse voltage... KAPOW...

Vacuum tube amplifier tech here with 40+ years experience.

Here's a 25uF @ 800V/900V-surge "firecracker" style.

https://www.tubesandmore.com/p...

More stuff here.

https://www.tubesandmore.com/

Even more here.

http://www.fliptops.net/

Another option is to series-connect two 450V or 500V capacitors to meet the 800V minimum rating requirement. I recommend placing a 100K Ohm 1-watt metal-film resistor across each of the two series-connected capacitors to make sure the voltage across each capacitor divides equally, as the ESR (effective resistance) of individual capacitors varies slightly from unit to unit and causes the voltage to divide unequally without the resistors which could possibly result in one of the capacitors "seeing" excess voltage. Usually not a problem, but why take a chance with a shortcut?.

The resistors also act as a safety feature as "bleeder" resistors to prevent accidental shock from a stored charge long after power has been removed by slowly discharging ("bleeding") the capacitors after power is removed.

As a safety tip, *always* keep one hand in your pants-pocket when performing tests/adjustments on live circuits to prevent completing a path to ground through one's chest. Human hearts don't take kindly to high voltage passing through them.

Be careful and good luck!

Strat

Time for new filter caps?

Likely so.. Getting a good filter cap that's gong to work at 800 Volts is going to be fun though. Electrolytic's don't like over voltage about as much as reverse voltage... KAPOW...

Vacuum tube amplifier tech here with 40+ years experience.

Here's a 25uF @ 800V/900V-surge "firecracker" style.

https://www.tubesandmore.com/p...

More stuff here.

https://www.tubesandmore.com/

Even more here.

http://www.fliptops.net/

Another option is to series-connect two 450V or 500V capacitors to meet the 800V minimum rating requirement. I recommend placing a 100K Ohm 1-watt metal-film resistor across each of the two series-connected capacitors to make sure the voltage across each capacitor divides equally, as the ESR (effective resistance) of individual capacitors varies slightly from unit to unit and causes the voltage to divide unequally without the resistors which could possibly result in one of the capacitors "seeing" excess voltage. Usually not a problem, but why take a chance with a shortcut?.

The resistors also act as a safety feature as "bleeder" resistors to prevent accidental shock from a stored charge long after power has been removed by slowly discharging ("bleeding") the capacitors after power is removed.

As a safety tip, *always* keep one hand in your pants-pocket when performing tests/adjustments on live circuits to prevent completing a path to ground through one's chest. Human hearts don't take kindly to high voltage passing through them.

Be careful and good luck!

Strat

You could still buy vacuum tubes in the late 70's and early 80's.

'70s and '80s? You can still buy them today. There are even companies (mostly in Russia, other former Warsaw Pact countries, and China) that still make tubes, so you can get brand-new ones for your gear.

That's just the one company I've bought from in the past to fix my old radios; there are others as well that should turn up with a little bit of google-fu.

Read datasheets. Look at National Semiconductor, TI, Maxim, Linear Tech. Most modern electronic stuff is made out of higher level building blocks, not individual parts.

For those who like them, tubes and more are still available.

Falcon

Mod Up. Old Victrolas only play at 78 RPM, but some had a speed adjustment IIRC. I think you can still get cactus needles from Antique Electronic Supply in Tempe, Arizona.

Dude, $10 plus shipping will get you a used 872 mercury rectifier from Antique Electronic Supply - http://www.tubesandmore.com/

That is, if what you're really interested in is the glow. If you want to change AC to DC at 2500 amps... well... good luck with that.

It's not the tubes themselves that are expensive ( about $8 for a 12AT7, to use a type someone else mentioned), but the equipment in which they're installed that often sells for insane prices.installed that often sells for insane prices.

Thanks for the link. Years ago I was nterested in building things and want to get back into it. One thing I want to do is build a shortwave radio and get my license. I'd like to use tubes to make it.

Tubes are still out there but you have to find them and they are expensive

It's not the tubes themselves that are expensive (about $8 for a 12AT7, to use a type someone else mentioned), but the equipment in which they're installed that often sells for insane prices.

As a side note, I built my amplifier from a great kit. It's a tube amplifier, and sounds better than anything I've heard anywhere near it's price range ($140). Of course the downside is no remote control (for now), but it does glow! To get any kind of serious sound out of a PC you MUST have an external DAC. I'm running the lossless digital sound out of a Turtle Beach USB sound card (around $30) straight from the PC to an external DAC (California Audio Sigma II, $750 new, bought for $400 used). The DAC outputs straight to the integrated amplifier, and I couldn't be happier. I hate having tons of CDs lying around, so I FLACed the collection...

Nice links. And here's some karma whoring (not that me needs it).

Creative people and projects:
- http://www.diyaudio.com/ (DIY audio equipment forum)
- http://sound.westhost.com/projects.htm (audio stuff schematics)
- http://headwize.com/projects/index.htm (DIY headphone stuff)
- http://www.hauptwerk.co.uk/pedalboard.html (DIY MIDI pedalboards, just add keyboards and software and you have a MIDI organ)
- http://www.diysubwoofers.org/ (what it says)
- http://www.plasmatweeter.de/eng_plasma.htm (DIY ionic tweeter)

Places to buy stuff:
- http://www.newark.com/ (major electronics retailer)
- http://www.mouser.com/ (major electronics retailer)
- http://www.tubesandmore.com/ (components for vintage electronics)

Getting stuff made:
- http://www.olimex.com/ (cheap PCBs)

You measure the impulse response of your desired tube system

Mmmmmmm..... if I recall correctly, an impulse is theoretically "white" so the response represents the system's response to all frequencies. That's with a n infinitely narrow (time) and high (amplitude) impulse.

