Reply
 
Thread Tools Display Modes
  #1   Report Post  
EC
 
Posts: n/a
Default Heathkit AA-151 cathode resistor mod

Hi All,

As an added bonus of asking RAT's about adding a choke to my
Heathkit aa-151 power supply, Patrick Turner had a once-over
of the schematic and made a few excellent suggestions. The
next one I'm going to tackle is changing the single cathode-
resitor-bypass-cap to the 6BQ5's.

The aa-151 is a PP 6BQ5 "ultra linear" integrated with a 5AR4
rectifier and cathode biasing, and aside from 6EU7's instead
of 12AX7's is like the Heathkit SA-2;
http://www.mods.com/heath-hifi/sa2ma...2schematic.gif

I've done the obligatory newsgroup search for this topic.
Maybe surprising, but some people have experienced negative
effects from going from one cathode resistor-cap to four
separate ones. The general argument being about improved DC
balancing with shared resistor-caps per channel (in PP).

So... I'm going to go half way, changing the one resistor-cap
into two, one for left, one for right.

Currently, shared between all four 6BQ5's cathodes is a 100ohm-
7watt resistor and a 50uf-25V bypass-cap. Patrick suggested
four separate pairs with 200ohm and 1000uf, a BIG change!

The 6BQ5 spec-sheet states for PP class AB two tubes, a typical
cathode-bias resistor of 130ohm.

What I'm wondering is the RAT's-eye-view of the values for these
resistor-cap pairs. I'm thinking 165ohm-5W and 80uf would be OK,
but maybe a bit conservative.

Thanks!

  #2   Report Post  
Steve O'Neill
 
Posts: n/a
Default

Hi:

You note that the 6BQ5 spec sheet shows 130 ohm cathode resistor for 2
tubes, class AB PP. Be aware that this is for designs at approx max ratings
of 300V A-K: the AA151 runs the 6BQ5s WAY over max plate voltage at
something like 360V A-K (similar to Dyna ST/SCA35). It seems reasonable to
assume that if the original design used 100 ohms for four cathodes,
equivalent for two pairs of two cathodes ea would be 200 ohms and this is
still running the BQ5s pretty hot. I'd be inclined to run more like 220-250
ohm @10W ea.

A real benefit of separating the common K resistor is that a matched quad of
BQ5s is no longer required, just two matched pairs. Heath (and Dyna) don't
really do a good job of alerting the user to this issue. Individual K
resistors reduce the need for matched pairs but if it were my amp, I'd still
go for them.

--
Steve


  #3   Report Post  
EC
 
Posts: n/a
Default

"Steve O'Neill" wrote in
:

Hi:

You note that the 6BQ5 spec sheet shows 130 ohm cathode resistor for 2
tubes, class AB PP. Be aware that this is for designs at approx max
ratings of 300V A-K: the AA151 runs the 6BQ5s WAY over max plate
voltage at something like 360V A-K (similar to Dyna ST/SCA35). It
seems reasonable to assume that if the original design used 100 ohms
for four cathodes, equivalent for two pairs of two cathodes ea would
be 200 ohms and this is still running the BQ5s pretty hot. I'd be
inclined to run more like 220-250 ohm @10W ea.

A real benefit of separating the common K resistor is that a matched
quad of BQ5s is no longer required, just two matched pairs. Heath
(and Dyna) don't really do a good job of alerting the user to this
issue. Individual K resistors reduce the need for matched pairs but
if it were my amp, I'd still go for them.

--
Steve




Good point! I was wondering about the reduced current sharing the
resistor 4 ways...
  #4   Report Post  
Steve O'Neill
 
Posts: n/a
Default

Hi:

Has it occurred to you that these design teams you cite had many conflicting
constraints they had to balance and OA sonic performance was just one of
them and maybe not the most important one. In the case of the AA151, low
cost was clearly a consideration. Surely, having been the owner of one of
these amps for 40 years you're intimately familiar with the strange line
level input design on this amp. For those who aren't, the line level inputs
are padded down by 24 dB at the input sockets and then fed thru the input
selector switch to what amounts to the second stage of the magnetic phono
preamp. I know of no sonic advantage to this scheme but it does result in
simpler (cheaper) input switching. The price is additional noise on the
line level inputs. Then there's the single cathode bias resistor for the
four output tubes. I know of no sonic benefit to this biasing scheme but it
does save the cost of an additional power resistor and cathode bypass cap.
It also just about demands a matched quad of output tubes to prevent one
tube from going ballistic. As you know, the conventional approach would be
to put each pair of output tubes on their own bias resistor. As you also
know, some of the top classic designs such as by Mullard even went as far as
individual cathode bias resistors for each output tube.

