Gently winding up Variacs

[Cursitor Doom]

Hi all,

If a piece of faulty equipment hasn't been fired up for like many
*years*, what rate would it be advisable to slowly wind up the supply
voltage to it so as not to blow anything? I'd guess 24hrs for a 240VAC DUT
would do it but it's just a guess. I blew something in a scope up one day
after being too impatient; very annoying. Whichever component it was that
went phut filled the room with acrid smoke. I still have yet to track it
down.
And I'm also guessing one could get away with starting the process at
50VAC? What does the Panel think?

[N_Cook]

Its not a panacea, just gives better odds against an electro cap
failure, a totally dry one will not reform.
I don't know if its on the WWW but the Colossus at Bletchley Park is
wound up daily via a geared motor drive , over 40 minites IIRC, and also
down again in the afternoon. As a result they just loose about 1
thyratron a year, replacing caps would be no problem

[jurb...@gmail.com]

Ever hear of a dim bulb tester ? This is an incandescent lamp wired in series with the mains. If you have a blown AC fuse you can just jump it out because the DBT will limit the current. In the US, a 100 watt lamp will limit the current to under an amp. On like a solid state audio amp or alot of other things it may light up in the beginning but will dim out as the main filters charge up. If it never dims you start disconnecting things until it does and that is your short.

Some technologies do not like this, here and there, some depend on the steep rise in main B+ to start, sometimes through a cap to a lower source but that is used less often because it precludes certain methods of line isolation.Some TVs that had scan (LOPT) derived sources had problems with it, some SMPSes have a problem with it and most things that are microprocessor controlled for the power on have a problem when the standby is up, then the inrush of the main power goes on and kills the AC. Steps must be taken to rectify this problem if you want to use the DBT on such units.

Tube units also need to be handled differently. If it has selenium or copper rectifiers, they are hellishly inefficient and you might need a higher wattage bulb. In fact I have been considering building one that has multiple bulbs that can be switched in and out for different equipment.

If you have a tube rectifier, like a 5U4 or whatever, you can probably just fire it up as is, because that B+ will not be applied all at once. It only comes after the filament of the rectifier tube warms up. Usually, when an ALL tube (valve) unit blows the AC fuse immediately it either needs a power transformer or a small noise suppression cap across one of the windings. But you do have to be a little more careful if it has solid state rectifiers. In that case, usually ohmmeter reading will tell you if you have a dead short.

Any caps that emit smoke at power up need to be replaced. A shorted power transformer stays shorted. Main thing is the smoke and smell really. Anything that smokes is bad, so mainly the DBT and variac protect DC coupled amplifier circuits and some regulator problems.

If you use the DBT in conjunction with the variac, you should be able to increase to full voltage in less than a minute unless the thing has massive filters in it. This IS an issues with some high fidelity amps that have like a half a Farad of main filtering. Some really do have that much, though 100,000 uF is more common. In any case you take the variac up a bit and the bulb lights up a bit and then dims down. When it dims down you give it a little more and a little more. When it stops dimming down (and this is with no signal and no load) THEN is when you look for the problem.

[Trevor Wilson]

**I start at zero when winding up my variable auto-transformer (aka:
Variac™ - Variac™ is a trade name, not the name of the device itself).
With modern DUTs (ie: anything manufactured within the last 30 years), I
don't bother too much. Older equipment will almost always have suspect
electros anyway. As other have stated, it's a crap shoot. I recently
refurbished a super 8 projector (European, 70s vintage, Beaulieu) for a
client. I started testing some of the electros and found that 70% had
either poor ESR or very low capacitance. I simply replaced the whole
lot. I didn't even bother testing them after the first half dozen.

I bet your old 'scope has a failed cap.

--
Trevor Wilson
www.rageaudio.com.au

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[Samuel M. Goldwasser]

This is fine most equipment with a linear power supplies. Switchmode power
supplies may be unhappy at significantly below minimum spec'd input voltage and
let out their smoke regardless of whether the caps are good.

