"Sander deWaal" wrote in message

"Arny Krueger" said:

Note also that most tube amps don't suffer from said effects because
of their inherent low pass filters,

OTOH, tubed amps are more prone to EMI problems due to unique
tube-only problems like grid rectification, Miller capacitance and
their high input impedances. I hard a lot more RFI problems during
the days of tubes than I do now.


Grid rectification: the voltage span of an average power amp input
tube is about 2 volts.

A serious problem because of the high impedances involved and the fact that
tubes are frequently run without local feedback.

The voltage span of an average base-emitter junction is what...20 mV?

Irrelevant because transistor inputs stages are always far lower than with
tubes and almost always run with emitter degeneration.


Miller capacitance: dependent on circuitry.

Also dependent on the tubes themselves.

*Every* amplifying device with inverting output suffers from mr.
Miller.

It's all in the quantification, and the quantities are vastly differnt for
tubes and SS.

Examples of said circuits would be CCC, CEC, CSC.

High input impedance: dependent on circuitry.

Of course, but as a matter of course tubed circuts have far higher input
impedances.

A tube amp with a 10 k resistor at the grid to ground won't be more
susceptible (sp?) to RFI than an average bipolar input.

Perhaps, but irrelevant due to the common practice of using far higher grid
resistors than 10K.

Let alone FETs or MOSFETs.

Oh my goodness, it's a red herring. Actually two of them.

What was the first transistor again in your FM-frontend, Arny? ;-)

Yet another red herring. BTW, the cross-modulation characteristics of SS FM
front ends are generally better than what we had when tubes were king.

Granted that most tube amps have higher value input resistors.

Thanks for agreeing that your argument based on unrealistically low grid
resistors was irrelevant, Sander.

BTW, SS amplifiers are also inherently low pass filters.

In general, SS circuitry is capable of handling higher frequencies
than tube equipment, consider an average output transformer with a
corner freq. at 50 kHz or so.

Actually 50 KHz or so is not an uncommon corner frequency for SS amps.

Of course, a good practice is to add an anti-slewing filter at the
input of the amp (even with tubes this might be beneficial!), but some
designers select a corner frequency of 150 or 200 kHz.

Slewing was a problem in someone's mind by the time it was publicized.

Besides, that is mostly a simple RC 6 dB.oct filter, not steep enough
to supress real strong RF energy.

A 6 dB/oct filter cornering at 50 KHz is down over 20 dB at 500 KHz, 40 dB
at 5 MHz and 60 dB down at the 50 MHz that Mike origionally mentioned.

hence even if Shakti stones work
as described on their website, they won't do very much for tubed
systems IMO (from a technical POV that is!).

From a Sander technical view, that is. ;-)

Gratuitous personal insult ignored.

Inability to gracefully perceive a gentle stab due to a technological
disagreement noted.