tubes age 135
theoretically last a lifetime. Of course the thermal shock of switching them on
and off may handicap the tube life way beyond 50%...maybe more like 90%. Any
additional thoughts from the group!
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Date: Sat, 01 Jan 2005 13:14:52 -0500
Subject: Re: [R-390] Off Topic - Transistor R390A sounding good.
One of the more interesting mysteries of the world is the enormous number of
transistor part numbers out there compared to the number of tubes. If you look
at a tube manual from the R390 era you will find roughly 1/100 the number of
tubes compared to the number of transistors and diodes in an equivalent solid
state book these days. We don't worry to much about a particular brand of tubes
in the 390 but the audio guys go a bit nuts on specific manufacturers of
"classic"
tubes. As far as I can see the R390 approach (don't sweat it) works just fine
except when you have a tube that's just plain bad. I have never seen a problem
that always happens with a specific brand of tube in a 390. If you look in your
390 there are a bunch of fundamentally different tubes in it. You are not going to
swap a dual triode for a pentode and have much success. Even if you stick to
triodes they come in a wide variety of bias and gain setups.
Bipolar transistors are different. You have two basic flavors NPN and PNP.
Provided you don't run to much power, current or voltage do their thing ok. At a
given current level the gain of most of them is very similar in a normal circuit. If
you already have a bag full of diodes or transistors, try plugging one in and see
what happens. It just may work and save you a major hassle.
The Lankford SSB mod on the 390A is an very good example of this. There are
probably thousands of diode part numbers that will work just fine in the circuit.
They are easier to find by body style than by part number. If the diode looks like
it will work it probably will.
So if transistors are more like each other than tubes - why so many transistor
types? Marketing rules ....
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Date: Sat, 1 Jan 2005 14:26:38 -0500
Subject: Re: [R-390] Off Topic - Transistor R390A sounding good-Audiophools
Dave the audiophool effect is most simply stated as "The more you $pend the
better it WILL $ound" There are some funny quotes at the Audiophool BS page:
(14 pages)
(10 pages)
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