My high freqs are dropping off
10k -2db
12k -4db etc

Happens on both channels though (maybe this is how the amp works
normally? I checked the Stereophile specs and it should be much better
than this. Also - I have checked on 3 different speakers)

"MD" wrote in message
...
My high freqs are dropping off
10k -2db
12k -4db etc

Determined by what method?
I've seen (heard) this in old men but not in old tubes. Women however do
have tubes and I bet they drop off when they get old. :-)




Happens on both channels though (maybe this is how the amp works normally?
I checked the Stereophile specs and it should be much better than this.
Also - I have checked on 3 different speakers)

MD wrote:
My high freqs are dropping off
10k -2db
12k -4db etc

Happens on both channels though (maybe this is how the amp works
normally? I checked the Stereophile specs and it should be much better
than this. Also - I have checked on 3 different speakers)


Which amp?

Which tubes?

How old are the tubes?

What about the bias for the outputs, has it changed, have you checked it?

And, how have you gone about testing this "drop off"? Listening?

More information might make for responses that would be more focused and
meaningful/practical.


_-_-bear

"MD" wrote in message
...
My high freqs are dropping off
10k -2db
12k -4db etc

Happens on both channels though (maybe this is how the amp works normally?
I checked the Stereophile specs and it should be much better than this.
Also - I have checked on 3 different speakers)

What amp are you talking about?

"MD" wrote in message
...
My high freqs are dropping off
10k -2db
12k -4db etc

Happens on both channels though (maybe this is how the amp works normally?
I checked the Stereophile specs and it should be much better than this.
Also - I have checked on 3 different speakers)

You'll may need to check the tubes on a tester. The symptoms of old (low
emission) tubes are of a muddier sound, loss of gain & dynamics and
sometimes go noisy. Signal tubes generally have a longer life than power
amplifier output tubes. If you decide to replace your power amplifier
output tubes then (dependent entirely on your particular amplifier) you may
need to complete a rebias procedure. Instructions for this are normally
included in the manual.

Mike

"MD" wrote in message ...

My high freqs are dropping off
10k -2db
12k -4db etc

..... if you are over 50 years old, your hearing loss is about normal ...

MD wrote:

My high freqs are dropping off
10k -2db
12k -4db etc

Happens on both channels though (maybe this is how the amp works
normally? I checked the Stereophile specs and it should be much better
than this. Also - I have checked on 3 different speakers)



What kind of amp, what kind of speakers? Also it sounds like you are
trying to determine the HF rolloff with your EARS!! How do you know
your EARS aren't getting old?

MD has posted this question on several NGs and has never revealed the type
of amp or other specifics, despite repeated requests. Agenda?
west

"Harry Lavo" wrote in message
...
"MD" wrote in message
...
My high freqs are dropping off
10k -2db
12k -4db etc

Happens on both channels though (maybe this is how the amp works
normally?
I checked the Stereophile specs and it should be much better than this.
Also - I have checked on 3 different speakers)

What amp are you talking about?

graham wrote:

"MD" wrote in message ...


My high freqs are dropping off
10k -2db
12k -4db etc


.... if you are over 50 years old, your hearing loss is about normal ...



Even at under 50 years old, exposure to high level sound on a regular
basis will probably have broken down the hearing at high frequencies
already.

Listening to 10K-12K test tones at high levels to see if a power amp is
rolling off, won't do the ears or the tweeters any good, either.

Gene Poon wrote:
MD wrote:

My high freqs are dropping off
10k -2db
12k -4db etc

Happens on both channels though (maybe this is how the amp works
normally? I checked the Stereophile specs and it should be much
better than this. Also - I have checked on 3 different speakers)




What kind of amp, what kind of speakers? Also it sounds like you are
trying to determine the HF rolloff with your EARS!! How do you know
your EARS aren't getting old?
Not using my ears - using a sound meter

AMC CVT-3030

On 3 different speakers - Mirage, PAradigm and Magepan

Bias is good

Tubes are about 6 years old but less than 1000hrs

I figure it can't be the tubes if the channels match?

MD wrote:

Gene Poon wrote:

MD wrote:

My high freqs are dropping off
10k -2db
12k -4db etc

Happens on both channels though (maybe this is how the amp works
normally? I checked the Stereophile specs and it should be much
better than this. Also - I have checked on 3 different speakers)


Not using my ears - using a sound meter

===========================

Okay, are you testing at nearfield, or distant?

Also, at what level? This could be the normal rolloff in power response
of ANY tweeter, if tested at too high a level.

MD wrote:
Gene Poon wrote:
MD wrote:

My high freqs are dropping off
10k -2db
12k -4db etc

Happens on both channels though (maybe this is how the amp works
normally? I checked the Stereophile specs and it should be much
better than this. Also - I have checked on 3 different speakers)




What kind of amp, what kind of speakers? Also it sounds like you are
trying to determine the HF rolloff with your EARS!! How do you know
your EARS aren't getting old?
Not using my ears - using a sound meter

AMC CVT-3030

On 3 different speakers - Mirage, PAradigm and Magepan

Bias is good

Tubes are about 6 years old but less than 1000hrs

I figure it can't be the tubes if the channels match?

It is very difficult to measure your amp's frequency response using a
sound level meter. You would be measuring the room's response and the
speaker's response, at the meter's position, instead of the amp's
response. Much better to simply use a voltmeter and measure the voltage
across the speaker terminals, using low level test tones.

