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In Reply to: RE: red plates ... bob and weave ... posted by tube wrangler on September 21, 2021 at 18:19:52
Dennis,
You wrote:
"How about a 12BZ7A (using both sections) driving a Lundahl
interstage,
Alternatively, use a 6SL7 at the front. The interstage tranny
will be a different ratio"
Did you actualy tried this? Do you know that a tube with a high Ri is not a good choice for an interstage?
Do you also know that that 12bz7 is not a very lineair tube?
Which Lundahl you want to use, you know how to use them?
Follow Ups:
12BZ7A is a lot like a 12BH7A-- in construction.
The 12BZ7 series has more grid turns than the 12BH7--
it's amp-factor is 100.
Both tubes, due to their large plate, grid and
cathode areas, are capable of handling large
momentary current pulses-- which is what music is.
Some would ask, "why not use the 12AX7-- same
amp-factor, but lower noise?" Not enough plate area
for many driver apps-- it works well on efficient
speakers with d.c.-coupled amps-- it can drive the output
tube-- a 2A3-- but cannot go further-- it is smaller in
active area.
I run them all the time on d.c. couples-- it works like
gangbusters on my speaker systems.
The speakers are not super-efficient,
I'm running GPA 604's inside a large MLTL cabinet which is
heavily built-- no unwanted resonances which steal
power.
Lundahls I have some experience with-- Kevin likes to
see 4 ma. or more on most models that would be used for
low power coupling. 10-14 ma. is the accepted published
data on some of those. K & K Audio uses Lundahl interstages
which run 4 ma. on the input side in preamps.
The Lundahls which I did use had something extra
over some other brands-- a large tolerance for
differing operating levels-- in other words, they're
more efficient at low power levels...
An interesting comparison of iron is when we were looking
at various output transformers for the 2A3, and the KT-88
series (KT 120, 150, etc.).
I'm going to stay away from mentioning brands here-- people
can fight over them somewhere else.
We used-- over years-- most of the highest regarded
output trans from Europe, Italy, all the High-End
Japanese brands, etc. We also used several from ultra
expensive custom winders here in the USA and in
Gt. Britain.
Some of these were excellent, and were used in my
commercial amps. Price-- for those amps-- was not
considered due to it being a small part of the overall
cost of building the amp.
Most sounded more than OK at their recommended idle
current levels. a very FEW (all US made) could withstand
LOWER operating D.C. currents than recommended.
While most of them started sounding "Generic"- (not
super high-end) as soon as the output tube plate current
was reduced, a FEW sounded excellent at almost any
lower current level you want to name.
Yeah! A WHOLE lot better design & construction. One
builder, a commonly "generic" supplier, sold us some
of their "super premiums"-- which were designed years
ago by one of their best engineers ever. They had sold
very few of those-- ever.
Guess what? The 14 lb E-I core monster was rated at
over 300 ma. I ran it at 43 ma. on a 2A3. What happened?
It greatly outperformed all the other transformers, period.
In every possible way-- including transparency, speed
and extended highs. Bottom was also better-- expected
because of the large inductance.
Lundahls are like that. They handle ALL of the signal--
for the most part, regardless of idle current.
That's good engineering.
I'm not trying to tell anyone how to run Lundahls.
I have more to learn from them, and frankly don't
yet know how low one can go in ma.. and which
models will allow that. Just as in tubes, they're
going to differ in ways that the specs don't show-- we'll
have to find out-- as usual.
6SL7 can be run in the current range you may need if
you have the right Lundahl. I recommend calling someone who
knows their line better than I do, and getting an
Engineer's ideas-- from several engineers.
If you D.C. couple a 6SL7-- amp-factor is about 70--
you'll have a little extra gain into a 2A3, say over a
triode of 40-45 A.F. This may or may not suit the user--
depends on his system gain. My systems use an amp-factor of 100.
If you choose to run a KT-88, and wish for an industry-standard
amp gain structure, and are D.C. coupling 2 stages,
you'll want an amp-factor of about 33 on the driver.
Don't be afraid of running lower milliamperes on chosen
vacuum tubes. Some are very superior running half or less
of their continuous ratings. Some (transmitting tubes)
must run hotter-- pure Tungsten parts, etc. They bear
no resemblance to receiving tubes, and are used differently.