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[Trevor Wilson]

On 24/08/2015 3:41 AM, Cursitor Doom wrote:

**One more trap for the uninitiated: NEVER crank up an audio amplifier
fitted with V-FET output devices on a variable auto-transformer.
Destruction will be assured under such a test.

[Phil Allison]

Cursitor Doom wrote:

>
>
> If a piece of faulty equipment hasn't been fired up for like many
> *years*, what rate would it be advisable to slowly wind up the supply
> voltage to it so as not to blow anything? I'd guess 24hrs for a 240VAC DUT
> would do it but it's just a guess.

** That would probably be very safe, but in most cases it can be done much faster. Filter electros are the troublemakers as they can require gradual reforming after a long period of idleness.

Had one like that the other day, a valve amp from the 1960s that had not been run in the last 10 years. With all valves removed, the AC supply current rose quickly with each voltage increases and then slowly fell back.

> I blew something in a scope up one day
> after being too impatient; very annoying. Whichever component it was that
> went phut filled the room with acrid smoke. I still have yet to track it
> down.

** That is what overheated electros do.


.... Phil

[gregz]

Not much more, but all depends, of course. Then you got tube rectifiers. I
like using dim bulb AND variac. I don't know if it helps, but sometimes I
let sit at zero, after slow increases.

Greg

[N_Cook]

On 23/08/2015 18:41, Cursitor Doom wrote:

Tantalum caps failing, can go off with quite a bang, leaving an
"electrical" smell

[jurb...@gmail.com]

>"**One more trap for the uninitiated: NEVER crank up an audio amplifier
>fitted with V-FET output devices on a variable auto-transformer.
>Destruction will be assured under such a test. "

You mean class D I assume ?

[Phil Allison]

** V-FETs were TO3 linear devices made and used by Sony and Yamaha in a number of hi-fi amplifers back in the mid 1970s. Common part numbers were 2SK82 and 2SJ28.

Then they suddenly stopped making them.

As a result, V-FETs and the few amps concerned are now rare and so have acquired a mythical status among the gullible.

BTW:

Do not confuse V-FETs with Hitachi's "Lateral Mosfets" that appeared later and were a huge success especially in high powered pro-audio amps.

Common numbers were 2SK135 & 2SJ50 or 2SK176 & 2SJ56.

Then they suddenly stopped in the late 1980s.

However, near identical TO3 MOSFETS are still made and carry numbers like BUZ901 and BUZ905.


... Phil












Google " Sony V-FET " and learn more than you ever wanted to know.

[Cursitor Doom]

On Mon, 24 Aug 2015 09:24:38 +0100, N_Cook wrote:

> Tantalum caps failing, can go off with quite a bang, leaving an
> "electrical" smell

Probably not a tant, then. I don't recall any bang and certainly no
electrical smell. Just choking, acrid smoke. Oh, and when I looked
inside, there was a light film of fine, sooty, black carbon powder over
much of the innards.
I suspect whatever had failed was concealed or screened as I couldn't see
any evidence of charred components merely from splitting apart the
external cases.

[pf...@aol.com]

Mpffff.... a variac without proper metering is worse than useless. And a dim-bulb tester, while infinitely better than an unmetered variac is still a blunt instrument.

A variac needs an ammeter that is accurate within a single % of the scale it is measuring. Such that one may watch even tiny variations in how the current comes up as the voltage is raised. A few things:

a) Anything with a tube (valve) rectifier will not pass B+ until the applied voltage is somewhere between 70% and 80% of the nominal voltage. So, reforming caps by way of slow uptake on a variac for such a devices is a complete myth. Those caps will see, all at once, no less than 70% of the operating voltage - not hardly a soft start.

b) If any device is using as little as 5% more current than it should-if-optimal, that current will be expressed somewhere as heat. If in the winding of a power or output transformer, that will, eventually mean *POOF*. If in an IF transformer for a tuner or receiver, also, eventually, *POOF*.

c) Electronics, old and new, do not typically 'cure' themselves of faults, even if cajoled, massaged and seduced very slowly. Sure, caps _can_ reform, but that reformation is unlikely to be either reliable or permanent. Given the low cost of caps these days, even the thought of reforming vintage caps should give one the cold shivers at the very least.

d) One can, with the proper instrumentation, figure out what is going on with any given piece of equipment typically within several hours anyway. 99-44/100% of them, within several minutes. Sure, individual component thermal failures or intermittents can be a huge diagnostic problem, but as to general function, that should take little time at all.

