GAS Son of Ampzilla transistor replacement questions

[Speedbump71]

Hello all,

I am currently planning a complete restoration on my Son of Ampzilla. I have decided to replace all of the capacitors and semiconductors, so the rectifier, diodes, transistors etc are being sourced.



I'm trying to decide on what the best currently available parts are to replace the following:

GAS101/GAS102: These are the original output transistors. Mine looks to have a mix of Sanken and original GAS parts. My plan is to replace the whole set with MJ15003G/MJ15004G from ON Semi.

2N6316/2N6318: ?? Maybe MJE15030/MJE15031 ??

GAS 107/108: Looks like they cross to MPSU06/MPSU56. Any modern equivalent for these that would work? Only source for originals seems to be Ebay at nutso prices.

GAS116/GAS117: Should just be a direct cross to MJE15028/MJE15029, but I am always interested in an upgrade or suggestions

MPS 8099/8599: These should be matched pairs. I see matched sets from China on Ebay, but I always worry about what I am getting when I order parts from overseas. If I replace these what is the best modern equivalent, and is there a good source for matched pairs?

MPS6001 Quad complimentary pair transistor IC: Should I even bother replacing these? Is there a better modern upgrade?

I will continue to do my own homework here, and I will update the thread with what I come up with, but appreciate anyone's suggestions on any or all of this. The amp powered up, and did not blow fuses, and there are no signs of any heat or failed components except for a couple of 1/4W resistors on the driver board that look to have some discoloration from heat.

 

[Superampman]

Hello all,

I am currently planning a complete restoration on my Son of Ampzilla. I have decided to replace all of the capacitors and semiconductors, so the rectifier, diodes, transistors etc are being sourced.



I'm trying to decide on what the best currently available parts are to replace the following:

GAS101/GAS102: These are the original output transistors. Mine looks to have a mix of Sanken and original GAS parts. My plan is to replace the whole set with MJ15003G/MJ15004G from ON Semi.

2N6316/2N6318: ?? Maybe MJE15030/MJE15031 ??

GAS 107/108: Looks like they cross to MPSU06/MPSU56. Any modern equivalent for these that would work? Only source for originals seems to be Ebay at nutso prices.

GAS116/GAS117: Should just be a direct cross to MJE15028/MJE15029, but I am always interested in an upgrade or suggestions

MPS 8099/8599: These should be matched pairs. I see matched sets from China on Ebay, but I always worry about what I am getting when I order parts from overseas. If I replace these what is the best modern equivalent, and is there a good source for matched pairs?

MPS6001 Quad complimentary pair transistor IC: Should I even bother replacing these? Is there a better modern upgrade?

I will continue to do my own homework here, and I will update the thread with what I come up with, but appreciate anyone's suggestions on any or all of this. The amp powered up, and did not blow fuses, and there are no signs of any heat or failed components except for a couple of 1/4W resistors on the driver board that look to have some discoloration from heat.

woodyzline09 on the bay has a line on the late James Bongiorno's estate with a large inventory of parts. You could probably rebuild it with all originals from him.

 

[FootFungus]

GAS101/102 - I'd use the MJ21195/96 or MJ21193/94.

2N6316/2N6318 - MJE15030/31

GAS107/108 - ZTX453/ZTX553

GAS116/GAS117 - I think these were 2SD525/2SB595 originally. MJE15028/MJE15029 is probably the best without resorting to TIP devices

MPS 8099/8599 - I've used matched quads of 2N5551/2N5401

MPS6001 - MPQ6002

 

[Speedbump71]

GAS101/102 - I'd use the MJ21195/96 or MJ21193/94.

Why would you select these rather than the MJ15003G/MJ15004G? A quick comparison shows a higher Collector- Base Voltage (400V vs 140v), a higher Collector- Emitter Voltage (250V vs 140V), and higher bandwidth (4MHz vs 2MHz). This amps rails are only 45V, I would think that the increased current capability of the MJ15003/4 might be desirable 20A vs 16A.

I might try running this amp on a set of Kappa 9s when finished, so any added durability in the output stage is certainly desirable, but I am just wondering whether the higher voltage part vs higher current part is the way to go.

Or I could be overthinking this

 

[FootFungus]

The SOA curves are the same except at low Vce. The MJ2119X parts do a better job maintaining hfe at higher currents. The MJ2119X theoretically have smaller capacitance too (assuming the MJ1500X parts haven't had a few die shrinks).

