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Old 26th February 2009, 02:23 AM   #1
native is offline native  United States
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Default Help with Ampzilla II

I have an Ampzilla II that has a popped channel. Q301 and Q304 are shot as well as Q104. I am looking for the correct part numbers to get this thing back on its feet. Is there a vendor that will match the outputs for me? Do they need to be matched?

Ive already replaced all the electrolytics with Pana FMs. Is there anything else I should look at while I have it on the bench?

Thanks for any help, Jay.
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Old 26th February 2009, 02:59 AM   #2
llwhtt is offline llwhtt  United States
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native,

Is it a II or IIa, what boards are in it "F" or "G". I have schematics for both along with a GAS cross reference for the semis. I think the most popular output devices for Ampzillas are the ON MJ21193/4 or MJ15024/5, those would be the Q300 series xsistors. I'd have to look to see what the other is. Let me know if you need the info. I'll need to scan it and email to you.

Craig
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Old 26th February 2009, 11:40 AM   #3
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Hey Craig,

The boards that are in it are rev F. Thanks for the info.
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Old 2nd March 2009, 06:57 PM   #4
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Does anyone know of a vendor who will match the output transistors for the Ampzilla?

Jay
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Old 3rd March 2009, 02:46 AM   #5
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While digging around in the 2 amp boards I have found a diode, GAS 109B, that is shorted. Does anyone know what available diode it crosses to?
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Old 5th March 2009, 10:13 AM   #6
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For reference:

GAS 109B = D302 and D303 = 1N5821
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Old 5th March 2009, 03:38 PM   #7
llwhtt is offline llwhtt  United States
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Jay,

Just found some more notes on Ampzilla pre internet. Some are from Peter at Soundsmith in NY and some are from Mike of Gasworks fame. 1N5820 will also work as a cross for GAS109. One may be easier to obtain than the other. The amp will run no problem without it, the main purpose of the diode is to eliminate crossover distortion in the milliwatt output range. Are both the upper and lower boards "F" or just the lower. The upper "F" board has been known to have stability problems. Supposedly the stability issues were straightened out on the "G" board. I remember Peter telling me "G" means good and "F" means F*&^ed. I hope you have a "G" board. The last version of the lower board was "F" so you're good there.

Craig
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Old 5th March 2009, 05:54 PM   #8
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Hi Craig

Both boards sets are indeed F. I wonder if anyone has come up with a fix for the instability problem. I will press ahead with this project, I am mainly doing it as a learning exercise, and boy have I learned a lot.

Just this morning I purchased a meter to start matching transistors since I havent been able to locate a vendor that offers that service.

If anyone needs any MPQ6001 bias ICs let me know. I located a stash and had to make a minimum purchase. The chips were fairly difficult to track down.
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Old 5th March 2009, 06:49 PM   #9
llwhtt is offline llwhtt  United States
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Jay,

There are some threads pertaining to the instabilities, you'll just have to search. If I remember correctly it was under only certain conditions. How long have you had yours and can you tell if it's been repaired before? Mine has the "G" boards and it was blown up when I got it and had been repaired at least once before, very crappily I might add, that was in 93 or so. Rebuilt it with advice from the two I already mentioned. Even had to draw my own schematic for it, that was a pain. Last month I stripped it down again to rebuild it with all of the new info and ON semis. Anyway, F or G it doesn't seem to matter much does it, both let the magic smoke out.

As far as matching goes the little ones are cheap enough to buy many more than you need, especially if you get from a surplus place like I assume the MPQs came from. The outputs are quite a bit more so you buy what you can afford and hope for some matches.

I might be interested in a few of those MPQs, I have an Ampzilla and Son to take of you know. PM with details.

Have you seen the Yahoo group, SAE Talk? There are few GASophiles there, even Sir James chimes in now and again.

Craig
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Old 5th March 2009, 07:08 PM   #10
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Hey Craig,

The amp came to me with the A channel blown. Doesnt look like it has ever been repaired. The caps were shot, two ouputs popped and it now looks like both of the -drivers are toast. Im just going to replace them and the 5551s and 5401s and see where it stands.

The SAE group has been of very little help.

Jay
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