where can I find a good intro to tubes...for distortions?

[LucifersTrip]

I've built a load of transistor & op amp effects but haven't done anything with tubes.

Firstly, I couldn't find any info in the faq here and with a quick www search, I didn't turn up a good "intro to tubes" site yet.

I'm not interested in building any type of amp...just a simple boost, distortion or fuzz. The first obvious choice would be the Valvecaster.

I have a lot of vintage tubes that I picked up along the way with the transistors I bought, so the first thing I looked for was a tube cross reference site. I found this:

http://www.nostalgickitscentral.com/info/tubexref1.html

Please let me know if there are better cross reference sites.  I have no tube tester and no guide book, but is there anything I can look for
in tube numbering or physical attributes (# of pins) when I look for a 12AU7 sub in my stash?

thanx much

[twabelljr]

Not sure if you found this, but it is very informative. Fred Nachbaur's Real McTube II. The article index includes basic tube theory, how it works, and all the good stuff. Hope it helps:

http://www.dogstar.dantimax.dk/tubestuf/mctube.htm

[Minion]

This PDF is a build guide for a simple 2 tube (12ax7 and el34) single ended tube amp .... it gives a lot of theory on how the tubes are biased and how to chooze an operating point ect ...... very informative and a pretty good amp to boot .....


http://www.ax84.com/static/p1x/p1-ex-theory.pdf

[LucifersTrip]

Not sure if you found this, but it is very informative. Fred Nachbaur's Real McTube II. The article index includes basic tube theory, how it works, and all the good stuff. Hope it helps:

http://www.dogstar.dantimax.dk/tubestuf/mctube.htm

Thanx alot...that looks like a possible project after the Valvecaster

[LucifersTrip]

This PDF is a build guide for a simple 2 tube (12ax7 and el34) single ended tube amp .... it gives a lot of theory on how the tubes are biased and how to chooze an operating point ect ...... very informative and a pretty good amp to boot .....


http://www.ax84.com/static/p1x/p1-ex-theory.pdf

Thanx....Though, I'm not interested in amps, it looks like has some theory that could be helpful in the future.

Before theory & notation, I guess I'm looking more for basic info on how to choose a tube (ie, do I need to use a 12AU7 or direct replacement if building a Valvecaster?), handle them, install them, additional tools & parts (sockets, etc) I may need....building do's & don'ts, etc....and of course any simple distortion circuits (like the McTube mentioned above) that would be a small step up from the Valvecaster

thanx again

[iccaros]

http://www.diystompboxes.com/smfforum/index.php?topic=91745.0

For the information on tube types at low voltage see the link in the first post

[tubelectron]

Hi LucifersTrip,

I only (for the moment) experimented HV tube pedals... I should experiment with LV to see if it's worth (I have some doubt but I may be wrong).

Here are some I own and/or built :



If you want to try something with HV, have a trial with this :



I have the original (above) and it's a very good sounding unit : wide gain range, smooth decay, warm tone...

Another one would be the Matchless HotBox, but I never took the time for a trial...

A+!

[amptramp]

You might want to try a non-polarized 10 µF cap to connect to the diodes in the schematic above or a pair of back-to-back 20 or 22 µF caps in series because the cap takes a relatively large pulse in the correct direction at turn on but operates in reverse bias after that.

[tubelectron]

amptramp,

You're not the first to point that cap problem (if any !), but the unit is from 1978 and the cap is original with no issue, so a common 10µF 63V electrolytic would also be convenient. I even built a clone at a time with a 4µ7 40V tantalytic, with the same success. But one day, to be sure, I'll make some measurements average/peak ACV/DCV start/stop to see if there is a real need for a bipolar capacitor.

A+!

[PRR]

> the cap takes a relatively large pulse in the correct direction at turn on

Negligible. The 266V surge is split with the 0.0022u cap and the 22u cap. Roughly 0.002/10 or 1/5000th of the 266V across the 10u cap..... 0.05V on my abacus.

> but operates in reverse bias after that.

Hmmm. Yes. About 2.7V-0/6V or a high 2 Volts. And what happens? The e-cap breaks-over like a diode, somewhere between 1V and 3V depending how much current-leakage "matters". No harm is done if current and heat is small. Can't be over 2.66mA available and likely under 1mA. Say a volt across the cap, 1 milliWatt, cap is not harmed. It may be part of "the sound".

If the unit is vintage and working good, I would not tamper.

Someone scratch-building might want to try the several options ("original wrong", "correct", bipolar-cap).

[Lurco]

Why is there a big el. cap at all on that side of the diodes? Couldn`t you just DC-isolate them by inserting a smallish cap between the last resistor and the level-pot?

[tubelectron]

Why is there a big el. cap at all on that side of the diodes? Couldn`t you just DC-isolate them by inserting a smallish cap between the last resistor and the level-pot?

Lurco : a smaller cap reduces the effect of the diodes : less clipping, more output level, or clipping on the highs, rather unclipped boost of the bass, depending on the value. The purpose of this cap is to cut DC current from V1 cathode. 4µ7 to 22µ works well, with slight differences as explained before.

And yes, PRR, the unit is vintage ('78-'82), all original inside, and works perfectly, with the exception of a light hum due to the integration of a mains transformer very close to circuit (misconception, but not dramatic).

A+!

[Lurco]

Why is there a big el. cap at all on that side of the diodes? Couldn`t you just DC-isolate them by inserting a smallish cap between the last resistor and the level-pot?

Lurco : a smaller cap reduces the effect of the diodes : less clipping, more output level, or clipping on the highs, rather unclipped boost of the bass, depending on the value. The purpose of this cap is to cut DC current from V1 cathode. 4µ7 to 22µ works well, with slight differences as explained before.

And yes, PRR, the unit is vintage ('78-'82), all original inside, and works perfectly, with the exception of a light hum due to the integration of a mains transformer very close to circuit (misconception, but not dramatic).

A+!

Not a smallish cap between the anode capacitor (which is smallish itself!) and the diodes, but isolate that cathode voltage from where it is needed to be isolated. That is through the 330k and 1M pot to ground. This path as well as the anode to diode path is pretty high impedance. The anode cap does not pass frequencies to the diodes that low that they would be needed lto be lead through an electrolytic capacitor? Or?

[tubelectron]

This path as well as the anode to diode path is pretty high impedance

Look at the schem : the end of the diode loop is 1K5 + 22µF, that is to say nearly a short-circuit to GND for audio signal until circa 5Hz. That's pretty low impedance...

A+!