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--- In ham_amplifiers@..., "zerobeat40" <zerobeat40@...>
wrote:

###> The 2 tone test is flawed, and isn't used anymore in the

commercial world. By juggling the spacing of the 2 x tones,

you can hit a .."sweet spot" and come up with really good IMD
numbers.

Z SEZ... That's usually with very wide spacing. At very narrow

spacing, you challenge the power supply bypassing, so the worst
numbers often occur at that test condition.

### Rauch sez the same thing....verbatim on his site...with no
explanation of course.


### OK... what am I missing here ??? I don't "get it". Why
would narrow two tone spacing... "challenge the power supply
bypassing" ??????

### Which supply.... the bias supply and or the HV supply???
What do you mean by "power supply bypassing"..... my giant 100 uf
C filter in my C input HV supply... or something else... like
bypass caps at the base of the plate choke ???

### When I look at the 2 x tone on the scope.... the envelope
varies from zero to full pep.

### What's supposed to happen... if say the two tones are
a multiple of each other... like 1000 hz and 2000 hz..... or 500
hz + 1000hz? This is supposed to be a big 'no-no'. Looks to
me like they would still be .."in phase" regardless of spacing ?

### What 'bad' is supposed to happen if the two tones are say
1000 hz.... and 1120 hz..... or 1000 hz and 1060 hz ??? Is
the 120/60 hz difference freq supposed to modulate the linear
at an audio rate or something ???

I'm completely lost.

later.... Jim VE7RF

--- In ham_amplifiers@..., "pentalab" <jim.thomson@...> wrote:

--- In ham_amplifiers@..., "zerobeat40" <zerobeat40@>
wrote:

###> The 2 tone test is flawed, and isn't used anymore in the

commercial world. By juggling the spacing of the 2 x tones,

you can hit a .."sweet spot" and come up with really good IMD
numbers.

Z SEZ... That's usually with very wide spacing. At very narrow

spacing, you challenge the power supply bypassing, so the worst
numbers often occur at that test condition.

### Rauch sez the same thing....verbatim on his site...with no
explanation of course.


### OK... what am I missing here ??? I don't "get it". Why
would narrow two tone spacing... "challenge the power supply
bypassing" ??????

### Which supply.... the bias supply and or the HV supply???
What do you mean by "power supply bypassing"..... my giant 100 uf
C filter in my C input HV supply... or something else... like
bypass caps at the base of the plate choke ???

### When I look at the 2 x tone on the scope.... the envelope
varies from zero to full pep.

At what rate? The rate of the diff between the tones. So, if your
two tones are, say, 3Hz apart, then the power supply is having to feed
out current that varies at a 3Hz rate. Not a prob with a bridge-cap
power supply, but can cause wild fluctuations in voltage for a
choke-input supply.

And, it's to test all the power supplies. The p-supply's job is to
feed out a fixed voltage, but let the current vary all over the place,
at any rate, without the voltage changing.

You can test it with CW pulses, then you have to use a scope to watch
power supply behavior. Or you can feed it two-tone IMD sigs, and
measure the IMD coming out to see if the power supply behavior is
impacting the amp performance.

No problem with a well-designed power supply, which has low source
impedance from DC to high audio freqs.

In my early days in RF amp design (the amps were then being used in
the telephone system, to multiplex many long-distance phone calls onto
a single twisted pair), we made the mistake of a too-large plate
choke. That plate choke, when forced to dole out current pulses that
were fairly slow (several Hz), rang and resonated with the PS filter
caps (microfarards were a precious commodity in the 30s) and caused
arcing in the tubes.

Maybe with modern PS design, it's a moot point. But, the point is to
test the PS regulation under dynamic load - varying pulse rates.Z

--- In ham_amplifiers@..., "pentalab" <jim.thomson@>

wrote:

--- In ham_amplifiers@..., "zerobeat40"

<zerobeat40@>

wrote:

### When I look at the 2 x tone on the scope.... the

envelope varies from zero to full pep.

Z SEZ.... At what rate? The rate of the diff between the tones.

So, if your two tones are, say, 3Hz apart, then the power supply is
having to feed out current that varies at a 3Hz rate. Not a prob
with a bridge-cap power supply, but can cause wild fluctuations in
voltage for a choke-input supply.

### I get it now... at 3 hz... this would be like slowly turning up
the drive to the linear.. when on say cw mode... with a dead cxr...
up down up down.. etc. So what.... any HV supply should be able
to handle that.... esp a resonant choke set up???

### IOW... what u are saying is with a 3-20 hz rate... u are in
effect MODULATING the HV supply... at an AUDIO rate ???




On my bias
supplies... they are just a string of 6 A diodes with a 5000-
10,000 uf cap across em.. end to end.... and some .01 uf discs
between each end of string.... and chassis for bypass.

### Maybe for the bias... we need bigger bypass caps on each end
to chassis... like 1-10uf non polarized ... as well as the
usual .01 uf disc caps ??? [stagger tuned]

Z SEZ.... And, it's to test all the power supplies. The p-supply's
job is to feed out a fixed voltage, but let the current vary all
over the place, at any rate, without the voltage changing.

You can test it with CW pulses, then you have to use a scope to

watch power supply behavior.

### a scope across the last HV lytic [cold end] in a HV supply
should work... or the last two x lytics. A battery operated
digital fluke storage scope would be ideal... even for ssb.. or cw.





Or you can feed it two-tone IMD sigs, and measure the IMD coming
out to see if the power supply behavior is impacting the amp
performance.

### I have wondered about that.... Voice IMD vs HV
regulation... esp a C input HV supply. Well, I can easily add in
100uf and 50uf banks of caps... up to a whopping 450 uf of filter
cap [11 kv rated]

Z SEZ... No problem with a well-designed power supply, which has

low source

impedance from DC to high audio freqs.

### OK.. will big lytics in a HV supply handle high audio
freqs ??? Same question on my variable bias supply ??

Z SEZ....Maybe with modern PS design, it's a moot point. But, the

point is to test the PS regulation under dynamic load - varying
pulse rates.Z

### agreed... which is why I like putting loads of uf into my HV
supplies... kills 2 x birds at once.... results in superb dynamic
regulation.... and <1 % ripple. [ripple freq is of course 120 hz]

### since I mess with ESSB... and can easily put out 1.5 kw with
20 hz sine wave, voice etc... going into the analog BM... maybe
I should base stuff on down to say at least 30-50 hz.

### Right now.. I have several 2 x tone generators... none will
allow close spaced tones...they are all fixed.

Tnx Z... U answered my question.

later....... Jim VE7RF