So, cutting to the chase, a metered variac with a precise meter that is capable of reading *accurately* in very small increments is a very fine diagnostic tool, especially at the triage level. A simple, unadorned variac is useful only for dimming the lights - its original purpose. IF that is all one has, put it aside and start with the dim-bulb tester and a number of different 'bulbs' to get a very-ballpark S.W.A.G. at how much current any given devices is actually using.

For the record, if it takes me more than 5 minutes to conclude how well behaved any given device might be under full power, that would be a long time. HOWEVER!! Once any new-to-me device is at full operating voltage and running, I will watch it like a hawk for several hours at least before deeming it fit for polite society. And very few very vintage (pre-1960) devices get even that far without at least the power-supply caps being redone. It is simply not worth the risk.

Peter Wieck
Melrose Park, PA

[pf...@aol.com]

On Monday, August 24, 2015 at 1:27:44 AM UTC-4, Phil Allison wrote:

> Had one like that the other day, a valve amp from the 1960s that had not been run in the last 10 years. With all valves removed, the AC supply current rose quickly with each voltage increases and then slowly fell back.

How would that happen unless the unit had a solid-state rectifier? Typically that quick-rise, slow-fall is due to the "empty" caps accepting inrush, then as they charge becoming more 'resistant-for-lack-of-a-better-word'. And the only way the caps would be in the circuit is if the rectifier was in place - hence the question.

Put another way, it is a bad idea to allow a tube amp to make B+ without a load. Many marginally designed amps ran their filer caps at very near their ratings - and both vintage and marginally capable caps running unloaded might just go *POOF*.

[Trevor Wilson]

**No.

[jurb...@gmail.com]

>"** V-FETs were TO3 linear devices made and used by Sony and Yamaha in a >number of hi-fi amplifers back in the mid 1970s. Common part numbers were >2SK82 and >2SJ28. "

I'll take your word for it, but that doesn't explain why. I dug around a little and found the TA-8650 which is 80 watts per and uses three complementary sets of 2SK60 and 2SJ18 per. Seems like alot for 80 watts but who am I to bitch about something being a bit overbuilt ?

There are a couple of things about that amp that don't make a hell of alot of sense. First of all, they are current sharing without source resistors, at least separate source resistors. you said there aren't many that can do that, apparently these are among them. And they use two source resistors, damn, for an extra ten cents they could have just used three. I also caught an error where they claim to have -85 volts on the base of a transistors with the emitter grounded. But I am used to that shit.

Also, they are drawn as depletion mode devices, yet have a higher source for the drivers. (they ARE depletion mode right ?) OK, that might just be for better linearity but I bet those outputs REALLY don't like hard clipping. Yeah sure don't do that, but it should not be destructive. shit happens like when switching sources or whatever sometimes.

And neither should brownouts. I don't see how running off a variac at reduced voltage would fry this thing. But my search indicates that such devices were also used in some serious high end monoblocks but I did not get those model numbers. Any come to mind I can look up ?

Sony failure modes have been a bitch for a long time. Seems like they used to love selling alot of parts.

[Trevor Wilson]

On 25/08/2015 9:32 AM, jurb...@gmail.com wrote:
>> "** V-FETs were TO3 linear devices made and used by Sony and Yamaha
>> in a >number of hi-fi amplifers back in the mid 1970s. Common part
>> numbers were >2SK82 and >2SJ28."
>
> I'll take your word for it, but that doesn't explain why. I dug
> around a little and found the TA-8650 which is 80 watts per and uses
> three complementary sets of 2SK60 and 2SJ18 per. Seems like alot for
> 80 watts but who am I to bitch about something being a bit overbuilt
> ?

