Maker Pro
Maker Pro

Building a Tube Amp

E

Eeyore

Jan 1, 1970
0
Guy said:
That's not true. I do a fair amount of work in recording studios,
and a guitar amp with a microphoe in front of it is a common sight.

It's the norm.

Graham
 
E

Eeyore

Jan 1, 1970
0
Jon said:
"Eeyore" wrote

FYI, Tube's break up differently than SS. Tubes have even order harmonic
distortion which is much more pleasent than odd order. This has to do with
how they clip... hence tubes are prefered over SS any time distortion is
involved. (and with the need for an overdriven sound for guitar it is
necessary)

Now I know what you're looking for you want to try and source something like a
Fender or Marshall copy (or rebuilt) output TX. These are WILDLY different
from the ones the hi-fi audiophools use.

Graham
 
E

Eeyore

Jan 1, 1970
0
Jon said:
I guess you guys don't know much about guitar amps?

I most certainly do. I used to service and repair them. I even have hand written
schematics somewhere.

Unfortunately as is often the case your OP was vague and didn't explain it was
for guitar !

Graham
 
E

Eeyore

Jan 1, 1970
0
That doesn't follow. What we do know is that it is lot cheaper to
distort a signal with semiconductors and subsequently amplify it with
semiconductors than it is to amplify and distort it with valves.

Wrong type of distortion. Compare the transfer characteristics. Tubes produce more
even-order harmonic distortion, transistors odd. And odd order sounds horrible.

That just gives the 'fuzz box' sound.

Graham
 
E

Eeyore

Jan 1, 1970
0
Since you seem to be planning on building a valve amplifier for your
guitar, you presumably don't have a clear idea of what you are doing.

On the contrary, you Bill are as usual the one without a clue.

Graham
 
E

Eeyore

Jan 1, 1970
0
Adrian said:
My own preference for P.A. amplifiers is a fixed dummy load, chosen to
just keep the voltages within safe limits and wired directly across the
transformer terminals. You lose a bit of power that way, but you don't
lose the amplifier when someone trips over the speaker wiring.

This can't happen with a built-in guitar amplifier until:
a) The loudspeaker goes O/C
b) Someone adds a switched extension loudspeaker socket and plugs in a
disconnected speaker.

...but you can still get an accidental O/C with a prototype on the bench
if you are not careful.

In my 'rougue's gallery' I have a pair of KT88s, one where the anode has
actually started to MELT from that kind of activity. During the 'tune up' on
stage too ! It was the roadie what did it ! I was there at the time and saw the
light show from the rear of the amp.

It actually killed FOUR KT88s and I had to let the poor guy pay me in
installments for the repair ! Damn lucky it didn't kill the OPT too. It would
have done on a Marshall.

It was an Orange 200 bass amp btw. They were superbly built (individual bias
trim on each output tube with locking collar for example and rack mounting
format) but I guess no-one thought of that problem.

Graham
 
J

Jan Panteltje

Jan 1, 1970
0
Um... actually I have build one guitar amp for my friend when he brought a
kit and couldn't get it to work... How many guitar maps have you built my
friend Jan?

Well, do not remember the exact number, but the one with 4 EL84 I build
has much to my surprize become a classic item:
http://www.drzamps.com/maz38.html
That is pretty much my configuration:)
Considering I designed an build that one in my high school days for
the band, and really knew a lot less about electronics then I do now,
amazing they still use the concept.
I remember when it was finished the lead guitar player came to me and said: "No, it is not load enough' or
something like that.
Then 10 minutes later he came back: 'It is just what we want, this sound'.

Remember EL84 x 4 is at most 35 W.

So, design a classic and come back :) LOL.

Now that really propped up my ego.
 
J

Jan Panteltje

Jan 1, 1970
0
Real men build amps where the plates are at least cherry red. If they don't,
you are not pushing the envelope.

Tam

I have seen them melt the glass.
 
