Re: The KISS AMP: a progress report

"pfjw@xxxxxxx" <pfjw@xxxxxxx> said:


Two chokes? Why? The 5AR4 is a pretty good, quite rugged (if expensive)
rectifier. And it would seem simpler to add additional capacitance on
the line-side of the first choke, thereby eliminating the need for the
second?


The 5AR4/GZ 34 rectifier is available from Sovtek for about $10, at
least here in my neck of the woods.
I agree that's more expensive than 2 1N4007s, but on par with the 5U4G
you mention.
It has indeed the advantage of being indirectly heated, thereby
avoiding high surge peaks on the electrolytics.
A second advantage, often neglected, is that the 300B will only draw
current after the GZ rectifier is warm.
This is much better for the 300B cathode, the tube will last longer.
A third advantage, though of little use in this amplifier design, is
the lower voltage drop wrt. a directly heated rectifier such as the
5U4G.

André could try to use a swing choke at the cathode, this drops the
voltage a bit, but when calculated correctly, also provides a certain
voltage stability.
Although a SE amp is always biased in class A, small voltage
variations can not be avoided (depending on the load as well).

I myself would have selected a more suitable transformer, or a
combination of 2 or more, but apparently, André used what he had lying
around in his junkbox, hence the series and bleeder resistors.


I question from the perspective of one who is usually presented with
smoking ruins and given the mandate to 'make it work'. Many times
without benefit of schematics, or if they are available, facing so many
whimsical modifications to make the schematics of dubious value. So,
"expected" and "actual" values are important things to know. At times,
I thank my lucky stars that this is a hobby.... so I do not have to
make a living at it. Otherwise, not 1 unit in 10 that I see would be
worth the time and trouble to fix.


So true, I am familiar with this :-)

However, being both a repairman and an amp designer and builder, there
are differences in approaching both.

--

- Never argue with idiots, they drag you down their level and beat you with experience. -
.

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