The problem with tube modeling is that the system is non-linear. The frequency response *changes* with amplitude. I've also heard that it changes with the blend of tones, though I take that with a grain of salt. The claim is that a strong bass note (for example) will affect the frequency response in upper registers.

I see the problem as an ignorance of the effects of inductance & reactance. RC systems are fairly easy to model digitally, but RLC systems are less well understood by digital implementors who blew through analog class without much respect.

Tube amps have giant-o-normous output transformers for matching high impedance tube outputs to low impedance speakers (I think- I'm one of those analog diss-ers trying to learn at a late age).

This causes low damping factor- the ability of the amp to deal with back EMF of the speaker and control it "tightly."

Bob Carver built some transistor amps with low damping factor as a demonstration that much of the tube "sound" was this simple property. High damping factors was something tube people always strived for so when transistor amps could do it easily, people *chose* to build amps that way.

Transformers also have problems like core saturation. Something that strikes me odd is that better (electrically, not audiophile-tweaky) transformers which might actually sound less "tubey" are valued by audiophiles.

Incidentally, tube guitar amps have an advantage of high input impedance: good when dealing with a monster coil like a guitar pickup. Bipolar transistor pre-amp stages are not a good idea, but FETs work if you want to be able to carry your amp outside on a cold night after practicing without hearing the sound of glass breaking. Anyone remember VOMs?

I'm planning on building one of these to drive a pair of these.

A very similar kit is availble from "Antique Electronics" and S5.

The build will give me a chance to bone up on my languishing soldering skills, but more importantly, I want to build a nice case like this guy did.

Search the internet for vacuum tubes. There's a huge movement in high-end audio back to using tubes, so a lot of places are selling new old stock tubes specifically for this purpose. BTW, another thing to think about is that if it has capacitors, some of them may be on the way out, which could also introduce a hum all the time.

If you're handy with a soldering iron, it might not be a bad idea to go through the entire thing and check all the parts to make sure none of them have gone bad. Older electronics tend to do that, especially when they are left sitting for long periods of time. A couple sites to check out would be here and here for vacuum tubes and other assorted old stereo equipment parts. Hope you can get it working, I think vintage stereo equipment is really neat (my speakers and amplifier both date to the mid-70s).

Actual performance of the product is not a real concern. It's all about conspicuous consumption. I bet you pay a nice premium for those tubes.

Most tubes aren't that expensive...Antique Electronic Supply has 12AX7s starting at $6.25 each (current-manufacture Chinese, quantity 10+). They have some more expensive varieties of that tube (NOS Amperex for $78.00 each, NOS Mullard for $67.00 each, NOS domestic-manufacture for $14.90 each), but how much you fork over for tubes depends mainly on how much audiophoole Kool-Aid you've been drinking lately. :-)

It's all about making it look like it performs well, which has led to a number comparisons between this crowd and another that does similar things to certain import sedans...

I definitely won't argue about the many similarities between the case modders and the rice boys. It's a wonder they haven't tried combining the two...how about a windowed hood on a Civic, or a nitrous bottle in an overclocked Celeron? (Then again, you couldn't see a windowed hood underneath the four-foot-wide "Type R" sticker...and it's not like there's anything worth looking at under the hood of the average rice burner anyway.)

I don't think you have it right. The article means traditional vacuum tubes - which are found in old radios and old TV's (pre-transistor electronics). They have not been common for a long time.

They're not common, but they're not too hard to find either. Dozens of businesses cater to the antique/vintage-radio, musical-instrument, and "audiophile" (quite often "audiophoole" would be more appropriate) crowd that would have a use for tubes, either new-old-stock tubes that were last made 30-40 years ago (or even further back) or brand-new tubes produced today in Russia, China, and similar countries. Antique Electronic Supply is one that comes to mind. They usually have specials on slow-moving types that you can snarf up dirt-cheap. Hell, even Radio Shack can still get tubes on a special-order basis, though I suspect their prices run a bit higher for it.

Keep in mind that the quoted article is over 40 years old, so its assumptions about what you're likely to find in the average household are more than likely dated somewhat. (I have a few old radios myself, and a small stash of tubes and related equipment...but I suspect I'm atypical in that regard. :-) )

52 years old... If they restore it to actual operational status I'll bet they don't run it for very long at a time. Spare tubes and such are gonna be a bear to find.

Tubes aren't as hard to come by as you might think. Lots of companies are still selling 'em. The biggest of 'em is Antique Electronic Supply in Arizona; a couple of others I can think of off the top of my head are CWest Tubes in Utah and Fair Radio Sales in Ohio. The audiophooles have driven the prices of some types (especially power triodes) through the roof, but many types still sell for just a few dollars each, including (IIRC) the 12A_7 types that boatanchor computers more than likely would've used by the gross. (If they're interested in economizing, they could retrofit the machine to use some of the goofball tube types developed for TV use, which are dirt-cheap...but since they're working with a one-of-a-kind machine, they probably don't want to hack it up too badly.)

In fact, I've heard from some people that it's actually harder to fix old transistor radios than it is to fix similar equipment built with tubes, since early transistors have become scarcer than hens' teeth. Early ICs can be equally hard to come by (some talk came up in comp.sys.apple2 a while back about the feasibility of reproducing the Apple I from schematics, and someone noted that some of the chips used in that machine's design are no longer available.

With all that said, the machine would more than likely be on static display most of the time. They might fire it up for special occasions or just to verify that it still works, but I doubt they'll have it participating in GIMPS 24/7. :-)