By inference, you are a professional engineer and as such, being an amateur,
I'd really appreciate hearing your opinions regarding the sonic advantages
of the line level input scheme and the four into one cathode bias
arrangement for the output tubes.

To me the bottom line here is that today's hobbiest doesn't have to deal
with the cost issues that constrained the original designers. In a
cost-no-object environment I'm certain that the original AA151 design team
would have done things a lot differently in many areas including the
addition of a filter choke or two, a more optimum output stage bias scheme
and definitely a different line level input circuit. Just because their
hands were tied doesn't dictate that ours should be now. If you want to own
and listen to a piece of equipment that would not be out of place in a
museum, that's fine. Others want to try for improved performance and on the
AA151 that's relatively easy to do. And since it's relatively uncollectable
and cheap to obtain, why not?

--
Steve


firedome wrote in message ...
I'd leave this amp alone...it sounds extremely good just as it is, IF
properly restored...I'm constantly amazed at the amateur engineers who
think they know better than the original design teams responsible for
creating many of the best of the vintage amps...I've had one of these
amps for 40 yrs. and it still sounds great...leave it be!
Roger in NY



  #5   Report Post  
Fred Nachbaur
 
Posts: n/a
Default



Steve O'Neill wrote:
Hi:

Has it occurred to you that these design teams you cite had many conflicting
constraints they had to balance and OA sonic performance was just one of
them and maybe not the most important one.
[... snip for brevity]
Others want to try for improved performance and on the
AA151 that's relatively easy to do. And since it's relatively uncollectable
and cheap to obtain, why not?

--
Steve


Bravo! Very well stated.

Cheers,
Fred
--
+--------------------------------------------+
| Music: http://www3.telus.net/dogstarmusic/ |
| Projects, Vacuum Tubes & other stuff: |
| http://www.dogstar.dantimax.dk |
+--------------------------------------------+



  #6   Report Post  
Steve O'Neill
 
Posts: n/a
Default

Hi:

John does indeed present an interesting (although not compelling to me at
least) case for the common cathode bias resistor. Don't have time for a lot
of discussion here but note that he didn't get around to actually verifying
his theories in a practical sense.

Overall, I'd agree that if taken to the extreme of an infinite number of
tubes, the single bias resistor may have benefit in eliminating what amounts
to undesirable positive DC bias feedback. It might also be argued that it
converges on fixed bias with it's improved power capabilities in AB
operation. However, four tubes is very different from infinite and I found
from actual measurement that the need for a matched quad (in terms of bias
current) remains (positive bias feedback remains). The fact that Dyna even
recommends matched quads for the ST/SCA35 is evidence that they were aware
of the practical limitations of the scheme. Regarding power output
capabilities, I measured no practical difference between four tubes on a
bias resistor vs two tubes per resistor. This was on an ST35 with
continuous signal, measuring both one channel driven and both channels
driven. Transients like music may provide different results. However, with
two tubes on a resistor I was able to achieve much better DC balance which
probably contributed to a little better low end performance because OPT core
saturation effects were reduced.

If you read the other archived posts I think you'll conclude like I did that
this is a controversial subject with theory on one side and practice on the
other. Fortunately the cathode resistor mod is really easy on the AA151 so
all you need to do is try it and trust your ears. Interestingly I ended up
with the single cathode resistor on my 151 but increased the bypass cap to
220uF AND use a quad of tightly matched EL84s. On my ST35 I ended up with
a cathode resistor for each pair of matched output tubes each bypassed by
220uF. On this one I tried everything inc fixed bias for four tubes, for
each pair and individually for each tube. Still came back to cathode bias
because of sound even though the fixed bias schemes produced a lot more
power. I also added a filter choke to the PS which made a huge difference
in hum and noise when using efficient speakers.

