Couple of nice MKIIIs

[3dzapper]

Quit arguing with me when i agree with you.[]

Rick

[NOSValves]

LMAO to funny Rick. Honestly I missed that post.

[Marvel]

So Rick, are you saying that the IRCL doesn't do any good in your amp?

That's what Craig said earlier. I'm not wanting to argue, but there are contradictions here.

Bruce

[3dzapper]

So Rick, are you saying that the IRCL doesn't do any good in your amp?

That's what Craig said earlier. I'm not wanting to argue, but there are contradictions here.

Bruce

No. By offering highest resistance at the initial turn on, it changes (slows) the RC time constant of the input capacitor and stress on the PT. It will not reduce the ultimate voltage seen across the PS caps before tube conduction begins. Therefore, it is imperative that the PS caps are rated high enough to safely operate.

The latter is Craig's point, the voltage on those Mark IIIs will surely exceed the voltage rating of that 500VDC rated cap.

Shannon specs 450 V caps in the ST-35 which is adequate for the smaller SCA-35 power transformer's peak voltage potential.

In the input to my Mark IIIs I have two 63uF/400VDC caps in series with balancing resistors. That gives the equivilant of a 32uF/800VDC cap. A 200 volt saftey margin. By using a .1uF/630VDC film bypass capacitor, I have lowered the PS maximum voltage to that 630V. Still within the safety range for the Mark III. I also have an IRC in series with the AC line as insurance against arcing in the valuable 5AR4 on turn on.

Rick

Rick

[Marvel]

I gotcha. Thanks Rick.

[NOSValves]

Rick,

Very good. But you should make folks aware that you are building your Mark III in large wood chassis where multiple large caps can be used. The same is hard to accomplish in the smaller Mark III chassis while still getting a reasonable amount of filtering beyond a couple hundred UF. Really in your project your playing it triple safe the only real time you need to worry about the 5AR4 arcing over is if the amp is cycled on off quickly when hot. On a cold startup the 5AR4 could careless unless you go insane with filtering on the first stage before the choke.

Craig

[3dzapper]

Yeah but an experienced builder like the person with these Mark IIIs should be able to put 2 of these together under the chassis

to come up with 25@1000VDC; 1.5H; 135@900VDC (CLC) don't you think. For $3/ amp plus 30 cents worth of resistors a stick on and a cable tie. http://cgi.ebay.com/NIPPON-270uF-450V-ELECTROLYTIC-CAPACITOR-200-PCS_W0QQitemZ7561763116QQcategoryZ4662QQcmdZViewItem

Rick

[NOSValves]

I've tore to many of them little beasts out in my day to trust the minature caps they just don't last in this application.

Craig

[D-MAN]

That is EXACTLY what I think about the caps in the SoundValves M-60's, too. Cheap surface mount C.R.A.P.

Cheasy = trouble eventually

DM

[Erik Mandaville]

Craig:

You're right. You described the function of a thermistor not only inaccurately, you described it completely incorrectly. A thermistor does NOT start working with an increase in temperature -- it's working the instant the power switch is thrown. In fact the resistance it presents to current at that moment is at it's highest. Even after warming up, and the resistance drops, there is still a small amount of series resistance against the AC supply.

Please elaborate more thoroughly on it's effective use with a 5AR4 type rectifier.

Erik

[NOSValves]

Mark,

Those are 180uF are out of the Blueberry? These aren't the super minatures I was thinking about. I was thinking about the really dinky ones that are used on the cap boards that are only 1" tall and maybe 1" around not sure what brand they are those are usually only rated at 300V or so.

Craig

[NOSValves]

Erik,

Go away! I said it works with current go read again. As CURRENT is drawn through it heats then releases the resistance to almost nothing. But with little current it does almost nothing this is pretty much the case with any instant on rectifier until the heaters of all the tubes warm up! You really are one clueless dude.

Craig

[NOSValves]

"Then factor in the the 5U4 is a instant on rectifier that will slam the can with 540V or more instantly everytime you turn it on and this voltage will stay that way until the output tube heaters warm up the cathodes. Net result cathode stripping hell and early failure for the power supply. There is a much better approach to solving this problem but it cost more."

