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Phase Linear 400 driver transistor substitution

I lived in Riverside between 1962 and 1972. Went to La Sierra High School. K & B Huh, they made a killer .40. IIRC at that time they OWNED most of the pylon records, hell of a motor. That's all I ran. I did try one of the Wankels when they came out and that was pretty interesting, not the same power to weight ratios as the ol K & B's but no vibration either.
 
Wow, we were almost neighbors. I graduated Long Beach Poly High School in 1970. I modified a K&B .40 that my pal flew in the open pylon nationals in Florida in 1971, I think, and it blew away the record. The airplane was called the Mirage and if I remember right, it went over 195 mph. They are doing 230 nowadays, but those planes also cost big bucks.
 
DAYAM!! we were close. Yep gone are the days when you could throw together a foam winged pylon racer for less that 50.00 minus radio....
 
I was more concerned with symmetrical clipping...to be honest I was just looking at my scope and twiddling the voltage range until it came into view. I'd have to measure it again to really know. I could just put my Fluke 87 (true rms ac) on it and get an rms figure...I'm going to leave that for tomorrow. Got to get up early...my wife and I are going to take a CCW class in the morning.
Thanks for your help, my friend!
 
Referencing the dim bulb startup issue, the amp puts out DC on startup until the AC input gets up to 50 volts or so. You can't have a load on the amp when starting with the bulb. If you watch it on the scope you can see the DC. It's a minor annoyance during normal turn on. The thump heard in the speakers at turn on/turn off is DC on the output. The output relay mod resolves this issue.

Oscillations won't appear without a load. I recall a conversation with Joseph King of White Oak Audio where he advised against using the same transistor for the driver and output on the negative rail due to possible oscillations. It's ok for the positive rail. The 2SD555's were more likely to oscillate. I'ved seen the zobel network burned up in amps with 55's. It had to sound horrible.

The XPL909's with the green ink were the real trouble makers.
 
laatsch55 said:
No, when I was flying RC I had a Heathkit 5 channel radio. In that pic I'm at my favorite fishing hole with my 9 ft, 7weight , Powell Freestone flyrod.

I also had a Kraft KP-5C radio.
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The Heath was a Kraft they put in kit form. I still have one I used in my HS days.

laatsch55 said:
K & B Huh, they made a killer .40.
Click to expand...

They certainly did!! I still have one of these as well.
 
d3imlay said:
Referencing the dim bulb startup issue, the amp puts out DC on startup until the AC input gets up to 50 volts or so. You can't have a load on the amp when starting with the bulb. If you watch it on the scope you can see the DC. It's a minor annoyance during normal turn on. The thump heard in the speakers at turn on/turn off is DC on the output. The output relay mod resolves this issue.

Oscillations won't appear without a load. I recall a conversation with Joseph King of White Oak Audio where he advised against using the same transistor for the driver and output on the negative rail due to possible oscillations. It's ok for the positive rail. The 2SD555's were more likely to oscillate. I'ved seen the zobel network burned up in amps with 55's. It had to sound horrible.

The XPL909's with the green ink were the real trouble makers.
Click to expand...

Yes, I remember Ed Blackwood advised the same. My 909's are all the blue ink. I changed all the drivers to ON Semiconductor MJ15022G and I think they sound better than the Motorola SJ2741 originals. With all the fake "vintage" semiconductors being peddled out there, I hope these will be a better driver than the options I had available...plus I had 5 of them in stock! At any rate, the amp appears to be stable and it sounds good, so I'm going to order some DC protections boards from Don and get them installed.
 
elza said:
The Heath was a Kraft they put in kit form. I still have one I used in my HS days.



They certainly did!! I still have one of these as well.
Click to expand...


The Heathkit servos were where I learned to solder with a very sharp point. A crowded audio PCB is not NEAR as crowded as one of those little boards were.
 
laatsch55 said:
The Heathkit servos were where I learned to solder with a very sharp point. A crowded audio PCB is not NEAR as crowded as one of those little boards were.
Click to expand...

Now I wonder why were you soldering on the servo's. Did we have a crash or two?:D
 
laatsch55 said:
If you keep the original boards run a 470uf/25 volt audio grade cap for C6. On the foil side of the board run 2 1N4148's back to back accross the leads of C6, that will keep the amp from latching up to the positive rail...

The 470uf cap will increase the low frequency response tremendously..
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Good day to you friend. I just started to rebuild my pl400 (hoping I end up with a decent amp, better then my Yamaha 7.1 receiver anyways lol rx-v1500) I'm going to hook my pl400 to my energy c8's and since the actual drivers are no longer available I would like to take as many precautions as possible to protect them from "flaming up" I did order a DC protection board off ebay, the better one with the 30 amp "audio" grade relays. But I will also do this upgrade with the back to back diodes along with the 470uf cap. Is there any diagrams or more extensive info you could point me to just so I can be sure I do this correctly. I eventually want to upgrade to the white oak boards but the piggy bank just can't right now. Any info on what I can do to protect my speakers and what the best way to spend my money is would be greatly appreciated. Thank you.
 
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