Single Ended Triode With An Interstage Transformer
YL Ito
I am planning to build either a single ended amp 1) 45/2A3/300B with an
interstage or 2) 801A with an inverted interstage transformer.
So, I am looking for someone who has built either type to share their
experiences. Basically, I would like their opinion on how the amplifier
sounded.
Currently, I am running a single ended 45 directly driven by a 6SN7 with a bias
supply. The bias supply sounds much beter than cathode biasing. Much more
detail. Voices and instruments separate.
Ed
Carl Seals
Ed:
You might try the Direct Heated Triode WWW page at www4.big.or.jp/~dh/
(thanks, Ned, for the excellent Links page). It is an interesting site
and I believe has one or more schematics and text on tube amps using
interstage transformers. You might also check out some of the other links
at www.triodeel.com. Good luck!
Carl Seals
In article <19980204034...@ladder03.news.aol.com>,
-------------------==== Posted via Deja News ====-----------------------
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SB9090
I recently finished a project building a pair of 300B mono blocks with an
interstage transformer. The design I used was based on a design by Simon
Shilton (www.netforward.com/audiophile/?sjs) -- he calls his the SE108it, Mk2.
I had Simon wind both the power transformers and the interstage transformers.
I've been meaning to write about this project in the group, so I'll ramble on a
bit, I guess.
My prior experience with a 300B circuit was the "Flesh & Blood" design (see
Sound Practices). I thought this sounded great but for me, lacked a bit in the
punch of the lower registers. Also, the top end could be a bit harsh, even with
AN paper-in-oil caps. So... I tried a direct coupled design using two 6SN7
stages and one 300B. Oh, so far, all of this has been using Bartolucci output
iron (3k, 90ma).
I had read articles about the magic of an interstage design and decided to
give it a try. In retrospect, I'm not sure I would go to so much
trouble/expense. I love the sound, but for the money spent, I'm not sure it was
worth it. My one mistake, I think, was under sizing the power supply on the
Flesh & Blood -- something that Herb Reichart advised against, but I did it
anyway. In the new mono blocks I finished, with the IT, I went a bit overboard
on the power supply -- it puts out 430v at 300ma with a choke input filter. I
think the better power supply accounts as much for the improved sound of this
amp as the IT does. Maybe more.
One reason I over sized the PSU was because I finally acknowledged the
need I have to continue exploring new ideas. I was frustrated by the old design
because I had painted myself into a corner. WIth the setup I have now, I can
convert the PSU to a cap input filter and run a much larger tube, such as a
SV572, or an 811.
Simon was good to work with, a bit long on turn around time, a sometimes a
bit slow with support help -- but he is always there to help if you need it.
One curious thing we discovered in building this amp was that, with the 417A
input tube the thing sounded terrible -- until I redesigned the line stage of
my preamp. The preamp had been a cathode follower and I changed it to an anode
follower at Simon's suggestion. Problem solved. I'm not an engineer, so I don't
know why this worked, but the difference was very significant.
If anyone is interested in hearing this design, and you're in the Portland,
Oregon area, I'd be happy to let you listen.
peter kalinkov
yl...@aol.com (YL Ito) wrote:
>I am planning to build either a single ended amp 1) 45/2A3/300B with an
>interstage or 2) 801A with an inverted interstage transformer.
>So, I am looking for someone who has built either type to share their
>experiences. Basically, I would like their opinion on how the amplifier
>sounded.
>Currently, I am running a single ended 45 directly driven by a 6SN7 with a bias
>supply. The bias supply sounds much beter than cathode biasing. Much more
>detail. Voices and instruments separate.
>Ed
I have been playing with a similar to yours setup: initially 6SN7
driving a 6A3 (same as 2A3 but 6.3v). Didn't like the sound much;
maybe it's the general sound of 6SN7, some call it cold, in my system
it's outright harsh and also can it drive the o/p tube? I know many
amps are built around it, in some it drives not one but two 300B, hmm.
