What do rectifiers do?

[MattAnonymous]

What do rectifiers do in general and what's their purpose in amps.  From what I understand, they filter out noise from power amplification, but I don't know if this is correct.  Also, does it matter as far as sound if the rectifier is vacuum or solid state?

[smoguzbenjamin]

They take AC and turn it into DC Like when you want 9vDC for your guitar FX, you take 240vAC (or 120vAC in the states), and use a transformer to turn it into 9vAC. Then you rectify it, making it a little more than 9vDC. Can anyone tell me the formula for that, I forgot it :oops:

Rectifiers are also the heart of an anvelope follower, usually

[Peter Snowberg]

Tube rectifiers are quite inefficient so if you put one in a power amp you end up with a condition called "sag". That's when you try to output more power than the supply has available and the result is that the available voltage decreases until you let up on the sound source at which point the supply recovers. That droop in supply voltage during pick attack and heavy power chords can sound very nice.

When you use a full wave bridge rectifier to convert AC into DC, the output voltage will be 1.41414 times the input voltage, less any leakage or loss in the filter cap after the rectifier.

Take care,
-Peter

[Joe Davisson]

Here's a good page that explains it:
http://www.guitaramplifierblueprinting.com/rectifiers.html

Looks like the 5Y3 has the slowest time. I think someone was emulating this effect? I guess when the power sags, the gain increases until it recovers?

-Joe

[Phorhas]

Do you think Tube rectifiers could be used in a practicle way in padals? to create that sag?
Will it worth the while?

[smoguzbenjamin]

a resistor in series with your power will do something similar. Although I think you need high voltage to make the effect noticable though :?

[Peter Snowberg]

The sort of sag that happens in a tube amp is happening with multiple watts being output. In a pedal you would need to replicate that in the micro-amps domain. It's just a different world.

The rectifier tube is often looked at as a necessary evil of some amp designs, but many people have gone in the direction of eliminating the tube and replacing it with resistors, chokes, and FREDs (Fast Response Epitaxial Diodes). Tube rectifiers just suck up too much power for what they do and all the currently made tube rectifiers leave something to be desired. Alas, there are almost no Mullard GZ34s left in the world.

I like the effect, but not in excess. It's like adding vanilla to a recipe... a little goes a long way and it can be an important contribution, but it's only a small piece of the picture.

Take care,
-Peter

[smoguzbenjamin]

I don't see why someone doesn't start a company producing high-quality tubes for people like us. Guess it isn't profitable huh? It would rock if someone made re-issues of the good tubes I hear you guys talk about. I'm too young to have experienced all that cool tubeness. :cry: I wish I had been born in the 50s then I could have been a hippy and played guitar all day with my buddies. Oh well playing in a garage band still rules

I'm getting a new guitar! For â,¬75 = $62,50!  Woot! :mrgreen:

[AL]

Smoguzbenjamin,

This may be a little off topic (I seem to be good at that) :oops:  but Groove Tubes just reissued Mullard pre-amp tubes and there is huge difference in tone. I was lucky enough to spend a few hours A/B 'ing different pre-amp tubes a few days ago. I used Chinese 12AX7's, ECC83's and the Mullards. I blind tested all of them in every concievable combination in 2 different amps. My tech stood behind the amp and swapped out the tubes without telling me which tube was which and I ended up with all Mullards in both amps.

Surprisingly the ECC83 were a little bassier. Just FYI. It was a lot of fun and I recommend doing that if you ever get the chance.

AL

[Peter Snowberg]

Ben, we may have both missed the "golden age of tubes", but we're here for the second coming of them!

Tube chemistry is a black art at the very least. Some of the cathode coatings of tubes past are just not safe to use, but in the 1950s radiation was a good thing. :?

I was born in San Francisco's "hippie central" district in 1970 and while I'm a little nostalgic about the change that was happening at the time and what it meant for human growth, you also have to take into account that the whole thing was in many ways reactionary to the suppressed culture that proceeded it. I'm actually glad to have missed those times in many ways because at that time we couldn't be having this conversation in 1967. There were no microprocessors to be had.

I've worked for-with-and around lots of people who loosely fit the description of a "hippy" (incl. myself) and although labels change over time.... idealism does not. There are more "hippies" today than there have even been. Cheer up, you live in a very hippy friendly country. Ride a bicycle down to your local coffee shop, go sit in a park with your (new) guitar, and enjoy the sunshine.

In the end, I think it's much better to be yourself than to be any kind of "label". There is no reason that you can't have major overlap with multiple groups. All of the best engineers I have personally delt with could easily be called "hippies", but they don't refer to themselves that way (at least most don't seem to, but if you call them hippies they won't deny it).

Too young for vintage tube coolness and social change.....? Make your own!

Take care,
-Peter