**The 2SK60/2SJ18 are rated at a pitiful 5 Amps, which is why so many
are required. Here is what is printed on page 6 of the service manual of
the Sony TAN7:

"Note:
1. Apply the rated ac line Voltage to the set directly. Do not increase
the Voltage gradually by using a variable transformer or other such
instrument; this will cause a V-FET failure."

>
> There are a couple of things about that amp that don't make a hell of
> alot of sense. First of all, they are current sharing without source
> resistors, at least separate source resistors. you said there aren't
> many that can do that, apparently these are among them. And they use
> two source resistors, damn, for an extra ten cents they could have
> just used three. I also caught an error where they claim to have -85
> volts on the base of a transistors with the emitter grounded. But I
> am used to that shit.
>
> Also, they are drawn as depletion mode devices, yet have a higher
> source for the drivers. (they ARE depletion mode right ?) OK, that
> might just be for better linearity but I bet those outputs REALLY
> don't like hard clipping. Yeah sure don't do that, but it should not
> be destructive. shit happens like when switching sources or whatever
> sometimes.
>
> And neither should brownouts. I don't see how running off a variac at
> reduced voltage would fry this thing. But my search indicates that
> such devices were also used in some serious high end monoblocks but I
> did not get those model numbers. Any come to mind I can look up ?

**I recall my first V-FET amp repair. I did not pay attention to the
Sony Warning. A new set of V-FETs and I was good to go, after blowing up
the first set. Every V-FET amp since has been VERY carefully dealt with.
No bench failures since the first one. The most expensive and unique amp
I've ever seen was the Yamaha B1. It was a beast, with over-sized
V-FETs. They LOOK like To-3 devices, until you see one in the flesh:

http://www.thevintageknob.org/yamaha-B-1.html

http://upload.review33.com/avforum/201507/201507092155125540.jpg

>
> Sony failure modes have been a bitch for a long time. Seems like they
> used to love selling alot of parts.
>

**No different to any other company.

[Dave Platt]

In article <d41uv0...@mid.individual.net>,

Trevor Wilson <tre...@SPAMBLOCKrageaudio.com.au> wrote:

>"Note:
>1. Apply the rated ac line Voltage to the set directly. Do not increase
>the Voltage gradually by using a variable transformer or other such
>instrument; this will cause a V-FET failure."

>**I recall my first V-FET amp repair. I did not pay attention to the
>Sony Warning. A new set of V-FETs and I was good to go, after blowing up
>the first set. Every V-FET amp since has been VERY carefully dealt with.
>No bench failures since the first one. The most expensive and unique amp
>I've ever seen was the Yamaha B1. It was a beast, with over-sized
>V-FETs. They LOOK like To-3 devices, until you see one in the flesh:

That feels to me more like a design flaw in the circuitry... something
which mis-biases the VFETs if the rail voltages don't come up and down
at the prescribed speeds. Possibly the gate voltages rise faster than
the drains, and the gate/source or gain/drain voltage limit is
exceeded?

A power amplifier that will fry its output stage if the mains voltage
bounces around (say, during a "brownout" of commercial power) really
seems like a poor design to market.

[Phil Allison]

pf...@aol.com wrote:

> Phil Allison wrote:
>
> > Had one like that the other day, a valve amp from the 1960s
> > that had not been run in the last 10 years.
> > With all valves removed, the AC supply current rose quickly
> > with each voltage increases and then slowly fell back.
>
>
> How would that happen unless the unit had a solid-state rectifier?

** It wouldn't.

Soon as silicon diodes became available in the 1960s, designers used them to replace the inefficient and troublesome valve rectifiers in TVs and amps of all kinds. A further efficiency was obtained by using four diode bridges or two diode voltage doublers and eliminating the centre-tapped secondary needed with valve "full wave" rectifiers.