The sound improved tremendously when the i/p was replaced with a 6SL7
and the driver with a triode strapped 6L6: bass, freedom from
distortion, drive (don't take my metaphors too literally, it's a bit
short of a Krell (oops, sorry)). It may have been better to simply use
another 6A3 as a driver but I didn't have extra. Now that I had a
reasonable driver (about 1.3kohm o/p resistance if not mistaken) a
logical step looked to use an IT transformer, it's also an elegant way
to apply fixed bias to the o/p tube. Of course you need good quality
preferably airgapped xformers. I used poxy little Hammonds and a few
nameless ones without much luck. The sound mellows down and becomes
pleasanly homogenous but at the expense of serious bandwidth limiting:
pleasant but lofi. What a really good IT transformer can do I have no
idea.
peter
André Jute
peter kalinkov <pe...@iafrica.com> wrote:
>
> Didn't like the sound much;
> maybe it's the general sound of 6SN7, some call it cold, in my system
> it's outright harsh
If you're using two 6SN7 in a cascade, using different brands can
sometimes prevent them ripping your ears off. But once you get them
right (bypassing the cathode resistor helps), nothing is more precise
and beautiful, given that your taste is austere rather than hedonistic.
(Jesus, if I carry on like this, Randy will come hold me up as an
example against the "Engineers". Better mend my ways quickly:)
>and also can it drive the o/p tube? I know many
> amps are built around it, in some it drives not one but two 300B, hmm.
Calculate the slew rate current, multiply by an arbitrary constant of 5,
and you have a good idea of how much drive a tube needs. It comes to
well under 5mA for a 300B (from memory actually 4.1mA), and (also from
memory) under 20mA for an 845, and under 13mA for a 212-E. It is for
this reason that the bigger tubes are so often driven by another power
tube in a booster configuration, and via an interstage transformer.
> The sound improved tremendously when the i/p was replaced with a 6SL7
A much warmer sound than a 6SN7, but less accuracy too. I'm not knocking
it; my first choke coupled 300B, a very successful amp, uses a 6SL7 for
a lovely warm, enveloping sound. You should also in zero feedback
situations check the SL's bandwidth with a very skeptical eye.
> and the driver with a triode strapped 6L6: bass, freedom from
> distortion, drive (don't take my metaphors too literally, it's a bit
> short of a Krell (oops, sorry)). It may have been better to simply use
> another 6A3 as a driver but I didn't have extra. Now that I had a
> reasonable driver (about 1.3kohm o/p resistance if not mistaken) a
> logical step looked to use an IT transformer, it's also an elegant way
> to apply fixed bias to the o/p tube. Of course you need good quality
> preferably airgapped xformers. I used poxy little Hammonds and a few
> nameless ones without much luck. The sound mellows down and becomes
> pleasanly homogenous but at the expense of serious bandwidth limiting:
> pleasant but lofi. What a really good IT transformer can do I have no
> idea.
Plenty.
I use the Lundahl LL1635-SE which is very keenly priced. I was looking
for an IST for a series of SE amps, so I asked Per Lundahl to make the
established LL1635-PP with an airgap for SE use. He will, if he hasn't
already, be cataloguing the LL1635-SE when I publish the circuits I
designed around it. It is a 1:1 IST capable of 9mA before it saturates,
requires no loading, and is recommended for 5mA, which is just right for
6SN7 driving 300B. It sounds great.
I use only 1:1 IST whenever I can, because that avoids bandwidth and
peaking problems that come with stepped transformers, requiring primary
or secondary loading which in turn brings added distortion.
I'm working with another tranny designer and windery on a very high
current interstage to use in my SV572 "Universal" design. But we're
still at the output tranny, so it will be a while before we know how
well the IST works.
