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mlucitt

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#22
Ed said Quote "You may also want to measure the value of the 10 ohm resistors (R128 and R180) located in the output stage. Most amplifiers had carbon composition type which are going up in value with age, etc. Ideally they should be 10 ohms which makes adjusting the bias a little easier. However they are usually a 10% tolerance part and the "DC voltage drop" will measure differently between the (2) resistors when the resistors are not closely matched in there values. I am beginning to replace these as a matter of course as they have caused me some grief."

Are these 1/2W resistors from Mouser a good choice to replace the 10 Ohm bias resistors in PL amps?
https://www.mouser.com/ProductDetail/660-MF1-2CCT52R10R0F
 

FredR

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#23
I have a request in with Ed for all the part numbers if he has them handy.

Ed said Quote "You may also want to measure the value of the 10 ohm resistors (R128 and R180) located in the output stage. Most amplifiers had carbon composition type which are going up in value with age, etc. Ideally they should be 10 ohms which makes adjusting the bias a little easier. However they are usually a 10% tolerance part and the "DC voltage drop" will measure differently between the (2) resistors when the resistors are not closely matched in there values. I am beginning to replace these as a matter of course as they have caused me some grief."

Are these 1/2W resistors from Mouser a good choice to replace the 10 Ohm bias resistors in PL amps?
https://www.mouser.com/ProductDetail/660-MF1-2CCT52R10R0F
 

grapplesaw

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#24
I upgrade these to 1 watt Dale

They are high heat 1% metal film. Do not get much better than these. This resistor failure has caused all sorts of Phase linear bias runaway problem so why not be safe.

Mouser # 71-CPF110R000FKEE6

They
 

mlucitt

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#25
I upgrade these to 1 watt Dale

They are high heat 1% metal film. Do not get much better than these. This resistor failure has caused all sorts of Phase linear bias runaway problem so why not be safe.

Mouser # 71-CPF110R000FKEE6

They
Those go to 446 degrees F! If my WOPL backplane gets that hot it is because the house is burning down...

I like that they say "Flameproof".
 

mlucitt

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#27
Those are what I use. Not low cost but very good. Tiny too.
I would like them more if they were 50ppm/C instead of 100ppm/C, still low, and probably not an issue. Calculated resistance values from temperature coefficient of resistance (TCR) at the extremes would be 10.295 to 9.7050 Ohms not including the rating tolerance.
 

Gepetto

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#28
Hi Mark
Then use the CMF6010R000FHEK which has a 50ppm/c tempco

Typically you will see a temp swing of no more than 45C at the control board which will induce a drift of ~+/-4.5 milliohms in a 100ppm resistor.
 

mlucitt

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#29
I guess I was confused. If the temp swing is no more than 45C, then why spec a resistor to 230C?

Sorry, it is taking me awhile to get back into this fantastic hobby after being away for awhile. There have been some improvements in technology over the past five years. Some of the parts I previously used are no longer available. I just want to use the best engineered parts, consistent with availability and value, for the designed functionality. I like to hear what parts & techniques other forum members are using, and I like to do independent research. Please excuse me if I go too far afield, sometimes I find myself talking to the only person in the room, me.
 

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#31
I guess I was confused. If the temp swing is no more than 45C, then why spec a resistor to 230C?

Sorry, it is taking me awhile to get back into this fantastic hobby after being away for awhile. There have been some improvements in technology over the past five years. Some of the parts I previously used are no longer available. I just want to use the best engineered parts, consistent with availability and value, for the designed functionality. I like to hear what parts & techniques other forum members are using, and I like to do independent research. Please excuse me if I go too far afield, sometimes I find myself talking to the only person in the room, me.
Hi Mark
They rate these resistors for applications much more severe than we use them in. These resistors are loafing with a huge amount of derating in our typical application. For the bias application, the dissipation is ~13mW but the resistors are rated for 1000mW which means that our derating factor is 98.7%. Huge.

On tempco, if we see a 45C swing inside the chassis then something is seriously wrong (like all the air vents have been blocked up. So that 45C swing we talked about really represents a corner case.
 

mlucitt

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#32
Sometimes I think of myself as George Bailey, "...this business of nickels and dimes and spending all your life trying to save three cents on a length of pipe."

I see how the bias resister function could be accomplished with a wet Popsicle stick, but we love these amplifiers and simply want the best, so we derate or over-rate the specifications of the resistors (and other parts) to some degree that makes engineering sense. How much engineering sense and associated cost is a subjective decision. I myself enjoy the hunt for the best parts that I can find, to effectively do the job at the least cost, if cost is a factor; and I think it should be while some may disagree. I would say no to $600 interconnects when the $24 Radio Shack cables perform just as well, subjectively, to me.
 

mlucitt

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#33
Which resistors do you guys recommend for the PL400 output transistor emitters? The original ones are .22 Ohm 2 Watt carbon composition, as you know.
 

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#34
Which resistors do you guys recommend for the PL400 output transistor emitters? The original ones are .22 Ohm 2 Watt carbon composition, as you know.
Hi Mark
The original 0.22 are wirewound, not CC. I recommend MOS in all emitter applications as they are not inductive. We use the 0.33 3W 2% which are recommended for the WO application as the release notes discuss.
 

mlucitt

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#35
Hi Mark
The original 0.22 are wirewound, not CC. I recommend MOS in all emitter applications as they are not inductive. We use the 0.33 3W 2% which are recommended for the WO application as the release notes discuss.
Joe, thank you for clarifying. The side note part of the release notes mention the .33 ohm emitter resistor, but I thought that only applied to the backplane kits. I ignored that because I was not using the kits this time around. Re-reading the note, I see it is a general, and not a specific, change in the application of the specs of the emitter resistors and the base-emitter resistors for the pre-drivers.

Are these the ones from Mouser that you use?

660-MOSX3CT631RR33G
 
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Gepetto

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#36
Joe, thank you for clarifying. The side note part of the release notes mention the .33 ohm emitter resistor, but I thought that only applied to the backplane kits. I ignored that because I was not using the kits this time around. Re-reading the note, I see it is a general, and not a specific, change in the application of the specs of the emitter resistors and the base-emitter resistors for the pre-drivers.

Are these the ones from Mouser that you use?

660-MOSX3CT631RR33G
Looks right Mark
 
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