--
Over and out
Steve


  #7   Report Post  
firedome
 
Posts: n/a
Default

Actually I'm a scientist, not a PE, big difference. Stating that alot
of these mods are proposed by amateurs does not infer I'm a PE, that
is simple logic...however one can presume the AA-151 designers were.

If you are talking subjective sound, I'd like to see the resulting
data from a proper double blind randomized comparison of these modded
units with the original design... The cost savings you mentioned are
relatively trivial, it's not like you are eliminating transformers .
What were OEM caps and resisitors then, a few cents? The production/yr
#s wouldn't justify it either. I believe it's a case of some
compulsive folks who can't leave anything alone - let's face it there
is a mod out there for every vintage piece ever made, did no one get
it right?

If you are talking measurable parameters, have you quantified the
increased noise in the line level inputs and from the original cathode
bias arrangement? In empirical terms, just what are the sonic
disadvantages of the original design...and what is the data base?

AA-151s are common, and if one wants to play with the circuit, have at
it. My point is that such re-arranging deck chairs is basically a
waste of time IMHO.
Roger in NY

"Steve O'Neill" wrote in message ...
Hi:

Has it occurred to you that these design teams you cite had many conflicting
constraints they had to balance and OA sonic performance was just one of
them and maybe not the most important one. In the case of the AA151, low
cost was clearly a consideration. Surely, having been the owner of one of
these amps for 40 years you're intimately familiar with the strange line
level input design on this amp. For those who aren't, the line level inputs
are padded down by 24 dB at the input sockets and then fed thru the input
selector switch to what amounts to the second stage of the magnetic phono
preamp. I know of no sonic advantage to this scheme but it does result in
simpler (cheaper) input switching. The price is additional noise on the
line level inputs. Then there's the single cathode bias resistor for the
four output tubes. I know of no sonic benefit to this biasing scheme but it
does save the cost of an additional power resistor and cathode bypass cap.
It also just about demands a matched quad of output tubes to prevent one
tube from going ballistic. As you know, the conventional approach would be
to put each pair of output tubes on their own bias resistor. As you also
know, some of the top classic designs such as by Mullard even went as far as
individual cathode bias resistors for each output tube.

By inference, you are a professional engineer and as such, being an amateur,
I'd really appreciate hearing your opinions regarding the sonic advantages
of the line level input scheme and the four into one cathode bias
arrangement for the output tubes.

To me the bottom line here is that today's hobbiest doesn't have to deal
with the cost issues that constrained the original designers. In a
cost-no-object environment I'm certain that the original AA151 design team
would have done things a lot differently in many areas including the
addition of a filter choke or two, a more optimum output stage bias scheme
and definitely a different line level input circuit. Just because their
hands were tied doesn't dictate that ours should be now. If you want to own
and listen to a piece of equipment that would not be out of place in a
museum, that's fine. Others want to try for improved performance and on the
AA151 that's relatively easy to do. And since it's relatively uncollectable
and cheap to obtain, why not?

--
Steve


firedome wrote in message ...
I'd leave this amp alone...it sounds extremely good just as it is, IF
properly restored...I'm constantly amazed at the amateur engineers who
think they know better than the original design teams responsible for
creating many of the best of the vintage amps...I've had one of these
amps for 40 yrs. and it still sounds great...leave it be!
Roger in NY

  #8   Report Post  
John Byrns
 
Posts: n/a
Default


Hi All,

Since I saw my name mentioned I thought I would throw my two cents into
this thread and also comment on the other AA-151 thread.

I am not sure exactly what you want me to do to verify my theory in a
"practical sense"? It seems to me that the main "practical" effort that
would be required is to collect and measure a large number of 6BQ5/EL84s,
to characterize their variations. This is not something I want to do,
maybe one of the tube vendors would like to do this for us? Once you have
an handle on the statistics of the tube characteristics, the rest is
mostly math, to compare the different cathode resistor schemes for balance
with different random selections of tubes.

