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plcguy 4th January 2010 09:58 PM

Phase Linear Power amp
 
I have a Phase Linear 400 series two. I want to rebuild one of the channels but I can not find the transistors. I have the schematic. It does suggest using MJ transistors which I can get. The problem is the bias transistor. 2N3403 It can not be found anywhere. Is there something else I can use? I was thinking along the lines of the BD series transistors. Any suggestions on choosing a substitute? As long as I get a transistor with similar voltage rating and hfe? I used a NTE sub and that did not last long at all. I have to replace the outputs and the bias transistor. Those output transistors aren't cheap either. I used the 2sd555. I see the MJ15024 are also recommended, and much cheaper. I was thinking of changing it to a cull complimentary output. They later sent a new service bulletin for this change. The only thing I see is that they added two resistors to the mail board and do some changes to the output current sense resistors. I had a warranty service center years ago for Phase Linear, Pioneer, Marantz, Harmon Kardon, NAD to name a few. Not bragging but was largest in the Pacific. That was when they knew how to build amps. Anyone ever did something like this. I know it is not the best sounding amp, but looks like fun to do and since one of the channels is blown, why not. :) It just sucks when transistors fade out or they use odd ball stuff. And one good reason for the full complimentary version is that the predrivers are the same as the outputs!

poynton 4th January 2010 10:34 PM

.

http://www.diyaudio.com/forums/solid...placement.html


Might be some help here !!



Andy



.PS there are more threads if you use the search function.

PLF 30th April 2010 06:39 PM

P/L transistors' replacements
 
Quote:

Originally Posted by plcguy (Post 2035111)
I have a Phase Linear 400 series two. I want to rebuild one of the channels but I can not find the transistors. I have the schematic. It does suggest using MJ transistors which I can get. The problem is the bias transistor. 2N3403 It can not be found anywhere. Is there something else I can use? I was thinking along the lines of the BD series transistors. Any suggestions on choosing a substitute? As long as I get a transistor with similar voltage rating and hfe? I used a NTE sub and that did not last long at all. I have to replace the outputs and the bias transistor. Those output transistors aren't cheap either. I used the 2sd555. I see the MJ15024 are also recommended, and much cheaper. I was thinking of changing it to a cull complimentary output. They later sent a new service bulletin for this change. The only thing I see is that they added two resistors to the mail board and do some changes to the output current sense resistors. I had a warranty service center years ago for Phase Linear, Pioneer, Marantz, Harmon Kardon, NAD to name a few. Not bragging but was largest in the Pacific. That was when they knew how to build amps. Anyone ever did something like this. I know it is not the best sounding amp, but looks like fun to do and since one of the channels is blown, why not. :) It just sucks when transistors fade out or they use odd ball stuff. And one good reason for the full complimentary version is that the predrivers are the same as the outputs!

Not sure you are still on the topic. If yes, here is maybe a helpful info:
2N3404 - Si npn Medium Power General Purpose - replacements: BFY50, 2N2297, KT630G (source: transistors_2N).

In some replacement tables there is also BC639 mentioned, as better in HF (http://www.datasheetcatalog.org/data...hild/BC639.pdf). However please check with your local dealers of Central Semiconductors - they still seem to produce 2N3403.

Other answers can be found here: Any Phase Linear Experts out there? - Page 5 - AudioKarma.org Home Audio Stereo Discussion Forums

Good luck!
.

d3imlay 28th May 2010 10:53 AM

The 2n3404 is used in the bias circuit for thermal tracking. It has a small heatsink to allow it to be mounted to output heatsinks. There are two NTE replacements. Thier difference is the pinout. Another option may be an MJF15030G or MJF3055G. Both of these come in a TO220 package that has an isolated tab. Another advantage is the leads are larger and would be less likely to break.

PLF 16th September 2012 07:25 AM

1 Attachment(s)
Quote:

Originally Posted by P.L.F. (Post 2171440)
Not sure you are still on the topic. If yes, here is maybe a helpful info:
2N3404 - Si npn Medium Power General Purpose - replacements: BFY50, 2N2297, KT630G (source: transistors_2N).

In some replacement tables there is also BC639 mentioned, as better in HF (http://www.datasheetcatalog.org/data...hild/BC639.pdf). However please check with your local dealers of Central Semiconductors - they still seem to produce 2N3403.

Other answers can be found here: Any Phase Linear Experts out there? - Page 5 - AudioKarma.org Home Audio Stereo Discussion Forums

Good luck!
.

Correction:
It seems that 2SC3421 or BD139 are probably the best & generally available replacements, however in different package (TO126/TO255), therefore pinouts to be swapped… They require isolation from heatsink.


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