I have heard it said that as long as the rectifier is vacuum tube, one does not have the risk and subsequent problems of instantaneous in-rush current. That's not true, as you mention above. A couple of things that can be done at not too great an expense (just a little work) involve the installation of standby mode, which could be as simple as a switch installed on the center tap of the of the high voltage winding of the power supply transformer. IOW, B+ isn't applied to the plates (manually, by making the switch) until the fiilaments have warmed the tube. The correct thermistor can also be used on the power transformer primary winding, which will provide something of a soft-start feature. These are actually very effective, and are inexpensive.

Erik

Sure the things you mention would help and can be done! But my question is why not fix the problem or at least install a can rated higher. This guy would rather save the $20 then buy a 525 volt can. He would also rather use a $5 5U4 then a proper 5AR4 that costs more and at least slows the voltage spike some and lessons its duration.

Oh and were not talking in-rush current here were talking voltage spike big difference between voltage and current. The voltage spike is caused by a lack of current draw. With a 5U4 an inrush current limiter (thermistor) will do little good because there is no current being draw on the B+ at start up these Thermistors work by current being drawn through them so no current little effect. They work fine with a 5AR4 because it affords some time for the filaments to warm up before producing B+ so when the B+ starts rising the in-rush current limiter will kick in and slow the process even further. Its all about experience and testing and not being cheap.

Craig

Erik,

Read this post again !!!!!!!!!

[Erik Mandaville]

Craig: Nah.....I'm not going anywhere. Other than for lesson plans, which I can do tomorrow morning, the only thing I've got going right now is an amp warming up for headphone listening a little later.

There are a couple of different kinds of thermistors, but in the context we were using them, you described the way they work in this application wrong. What we were looking for is a certain high resitance at turn on, which will drop off with an increase in temperature. That's the behavior of the type of current limiter being discussed here.

Why should you stay and I leave? As has been mentioned often to you, this is a public forum, and I have the same right you have in terms of sharing my opinion on something.

With the amount of work that goes into the complete overhaul and refinishing of these amps, they are great for the price. Sorry Rick, I don't agree with you on that.

Erik

[NOSValves]

Craig: Nah.....I'm not going anywhere. Other than for lesson plans, which I can do tomorrow morning, the only thing I've got going right now is an amp warming up for headphone listening a little later.

There are a couple of different kinds of thermistors, but in the context we were using them, you described the way they work in this application wrong. What we were looking for is a certain high resitance at turn on, which will drop off with an increase in temperature. That's the behavior of the type of current limiter being discussed here.

Why should you stay and I leave? As has been mentioned often to you, this is a public forum, and I have the same right you have in terms of sharing my opinion on something.

With the amount of work that goes into the complete overhaul and refinishing of these amps, they are great for the price. Sorry Rick, I don't agree with you on that.

Erik

Erik you have no clue what your talking about. The cold resistance of a thermistor does ZERO good until current it drawn through it. Go take a 9V battery and attached a resistor too the plus terminal then measure the voltage on both sides of the resistor they will be identical resistance does nothing without current being drawn. Man this is simple stuff and you still don't get it. Yes I made a slight error in my third statement about thermistors but this was a just a simpe error. You and Shawn for that matter still don't get it which is absolutely hilarious.

I can't believe you would be so silly not to take my "go away" as meaning go away and leave me alone not leave here......... now go away

Craig

[3dzapper]

"Cheasy = trouble eventually"

DM, Those particular caps are used in high power commercial power supplies I found with a google search. Very good quality actually with a 105 degree C temp rating. A higher rating than the 85oC that some use in high quality audio monoblocks. That particular value of that model has appearantly been discontinued. Judging from the other values still offered in the line, it should offer about 750 mA of ripple current. Quite stout.

I don't have any need for such a quantity of caps. I just quickly found a surplus example with a picture. They won't fit under a Mark III chassis standing up as they are about 13/4" tall.

One thing to remember, back in "the day" electrolytics used paper impregnated with acidic gel as their dielectric. The advances since then in plastic films have allowed caps of the same or better specifications in a smaller package.

Erik, No need to appologize.

Rick

[Marvel]

Erik you have no clue what your talking

about. The cold resistance of a thermistor does ZERO good until current

it drawn through it. Go take a 9V battery and attached a resistor too

the plus terminal then measure the voltage on both sides of the

resistor they will be identical resistance does nothing without current

being drawn. Man this is simple stuff and you still don't get it. Yes I

made a slight error in my third statement about thermistors but this

was a just a simpe error. You and Shawn for that matter

still don't get it which is absolutely hilarious.