All I can say is that I put my money where my mouth is, for example see my
25L6 amplifier on my web pages. I am not obsessive about tube balance,
some people even tolerate single ended amplifiers, the ultimate in
unbalance. I do not like to even bother with matched pairs. It is of
course desirable that the output transformer be designed to handle any
likely unbalance. For unmatched, randomly selected tubes, four separate
cathode resistors will give the best balance, the single cathode resistor
shared by four tubes is next best, and two cathode resistors, one for each
channel, is the worst choice if you aren't using matched tubes. Of course
if you are really obsessive about balancing the DC in the transformers, it
is easy enough to add a couple of DC balance pots to the circuit, then you
can set the balance in each channel right on, even with four tubes sharing
a single cathode resistor.

As far as the power supply chokes go, that were mentioned in the other
thread, I suspect that in general it wasn't entirely a matter of
economics, as even many higher end amplifiers didn't use chokes in the
power supply. I suspect this was because they were all trying to cram a
stereo amplifier into a low profile cabinet that was as small as
possible. Of course in the case of the AA-151, economics would have
prevented the inclusion of a choke even if there was space for it. Anyone
know if there is space in the AA-151 to do a neat job of adding a choke?
I would add one if it could be done so that it looked like it came from
the factory that way.

As far as tone control modifications go, I like tone controls, so I would
keep them. If I could find suitable switches, of about 11 positions, with
enough poles, that would work with the stock Heathkit knobs, I would get
rid of the pots, and go to switched tone control networks.

As far as the phono preamp goes, I would put DC on the phono preamp
heaters by putting the two preamp tube heaters in series and using them to
replace the common output stage cathode resistor. A resistive divider
would be used across the preamp heater string to get the correct bias
voltage for the output tube grids. I don't have the AA-151 schematic, but
the SA-2 is similar and the schematic indicates that the total cathode
current for the output tubes is 160 mA. A resistor in parallel with the
preamp heaters could absorb the extra 10 mA, or the current could be
backed off slightly which would make life easier for the output tubes.
The extra 6.6 volt drop across the cathode "resistor" would also help the
tubes a bit, although slightly reducing power output.

Someone mentioned the input switching, and that is one of the things I
dislike most about Heathkit amps. Assuming the switching in the AA-151 is
the same as in the SA-2, the existing input selector switch could be used
to switch the high level inputs directly into the volume control. I can't
believe that with a pentode gain stage at that point, there isn't enough
gain to feed the high level inputs in at the volume control, I suspect
Heathkit provided and excess of gain in these amplifiers, or am I missing
something? The only problem I see is that this would probably mess up the
relative gain between the MM input and the high level inputs, so it might
be necessary to reduce the gain of the phono preamp a bit.

I have an AA-151 sitting under my workbench that I got for a bargain
price, and have never even had the cover off. I was planing of selling it
someday, when I happened on a likely buyer. Maybe instead I should get a
schematic and try the choke, preamp heater, and input switching mods.


Regards,

John Byrns


In article ,
"Steve O'Neill" wrote:

Hi:

John does indeed present an interesting (although not compelling to me at
least) case for the common cathode bias resistor. Don't have time for a lot
of discussion here but note that he didn't get around to actually verifying
his theories in a practical sense.

Overall, I'd agree that if taken to the extreme of an infinite number of
tubes, the single bias resistor may have benefit in eliminating what amounts
to undesirable positive DC bias feedback. It might also be argued that it
converges on fixed bias with it's improved power capabilities in AB
operation. However, four tubes is very different from infinite and I found
from actual measurement that the need for a matched quad (in terms of bias
current) remains (positive bias feedback remains). The fact that Dyna even
recommends matched quads for the ST/SCA35 is evidence that they were aware
of the practical limitations of the scheme. Regarding power output
capabilities, I measured no practical difference between four tubes on a
bias resistor vs two tubes per resistor. This was on an ST35 with
continuous signal, measuring both one channel driven and both channels
driven. Transients like music may provide different results. However, with
two tubes on a resistor I was able to achieve much better DC balance which
probably contributed to a little better low end performance because OPT core
saturation effects were reduced.

If you read the other archived posts I think you'll conclude like I did that
this is a controversial subject with theory on one side and practice on the
other. Fortunately the cathode resistor mod is really easy on the AA151 so
all you need to do is try it and trust your ears. Interestingly I ended up
with the single cathode resistor on my 151 but increased the bypass cap to
220uF AND use a quad of tightly matched EL84s. On my ST35 I ended up with
a cathode resistor for each pair of matched output tubes each bypassed by
220uF. On this one I tried everything inc fixed bias for four tubes, for
each pair and individually for each tube. Still came back to cathode bias
because of sound even though the fixed bias schemes produced a lot more
power. I also added a filter choke to the PS which made a huge difference
in hum and noise when using efficient speakers.