> > Typically that quick-rise, slow-fall is due to the
> > "empty" caps accepting inrush, then as they charge
> > becoming more 'resistant-for-lack-of-a-better-word'.

** Inrush surges as you increment a variac are normally very brief, but in this case they were sustained, taking many minutes each time for the current to fall back to the residual being drawn by the primary of the transformer. I well knew this meant dodgy filter electros.

On my bench, the variac's output is followed by a 3.5 digit current meter with 1mA resolution and a (safety isolated) waveform output to view on a scope. 100Hz current pulses being drawn by filter electros appear very distinct from the steady 50Hz current draw of the power transformer.

With good electros and no valves installed (or the standby off), current pulses should be absent.

> Put another way, it is a bad idea to allow a tube amp to
> make B+ without a load. Many marginally designed amps ran
> their filer caps at very near their ratings - and both
> vintage and marginally capable caps running unloaded might
> just go *POOF*.

** It's something to be aware of and one should check electro voltage ratings to make sure they are not being exceeded in this condition.

BTW: I have come across a few modern valve amps where electros further down the chain from the main filters were of such lower voltage that removing some of the preamp valves caused their rating to be exceeded.


.... Phil

[Phil Allison]

Dave Platt wrote:

>
>
> >"Note:
> >1. Apply the rated ac line Voltage to the set directly. Do not increase
> >the Voltage gradually by using a variable transformer or other such
> >instrument; this will cause a V-FET failure."
>
>

> That feels to me more like a design flaw in the circuitry... something
> which mis-biases the VFETs if the rail voltages don't come up and down
> at the prescribed speeds. Possibly the gate voltages rise faster than
> the drains, and the gate/source or gain/drain voltage limit is
> exceeded?

** Take a look at the power stage schem here:

http://www.angelfire.com/sd/paulkemble/sound8f.html

Note the unusual crosswise connection from the drive stage to the six V-FET followers.

The V-FETs used behave like J-FETs requiring reverse polarity gate bias voltage to turn them off, with zero bias they conduct heavily - the opposite of the case with transistors and MOSFETS.

So, when using a variac, a condition must exist where the needed reverse bias is missing but the V-FETs have enough DC supply available to fry themselves if held there.



.... Phil

[jurb...@gmail.com]

>"So, when using a variac, a condition must exist where the needed reverse bias >is missing but the V-FETs have enough DC supply available to fry themselves if >held there"

I understand that, but there should be a way to design around it, prevent it from happening. Piss poor IMO. Asking for trouble. How many times the power went out and came back dim, like half voltage. And varied. Would they cover that under warranty or would I have to sue the power company ?

They might be able to design a lower distortion circuit than I but they leave much to be desired in practicality, especially in a supposedly high end unit. If they are going to charge top buck for this shit they should have included a UPS. Or something.

I do not mind making money off of their follies, but that puts my name on it. What, I gotta install a light sensor to see if the customer's lights dim which voids the warranty on the work ? Ridiculous. Tell you what, they are scrap on sight as of now.

Fuck, there are so many ways to prevent that failure mode it is ridiculous. One stupid power relay that removes the rail voltage form the outputs would do it, and then they wouldn't need one at the speaker output. Very low cost.

Fucking assholes. I really used to like Sony stuff, but not so much their audio. I didn't like the sound of it. Now I am glad, I didn't buy that thing, I didn't buy the highly coveted STR-V6 I had on loan for like a couple of weeks. I did buy one of their cassette decks though and it was alright. And I do still have their (real) VCRs. And SLV-920HF I need to lube before firing up and an SL-HFR60 with the processor. I have a shitload of beta tapes. I am looking for a good deal on a standalone DVD recorder so I have real backup and then I intend to rip to harddrive certain things., I will be a youtube star, Man those times were wild. Like when I almost got run over by a car taping an outdoor concert on someone's porch. Instructions on how to roll a joint. Damn, there is so much I forgot, but the deal is this is so old that I might only get one chance, so I am not sitting here playing it. In fact I owuld like to have a beta rewinder so I don't have to beat on the reel motor, they were a high failure item.