I can't believe you would be so stupid not to take my "go away" as

meaning go away and leave me alone not leave here......... now go away

Craig

Actually, a resistor across a battery like that has current flowing

through it. Your battery will deplete at a rate dependant on that

resistance and voltage.

[sfogg]

" I suggest you quit using techno babble"

I suggest you attempt to learn even basic electronics and things like OHM's Law. Then it won't be techno babble to you.

"Yes for a very brief instant the thermistor will see some current but

that stablelizes in like 3 seconds not even long enough for a meter to

register it. "

If your meter can't register current in 3 seconds you need a better

meter. Put an analog meter in series with the AC measuring current and

as long as the needle isn't over damped you can see the current spike

at power on then the steady decline in current till it levels out.

Without the inrush current limiter in place the initial spike will be

stronger (on a cold amp) no matter what type of rectification is in the

amp. With the inrush current limiter in place the current surge will

again be smaller no matter what type of rectification is in the amp.

If voltage is flowing through the thermistor (which it is if the

circuit is on) then so is current. Again... basic Ohms Law... if you

measure the voltage and your measure the resistance of the entire

circuit the current can be calculated.

" How things are drawn out on paper is not always how they work."

Only when you don't understand the topic well enough to properly draw it out on paper.....

"The only way a thermistor will work to stop in-rush current with a

instant on B+ voltage source is with a stand by switch to get the

heaters warm on the tubes. Been there tried it, just installing one

does little or no good at all. "

Wrong, it will reduce the inrush *current* no matter what type of

rectifier is being used. That techno babble Ohm's Law again. Adding

resistance to a circuit lowers current flow through it. The inrush

current limiter limits the inrush current because it added resistance

to the circuit at turn on. As the limiter warms up its contribution to

the resistance in the circuit drops.... and therefor its limiting of

current drops too. If the rest of the circuits resistance stayed the

same the current through the circuit would increase. But the rest of

the circuits resistance increases while it in turn is warming up, which

in turn lowers current. The circuit without the limter starts out at a

low resistance (high current) when cold and the resistance increases

with temperature to lower the current flow through the circuit. The

inrush current limit acts very roughly as the inverse of what the

circuit does to limit that initial high current surge through the cold

low resistance circuit.

What it won't do as already mentioned is drop the voltage.

If you put a standby switch in the inrush current limiter is going to

already have been warmed up (by the current drawn with the

filaments) and no longer limiting current by the time you throw

the standby switch.

As far as the 'Been there tried it,' you were measuring voltage when

you tried it, not current. Still haven't figured out the difference

between a current surge and a voltage surge? That is getting back to

the discussion we had last time when you were claiming the resistance

in the circuit didn't matter for a *current* surge. Wait for it....

learn Ohm's Law......

"Yes I could of explained the thermistors relation to heat better"

You could have explained it better if you actually undetstood how they

work. As you explained it you had it exactly backwards (explaining a

PTC thermistor... which isn't what an inrush current limter is... they

are NTC thermistor) which makes your explanations of why they work with

a 5AR4 also wrong. For example....

"They work fine with a 5AR4 because it affords some time for the

filaments to warm up before producing B+ so when the B+ starts rising

the in-rush current limiter will kick in and slow the process even

further. Its all about experience"

And if you had actual experience (and understanding) measuring the

resistance of the inrush current limiter you would see that by the time

the 5AR4 is heating up the inrush current limiter is already well on

its way to not limiting the current through the circuit. It is doing

anything but 'kicking in' then. But you don't understand that because

you haven't grasped Ohm's Law and dismiss it as techno babble.

" I for the life of me can't figure how you can not understand why this pisses me off. "

Because a BSer doesn't like it when they are called on their BS....

Shawn

[mike stehr]

"I also have a huge sack of slighty used Hovland MusiCaps - 2uF @ 400V. These are $20/pr. They are "short leads" however, as they are pulls from BB-->BBX conversions. Nicely "broken in" I might add. I just coudn't bring myself to toss all these nice caps. Email if you need any.

md"

Wotta drag.....I can't even swing 20 bucks at the moment. That's a good deal, and the value I could use........

