All tubes
passed testing just fine. You may hear small differences when
using a different audio tube in a particular application. But
the differences should be minimal.
The
transconductance on the data sheets represents the maximum value at a
particular plate voltage and grid bias. I could not easily
duplicate those parameters with out building an extensive test facility.
However those tubes fall within operational parameters both on the
calculated data sheet and with the B&K Dynajet 700 tube tester.
The EL95 is a
tube initially developed and designed for automobile radio use putting
out a maximum of 3 watts per tube with max plate voltage. It
is not the cleanest tube that faithfully reproduces a sine wave signal
as indicated by the specified total harmonic distortion (THD) of 12%.
The lowest THD achievable is 3.5.% in class B push-pull operation with
two tubes. Normally an audiophile would prefer less than 1%THD.
So in my opinion do not expect too much from the EL95 in the way of
sonic purity.
Download the
free software from this site: http://tdsl.duncanamps.com/
and compare the tubes. Use the Short Data tab for quick
information. Compare the EL95 with a 6L6. The 6L6 in push-pull
operation will yield 0.6% THD. Other 6L6 configurations render a
poor 15% THD. You can use this software to look up tubes, find
substitutes and have an idea to predict how the radio or amp will
perform.
The ECC83
tubes seem to be just fine. There are a few with higher gain and
one or two on the low end. But all indicate just fine in the
Dynajet 700. All should be serviceable in your unit. Noise,
tonality and microphonics are a subjective matter. So choose the
tube that you thing sound best for a particular application. If
you are having difficulties with a particular unit look towards the
individual circuit parts like capacitor, resistor and the power supply
keeping up with the load demand.
Microphonics
is the physical vibration of the metal tube elements. If it is extreme
acoustic feedback can occur. I have experience this extreme
microphonics. Tubes can be constructed to minimize microphonics
with internal changes and supports. It is similar to an
incandescent lamp manufactured for rough physical service (paddle
fans). The manufacturer installs additional filament supports to
reduce the shaking of the hot filament. All tubes will produce
noise, vibrations or Microphonics if struck hard enough. It is the
tubes that pick up normally expected vibrations (i.e., guitar amp
speaker cabinet vibrations) or feedback that are problematic. Do
not set your sensitive tube amp on top of your Hi-Fi speaker. And
make sure all the rubber standoffs and speaker washers are in good
conditions or your radio may experience acoustic feedback.
Tubes
have what is called Shot Noise. That is similar to a bunch of BBs
hitting a metal plate. The electrons impact into the tube elements
and cause this shot noise. It can sound like static. Some
tubes may have reduced shot noise. Tube testers do not indicate
shot noise unless equipped with a head phone monitor jack.
Reducing the impacting electrons will reduce shot noise. That is
accomplished by reduced plate voltage. But you give up gain
(transconductance). There is always a trade off.
Carbon
composition resistor go bad with decades of time or if they have been
overheated during soldering. They go bad even in storage.
They will typically drift high out of tolerance when bad. A
questionable carbon composition resistor especially if others
around it are bad it will most likely soon go bad with use. I found this
out the hard way with an old radio that I replace the resistor only when
they went bad. I had the unit on the bench at least 4 times before
I just "shotgun" replaced all the resistors. That fixed
it. I typically replace resistors with Carbon Film unless they operate
in RF above 18 Mhz. An old carbon composition cathode resistor may add
shot noise and make the tube sound bad. Try a carbon film or metal
film or metal oxide resistor.
Other non
tube parts can cause problems. Carbon Composition resistors, by
design of the compressed carbon particles and insulation, will be
noisier than carbon film, metal oxide resistors or resistors made from a
homogeneous strata of material. One can study the manufacture's
data to make these conclusions.
Capacitors do
not typically come with noise specifications. But some military
specified (mil spec) do. Capacitors constructed for severe RF
service (satellite spacecraft, medical apparatus, defense systems, etc)
would render a design crippled if they contributed large amounts of
distortion or noise. So those caps should operate very clean in
audiophile circuits.
With an
eye to selection and specifications one can choose parts that will
perform (with tested and proven operations and life specifications)
admirably in audio circuits with out spending vast amounts of cash.
Power
supply "sag" can cause strange problems. The volume can
drop and the dynamic response of the amp can be compressed. Sag is
when the power supply can not keep up with the demands of the amplifier
circuit. Loud, continuous and/or bass passages drain down the
filter capacitors (electrolytic) faster than the transformer and
rectifiers can recharge them. There may be bad power supply
components including the electrolytic filter capacitors. If you
hear hum that may indicate a dried out electrolytic capacitor that needs
replaced. A small amount of sag us usually attributed with vintage
tube power supplies. Sag can be a desirable artistic quality in
musical instrument amps. But it is hardly tolerable in an
audiophile or PA system.
The ECC85 is
for RF service. There is a lot more going on with these tubes than
just pure gain. In the RF world interelectrode capacitance plays a
big roll. Some times more than gain. So one tube may work
just fine in one radio and be questionable in an other. They all
pass in the Dynajet. Tube #15 is a bit unbalance from side to
side. It may not work well in circuits that need a matched set of
triodes. But #15 will do fine in circuits using the triode
sections in different stages. Keep in mind this is only an outside
guess by looking at the numbers only.
