On 09/10/15 08:05, Peter Wieck so wittily quipped:
On Thursday, September 10, 2015 at 1:23:36 AM UTC-4, Big Bad Bob wrote:
On 02/02/15 21:36, Patrick Turner so wittily quipped:
Hi Stephie and Andre,
Happy Feebleweary!
It is now 2015, I will be 68 y.o. in a few weeks. I am now enjoying life with M.D. Rx meds. No more street stuff for this geezer 
I am still in Texas. The new guvner thinks Open Carry is the real deal. Sigh. Texas is a big state. Possibly not all of one mind, or sometimes any mind. My room sounds pretty good. No accounting for neighbors...
Happy Ears!
Al
P.S. Today's Nightma
Imagine being beheaded by an ISIS operative with a Canadian accent!
Oooh, scary...
Hiya Al,
Only 68 yo, and no more off the street meds!
I'm now 67, dunno if I reach 70, depends on meds more than luck.
Other than this, I have little to add to what seems a bit undecipherable due to cultural differences between US and Oz.
My single EL34 is still going in kitchen since 1999, and after 20 years before 1999. Listening is fine....
Keep well, and if you can't, at least try to stay sane.....
Patrick Turner.
how's the land down under doing you? with mains that exceed 250V even!
makes the case to use switching power supplies on tube amps, allow up
to "whatever" volts on the input, but still works on 115V for USA. If
laptop computers can do it...
Switching power-supplies can be incredibly noisy. Not so much an issue with computers, cell-phone chargers, and other items. But of considerable issue with audio and instrument amplification. Brute-force power-supplies based on conventional technology tend to do better for these purposes.
Peter Wieck
Melrose Park, PA
not saying there aren't problems to overcome, but that's the general idea.
'ground loop' can sometimes be an issue as well. 'Direct' output would
probably need a ground loop isolator.
And switchers notoriously make "bumpy" voltage output. Even when it's
filtered I see ~1Hz "noise" of +/- 1V at 400V. it's less than 1%
deviation, which is GOOD, but because it bumps up and down all of the
time, randomly, it really messes up tube pre-amp circuits. Power supply
rejection with those is poor, at best, and you'd need a VERY fat
capacitor to filter out ~1Hz noise sufficiently. [solution, solid state
regulator].
I priced power transformers at about twice what I'd pay for an output
transformer [not exactly, but relative pricing]. So if the output is
$100, then $200 for the power transformer, and it weighs at least twice
as much so the amp becomes 'less portable' having a big iron power
transformer.
I can build the switcher for significantly LESS (money AND weight), even
if I need to use slightly complex linear regulators for the pre-amps and
screen supply.
I did a proof of concept for pre-amps using a 12AX7 (2 stage with open
loop gain) to test the 'worst case' problems [like what a 'bumpy' B+
will do to a pre-amp, and how to properly overcome it].
Seems any LF noise in the power supply gets amplified significantly, and
shows up in the output.
I tried one type of regulator (cheap design), which helps but not
enough. An RC filter isn't enough. You need a stable voltage reference
and a diff amp to control the regulator. 3 transistors, and a handful
of other parts. Now I just need to order the parts, to prove the concept.