[Patrick Turner]

On Jan 25, 2:45*pm, "Watt? Me worry?" wrote:
Hi RATs!

ARC builds status symbols for buyers with more money than brains. They
are legion.

ARC is a business. In business, designers are not in charge of much,
unless they also are the owner. But, owner/designers are not all
geniuses. Some may think they are...

______

I have worked on old tube gear. The 110Vac it was designed for is
hidden in the 122.5 Vac in my wall socket.

I put pairs of resistors, one on each end of the power transformer
primary, until the measured at the pins heater voltage is 6.3V, MAX. 6
volts is adequate. (OK, 12.6 volts MAX, as required)

Yes, the Rs take up space and create heat. No, that excess power and
heat never get into the unit.

Putting Rs between the PT and the OPT maximizes the damage done by the
too high voltage and only addresses part of the problem.

Once the heaters are not frying the tubes, I proceed to tune the
circuits.

Often, the circuits are well within specs, once the heater voltage is
tamed.

Sixteen 6550 tubes is not design, it is style. Style sells. People buy
sizzle, not steak.

Some ARC owners never complain. They never turn them on. They look
cool, that is all that is required.

They tell the tech they listen all the time, but, only get it fixed to
sell it.

______

Patrick, are you near the floods? I thought you were in western Oz,
but, I imagine more than I remember, these days.

Music is a joy. I used to know some interesting stuff about that, too.

Happy Ears!

Al

Thanks for your thoughts Al.

In the two VM220 ARC amps I have here now the series R between HT
winding and diodes for B+ is made of 6 x 100 ohms in parallel then
siliconed to heatsink and held tight with bolted bracket off the
chassis. The 16 ohms series R is quite sufficient to lower B+ to a
safe level even if Ik in each tube is adjusted to a mild 33mAdc.
if the Ik dc is adjusted to 67mA, the the B+ reduces further but the
heat liberated in the resistor is still not excessive, and not as much
as any one of the 8 x 6550 tubes. The actual value of such a series R
is critical in that just the right value for B+ reduction and low Pd
is chosen.
Another way is to use say 2 x 60uF plastic motor start caps in series
to make 30uF off the rectifiers, each rated for 400Vdc, then install a
choke to the total of 3,750uF which ARC have as the capacitance
between OPT CT and 0V. There can be high ripple with no Pd in the
30uF, and Vdc is then lowered without heat.
The choke need only be 1.7H. Easy, but that all involves more
work&expense than other methods.

I am on high ground well away from huge regions of Oz which are so
flat that if rivers rise 5 metres there are lakes of water extending
many miles each side of the rivers. Oz has slow cycles of rainfal
between severe droughts lasting maybe 10 years and then rainy seasons
with biblical rains and floods lasting a year in some places.

But the flooding troubles of Oz at this time are nothing but slightly
inconvenient puddles of water when compared to what happened last year
in northern Pakistan where 20 million ppl were ****ed up big time, and
there was no help from anyone, and there is corruption in govt, and
there are the ****ing Taliban, and there is desease and famine and the
whole full catastrophe. Bangladesh also cops water **** and all these
places have far more troubles than us where ppl just clean up, get a
Govt hand out, and buy new furniture and wait another 10 years for the
same thing to happen again. There is not enough high ground for ppl to
live, and increase in population meant planners began to allow
development in flood prone areas and the style of houses has changed
to low level single storey on a concrete floor slab instead of the
traditional style with living on a first floor with level 3 metres
above ground, so that the whole ground floor area is a nice cool place
to be during summer, and one uses upstairs only for sleeping at night
and staying above most floods.

Meanwhile the price of farm produce such as fruit and vegetables has
risen hugely, and everyone has to pay.

Patrick Turner.