"Kirk Patton" wrote in message
y.com...

"Marko" wrote in message
...
I was told that metal film resistors should not be used with tubes
because
they make the circuit ring. Carbon films sound better.

Hi Mark,

I have seen some concern about inductive and capacitive aspects of certain
types of metal films in certain applications -- even though most specs say
they are 'non-inductive' or don't address the issue. Anecdotally, I have
seen RF transmitters, broadcast exciters, etc. with lots of metal films
throughout, and carbon composition resistors retained in the
high-frequency
areas. This may be the source of the 'ringing' comment you mentioned . .
..

I don't know that metal films do have a tonal effect. I was only told this.
The advice I received was that metal films tended to cause supersonic
oscillations. I know that actual inductance of metal films is no more than
carbon, they are both spiralled similarly. I thought mabey it had to do
with some sort of molecular peculiarity, possibly due to some strange
circular patterns the electrons may take within the path through the
resistor element. Sort of like little molecular eddy currents. I rebuilt
my first tube amp, a Heath W-2 with metal films. I don't like the sound of
it. I used Arco paper/mylar caps which have the classic paper sounds so I
know the caps aren't the problem. I think the audiophile rage about
polypropylene is unfounded. The hard dielectrics seem to have a hard sound.
Paper is flexible. I say this because I have some teflon caps which sound
like paper. Teflon is very flexible and has a sound similar to a Vitamin-Q.
Teflon's are rare special order components for hi-temp. If they ever catch
on audio may improve in general.

I do think it is safe to say that the level of extra reactance in modern
metal films is low enough to be extremely unlikely a point of concern in
tube audio electronics -- maybe in a tube VHF transmitter you might worry
about it. It is also safe to say that modern metal films definately have
substantially lower noise and tighter tolerances than carbon composition
resistors (even modern carbon comps), and thus it is very possible for
them
to change the sound of the device in question.

Definately, there is much lower noise, in metal film. thick film resistors
which are not sputtered but painted have noise comparable to carbon, as do
metal oxide.

As a general rule, I believe in preserving the value of collectable and
valuable historic equipment by using original parts when appropriate, but
for new designs or substantial modifications I feel that the more the
artifacts of the parts are reduced, the closer you will be to hearing the
sound of the circuit itself . . . and hopefully if the circuit is doing
its
job, closer to the sound of the music.

Agreed, but although I have a massive assortment of NOS carbon comps, easily
100,000 of all values and all wattages, they are basically unuseable because
they have gone out of tolerance as much as 30%. A design engineer from the
60s said they had to "bake" their design assortments of comps every couple
years to bring them back into tolerance.

I recommend that you heed the advice others have posted regarding voltage
ratings, and enjoy the performance of modern resistors -- if there is
indeed
any ringing, it can be measured, analyzed, and dealt with through proper
circuit changes rather than blindly swapping parts.

I doubt that they will ring, but I thought I would check with you guys
first. I would be using RN70D metal films for the most part so the voltage
rating wouldn't be a critical factor. Good point though. I also have a lot
of old NOS Dale and T.I. military carbons which I suspect will have a much
better sound than the metal films. Just a strong hunch. Thanks for the
interesting reply, Mark

Best regards,

Kirk Patton