"MD" wrote in message
...
Gene Poon wrote:
MD wrote:

My high freqs are dropping off
10k -2db
12k -4db etc

Happens on both channels though (maybe this is how the amp works
normally? I checked the Stereophile specs and it should be much better
than this. Also - I have checked on 3 different speakers)




What kind of amp, what kind of speakers? Also it sounds like you are
trying to determine the HF rolloff with your EARS!! How do you know your
EARS aren't getting old?
Not using my ears - using a sound meter

AMC CVT-3030

On 3 different speakers - Mirage, PAradigm and Magepan

Bias is good

Tubes are about 6 years old but less than 1000hrs

I figure it can't be the tubes if the channels match?

I'd be getting a new set of tubes anyway, just to test it out and to learn
what, if any differences or improvements
might be heard. It's nice to have some spare back-up tubes for the obvious
reasons including scarcity and rising costs. I have several spare sets for
vintage pre-amp that I play with now and then. After all it is a hobby,
isn't it?

"MD" wrote in message
...
Gene Poon wrote:
MD wrote:

My high freqs are dropping off
10k -2db
12k -4db etc

Happens on both channels though (maybe this is how the amp works
normally? I checked the Stereophile specs and it should be much better
than this. Also - I have checked on 3 different speakers)




What kind of amp, what kind of speakers? Also it sounds like you are
trying to determine the HF rolloff with your EARS!! How do you know your
EARS aren't getting old?
Not using my ears - using a sound meter

AMC CVT-3030

On 3 different speakers - Mirage, PAradigm and Magepan

Bias is good

Tubes are about 6 years old but less than 1000hrs

I figure it can't be the tubes if the channels match?

It must have occurred to you that if the tubes are not at fault, it's one of
your components?

"Chung" wrote in message
...

It is very difficult to measure your amp's frequency response using a
sound level meter. You would be measuring the room's response and the
speaker's response, at the meter's position, instead of the amp's
response.

Indeed, but he said it rolled off as compared to previous measurements,
which we can assume were carried out under similar circumstances.

Norman M. Schwartz wrote:
"Chung" wrote in message
...

It is very difficult to measure your amp's frequency response using a
sound level meter. You would be measuring the room's response and the
speaker's response, at the meter's position, instead of the amp's
response.


Indeed, but he said it rolled off as compared to previous measurements,
which we can assume were carried out under similar circumstances.


In my old VTL Compact 100 mono amps, the sure sign that the tubes were
getting old was that it would blow out a bias resistor, blow the tube,
and shoot a flame a few feet above the unit. My silly wife determined
that this also signalled that tube audio wasn't compatible with our
toddlers and I've since "downgraded" to a solid state amp. Sigh...

Oh, and there are also tube testers available. Back in the day, I had a
Hickock tester, but sold it on Ebay a few years ago.

Cheers,

Norman M. Schwartz wrote:
"Chung" wrote in message
...

It is very difficult to measure your amp's frequency response using a
sound level meter. You would be measuring the room's response and the
speaker's response, at the meter's position, instead of the amp's
response.

Indeed, but he said it rolled off as compared to previous measurements,
which we can assume were carried out under similar circumstances.

But any change in the room acoustics, or even a slight repositioning of
the sound meter, can cause changes in the readings of a couple of dB's
as read on the meter. What is the problem with using a voltmeter?

"MD" wrote in message
...
Gene Poon wrote:
MD wrote:

My high freqs are dropping off
10k -2db
12k -4db etc

Happens on both channels though (maybe this is how the amp works
normally? I checked the Stereophile specs and it should be much better
than this. Also - I have checked on 3 different speakers)




What kind of amp, what kind of speakers? Also it sounds like you are
trying to determine the HF rolloff with your EARS!! How do you know your
EARS aren't getting old?
Not using my ears - using a sound meter

AMC CVT-3030

On 3 different speakers - Mirage, PAradigm and Magepan

Bias is good

Tubes are about 6 years old but less than 1000hrs

I figure it can't be the tubes if the channels match?


Just as well, as its not so easy on the CVT-3030 to straight swop output
tubes. The EL34's are soldered to daughter boards, fine if you have matched
pairs and are handy with a soldering iron otherwise its a dealer or factory
job. When you say 'bias is good' I trust you mean that all bias measurements
readings were in spec and didn't need to adjust any of the bias
potentiometers?

-=Mike=-

"Ritz" wrote in message
...


In my old VTL Compact 100 mono amps, the sure sign that the tubes were
getting old was that it would blow out a bias resistor, blow the tube, and
shoot a flame a few feet above the unit.

Something like this happened to one of my ARC D76As, when the bias happened
to be way off. In addition to the flames and smell of smoke, I believe some
tubes burned out. I never went back to that unit and sold both my D76As to a
collector who came to my home with USD in hand and relieved me of them.
Those amps failed when it came to driving speakers with impedance less than
8 ohms, and since those were the only speakers which I was attracted to,
they proved to be useless. I understand that modern tubes amps can drive
such loads effortlessly, but their maintenance is too much of a PIA for me.

In article ,
Norman M. Schwartz wrote:

Those amps failed when it came to driving speakers with impedance less than
8 ohms, and since those were the only speakers which I was attracted to,
they proved to be useless. I understand that modern tubes amps can drive
such loads effortlessly, but their maintenance is too much of a PIA for me.

Curious; never had problems driving a double pair of KLH Nines with 4
slightly modified Dyna MK III's, and if my old GR 650A was to be believed
the Nines had an impedance of about 1/2 ohm, almost all capacitative, at
20Khz.

I much preferred the D75N to the D76, but never took the time to figure
out why.

On the other hand the Nines did sound much better being driven with the
dB Systems DB-6, and long-term operation was a lot cheaper since even then
matched pairs of 6550A's were not cheap.

Mike Squires
--

Mike Squires (mikes at cs.indiana.edu) 317 233 9456 (w) 812 333 6564 (h)
mikes at siralan.org 546 N Park Ridge Rd., Bloomington, IN 47408