Re: The KISS AMP: a progress report


Sander deWaal wrote:
"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.

Those Mullard designed GZ types also sound pretty good.

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.

The point of a swinging choke is to provide a fractional delay while
capacitors charge up. The slow heater on the GZ34 already provides a
delay. Furthermore, a hefty bleed loads the choke even with an
instantly-on rectifier so that there is also an instant demand for
current. All these matters tend to reduce the need for a swinging
choke, which today is a very rare item.

Although a SE amp is always biased in class A, small voltage
variations can not be avoided (depending on the load as well).

Yes, that is indeed the great advantage of the choke input filter over
the cap input filter for SE amps where the demand is essentially
static.

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.

The T68, under discussion here, is a proto to prove the driving stage
of a bigger amp. I simply lost the two 300B and used what was on the
plate, adding droppers to make it work. It would be better, if Peter
really wants to learn something about SE power supply design, to
discuss the proper T39 amp here:
http://members.lycos.co.uk/fiultra/T39-KISS-300B-Ultrafi-crct.jpg

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.

Vast, apparently.

--

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

Andre Jute
Visit Jute on Amps at http://members.lycos.co.uk/fiultra/
"wonderfully well written and reasoned information
for the tube audio constructor"
John Broskie TubeCAD & GlassWare
"an unbelievably comprehensive web site
containing vital gems of wisdom"
Stuart Perry Hi-Fi News & Record Review

.

Relevant Pages

  • The KISS AMP: square-rooting the noise
    ... thrombie over the cost, John. ... advantages of my screw-the-cost-engineers method of a split choke ... But in this amp the sonic imperatives dictate topologies that tend ... to conservative use and protection of the rectifier. ...
    (rec.audio.tubes)
  • Re: OLD style JTM 45 power supply
    ... cap and feeds the O/P trans center tap. ... the choke as the first node feeding the B+ to the O/P trans center tap. ... I have confirmed this design with an area collector and his ... note that the donor amp was an EL34 amp. ...
    (alt.guitar.amps)
  • Re: The single ended myth
    ... a similar power supply for both. ... Well, this amp sounded better PP than SE, although if not pushed hard ... Depending who is at the tiller to steer the design parameters the PP/SE ... Choke input PS are not included in any of my designs because they are ...
    (rec.audio.tubes)
  • Re: New Low for the Krooborg
    ... Also, one repair of a Chinese knockoff of a 45 design, that didn't ... The 45 is a good tube in its own right, ... I'd have to build an amp with them.. ... I definitely think there's more than just swapping the rectifier. ...
    (rec.audio.opinion)
  • Re: Deep Space 845 55W SET amps.
    ... To see paragraph marks, switch on ... there isn't room to put a choke. ... But there is an LC resonance between 4H and 235uF at 5.2Hz, and the amp ... some added series R of approximately 1.4 x XL or XC at Fo, ie, 180 ohms. ...
    (rec.audio.tubes)