But after that, Sony and I are through. I will never buy a new product from them again and I have serious doubt about a used one. Yes, I bought that thousand bucks worth of VCRs brand new.

But now that we're on the subject, it might be a good idea to mention other things that do not take kindly to a variac or a DBT. They are out there. I can see that some of the class D amps would not like it. Things with SMPSes. What else ? I am sure there are more but I just don't know what.

[Phil Allison]

jurb...@gmail.com wrote:

>
>
> > "So, when using a variac, a condition must exist where
> > the needed reverse bias is missing but the V-FETs have

> > enough DC supply available to fry themselves if held there."

>
>
> I understand that, but there should be a way to design around it,
> prevent it from happening. Piss poor IMO. Asking for trouble.

** Only if you use a variac with one.

> How many times the power went out and came back dim, like half voltage.
> And varied.

** I have seen that happen only once in my life, about 20 years ago.

Of course you need to have the amp switched on and not bother to turn it off when the power outage happens. Prolonged brown can damage stuff, like the compressor motors in fridges - and they are always left on 24/7.

> Fuck, there are so many ways to prevent that failure mode
> it is ridiculous. One stupid power relay that removes the
> rail voltage form the outputs would do it, and then they
> wouldn't need one at the speaker output. Very low cost.

** The amp is already bristling with add on circuits that constantly tweak the bias, protect the V-FETs from current overload and stop DC appearing at the speaker terminals. All not shown in the simplified schem I linked.

FYI: the DC bias across R737 is anywhere from 20 to 50 volts, depending on the particular V-FETs actually fitted, the ambient temp and the DC supply voltage.

> Fucking assholes.


** Crikey, it don't take much to wind "jurb" up.



... Phil

[Phil Allison]

jurb...@gmail.com wrote:

>
>
> > http://www.angelfire.com/sd/paulkemble/sound8f.html

>
>
> There are a couple of things about that amp that don't make a hell of alot of sense. First of all, they are current sharing without source resistors, at least separate source resistors. you said there aren't many that can do that, apparently these are among them. And they use two source resistors, damn, for an extra ten cents they could have just used three.

** The parallel 0.47ohm resistors are there for the VI limiter circuit ( not drawn) saving the V-FETs from destruction if driven into a low impedance or short.

> Sony failure modes have been a bitch for a long time.
> Seems like they used to love selling alot of parts.

** Sony seem to like showing everyone how clever they are with over-complicated circuits and mechanics too.

Reminds me a lot of Grundig, Crown and Dynacord.


... Phil

[Cursitor Doom]

On Mon, 24 Aug 2015 23:38:28 -0700, jurb6006 wrote:

> But now that we're on the subject, it might be a good idea to mention
> other things that do not take kindly to a variac or a DBT. They are out
> there. I can see that some of the class D amps would not like it. Things
> with SMPSes. What else ? I am sure there are more but I just don't know
> what.

Hopefully the device Phil mentioned is unique in this respect!
So far as SMPSs are concerned, though, I don't believe they can be
actually *damaged* by under-voltage; not start/function properly, yes,
but damage? I'm very doubtful about that.

[Phil Allison]

Cursitor Doom wrote:

>
>
> So far as SMPSs are concerned, though, I don't believe they can be
> actually *damaged* by under-voltage; not start/function properly, yes,
> but damage? I'm very doubtful about that.

** There are certainly many SMPSs with start up modes that create brutal current surges for the switching mosfet or mosfets. The electros on the secondary side of the switching tranny present a near short until charged and there has to be some effective means built into the circuitry to limit peak currents until this happens.

Using a variac, it is sometimes possible to find a setting where the PSU attempts to start, surges repeatedly, but cannot successfully run - likely because the secondary voltage does not rise enough for the control loop to stabilise.

Reckon it is wise to avoid lingering at such a setting.


... Phil

[jurb...@gmail.com]

>"attempts to start, surges repeatedly, but cannot successfully run..."