Running your own plate curves is easy. You need two
variable power supplies, and some milliampere meters,
and your graph paper. Set a plate voltage, set a load,
and insert different grid biasses and plate voltages and
plot all the points on the paper. You'll find out things
about the tube in question that aren't answered on tube
MFR data.
-Dennis-
Dennis,You only speak horse shit. The 12BZ7 is a bad tube and NOT suitable to use with an interstage. The 6SL7 has the same problem but is much more linear
You talking all the time about dc coupled stage but is it really dc coupled? You not using ANY kathode capacitor?
btw, your plate area story is also horsshit
Edits: 09/23/21 09/23/21
"My systems use an amp-factor of 100."Dennis, you use a driver tube with an amp-factor of 100. The stage you are running it in has a gain of less than 70. Edit, after recalculating I should have said "less than 80".
The amp-factor of the tube (also called "mu") is (in theory) the maximum gain you could get from a stage built with that tube and can never be fully obtained. You need a horizontal load line to get you close. 285k ohms will not give you a horizontal load line for a 7b4.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 09/24/21
Correct in that you don't normally
obtain all of a tube's amp-factor.The 7B4-- as a driver for a 2A3 has
been very difficult to beat. Theoretically,
it's not ideal.The trouble is-- it IS almost ideal in
this app.I get a kick out of the 12BZ7A discussions.
That's just THEORY. In actual use, it's
one of the very few driver stage tubes that
actually works!Run your own tube tests whenever you have
a question about whether published plate
curves are correct. In most cases, they're
not even close to the tubes we actually buy and use.-Dennis-
Edits: 09/23/21
Dennis,
You don't understand anything about theory, so don't even try.
Once again you have shown us that you have absolutely no idea how to design.
Please shut up and don't bother anyone with your ideas. It would be so much better if people like you were just put behind a fence somewhere so no one is bothered.
On Sale! And here locally Steve Rouse kept lowering his price in CT until they sold...if they ever did.....would love to know which MLP participant unloaded his?
Edits: 09/23/21 09/23/21
Even if the new price was $3999 it was already $3000 to much. No serious output transformer was used for instance Edcor? Magnequest?
Edits: 09/24/21
What's wrong with Magnequest? My experience with their products was very good.
If one of our posters thinks that Magnequest transformers--
especially the ones I helped design-- are going
to get beat by anything out there-- well, think again.It just doesn't happen-- not musically.
-Dennis-
Edits: 09/24/21
The Magnequest is a great output transformer but it's the wrong impedance (2.5k but should be 3.9k) for the plate voltage and idle current Dennis is running if he cared about HD.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
3.9K is only a calculation, and it is correct
in that published distortion figures will
be lower than 2.5K on a 2A3.
2.5K does something better: at the cost of slightly
higher distortion numbers, it delivers what a 3.9K transformer
(on a 2A3) can't: a tactile feeling-- a direct contact with music.
Only two amp stages, and DC coupling also improve that.
Remember these amps were designed to LISTEN TO, not just
to perform measurements on. There is ZERO chance that a
3.9K transformer will deliver what we have. It will be a
bit cleaner, it will measure better, and 4K has been
tried. Also, 8 ohm speakers have been driven superbly
when connected to the 16 ohm tap of the 2.5K transformer.
The real question is always-- what is the DCR of the power
supply, and are its capacitors small enough and fast enough,
and are the power supply chokes low-DCR and low-inductance
enough so that short-term dynamic peaks are well reproduced..
The 3.9K output trans will handle short-term dynamic events
in a far less convincing manner-- we have experimented with 4K..
2.15K could be better yet. 2.5K is readily available and does
what it should do, musically, so we're very happy with it.
Harmonic distortion is nice to measure and theorize
about. Real life dynamics is something that is essential
to people who enjoy dynamic, complex music.
Speakers are the ultimate challenge here. They must
work, or you go to higher power. If H.F. radiators
have too little surface area, and try to fire from a tiny area,
then all forms of harmonic distortions must be lowered
to control the sub-standard tweeter's departures from
natural dynamic handling of a listening area..
