"Pooh Bear" wrote
in message
Bret Ludwig wrote:

Arny Krueger wrote:
snip
If you use them a lot, the tubes wear out.

This is why they still make'em.

There
are no proprietary parts that are likely to wear out
with normal use.

Tubes have always been proprietary parts. OK, you HP
200C has say a 6SN7 in it. Which manufacturer's 6SN7 is
the right one to use?

My experience is the box works with any of them.
Probably one yields best case distortion or dial
tracking. I have never had it be an issue.

The tube-bigot lie here is that most ICs in good audio
test equipment are standard parts, or can be readily
replaced with standard parts.

IIRC the 8903 has a proprietary diff amp that is close
to unobtanium. HP solid state RF gens use a lot of
proprietary silicon-8640s are slowly dropping, which is
a shame, they are the low phase noise solution even
today. The Ollies couldn't copy this stuff on their own,
or they would-they need Western capital and management.
Too bad, I'd love seeing Agilent hoist by their own 35
year old petard!

Audio Precision test oscillators offer THD residuals in
the 0.0006% region ( -104dB )

I looped-back a little XP PC with an Audiophile 24192 in it the other day,
running the freeware Audio Rightmark Program. *All* spurious responses were
112 dB or better down (most in the -120 dB range), and THD+N was something
like -106 dB.

Not a toob in sight !

AFAIK toobed audio generators and analyzers never got within 2-3 orders of
magnitude of -106 dB residuals. Something like 0.05% midband, and 0.1% at 20
and 20 KHz was about as far as toobs got.

When the first generation SS audio test equipment like the HP 331-334
first hit the market, residuals *instantly* improved by like an order of
magnitude.

http://mywebpages.comcast.net/mnowlen/hp334a.htm

Heath made a cheap clone of this box (IM5258) that I was able to improve so
that it had mid-band residuals in the 0.001-0.003% range.