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G.A.S. Ampzilla

eiraved said:
Why is the 2SB554 not usable as a replacement?
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The Son would have had SanKen output transistors from the factory. The Toshibas would work OK but I'm guessing only one of the SanKens was bad and mixing of outputs in one channel is a bad idea.
 
llwhtt said:
The Son would have had SanKen output transistors from the factory. The Toshibas would work OK but I'm guessing only one of the SanKens was bad and mixing of outputs in one channel is a bad idea.
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Thanks for the input, I didn't think there was anything fundamentally wrong with using it as a replacement.
 
John Mazurco said:
reply and quote is all I see, no delete.
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"Quote Reply" is on the lower far right side of your post. "Edit Delete Report" is on the lower far left side. It should be there, as I was able to delete your address from my post this morning.

Remember, you have to look at something you posted, as "Edit Delete Report" will only appear your posts. You won't see it on my posts, or anyone else's for that matter.
 
Whoever was working on it destroyed more parts so John brought to my shop and I stripped it and started over. It's a brand new amp now.

Craig
 
FootFungus said:
Mouser carriers the MPQ6002 which will drop in for the GAS100A/MPQ6001 (its a higher gain bin). As for everything else (thanks to Gasworks Audio):

GREAT AMERICAN SOUND TRANSISTOR CROSS REFERENCE
GAS 101 = 2N5631 OR MJ15022 OR 24
GAS 108B = MPS8599
GAS 101B = 2SD424 OR 2SD555
GAS 108C = 2N5401
GAS 101C = 2SC1586 OR 2SD424 (NPN)
GAS 109 = MPSU07
GAS 102 = 2N6031 OR MJ15023 0R 25
GAS 110 = MPSU57
GAS 102B = 2SB554 OR 2SB600
GAS 112 = 2N5088
GAS 102C = 2SA909 OR 2SB555 (PNP)
GAS 112C = 2N5551 (NPN) match hfe to compliment
GAS 103 = 2N6316 OR 2SD525
GAS 114 = 2N4401 (NPN)
GAS 103B = 2SD525
GAS 114A = 2N5210 match to compliment
GAS 104 = 2N6318 OR 2SB595
GAS 115 = 2N4403
GAS 104B = 2SB595
GAS 115A = 2N5087
GAS 105 = 2N3584
GAS 116 = 2SD613 OR MJ15028 low hfe <150
GAS 106 = 2N6421
GAS 117 = 2SB633 OR MJ15029 (PNP) low hfe <150
GAS 107 = MPSU06 OR 2N5551 match hfe
GAS 118 = 2SB554 (PNP)
GAS 107B = MPS8099
GAS 119 = 2SD424 (NPN)
GAS 107C = 2N5551
GAS 100 = CA3086 Transistor Array (5 NPN)
GAS 108 = MPS56 OR 2N5401 match hfe
GAS 100A = MPQ6001 OR MPQ6002 ( 4 transistor array, complimentary)

DIODES ACROSS AMPZILLA EMITTER RESISTORS ARE 1N5821

NOTE: ALL VERSIONS OF
GAS 107 CAN USE JAP 2SC2240 ( NOTE THE DIFFERENT PINOUT ) ALSO
GAS 108.. 2SA970
BEST STABILITY IS ACHIEVED WITH MATCHED QUAD SETS WITH HFE IN THE 150 TO 250 RANGE.
ALL VERSIONS OF THE
AMPZILLA CAN USE MJ15022 / MJ15023 AS THE OUTPUTS.
USE ONLY THE MOTOROLA TRANSISTORS THOUGH
DO NOT USE REPLACEMENT TYPES FOR ANY ORIGINAL TRANSISTORS IE: NTE, SK, ECG, ETC.
THE FETS USED IN THE THAEDRA/THOEBE LINE AMPLIFIER CAN BE REPLACED WITH 2N5459 N-CHANNEL 2N5462 P-CH (MATCHED AS BEST AS YOU CAN FOR FETS)
THE BIAS SETTING FOR THE AMPZILLA IS 30MV ACROSS THE EMITTER RESISTORS OF THE OUTPUT TRANSISTORS
THE SON OF 22MV SAME PLACE.
OFFSET IS ALWAYS SET FOR .000V +/- .015V
DRIVER TRANSISTOR SHOULD ALSO HAVE HFE'S LOWER THAN 200 FOR BEST STABILITY


For more information, e-mail us at gasworks@gasaudio.com <mailto:gasworks@gasaudio.com>
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This page last updated on Feb, 2002.
Copyright (c) 1996-1999 GASWORKS
Names used throughout the GASWORKS sites are trademarks of their respective companies.
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Can anyone tell me if thies are good and why??
 

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Just for clarification. On my son of Ampzilla I have Q101 is a GAS116, Q102 is a 2N6318, Q105 is a GAS117, and Q106 is a 2N6316. What are the best replacements/ upgrades for these? I am seeing posted MJ15028/31/29/30 respectfully. I thought these would be matched pairs. Please advise. Thanks so much for any help.
 
Joe Kraft said:
Just for clarification. On my son of Ampzilla I have Q101 is a GAS116, Q102 is a 2N6318, Q105 is a GAS117, and Q106 is a 2N6316. What are the best replacements/ upgrades for these? I am seeing posted MJ15028/31/29/30 respectfully. I thought these would be matched pairs. Please advise. Thanks so much for any help.
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Yes all four transistors on that heatsink can be those. You don't have to match them.

There's many SOA rebuild threads with links and photos, the more you replace the better.
 
Also, on both of my amplifier boards D105 and D106 are missing and I have seen this in pics of some other people's boards as well. What are they for? Do I leave them out? Thanks

SOA Board.jpg
 
Those diodes limit the difference between the input and output of the differential input transistors to +/-.6 volts. I usually install them, all of the original boards I have on hand here have them installed.

Craig
 
Craig, I appreciate so much your input. I am not an electronics technician/engineer/designer but can follow orders very well and I am meticulous in my attention to detail. I restore vintage audio gear as a stress relief. I hate to take up too much of your time, but you seem to know this SOA amp quite well. I would like to write a summary of recommendations for restoration (not necessarily modifications) of this piece for future reference for others doing the same and get input from you and other members of the SOA think tank, but for now, one quick question…replace or remove VI limiter transistors? Thanks again, Joe
 
Home stretch on my SOA restoration.
1. What are your recommended replacements for the VI limiter transistors (Q103 and Q104)?

2. What diodes do you recommend for those D105 and D106? Mine were missing.
Thanks so much.
Joe
 
All diodes on that board are 1N4148s except for the two 28V Zeners. There is no consensus on the correct adjustment of the VI limiter circuit so I usually leave out all of the VI circuit parts.
 
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