--
Over and out
Steve



Surf my web pages at, http://users.rcn.com/jbyrns/
  #9   Report Post  
Steve O'Neill
 
Posts: n/a
Default

Hi:

I'm the one that mentioned "practical sense". I was referring to two issues
here. Issue #1: In your posts circa 1999 you speculated that the the
common cathode resistor scheme might produce more power under certain
conditions in an AB output stage (such as the AA151 or Dyna ST/SCA 35 are)
which could be an advertising advantage at the time these amps were
marketed. What I found by actual measurement was that there was no
appreciable difference in max power output between two tubes on a cathode
resistor vs all four tubes on a cathode resistor with either both channels
driven or one channel driven. This was on Dyna ST35. Signal was a sine
wave at various frequencies. Admittedly, music is not a continuous signal
so the results might be different with transients or tone bursts. At any
rate, I was unable to verify the theory that the common cathode resistor
would allow more power in any of the various cathode bias schemes.

Issue #2: You also state that best output tube balance is achieved with
individual cathode resistors, next best with four to a resistor and worst
with two to a resistor. By balance I assume you're referring to the
relative equality of bias current at idle. My understanding and experience
regarding the various biasing arrangements is that the ranking you give them
is really more by order of the degree of influence one output tube has on
the others tied to the common cathode resistor. Obviously, individual
cathode resistors provide the greatest degree of isolation. Due to
averaging, four tubes to a resistor is next with two to a resistor being
worst. So if one inserts four randomly chosen tubes into the amp, tubes
with the individual cathode resistors will bias up to some idle current
value dictated by individual tube characteristics at the chosen operating
point. However, each tube will probably idle at a different current. In
the case of two randomly chosen tubes to a cathode resistor, the tube
tending to draw more current at the operating point will tend to turn off
it's lower current mate thus exacerbating any imbalance between the two.
The case of four randomly chosen tubes to a cathode resistor is intermediate
between the two cases in that the influence of any one tube on the others is
reduced by averaging. However, aren't most PP amps designed on the
assumption that current imbalance betw output tubes is minimized? While
most OPTs will tolerate some degree of imbalance, on the whole, idle current
balance is desirable.

If one agrees that idle current balance is important then one will tend to
used matched pairs in the output stage of a PP amp. This is where real
world conditions may reduce the potential benefits of the four into one
cathode resistor. Assume two matched pairs of tubes where matching betw
tubes in a pair is close but matching betw the two pairs is not: a real
world situation in my experience. If this set of tubes is inserted into a
PP stereo amp with individual cathode resistors everything is fine. If
these tubes are inserted into the same amp but with individual cathode
resistors per pair of tubes, everything is still fine even though one pair
draws more current than the other. Finally, if these tubes are inserted
into the amp with all four tubes on a single cathode resistor, the hot pair
will tend to turn off the cooler pair similar to the effect of two
unbalanced tubes on one cathode resistor. The difference here is that
presumably, tube to tube balance will be maintained on each PP pair although
not at the expected values. I'm reasonably sure this is why Dyna
recommended a matched quad of 6BQ5s for the ST/SCA35 although they stated
that two matched pairs would work. By your statement "I am not obsessive
about tube balance,some people even tolerate single ended amplifiers, the
ultimate in unbalance." you obviously give output stage balance a lower
priority than is traditional. As you're aware most higher end "golden age"
PP designs had provisions for output stage bias balancing (inc those using
cathode bias) as do most modern PP designs (notable exception is McIntosh).
Also, although a single ended output stage may be the ultimate in imbalance,
the circuit and/or magnetics are designed to handle the imbalance: most PP
output stages assume a fairly good balance for best performance.

