[Patrick Turner]

On Jan 28, 1:06*am, wrote:
On Jan 25, 6:40*pm, Patrick Turner wrote:





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

BTW, I forgot to mention that ARC amps with lotsa multiple 6550 can
sound very good despite all you say about style, and agony, which
people a putton on all the time in many ways including when they buy
an ARC amp.

But lets not be fooled, any keen audio amatuer may get excellent sound
in his lounge with just 2 x 6550 or even less if he knows what he's
doing. I once got into trouble with an audio club for saying the ARC
reference 600 monbloc was like a Rolls Royce with 16 wheels. Kind of
excessively capable.

But we live in times where every man may live as well a a king if he
so choses in the Land Of the Free, the Land of Glory, Land of
Opportunity, *etc, and more BS etc, *Good 'Ol USof A, where the
doctors and dentists and lawyers are outrageously expensive.

Whoopee, gimme all those 6550, we demand it, they all cry.

Set up properly, the 6550 plus a decent drive amp can make pass music
without damaging its soul.

Patrick Turner.- Hide quoted text -

- Show quoted text -

In the Land of the Free aka as Home of the Brave, *when the mains
voltage is is off 10--20% we use Variacs . And no need to monkey
around with unnecessary 'modifucations' .- Hide quoted text -

- Show quoted text -

Indeed a variac is one other solution. But to run a pair of VM220 one
would need a variac rated for 1kVA and then if someone turns the
control knob the wrong way......

The mods I'm doing are rather minimal, and easily bypassed, and a heck
of a lot cheaper than buying a suitable variac or well rated 240V:220V
step down tranny although making up a box as Alaex suggests and which
I explained before with a 240V : 24V transformer within and rated for
120VA is probably the easiest way to avoid any mods and a high cost.
When i talk soon to the owner of the VT200 which he does not want
modded, I will explain all and give him his options, but until he
decides the bias will be adjusted to reduce the Ia considerably to
prevent tubes burning out so easily.

He has said he wants to sell his VT200 because he thinks there is not
enough power and that he might get ARC 300W monoblocs instead. Well
maybe he'll have the same problems so I need to explain all and let
the guy decide.

Some 5 years back I had a client with a very heavy 70W per channel
stereo VAC amp which he'd bought on E-bay fairly cheaply. it had 8 x
300B in it. Soon it began to smoke and blow fuses and hum badly.
Tubes had individual cathode bias RC networks but although this
regulated the Ia fairly well, the idle condition was Pda = 37W
average, and of course 300B started failing soon and it still sounded
well with 3 dead tubes because there was enough NFB and there was at
least one 300B working on each side of the PP circuit on both
channels. It came to me shortly after I heard it and there were 4 dead
or faulty 300B. This amp had had a small fire around one 300B socket
from excessive heat; a whole square inch of the 1/8" PCN had become
charcoal. A bodgy repair had been done, and solder joints had gone
dry.

I gutted the whole amp and put in my own simpler circuit but with much
better B+ filtering and set it to to make 50W AB max with all tubes
idling at less than 28W.
Hum vanished, and no more smoke because I removed most of the design
faults VAC had so unkindly included.
Its never missed a beat since. There is plenty of power, and sound is
blameless. Active protection is fitted and if any 300B conducts too
much Ia for longer than 4 seconds, the amp turns off automatically.

Patrick Turner.