Andre
--
Andre Jute an...@indigo.ie COMMUNICATION JUTE
--see our pages for music lovers, writers and audiophiles at
http://indigo.ie/~andre/ComJuteF1.html
http://www.foundmark.com/ComJute/ComJuteF1.html
Robert Ang
Try looking at my web page, as I have experimented with a 12AU7 direct-coupled with
a triode-wired KT66 through a Tango NC-20 interstage driving an 845. Enlightening
stuff.
http://opera.iinet.net.au/~rang
Rob.
fdeu...@bfm.com
In article <1d4as41.1t...@ts01-47.cork.indigo.ie>,
an...@indigo.ie (=?ISO-8859-1?Q?Andr=E9_Jute?=) wrote:
[Much nonsense snipped.]
> I use the Lundahl LL1635-SE which is very keenly priced.
Hmmm, what does price matter if you aren't paying for them?
Care to tell us how many Lundahl transformers you have bought, Andre?
Did you buy 100? Did you buy 27? (They are the Chosen Transformer for
your Real McCoy 'Lundahl' amps, right?) Did you buy 10? Did you buy 2?
Did you even buy a single Lundahl transformer, ever??!!!
> I'm working with another tranny designer and windery on a very high
> current interstage to use in my SV572 "Universal" design. But we're
> still at the output tranny, so it will be a while before we know how
> well the IST works.
Who are you scamming now, scum? Do they know your deal, that you refuse
to return review samples *loaned* to you? (How many people have you
pulled this scam with anyway?)
> Andre Jute an...@indigo.ie COMMUNICATION JUTE
> --see our pages for music lovers, writers and audiophiles at
> http://indigo.ie/~andre/ComJuteF1.html
> http://www.foundmark.com/ComJute/ComJuteF1.html
Advertising, all advertising. But the question is: were the companies
and products highlighted on your pages aware of the deal -- advertising
and promotion in exchange for free components -- before the fact, or are
you simply providing the promotional service to appease them after the
fact, after you have refused to return the review samples they loaned
you?
Shall we post a public tally of what the various suppliers have told us
about your scams? (Oh, and by the way, how is Mr. Andrew Taylor, your
partner in the "Taylor-Jute Manuscript Review Service" you advertise?)
-frank (I have taken the liberty of having a copy of this post e-mailed
to Mr. Jute, as he is claiming to be using a killfile....)
Luis Correia
I found your 845 circuit and I would like to know more about it. Where can I find more information?
Thanks in advance.
Regards.
Luis
Big Bad Bob
decades ago!!
Can you paste the link you found, or maybe put it up on a sharing site
of some kind so the rest of us can look at it and see what you're
talking about???
You can direct couple 12AU7 to the grid of a power tube (like KT88) as
long as you put the correct bias on the 12AU7's grid and use a cathode
resistor to an appropriate negative voltage. You will need to maintain
somthing like -50V on the power trube grid with no signal if I remember
correctly (maybe it is more). It depends on the tube, of course.
Usually it's easier to RC couple. Just use a series resistor on the
power tube's grid to limit current if it goes into AB2 (which it will if
you want some REAL power out of it, depending). That causes some
nonlinearity but you can use NFB to compensate.
Anyway, I can think of a bunch of configurations using positive and
negative power supplies and clever voltage dividers (and isolating
capacitors at some point) that would let you direct drive a power tube's
control grid from a 12AU7, even from the plate.
It's not like trying to do direct coupled with only NPN bipolar
transistors. You sometimes get clever with cascode and other configs.
https://en.wikipedia.org/wiki/Cascode
https://worldradiohistory.com/Archive-DX/QST/40s/QST-1945-06.pdf (see
pg 17)
other references available, of course - these just popped up really fast
in an online search.
--
(aka 'Bombastic Bob' in case you wondered)
'Feeling with my fingers, and thinking with my brain' - me
'your story is so touching, but it sounds just like a lie'
"Straighten up and fly right"
Luis Correia
Peter Wieck
The internet is your friend.
Peter Wieck
Melrose Park, PA