The reason I used the term "practical sense" in the first place is that I
more or less did what you suggested, I collected about 80 new mfg, NOS and
"good used" 6BQ5s by various mfgrs and characterized bias at the ST35 and
AA151 operating points. The idea here is that a mix like this is now what
is available the the 21century tube user. All tested good or better on a gm
type tube tester. What I found was that bias varied over a very wide range,
even when gm was fairly closely matched. The results explained why one tube
in a "matched" quad" I purchased from a reputable source would go red plate
in my ST35. Obviously the quad had been matched for gm only. The hot tube
would run at about 20 mA more than the others in the quad at operating
conditions. I suppose it's debatable that a sample of 80 is statistically
significant. OTOH, the quantity of tubes produced today is miniscule
compare to the good ol days so maybe 80 is significant esp if considering
the population of 6BQ5s available for my use.

Summarizing, I fully understand what you were saying in you earlier posts
about the theoretical advantages and disadvantages of the various cathode
biasing schemes. No disrespect was intended when I stated that your theories
were unverified. However, based on my experience, the real world variation
in tubes combined with my understanding that PP output stage balance is
desirable means that the theoretical advantages of four into one cathode
biasing will probably not be realized: Power output capability is not
increased and the requirement for bias matching remains. Therefore, I still
contend that Heath's and Dyna's use of the single cathode resistor was
driven primarily by cost considerations i.e save the cost of a cap and
resistor and indirectly burden the end user with the additional costs of the
matched quad nec. for optimum operation. Any functional advantages were
incidental and secondary.

As an aside, one poster commented that it was doubtful that a company like
Heath or Dyna would attempt to save a few cents on the addl parts nec for
individual bias resistor if that was a better way of doing things. My day
job is with one of the few remaining manufacturers of "physical objects" in
the US. I can assure you that a few cents per unit over a production run of
thousands of units will get attention.

As always, if my logic is warped I welcome enlightenment as to the error of
my ways.

--
Steve


John Byrns wrote in message ...

Hi All,

Since I saw my name mentioned I thought I would throw my two cents into
this thread and also comment on the other AA-151 thread.

snip



  #10   Report Post  
EC
 
Posts: n/a
Default

Well, I know for sure that if I had an amp with an infinite number
of 6BQ5's... my wife would kill me... It might just about power
all the speaker "projects" I got in the basement though! )

John, I've just done the choke-thing, and as suggested by Bob
Fitzgerald, mine fit really nicely on top of the deck, in front of
the aluminum plate by the power transformer, with a 100uf mini-can
cap bolted to it. I added another 4.7uf Solen fastcap mounted to
that aluminum separator, between the 6AU6's and the 6AN8's. This
is meant to help "speed up" the bigger cap (I guess I've read TOO
many RAT postings eh!). Anyrate, this mod I really like, reduced
the "boominess" of the bass... nice! You should know it looks
nothing like stock, but hey, the aa-151 has a face not even it's
mother can luv... I ended up building a gloss black cage, and
changing the front to black knobs and black tolex... still looks
nothing like a Macintosh!

I have backed off on the 4 or 2 separate cathode resistors, as I'm
now not sure it will have that much possitive effect. I did add
an extra 50uf to the bypass cap (mostly because I had one lying
around).

Next I plan to replace the last pf-range ceramic caps; at the AUX
and TUNER inputs, the 56pf shunt for the 6AN8's and in the NFB.
These first two are differnt than on the SA-2 schematic BTW. I'm
also going to reduce the NFB a bit, and replace a few resistors
that are wandering out of tolerance.

All I can think to do after that is pluck up da' nerve to ask
Patrick Turner how to do the 6AU6's as triodes mod in the preamp
he mentioned, but I've got enuff to keep me busy for a bit!



  #11   Report Post  
TubeGarden
 
Posts: n/a
Default

Hi RATs!

MTBF (Mean Time Between Failures) vs parts count is not the linear relationship
direct logic might presume.

As systems endure the rise and fall of the random ravages of time, larger parts
populations exhibit more stable performance than smaller parts populations.

Parallel resistors and other stupid wastes of time and money are not so stupid,
statistically.

The interesting thing to me about circuits is how they sound at this moment.
All the rest is engineering mumbo-jumbo and only of interest to off world
intellectuals and money grubbing employees.

Each of us hears what we listen to and only learn anything epiphanally useful
by happenstance and ironic cognitive dissonance.

Pretending MTBF has any useful application relative to listening to Bach is
simply posturing one's ego as greater than one's soul.