-Dennis-
"Also, 8 ohm speakers have been driven superbly
when connected to the 16 ohm tap of the 2.5K transformer."That would load the 2a3 at 1250 ohms. You are free to like the resultant sound but just because you like it and call it "driven superbly" doesn't mean that those speakers are being driven superbly.
At 1250 ohms the load line for the 2a3 would be rotated towards the vertical and the harmonic distortion will be increased a lot. From 4.44% THD to 11% THD. "Superbly driven" is not a good description of what is really going on here. Distortion is not just a measurement. Distortion can be heard.
I think you like the sound of distortion. Your statement above indicates that you do.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 09/25/21 09/25/21
.
Have Fun and Enjoy the Music
"Still Working the Problem"
Tre,
Remember that Dennis only listens to his amplifiers, the asymetric clipping is part of the sounds: It's amazing, it's the best there is.
Probably he could be presedent too
.
Have Fun and Enjoy the Music
"Still Working the Problem"
Dennis,You are just a salesman trying to sell horse shit like grapes. I have heard salesmen like you many times and I don't believe a word of it.
Edits: 09/24/21
Nobody has ever asked you or anyone else
to believe anything.
What you got is an
honest discussion of why a
thing is done in a certain way.
Designing a system to SOUND LIKE the real thing
is VERY different from getting it to MEASURE like
the real thing.
The SOUND is done IN A ROOM, using human hearing.
The MEASUREMENTS are done with test instruments.
The assessments are made when a recording playback
agrees-- USING THE HUMAN EAR-- with the recorded
venue.
When industry experts HEAR the real thing in a
listening room, they know it and they understand it
when it happens.
No recording engineer who has acquired amps that
were built in the ways that are described-- ever
parted with them. 2 or maybe it's been 3-- audiophiles
have parted with theirs. Audiophiles buy and sell
every day. I have never met an audiophile who kept
a given system together for more than 2 or 3
years-- most change some important part of their
systems every few months.
That's anybody's right-- to do so. No opposition
from me.
But the vast majority of people who have built
systems the right way from the start-- aren't into
parts changing all the time, especially of amps &
speakers.
More than 96% of the amps I ever built in the ways described
in older posts are with the original owners. 100% have never had
a parts failure-- ever.
-Dennis-
And the horseshit continues.....
Dennis, read some of your colleagues' ads . Some of them look exactly like yours.
Never did the trick
Who knows why people like these amps. Sort of like John Hogan who used the same PP Webster Organ outputs for all manner of tubes from 2A3, 300B, 45 etc and people swore by the sound.
Tre',
Given a plate to cathode voltage of 220-250V I'm curious where you come up with 3.9K?
I *think* Paul Joppa may have eluded to successful use of 2.5K here - and 2.5K seems to be a standard value for a 2a3 at 250V.
It seems to me that winding SE transformers with lower impedance requires less skill and engineering for a given design, at least for HF response. From my limited observation.
"2.5K seems to be a standard value for a 2a3 at 250V"
2.5k is the standard for a 2a3 at 250volts plate to cathode but at 60ma.
Dennis runs at 43ma.
"Paul Joppa may have eluded to successful use of 2.5K here"
In fact it is Paul's math I used to determine 3.9k.
Paul's math follows the Western Electric chart very well.
If you want the least HD (across the board) while still having some power, it's a good rule of thumb.
load impedance = (voltage / current) - (2.38 * plate resistance)
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
It is all about the delta V caused by the load R and the delta-i through it. At lower current there is a larger voltage to swing across between idle B+ and where the load line hits 0V. keep in mind this same voltage ideally must be supported by R as you take the idle current towards zero. With too little R, the line is steep and you hit zero current way too soon compared to going the other way... :)
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
thanks tre', appreciate your well explained answer.
Edcor has the CXSE 3K that claims 41H of inductance.. I'd like to give that transformer a try as I hope it may be a good compromise between 2.5K and 5K... (their 5K is rated 50H!)
Edcor dos not say how they measure so you realy don't know what there datasheets mean. This is also true for Magnequest.
They don't give real measurements with a tube for instance (or with a specefic Ra).