Plus they can do that all by themselves. Many have a low current mode, basically a "wait to start" that allows a 50K resistor or whatever to bleed up a cap big enough to run the main chopper enough to start and then a rectifier coming off a, well tertiary primary ? Works. the it feeds the driver chip. When that filter gets ESR or low capacitance, then this happens even at rated line voltage.

However this does not always cause a catastrophic failure. Some units can sit there for weeks and still only need that one cap. And others could be alive one day and dead the same day. It all depends on what is critical and what is not.

[jurb...@gmail.com]

>"** The parallel 0.47ohm resistors are there for the VI limiter circuit ( not >drawn) saving the V-FETs from destruction if driven into a low impedance or >short. "

I saw the real schematic, I have it. Yes it is a doosey (sp) Runs you all over the place but oh well, I still got the jist of it. The VI limiter circuit as you call it, which I would simply call a current limiter (with an enhancement to allow said current at higher output voltages)should be able to handle this. Usually it is basically called a dual slope detector, but what Sony likes to do apparently is to get ten nerd who actually did solve not only that rsistor cube, but that other thing going around on the net.

Why do you want to get every last iota of power or whatever of whatever you use ? Well basically because you got shareholders. Every old thing we own is their mistake.

I used to be almost Mr Sony but did not want their speakers and most of their amps I could afford. I worked for a Sony Signature dealer and ASC, I also worked for another Sony ASC a bit later. Well actually at the same time which they didn't want me to do but so what.

but I was always with it for their video equipment, but I did not like the Access systems, I thought they were junk. And then it seems they got skitzoid, like almost being two companies. Alot of them got like that, they got the cheap line and they got the good line. Let's run that credit card and see what you want. I shit you not.

Where were we. (damn that was easy to type)

Anyway, thusfar we have been dealing with a certain paradigm. Now here is something, and it is not even solid state. Tube/valve circuits that use those regulator tubes. the gas fired ones like 0A2 or some shit, I don't remember. It is lucky there are not alot of these around I think, with all the variacs and DBTs out there, I really think that some of those circuits might be damaged bringing up the voltage slowly.

This would happen if say the main rectifier tube took a certain time to warm up and did not give the 0A2 enough voltage fast enough to catch the regulator tube and blew an electrolytic somewhere. Or possibly cause an arc in a totally innocent ECC83 somewhere.

[jurb...@gmail.com]

>"
>Using a variac, it is sometimes possible to find a setting where the PSU >attempts to start, surges repeatedly, but cannot successfully run - likely >because the secondary voltage does not rise enough for the control loop to >stabilise."

Not to forget the days of the earlier bipolar ones that needed real drive current of the FET ones that needed real drive voltage. (like that bastard Sony)But actually I mean regular MOSFETs. I they didn't get a certain voltage drive they would run away, literally.

>"Reckon it is wise to avoid lingering at such a setting. "

For what reason would one linger at a setting ? I can understand under certain conditions doing advanced Tshooting, but just firing up old stuff is different and they have NO reason to linger at any setting. If the current goes up too much you shut the motherfucker down now. If it is worth using a variac on it is worth using it right. Godammit.

But really you meant what I said, or some shit. That current climbs abnormally you shut down and try to figure it out. If nothing else start disconnecting shit.

And actually the DBT is a pretty good current meter.

What I want is some incandescent light bulbs from the UK or whatever, and of course sockets to match, because they are 240 volts. sometimes I needed to discharge a cap that I KNEW was at like 300 volts, and I do not mean on tubes, I mean on like a plasma TV. Using a 120 volt bulb is not all that cool, it could fail leaving you with an insidious problem.

I have considered two in series but if I ever want to change the wattage that makes a mess, and I do not want any switches.

I will do it in digital. Almost. Banks of bulbs, all controllable by unscrewing the lead bulb in any series. And there are a few series' which make an array.

Are you with me here ? This is going to look better than a Gene Wilder movie.

[Cydrome Leader]

Television sets (with CRT) really don't like brownouts either.