I blew out a couple output transistors on my PL400, what next?

rollcentre

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Mar 22, 2021
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#81
Everything is the same on both sides except connection 10 and 9


10L is .375
10R is .032

9L is .960
9R is .499
 

George S.

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#82
Prior post #59 you mentioned D3 and D4. Looks like you have a resistor in D4. Might want to verify this is correct. Can't help any more, on the road with phone.
 

rollcentre

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#85
Also, you haven't populated the complementary output portion of the control board have you? Looks like every component has been stuffed (complementary and quasi) unless I'm missing something. When I build a control board the first thing I do is fill component locations I won't be using with solder so I don't inadvertently stuff them.
Thanks George. I'm thoroughly perplexed now.
I've been double checking the quasi BOM, and went back and looked over the baggies that had the optional full comp/ quasi parts to make sure I actually put in the quasi parts. It appears I did. I Reflowed all the solder joints on that side, and cleaned up the top of the board with ipa.

I just ordered a optivisor, I can see more details in the picture of the control board than the actual board in my hand.
 
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rollcentre

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#92
I got both amps hooked up to my Infinitys and they are rockin'. I gave it the gusto last night and they REALLY sound nice :laughing6:

The LED boards are very cool. I love watching the meters dance while on the most sensitive setting. The dimmer comes in handy to get the brightness in both amps to match. One amp has Jewell meters and the other one has Dixon meters, the Jewell ones have a darker tint. I can dial them in to look identical.

Thanks for the help fellas :occasion5: you guys rock.



I have the fans installed and blowing on to the back wall, is there any reason not to go ahead and put the metal strips that cover the output transistors back on? Would that help or hurt the thermal bias tracking with the fans?

Also, would there be an any advantage to putting a 14ga power cord on these? I have some 14ga non polar power tool cords I bought earlier for them with some heyco bushings. I can get it to work if I take a little material off the inside of the bushing. Jw if it would be worth the effort.
 

George S.

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#93
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#96
As Perry would say...Huh??

Phase Linear Pre-Driver and Driver Selection

This post is to provide a set of guidelines for selection as the sources for original devices are drying up and substitutes will have to be sought.

First let's get the definitions clear:

Pre-Drivers are classic RCA410 location. Typically Q11 and Q12 in the PL400 and the PL700B.

Drivers are the classic PL909 location. Typically Q13-Q18 in the PL400 or Q13-Q22 in the PL700B.

Pre-Driver Requirements (less demanding than the Driver requirements):

TO-3 Package

Vce = 200V min.

Slow, Ft less than 1/2 of the output device. Or alternatively 2X it. But not the same. The larger separation, the better. This requirement affects the negative half side of each channel (typically Q12) in order to ensure stability of the quasi-PNP transistor that is formed by the local feedback combination of Q7, Q12 and Q14, 16, 18 (also Q20 and 22 for the PL700B). The positive half side of each channel can use the same Pre-Driver as the Driver as there is no such local feedback condition on the positive half.

Low current gain (this contributes to the low Ft).

Lower noise is better (hardly ever specified, determined by measurement)

Recommended devices (in order of preference, the first 2 were the only types specified by Phase Linear): RCA410, SJ2741, MJ410, MJ413, MJ423. possibly 2N6678

Driver Requirements:

TO-3 package

Vce>= 250V

Large SOA, especially ability to sustain more current in the 50msec range at 200V (160V for the PL400) is important. The more current it can withstand, the better. The 21196 is well suited in this regard in that it will safely sustain 1.5A for 50msec at 200V (this is the half sine-wave time duration for a 10Hz signal).

Ft >= 2X the predriver is ideal, the higher the better. Minimum 4MHz is acceptable, higher is better.

Lower noise is better (hardly ever specified, determined by measurement)

The more current gain, the better. The 21196 has hFE between 50-75 at 3A.

Recommended devices (in order of preference): MJ21196, MJ21194, MJ15024

What is the difference between Quasi Complementary and Full Complementary?

With fully comp circuit topology, the positive half and negative half of the signal are amplified through the final current gain sections with symmetrical circuit design through the use of NPN drivers in the plus half of the signal and PNP drivers in the minus half of the signal.