If you want realiable measurements Tango is the ONLY manufacturure that dos give accurate measurements.For those who use Lundahl, Tribute or Monolith Magnetics.... Please publish your measurements so people here can learn how these transformers behave in real life. I guess only MM will do a decent job (but there site sucks, but is a lot better then Lundahl or Tribute)
Edits: 09/24/21
There is nothing wrong with the Magnequest if it was a cheaper transformer (maybe a little more expensive than an Edcore). Or there is nothing wrong with an expensive amplifier if they also used a special quality transformer.
The advertisement was originally for a $18000 amplifier (ok, a silly price) but even $4000 is way too expensive if we look at the components used and or the technology used (no real dc-coupled amplifier)For the Magnequest, it is EI laminates, probably M6 grade 0.35mm. That's the quality of 1960. Nowadays we have M4..M3..M2..M0 and even better than that. Also EI laminates are not very good, we have C cores. The thickness of the lamination of standard high quality c-cores is much thinner, so we have less eddy currents in the core.
For specials we also have old-fashioned Permalloy but that too is pre-historic. We now have Amorphous and nanocrystalline cores.And I've been working with amorphous cores for over 30 years so people here are asleep......
Edits: 09/24/21 09/24/21 09/24/21
"There is nothing wrong with the Magnequest if it was a cheaper transformer (maybe a little more expensive than an Edcore). Or there is nothing wrong with an expensive amplifier if they also used a special quality transformer.
The advertisement was originally for a $18000 amplifier (ok, a silly price) but even $4000 is way too expensive if we look at the components used and or the technology used (no real dc-coupled amplifier)
For the Magnequest, it is EI laminates, probably M6 grade 0.35mm. That's the quality of 1960. Nowadays we have M4..M3..M2..M0 and even better than that. Also EI laminates are not very good, we have C cores. The thickness of the lamination of standard high quality c-cores is much thinner, so we have less eddy currents in the core.
For specials we also have old-fashioned Permalloy but that too is pre-historic. We now have Amorphous and nanocrystalline cores.
And I've been working with amorphous cores for over 30 years so people here are asleep......"
I had the Magnequest DS-025. I believe they were M4 lams on that transformer.
It would be nice if you have real data. M4 is better but compared to HiB in some Japanese transformers still lower quality (a lot lower).
Have you read this?
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
"Have you read this?"
Interesting he seems to prefer M19 for SE transformers.
"due to no zero crossing"
"M6 is more costly and its attributes not used in SE service"
Tre' I believe you have some Electraprint SE transformers. Are they M19?
(if my memory is wrong I apologize!)
It's not so important what the people at Electra print think about core materials because they don't understand the datasheets about those materials.Look at:
https://www.nipponsteel.com/product/catalog_download/pdf/D003jec.pdf
and
https://www.nipponsteel.com/product/catalog_download/pdf/D005je.pdfM19: http://lookpolymers.com/pdf/AK-Steel-DI-MAX-M-19-Nonoriented-Electrical-Steel.pdf
For those only interested in the outcome of those data sheets: M19 is even more junk (it's for electro motors)
Edits: 09/30/21 10/01/21
Perhaps Denis is interested in non-oriented SiFe core?
North American Iron is where its at Mr Kobasa.
Hammond, Heyboer, Edcor, Electraprint, Intact. (in no particular order)
Exotic core materials are fine - we have that too. If you can hear the difference. I personally don't have the need for that level of detail.
It helps that we have excellent ganja and beer...so really even the old tubed tabletop radio sounds pretty good after enough substance enhancement.
Of all the names you mention, none make transformer cores, but you can find many good transformer core manufacturers in the US of course.
About the ganja and beer I'm not sure, I bet both are better in Europe (although I don't use ganja but Nederwiet is famous). But I agree that if you use it, none of that transformer stuff matters anymore.
the sharpest guy I know with regards to output transformers is Pakprotector.. he's told me of Thomas and Skinner and their SuperOrthoSil laminations.
I looked to order some in M4 but the quantity was beyond my budget. As we agree - for my tastes and listening conditions I may not benefit from higher quality laminations.
https://www.thomas-skinner.com/transformer-laminations/
I know this company. Skip them...
If you want good prices and good material: China
The best market for good cores is asia in general. All the big manufactures are there (also USA based companies)
I know this article, just skip it because it's not very good.
Got it. I used them at normal 2A3 op points. They sounded pretty good compared to other outputs I had in hand.
I should be beaten mercilessly.
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