J

Jan Panteltje

Jan 1, 1970
0
theres a fix for that.
a series of power diodes on each plate, anode to
ground and high voltage disk cap across them
plate to ground, stops back emf from transformer
from flashing over the tubes.

VDR (Voltage Depndent Resistors) across the transformer?
 
J

Jan Panteltje

Jan 1, 1970
0
I'm supprised most of these guys here think that a transistor or tube can be
simply modeled with a formula.

You have never used spice?
 
J

Jan Panteltje

Jan 1, 1970
0
Wrong type of distortion. Compare the transfer characteristics. Tubes produce more
even-order harmonic distortion, transistors odd. And odd order sounds horrible.

That just gives the 'fuzz box' sound.

Graham

You should read 'semiconductors' in the widest sense.
As I pointed out AD - EPROM[s}- DA can make any curve,
and those are semiconductors too.
I used that to make gamma curves for a lightshow, it works for
audio too.
You could perhaps do that in FPGA and use blockram, and have different curves
selectable on the fly.
Or just use SRAM and some multiplexers in good old 74HCXXX logic, done
that too, have the PC or a micro write the curves to the SRAM.
Not so many points for 16 bit audio, although for guitar 8 bits would do likely ;-)
mm maybe they even only use 20 dB dynamic range....
hehe
 
Yep, but they are so hard to see.

Depends. Not all tubes are designed to have cool anodes, some run the
anodes quite hot, like x-ray tubes. Some have spinning anodes to
prevent spot heating.
But in a discussion about the modest power levels for an audio amp (as
long as it's not PA) I'm guessing glowing anodes are a bad thing.
As for pushing the envelope, glass envelopes benefit tremendously from
reduced operating temperature, so running anodes red hot in a glass
tube is a bad idea IMO.

Glowing cathodes are easy to see on tubes like the 6080. I'm guessing
the reason people don't put coolers over power tubes is that they want
to see the glow...

http://www.pearl-hifi.com/06_Lit_Archive/Lit_Archive.html
 
T

TheM

Jan 1, 1970
0
John Larkin said:
I suppose that people who don't know much about electronics can do all
sorts of weird stuff.

Hey, at least its galvanically isolated ;)

M
 
R

Rich Grise

Jan 1, 1970
0
....

But what gets used "normally", if you can pick just a few examples of
"normal"?

If you want a sample of one, I can email my brother and ask what his band,
Tamarak, uses:
http://www.tamarak.iwarp.com/
but I don't know how long he'll take to reply.

Cheers!
Rich
 
J

Jan Panteltje

Jan 1, 1970
0
Ever hear of a 6L6 operating upside down in a pail of water, running 800 V
on the plate?

Tam

No, but I do remember a similar tubes in the Ampex quadruplex video recorder VR1000
head drive mounted upside down, and un-soldering themselves from the socket, falling down.
That happened when the cooling fan failed, and the air flow detection (some vane)
also failed.
http://www.pharis-video.com/p4455.htm
If you like tubes, look at the cabinet to the left of the recorder console,
see the capstan and head drive amps, modulator, demodulator, servo...
Had to keep that lot running.....
 
R

Rich Grise

Jan 1, 1970
0
Of course. We are talking about the subjective opinions of people who
are probably drugged-out most of the time and hearing-impaired all of
the time. None of which involves electronic design.

My "little" brother (who turns 54 or so this year) has been a musician
for decades. He has a little story about that. They used to play while
high - he says, "It sounded real good to _us_! Then we heard ourselves
on tape while we were straight, and all said, "OOps!"" (or something
to that effect.)

Cheers!
Rich
 
E

Eeyore

Jan 1, 1970
0
John said:
So, there are nonlinear transfer functions that only overloaded tube
amps and speakers can make?

There have been attempts to re-create them in DSP (including in marketed
products) but they're a pale shadow of the real thing.

The speaker plays a very large part too. They are almost intentionally 'low
quality'.

Graham
 
Top