A common pose, but, hardly noble. Just smug

If you like what you hear, you are in the right place.

If you think you know what others hear, you have your head in a dark, smelly
place.

If you know what others should hear, your head IS a dark, smelly place

Listen and let listen!

Happy Ears!
Al


Alan J. Marcy
Phoenix, AZ

PWC/mystic/Earhead
  #12   Report Post  
Fred Nachbaur
 
Posts: n/a
Default

Wow. Another great post, hopefully to appear in Al's "Zen in the Tube
Garden." I especially liked the line, "Each of us hears what we listen
to and only learn anything epiphanally useful by happenstance and ironic
cognitive dissonance."

Thanks, Al. Live long and prosper!

Cheers,
Fred

TubeGarden wrote:

Hi RATs!

MTBF (Mean Time Between Failures) vs parts count is not the linear relationship
direct logic might presume.

As systems endure the rise and fall of the random ravages of time, larger parts
populations exhibit more stable performance than smaller parts populations.

Parallel resistors and other stupid wastes of time and money are not so stupid,
statistically.

The interesting thing to me about circuits is how they sound at this moment.
All the rest is engineering mumbo-jumbo and only of interest to off world
intellectuals and money grubbing employees.

Each of us hears what we listen to and only learn anything epiphanally useful
by happenstance and ironic cognitive dissonance.

Pretending MTBF has any useful application relative to listening to Bach is
simply posturing one's ego as greater than one's soul.

A common pose, but, hardly noble. Just smug

If you like what you hear, you are in the right place.

If you think you know what others hear, you have your head in a dark, smelly
place.

If you know what others should hear, your head IS a dark, smelly place

Listen and let listen!

Happy Ears!
Al


Alan J. Marcy
Phoenix, AZ

PWC/mystic/Earhead


--
+--------------------------------------------+
| Music: http://www3.telus.net/dogstarmusic/ |
| Projects: http://dogstar.dantimax.dk |
+--------------------------------------------+

  #13   Report Post  
Fred Nachbaur
 
Posts: n/a
Default

Hi,

I think that much of what Al writes is not to be taken literally, rather
just go with the flow and the intent will come across. Some of his
writing reminds of John Lennon, one of the most illustrative and classic
pieces is "I Am The Walrus."

Applying the intellect to posts like this is using the wrong tool for
the job. Read viscerally.

The MTBF comment is, IMO, a reiteration of the idea that when you're
listening to the system, (perhaps pondering your probable position on
the composite MTBF bell-curve), you're not listening to Bach.

Reminds of a story told by Peter Pringle, arguably the greatest
thereminist alive today. He was visiting a friend, who happens to be a
world-famous Japanese symphony conductor. As he arrived, this fellow was
listening to a cassette tape on a crappy little table-top cassette
recorder. Flabbergasted, Peter exclaimed, "Here you are, a world-famous
conductor, what in Sam Hill are you doing listening to that thing?"
Replied the conductor, "Oh, I'm not listening to the tape deck. I'm
listening to Bach!"

Whether we're listening to a crappy little cassette deck, or to a
Macintosh or a homebrew or a Krell, almost doesn't matter. If we're
aware that we're listening to a machine, then the machine isn't doing
its job. If the machine is so "good" that we admire how realistic "it"
sounds, we're still listening to "it"!

Cheers,
Fred

Steve O'Neill wrote:

Hi:

I didn't understand most of the content of the original post and was too
intimidated by the references to head locations to ask Al directly for an
authors insight into the intended message. Many authors of profoundly
philosophical statements such as this one seem to take offence when those of
lesser reasoning abilities ask for elucidation. Apparently the very act of
asking demonstrates a certain intellectual laziness. So...could you, not
being the author AND clearly having achieved a certain intellectual
resonance with the author please translate the entire passage for me?

The one statement I mostly did understand "Pretending MTBF has any useful
application relative to listening to Bach is
simply posturing one's ego as greater than one's soul." strikes me as
potentially wrong (pending translation). My experience indicates that if
one intends to listen to Bach using electronic music reproduction devices,
the concept of MTBF does indeed have useful application and may be the
difference between listening and poring over a schematic.

--
Steve


Fred Nachbaur wrote in message 9Wu4b.118401$K44.58799@edtnps84...

