[[email protected]]

Hi guys, i'm fairly new to tubes, and after a month or so of using my
self-designed and built amplifyer i've decided that i like the sound
and the relitive ease in working with these beautiful pieces of
glassware.

my current setup is a 5W/channel stereo amp, 1/2 a 12BH7A driving a
6CZ5 single ended. this pushes my General Motors brand speakers nicely,
and is a great improvement over my regular PC speakers. All of the
parts required, with the exception of the output transformers, were
pulled from a pair of Tek 561A oscilloscopes. I had three, and two were
donors to keep the one working. I ended up replacing all the tubes in
the working scope, and parting out the other two.

Now that background is taken care of, I'd like to explore other
combonations of tubes in the same style of amp, but i'm not too
knowledgeable in the area to just start pluggin numbers.

In other words, You may use up to three tubes. (don't include PSU
rectifyer) target is 5-10W output into 8 Ohms, PP or SE.

What tubes would you use? Justify your answer. (i'm a college
student, so 50$ tubes are not going to happen)

[maxhifi]

wrote in message
oups.com...
Hi guys, i'm fairly new to tubes, and after a month or so of using my
self-designed and built amplifyer i've decided that i like the sound
and the relitive ease in working with these beautiful pieces of
glassware.

my current setup is a 5W/channel stereo amp, 1/2 a 12BH7A driving a
6CZ5 single ended. this pushes my General Motors brand speakers nicely,
and is a great improvement over my regular PC speakers. All of the
parts required, with the exception of the output transformers, were
pulled from a pair of Tek 561A oscilloscopes. I had three, and two were
donors to keep the one working. I ended up replacing all the tubes in
the working scope, and parting out the other two.

Now that background is taken care of, I'd like to explore other
combonations of tubes in the same style of amp, but i'm not too
knowledgeable in the area to just start pluggin numbers.

In other words, You may use up to three tubes. (don't include PSU
rectifyer) target is 5-10W output into 8 Ohms, PP or SE.

What tubes would you use? Justify your answer. (i'm a college
student, so 50$ tubes are not going to happen)


Here is what I would do, given your problem. Others may have a different
idea.

Thinking of available output tubes, my choice is the 6AQ5. It is a 7 pin
miniature version of 6V6, and was popular in 1950s tv's and some radios.
It's much cheaper than a 6V6, and 7 pin sockets are also cheap.

Now, with only one tube to drive two 6AQ5's in push pull, it dosen't leave
much gain, so I'd use a triode/pentode, like a 6U8... use the pentode
section wide open for gain, direct coupled to the pentode, which will be set
up as a concertina. (think dynaco ST-70)

Connect the output tubes in pentode, not ultra-linear, and if possible,
regulate the screens (zener diodes, or possibly gas regulators), use as much
negative feedback as is possible given your output transformers. Seeing as
you're a college student, I'd strongly recommend to check your college
library for books on tube amplifier design - mine was loaded with them.

For the power supply, a full wave silicon rectifier feeding a large
capacitor (say like 200uf) should do the trick. At this price level, don't
worry about chokes or tube rectifiers. Also, a good thing to keep in mind,
is that you can easily use a 120:240V transformer feeding a full wave bridge
rectifier here... or even a 120:120 isolation transformer feeding a voltage
doubler. Buy what's cheap and available and make it work somehow here, and
sink as much money as possible into the output transformers, as they will be
the limiting factor in your amplifier.

For output transformers, you want something like 8000:8 ohms, or 10000:8
ohms. I would say go for one of the Hammond units, but the black ones, not
the really cheap 'universal' ones.

Good luck!

[[email protected]]

In other words, You may use up to three tubes. (don't include PSU
rectifyer) target is 5-10W output into 8 Ohms, PP or SE.

What tubes would you use? Justify your answer. (i'm a college
student, so 50$ tubes are not going to happen)


Here is what I would do, given your problem. Others may have a different
idea.

Thinking of available output tubes, my choice is the 6AQ5. It is a 7 pin
miniature version of 6V6, and was popular in 1950s tv's and some radios.
It's much cheaper than a 6V6, and 7 pin sockets are also cheap.

Now, with only one tube to drive two 6AQ5's in push pull, it dosen't leave
much gain, so I'd use a triode/pentode, like a 6U8... use the pentode
section wide open for gain, direct coupled to the pentode, which will be set
up as a concertina. (think dynaco ST-70)


Sounds like a good one. I'm also a good scrounger, so as my university
dumps old tube equipment, i pick it up. This reply reinforces my
thoughts that i am in the right place to learn. i've got a decent job,
so buying tubes is not a problem, but seeing the prices on some of them
(2A3 for 45$? I can't do that!) is terrifying. i still have quite a few
tubes that i've picked up out of oscilloscopes over the years, but i've
never run into a TV old enough to have tubes.

I wonder if i can get a 6AS7G to do that nifty blue glowy thing, like
my 6CZ5's do. I'm told that the type of glow that i have on those is
the good kind, indicating a healthy tube. 6AS7G isnt really my kind of
tube electrically, but it's a very astheticly pleasing one,
nonetheless. hop the gain up some, to the range of 9-12, though, and i
could find many a use for it...

[[email protected]]

Hi RATs!

Antique Electronic Supply

www.tubesandmore.com

has good books and also sells the student's best friend: Used Tubes.

Also lots of other stuff

Get a GE or RCA receiving tube manual. You can look up tubes that are
for sale cheap to see if they might bring more tunes into your life.

Also, DC power supplies are handy for builders. You can get working
used ones cheap at electronic surplus shops.

Happy Ears!
Al

[maxhifi]

wrote in message
oups.com...

In other words, You may use up to three tubes. (don't include PSU
rectifyer) target is 5-10W output into 8 Ohms, PP or SE.

What tubes would you use? Justify your answer. (i'm a college
student, so 50$ tubes are not going to happen)


Here is what I would do, given your problem. Others may have a different
idea.

Thinking of available output tubes, my choice is the 6AQ5. It is a 7 pin
miniature version of 6V6, and was popular in 1950s tv's and some radios.
It's much cheaper than a 6V6, and 7 pin sockets are also cheap.

Now, with only one tube to drive two 6AQ5's in push pull, it dosen't
leave
much gain, so I'd use a triode/pentode, like a 6U8... use the pentode
section wide open for gain, direct coupled to the pentode, which will be
set
up as a concertina. (think dynaco ST-70)


Sounds like a good one. I'm also a good scrounger, so as my university
dumps old tube equipment, i pick it up. This reply reinforces my
thoughts that i am in the right place to learn. i've got a decent job,
so buying tubes is not a problem, but seeing the prices on some of them
(2A3 for 45$? I can't do that!) is terrifying. i still have quite a few
tubes that i've picked up out of oscilloscopes over the years, but i've
never run into a TV old enough to have tubes.

I wonder if i can get a 6AS7G to do that nifty blue glowy thing, like
my 6CZ5's do. I'm told that the type of glow that i have on those is
the good kind, indicating a healthy tube. 6AS7G isnt really my kind of
tube electrically, but it's a very astheticly pleasing one,
nonetheless. hop the gain up some, to the range of 9-12, though, and i
could find many a use for it...


6AS7 is going to be more tricky to drive - if you want a tube that looks
like a 6AS7, I'd get a 6L6G, 6V6G etc. (oops - I guess those cost $$$ these
days!)