[NOSValves]

" I suggest you quit using techno babble"

I suggest you attempt to learn even basic electronics and things like OHM's Law. Then it won't be techno babble to you.

"Yes for a very brief instant the thermistor will see some current but that in like 3 seconds not even long enough for a meter to register it. "

If your meter can't register current in 3 seconds you need a better meter. Put an analog meter in series with the AC measuring current and as long as the needle isn't over damped you can see the current spike at power on then the steady decline in current till it levels out.

Without the inrush current limiter in place the initial spike will be stronger (on a cold amp) no matter what type of rectification is in the amp. With the inrush current limiter in place the current surge will again be smaller no matter what type of rectification is in the amp.

If voltage is flowing through the thermistor (which it is if the circuit is on) then so is current. Again... basic Ohms Law... if you measure the voltage and your measure the resistance of the entire circuit the current can be calculated.

" How things are drawn out on paper is not always how they work."

Only when you don't understand the topic well enough to properly draw it out on paper.....

"The only way a thermistor will work to stop in-rush current with a instant on B+ voltage source is with a stand by switch to get the heaters warm on the tubes. Been there tried it, just installing one does little or no good at all. "

Wrong, it will reduce the inrush *current* no matter what type of rectifier is being used. That techno babble Ohm's Law again. Adding resistance to a circuit lowers current flow through it. The inrush current limiter limits the inrush current because it added resistance to the circuit at turn on. As the limiter warms up its contribution to the resistance in the circuit drops.... and therefor its limiting of current drops too. If the rest of the circuits resistance stayed the same the current through the circuit would increase. But the rest of the circuits resistance increases while it in turn is warming up, which in turn lowers current. The circuit without the limiter starts out at a low resistance (high current) when cold and the resistance increases with temperature to lower the current flow through the circuit. The inrush current limit acts very roughly as the inverse of what the circuit does to limit that initial high current surge through the cold low resistance circuit.

What it won't do as already mentioned is drop the voltage.

If you put a standby switch in the inrush current limiter is going to already have been warmed up (by the current drawn with the filaments) and no longer limiting current by the time you throw the standby switch.

As far as the 'Been there tried it,' you were measuring voltage when you tried it, not current. Still haven't figured out the difference between a current surge and a voltage surge? That is getting back to the discussion we had last time when you were claiming the resistance in the circuit didn't matter for a *current* surge. Wait for it.... learn Ohm's Law......

"Yes I could of explained the thermistors relation to heat better"

You could have explained it better if you actually understood how they work. As you explained it you had it exactly backwards (explaining a PTC thermistor... which isn't what an inrush current limiter is... they are NTC thermistor) which makes your explanations of why they work with a 5AR4 also wrong. For example....

"They work fine with a 5AR4 because it affords some time for the filaments to warm up before producing B+ so when the B+ starts rising the in-rush current limiter will kick in and slow the process even further. Its all about experience"

And if you had actual experience (and understanding) measuring the resistance of the inrush current limiter you would see that by the time the 5AR4 is heating up the inrush current limiter is already well on its way to not limiting the current through the circuit. It is doing anything but 'kicking in' then. But you don't understand that because you haven't grasped Ohm's Law and dismiss it as techno babble.

" I for the life of me can't figure how you can not understand why this pisses me off. "

Because a BSer doesn't like it when they are called on their BS....

Shawn

Shawn,

You still don't get it!! and its absolutely making me roll on the floor. You have too stop your making my cheeks ache from laughing so hard.

You better get out the ohms law book again. Yes an inrush current limiter has resistance when cold, yes no matter when the current begins to be drawn it will slow it down. THE POINT IS IN A TUBE AMP NO CURRENT IS SUSTAINABLY DRAWN UNTIL THE HEATERS IN THE POWER TUBES AND FRONT END TUBES WARM UP.

WHY CAN YOU NOT UNDERSTAND SOMETHING SO FRICKEN SIMPLE?????

Answer one simple question if 500V is applied to a resistor or thermistor but there is no current to speak of being drawn through the resistor or thermistor what will be the voltage measured on both sides of the resistor or thermistor? Just for discussion sake lets say the resistor or thermistor is just hanging in the wind on the opposite side of the voltage.

Just answer this simple question. Please no more side stepping answer this simple basic electronics question. Ohms law if you will....

Craig