Strange PL 400 outputs transistor failure

[laatsch55]

On the Secore, HFE gain was north of 500 as that's as far as it goes, it was pegged. On the leakage test, average was 100 milliamps, and 2 tested with NO LEAKAGE,


The one that was blown Read open between B-E, shorted between B-C.

 

[laatsch55]

Beins we have a junker, putting a razoor blade on the Dremel---TIME TO DECOSTRUCT!!!!

 

[premiumplus]

That's in line with what I measure too, Lee. Thanks for getting white stuff on ya! The confusing thing is that 1/3 of them measure infinity from B to E in one direction, and the standard approx .5 volt in the other.
I think what I'm going to do is install the new ones in the morning with the RCA 410 drivers. The amp has the PL-14 driver board in it. There has been talk about oscillations using the new output transistors with the old board. Has anyone else had that problem, and what frequencies are we talking about?

 

[NavLinear]

Well Jeez, I could have done that. Was hoping for a treatise on the design, manufacturing and application of said devices along with all the inside tricks and hints....

I can't seem to find a data sheet for this paticular device but I have seen darlington transistors with two internal series resistors between the base and emitters of both transistors that could change your b to e and e to b readings. There can be a diode between the collector and emitter providing reverse polarity protection.

 

[NavLinear]

On the Secore, HFE gain was north of 500 as that's as far as it goes, it was pegged. On the leakage test, average was 100 milliamps, and 2 tested with NO LEAKAGE,


The one that was blown Read open between B-E, shorted between B-C.

With darlingtons having an HFE over a 1000 is not uncommon. If the first transistor has an HFE of 100 and the second an HFE of 20 the total HFE would be the procuct of the two.

 

[laatsch55]

Oscillations would be ultrasonic in nature , in the megahertz range usually. It will appear as a parasitic signal riding the fundamental sinewave. Physical and visual clues will be VERY hot running and a vibrating chassis. I haven't had any 21196's oscillate with a pl14 board.Had lots of 2SD 555's oscilllate and occasionally an MJ15024.

 

[laatsch55]

On the PL14 board, get some 470uF Nichicon KZ Muse caps, 25 volt and put in place of C6, the 10 volt 100uF origfinal. Then as a cure to a latchup to the positive rail add 2-1N4148's back to back reversed polarity to the leads of C6 on the back of the board. The 470 cap really extends the bass frequency response of the 14 board. The diuodes keep the PL from occasionally "Latching up" to the positive ral voltage.

 

[laatsch55]

Her's what I got before the camera battery died.

 

[laatsch55]

More.....

 

[NavLinear]

Those are some big ass bonding wires. I've seen the insides of many ICs but never a power transistor. Those are some cool photos. Did you get to the base connection? I'd like to see that if you dug deep enough.

 

[Skratch]

There are resistors inside a Darlington transistor

 

[premiumplus]

I just spent an hour looking for a datasheet for the XPL-909. In this case, Google isn't my friend. If anyone has a link or a copy in their files, I'd really appreciate seeing it. I hate unsolved mysteries.
It's interesting that Phase Linear advises that the only meaningful test for it is an in-circuit evaluation; I haven't seen that since tubes.
Ah well, I have 30 MJ21196G's on their way to my door as we speak, and I guess it's time for this amp to join the 21st century. Why 30, Dave? Because I'm in the market for a clean 700B to rebuild the White Oak way.

 

[laatsch55]

Here ya go..

The XPL-909 is a rebadged RCA DTS-411, I'll post the data sheet in a minute here..

 

[laatsch55]

Here...

 

[Skratch]

I just spent an hour looking for a datasheet for the XPL-909. In this case, Google isn't my friend. If anyone has a link or a copy in their files, I'd really appreciate seeing it. I hate unsolved mysteries.
It's interesting that Phase Linear advises that the only meaningful test for it is an in-circuit evaluation; I haven't seen that since tubes.
Ah well, I have 30 MJ21196G's on their way to my door as we speak, and I guess it's time for this amp to join the 21st century. Why 30, Dave? Because I'm in the market for a clean 700B to rebuild the White Oak way.

You cant go wrong with a complete White Oak upgrade. When you are finished your grandchildren will still use it.

 

[laatsch55]

Yep, but not the same music I'm thinkin...

 

[premiumplus]

Thank you, Lee. I just finished upgrading the PL-14 board with 470uF caps and back to back diodes, and installed all new output transistors. The bias on the right channel won't come down below 0.410, cold. The other channel will come down to around 0.320 or so. I did the current sharing test and all were very close, using the RCA-410 drivers too.
It's running in my shop right now, driving a pair of Klipsch KG-4's and sounds damn nice. I'm waiting for Don's protect boards to arrive hopefully today, so I can hook it up to my Dahlquists.
Is the high bias current a concern? After warmup it drops to 0.388, that's with the adjustment pot all the way down.

 

[Northwinds]

You cant go wrong with a complete White Oak upgrade. When you are finished your grandchildren will still use it.

Funny that you said that because my 15 year old called dibs on the 400 awhile back LMAO. Until Jer sent me it, my Son was more interested in his iPad for music. I made him stand in the sweet spot one day when he literally jumped in the air from a transient impact at Mach 3. He had this look of wonder on his face when he said "Dad, I think I get why your such a nut about stereos, that was AWESOME"

 

[Skratch]

Funny that you said that because my 15 year old called dibs on the 400 awhile back LMAO. Until Jer sent me it, my Son was more interested in his iPad for music. I made him stand in the sweet spot one day when he literally jumped in the air from a transient impact at Mach 3. He had this look of wonder on his face when he said "Dad, I think I get why your such a nut about stereos, that was AWESOME"

I have had youngsters that have never seen a LP or reel to reel or vacuum tube with their eerie glow taking pictures of my setup with their smartphones after they were blown away by the volume of music and vibration of their bodies. I know exactly what your talking about.

 

[laatsch55]

Thank you, Lee. I just finished upgrading the PL-14 board with 470uF caps and back to back diodes, and installed all new output transistors. The bias on the right channel won't come down below 0.410, cold. The other channel will come down to around 0.320 or so. I did the current sharing test and all were very close, using the RCA-410 drivers too.
It's running in my shop right now, driving a pair of Klipsch KG-4's and sounds damn nice. I'm waiting for Don's protect boards to arrive hopefully today, so I can hook it up to my Dahlquists.
Is the high bias current a concern? After warmup it drops to 0.388, that's with the adjustment pot all the way down.

If it's not getting hot .388 is almost factory spec . Factory spec is 385.