Wow. Another great post, hopefully to appear in Al's "Zen in the Tube
Garden." I especially liked the line, "Each of us hears what we listen
to and only learn anything epiphanally useful by happenstance and ironic
cognitive dissonance."

Thanks, Al. Live long and prosper!

Cheers,
Fred



--
+--------------------------------------------+
| Music: http://www3.telus.net/dogstarmusic/ |
| Projects: http://dogstar.dantimax.dk |
+--------------------------------------------+





--
+--------------------------------------------+
| Music: http://www3.telus.net/dogstarmusic/ |
| Projects: http://dogstar.dantimax.dk |
+--------------------------------------------+

  #14   Report Post  
TubeGarden
 
Posts: n/a
Default

Hi RATs!

Well, it is true that extremely short MTBF would make listening to an entire CD
impossible My position is simply that as audio experimenters, we can focus
simply on sonics, and leave other engineering miracles for the production
types.

None of my circuits have died, they have all been murdered by me in the name of
sonics. Oops, the 315A transmitter tubes for IFFR didn't last long as audio
tubes, on the order of weeks, 24/7, but that was one out of hundreds. And, they
did look cool as anything I have tried

My point was using MTBF as some sense of quality in a private system is simply
not very useful. Nor am I interested in watts consumed to produce the
milliwatts that drive my speakers. Those are indeed real things, but, I only
have ears for the music. The techno parallel universes are not of concern for
me.

I do not hope to leave this life with a place in history, just a smile

Happy Ears!
Al


Alan J. Marcy
Phoenix, AZ

PWC/mystic/Earhead
  #15   Report Post  
Choky
 
Posts: n/a
Default

oooooooooooowow!
longggggg posssssssssst!

they sing -or they not sing.
pure facts
we agree.

--
Choky
Prodanovic Aleksandar
YU


"TubeGarden" wrote in message
...
Hi RATs!

MTBF (Mean Time Between Failures) vs parts count is not the linear

relationship
direct logic might presume.

As systems endure the rise and fall of the random ravages of time, larger

parts
populations exhibit more stable performance than smaller parts

populations.

Parallel resistors and other stupid wastes of time and money are not so

stupid,
statistically.

The interesting thing to me about circuits is how they sound at this

moment.
All the rest is engineering mumbo-jumbo and only of interest to off world
intellectuals and money grubbing employees.

Each of us hears what we listen to and only learn anything epiphanally

useful
by happenstance and ironic cognitive dissonance.

Pretending MTBF has any useful application relative to listening to Bach

is
simply posturing one's ego as greater than one's soul.

A common pose, but, hardly noble. Just smug

If you like what you hear, you are in the right place.

If you think you know what others hear, you have your head in a dark,

smelly
place.

If you know what others should hear, your head IS a dark, smelly place

Listen and let listen!

Happy Ears!
Al


Alan J. Marcy
Phoenix, AZ

PWC/mystic/Earhead






  #16   Report Post  
TubeGarden
 
Posts: n/a
Default

Hi RATs!

Perhaps one of us is wise?

Happy Ears!
Al

we agree.



Alan J. Marcy
Phoenix, AZ

PWC/mystic/Earhead
Reply
Thread Tools
Display Modes

Posting Rules

Smilies are On
[IMG] code is On
HTML code is Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
FS: Heathkit tube tuners (AJ-32 & PT-1) and Scott 344B sell_tech Marketplace 0 February 21st 05 08:21 PM
FS: PAIR Heathkit W-5M, PAIR Pilot FA 540, one Heathkit WA-P2 Chuck Marketplace 2 October 27th 04 03:37 AM
FS: HEATHKIT AA-21 Amp Joe Kramer Marketplace 0 March 29th 04 08:20 PM
FS: Heathkit AS-101 loudspeaker [ALTEC] TV Marketplace 0 November 11th 03 04:32 PM
FS: Heathkit AS-101 loudspeaker [ALTEC] TV Marketplace 0 November 11th 03 04:32 PM


All times are GMT +1. The time now is 01:01 PM.

Powered by: vBulletin
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Copyright ©2004-2024 AudioBanter.com.
The comments are property of their posters.
 

About Us

"It's about Audio and hi-fi"