My New Early Model PL400 w/ 4 Fin Heat Sink

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Jan 8, 2019
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The strap, if you will, for my transistors doesn't completely enclose the Q6. Is that something anyone would have a couple of? Once I remove the heatshrink etc I don't think the bracket I have will hold a TO92 part.
 
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While I'm at it would it be of benefit to replace the .22 emitter resistors and the 10 and 150 resistors? What wattage would they be? Is a metal oxide the right part?
 

rinman77

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Apr 6, 2019
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I'll be following this thread very closely--I just received my 4-fin PL400. I listened to it on my system--there's some things I really like about, like the presentation of the snare, and the drums in general. It's not a clean as my current amp, but has a very engaging sound. I will be interested to improve anything that can be improved. I guess I should start a new thread, my board looks substantially different than the Punchback board shown in an earlier post.
 

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Gepetto

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PM me your address Alan and I will snail mail you a pair.
Hi Alan
I mailed you 2 empty P-straps and 2-2N5088 transistors. Looking at the 2N5088 flat with leads pointing down the pinout is E-B-C (brown-black-red).

The P-straps are slightly open. Slide in the 2N5088 transistors in the orientation that works best for your setup, clamp the P-strap fully closed and apply a small dab of instant glue to hold the transistor in place. Proceed with your installation thereafter.

The best size wire to use for the 3 lead out wires is 26 AWG as it puts less stress on the bias transistor leads which are fragile in nature.
 
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I think I'm going to rebuild the back wall. A couple of questions. What I have differs slightly from the schematic included with the narrative wiring instructions. Resistors R36&37 are 150 ohm, on the schematic, but I have 100 ohm. Assuming I rebuild it should I get the 150's?

** Regarding the resistor type. Is it OK for the .22 emitters, 10 and 150 to be metal oxide ?
** Is 5 watt enough for the emitter? I'm looking at the KOA .22 5W .
** The 10 and 150 (100 in my case) are the same size as the majority of the resistors on the original PL400C board. Is that 1/2 or 1/4 watt?
** I guess a 1N4004 is a 1N4004
 

Gepetto

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Hi Alan
You are better off using 0.33 ohms for the emitter resistors. Metal oxide, not wirewound (the originals are WW) for this application. 3W is overkill. The originals are 2W. Try and get the 2% precision on these.

Use 150 in place of the 100 that you have installed now. 1/4W is sufficient for this one as is 1/2W. Use 1/2W for the 10 ohm resistor.

Both the 150 and 10 ohm should be metal film 1% types.

Hope this helps. Yes 1N4004 are not really part of the active circuit except under fault conditions.
 
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