No fans for me. Really not concerned about keeping the covers stock as little of the amp is unmodified. Drilling can be tastefully and logically done. Or new covers fabbed. The original venting could be improved.
Phase Linear 400 Odd Heatsink.
- Thread starter FredR
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You will mess up your bias servo if you go cooling the innards of the amplifier...
Top and bottom covers are identical unless a previous owner altered that
Good deal. Probably use same size bit as vent width, extend them, add another row or two or three. Keep same spacing so it's pleasing to the eye. Lay it out on the drafting board, cut it out and glue on with rubber cement. Center punch, drill thru all 4 plates at once, remove the paper, rub off the rubber cement, de-burr with a countersink bit.
Then again, I really don't need to do this, but may pay off in the long run. Be interesting to see if it makes a difference.
And then again, it's a bunch of work. Probably better off doing something else with my time.
Then again, I really don't need to do this, but may pay off in the long run. Be interesting to see if it makes a difference.
And then again, it's a bunch of work. Probably better off doing something else with my time.
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mlucitt
Veteran and General Yakker
There are PL purists all over the world cringing at this thought process. Plus, Joe basically saying, "Don't drill your covers."
I will buy your unmolested original covers for $20.00, then you can fabricate some new covers and go crazy with your drill, hole drill, roto-zip, Sawzall, or whatever you wish.
I might fab some new covers just to see if there is a difference. Really thinking about 3/8" holes in a tight grid. There's a metal supplier near me that will cut to my specs and very reasonable cost. If I do it I want to do it right, really don't want to drill around the vents. The design wouldn't be "pure". So we'll see if it happens. I won't drill those original covers. You raise a valid point, however I did drill the bottom covers for feet.
mlucitt
Veteran and General Yakker
The horror...
Actually, we are interested in hearing about your results. Keep in mind that electronics are happy at temperatures between 100F-150F. This reduces moisture and makes the electrons move faster. The components are not like humans, we like 68F-72F.
And keeps the ever important bias transistor servo working properly. Bias transistor too cool compared to the heatsinks spells disaster...
I think covers need to be installed to help preserve the structural integrity of the chassis. It's pretty damn thin and flimsy, luckily mine don't appear to have ever been rack mounted, that's good.
Even with the covers off, I tend to think there's enough inherent heat to support the bias transistors working properly, or am I wrong?
Been wanting to try some home anodizing for some time. Thinking fabricating some drilled covers might be a good reason to pursue anodizing.
At the end of the day, my 400s don't have any issue with heat, but, if drilled covers would better vent the chassis, then why not pursue that.
Even with the covers off, I tend to think there's enough inherent heat to support the bias transistors working properly, or am I wrong?
Been wanting to try some home anodizing for some time. Thinking fabricating some drilled covers might be a good reason to pursue anodizing.
At the end of the day, my 400s don't have any issue with heat, but, if drilled covers would better vent the chassis, then why not pursue that.
As did Phase Linear...too much bias is a very dangerous thing when the amp warms up. As the amp heats up, the bias voltage moves down because the B-E forward voltage of the driver and output stages likewise go down as they heat up. If you cool the bias transistor on an operating amp with the hot heatsinks, you are headed for cross conduction
Maybe I am too subtle... 
Will be more assertive the next time
The control board electronics are truly loafing in there, huge overkill...
Will be more assertive the next time The control board electronics are truly loafing in there, huge overkill...
Joe, "bias servo", thought you were joking, as I thought Mark was when said he said those vents were designed by a engineer. Thought servo's were mechanical assemblies, and the designers liked the grills of their new 69 Camaros so they kind of copied them for the vents. Ya got to be more direct! Thanks.
mlucitt
Veteran and General Yakker
Whew, crisis averted. George, a proper servo has a transmitter and a receiver. Think of when a Naval gun points out over the Starboard side, the little servo receiver on the bridge spins a dial that points to 90 degrees relative.
So it is with the PL amps, Q6 is the transmitter of a voltage signal change due to heat generated from the bottom of the heat sinks (near the drivers). The receivers are the driver and the output transistor bias voltages that respond to the signals sent by the transmitter (Q6).
So it is with the PL amps, Q6 is the transmitter of a voltage signal change due to heat generated from the bottom of the heat sinks (near the drivers). The receivers are the driver and the output transistor bias voltages that respond to the signals sent by the transmitter (Q6).
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Maybe I am too subtle...
The control board electronics are truly loafing in there, huge overkill...
I thought you were pretty clear.....twice...George will learn...
Yeah, a late reply, but I just acquired a second PL400S2 which has the heavy sinks, and find the opposite is true. This one is somewhat early production - quasi, the 1.8K dropping resistors, and LF356 (dip) op amp. The other (that I have had since 1983 or so) is a factory comp and late production, and has the thin sink. Also note that the thick heatsink is shorter as well . . . FWIW