The quasi comp used NPN on the plus half, like the full comp version but the minus half had the PNP driver emulated by a combination of a small PNP transistor coupled with 2 NPN pre driver and driver instead of using PNP devices. When the Phase Linear was initially introduced, this is what the designers had available to design with so they went with it.

In the last of the PL400 and PL700 production, PL did convert to fully comp on a small number before end of life of the product.

Some benefits, amp gain is more equal on the positive and negative half of the signal. In the quasi comp version, the gain of the negative side was always higher than the positive half. The global feedback compensated for this difference however and quite effectively nulled it out.

The bias settings are now extremely close for both positive and negative half. Part of this comes from the use of precision 1% resistors in the bias resistor locations, the balance comes from the symmetrical topology.

The current limit protection circuits are also now fully symmetrical leading to a more balanced onset of protection for each of the plus and minus sides.

Of course with this PL400 Backplane board, the configuration of full comp or quasi comp is easily selected by several components, jumpers and of course the choice of output drivers.

In the full comp versions, the MJ21196 (NPN) is used in the pre driver and driver positions on the plus half and the MJ21195 (PNP) is likewise used in the pre driver and driver positions on the minus half.

The use of these outstanding drivers everywhere leads to a more robust output stage as a side benefit.
Sir, that is simply the clearest, most concise overview about the +'s & -'s of quasi vs. fully complementary PL output stages I've read anywhere.

****

You know, at one time I used to hate spending money with any body shop. I would listen to what they promised, discount by a factor of 2, hold my nose when I paid the bill...and *still* managed to be completely disappointed in the finished product. (!)

And then there was Mark. Word of mouth amongst the enthusiasts was that he was the real deal, and ran a small 'destination body shop' deep in rural VT. So I went there, and from our first conversation, I knew that he *knew* what I was looking for even before I described it to him. (Just like I described it for everybody else...I mean, if you are going to spend the $$$$, shouldn't you enjoy the results afterwards? You know, if it ain't fun, why do it?)

Guess what? When he did his first work for me, I was so impressed I actually *enjoyed* paying the bill. And the 2nd time. And the third time.
(NOTE: As a cost avoidance/saving for *this* long-promised audio project I've since switched to doing my own repair/paint/wetsand/polishing.
Not quite as good as Mark's work, and not nearly as easy...but it's a late in life priority thing. If you can't have it all, then just do what you enjoy most, & don't sweat the rest... :0)

****

What does this have to do w/you? I've got this distinct feeling that you are going to be my 'Mark' of audio (WOPL) land...

Just gotta finish figuring out the shopping list - this Christmas is shaping up to be a way better one for me than I was originally forecasting for myself... :0)
 
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#97
Sure nuff is! just been too busy headbanging and watching the meters dance. It's a sweet piece. So far so good.

The dual voice coil Watkins woofers sound so alive with these amps. Awesome punch and impact.

Greetings rollcentre,

I'm reading through your thread, and I'm shaking my head up & down while reading your comments amount how the Watkins woofers sound so alive on PL gear. (I have a set of QLS-1s upgraded from the original paper/pulp to the newer Polypropylene Watkins woofers)

The best way I can explain it is that after years of listening & enjoying (yet wondering how much better it could still be improved upon) ...now the bass is so right (& is so completely integrated w/the music as to be the actual foundation of the song itself) ...that it allows me to simply relax & focus on the music itself. (!)

Of course it doesn't have be the PL/WOPL/Infinity/Watkins string. From the sounds of their comments, the Klipsch guys with the PL/WOPL setups are getting the same rush while enjoying a serious listening session.

This is why we do what we do. And it's time invested, not time wasted.

I haven't read the whole string yet...but at this point you are where I hope to be someday...

Thanks for sharing -- learned a lot reading your saga...some serious talent in these parts. (!)
 
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#99
Lee, my reading assignment is pretty much this entire forum...and in particular, reading for comprehension when Gepetto holds forth. :0)

Anyway, thanks for the pointer -- haven't seen it yet, but will track it down next!

At this point, just as soon as I figure out the shopping list, I want to get that on order, and then while I wait for that to arrive, start building the electronics bench that will see me the rest of the way through this ride...

I'm like a teen in the local speed shop. Remember those? :0)
 
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