 

[DEAFASABAT]

And I would strongly suggest that you test and reasonably match all new transistors with a curve tracer.

The precision required to redo this amp properly is not to be taken lightly.
Correctly done, very much worth the effort.

Did you know there is a sub group within this SOLID STATE forum regarding GAS products, et al?

 

[DEAFASABAT]

woodyzline09 on the bay has a line on the late James Bongiorno's estate with a large inventory of parts. You could probably rebuild it with all originals from him.

Speedbump71,
I just talked to woodyzline09 on the phone. He said send him a message through his ebay store regarding what you need. The store is also known as AudioPartsPlus. the letters A,P, &P in the title need to be capitals.
If you can't get through via those channels, send me a PM and I'll ask him to contact you, OK?
Rich

 

[blhagstrom]

Got one tucked away waiting for a rebuild.

One of these years...

 

[Speedbump71]

My parts list is almost complete. I will publish it in this thread when complete and have you guys look it over. Any suggestions on the new trimpots? specifically the 1K trimmers for the front end and

DEAFASABAT, thanks for the contact info.

Mike Bettinger suggests removing the transistors from the protection circuit and running the amp like that. As I mentioned earlier, I plan on strapping this to some Kappa 9's after it is complete, so my guess is I just rebuild that circuit as well and move on.

 

[llwhtt]

The big question is how to adjust the VI limiter circuit, I asked Mike B. years ago and he had no answer. I think the reasoning behind defeating/eliminating the VI limiter circuit is because the output stage has such a large SOA. The voltages are relatively low and the current capability is high.

Another amp I know of that has an adjustable VI limiter is the Pioneer Spec 2, maybe that procedure would work.

Some Marantz units also have an adjustable limiter but the the procedure needs two o'scopes.

IIRC somebody also suggested using a 2 Ohm load and adjust until the output signal folds back.

Craig

 

[nj pheonix]

I had one of the last sons Mike B did before he closed up and moved to NJ and VPI
He did a jfet front end mod as well. It was crystal clear but I found it harsh. It was another piece I wanted to love but just didn't (please don't read that as it sounded bad).
I was hoping it'd be an endgame piece.
The Thaedra he did for me was pretty special

 

[Speedbump71]

Well...order has been placed. Went Nichicon FG for all electrolytics since I have some 10000uf 63V Gold Tunes from a project I decided not to do, and upped voltage where size permitted. New TDK 5% ceramics for the pf stuff. Wima films for all of the 0.1uf ceramics. New semiconductors down to the zeners and 4148s. I have both original 8099/8599 pairs coming, along with a stack of mpsa06/mpsa56 to match up. I am still debating whether or not to leave the limiter transistors in, but if I do they will be new as well.

$125 bux for the whole shebang. Wonder what I'll be up to for the next week or so......

 

[Superampman]

Well...order has been placed. Went Nichicon FG for all electrolytics since I have some 10000uf 63V Gold Tunes from a project I decided not to do, and upped voltage where size permitted. New TDK 5% ceramics for the pf stuff. Wima films for all of the 0.1uf ceramics. New semiconductors down to the zeners and 4148s. I have both original 8099/8599 pairs coming, along with a stack of mpsa06/mpsa56 to match up. I am still debating whether or not to leave the limiter transistors in, but if I do they will be new as well.

$125 bux for the whole shebang. Wonder what I'll be up to for the next week or so......


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I ran my Kappa 9s with this amp also with no problems but keep in mind the power draw capability due to impedance won't necessarily result in the over all spl you may anticipate. You're looking at maybe 105db peaks at best.

 

[Speedbump71]

I ran my Kappa 9s with this amp also with no problems but keep in mind the power draw capability due to impedance won't necessarily result in the over all spl you may anticipate. You're looking at maybe 105db peaks at best.

I have bigger, newer amps to run if I don't get the volume I want out of this guy on the Kappas. I'm just trying to bulletproof it the best I can for another 40 years, and the Kappas will likely be as challenging a load as this amp will ever see. I like the modular design of the thing, it makes me want to work on it

 

[llwhtt]

I noticed new RCA connectors in your pictures, make sure NOT to isolate them from the chassis as they NEED to be grounded at that point.

Craig

 

[Speedbump71]

Zombie thread...back from the dead. I finally worked my way back to this amp. I have so far rebuilt the power supply board, and am systematically replacing everything but the resistors on the amp/driver boards. I am almost done with one side, and have spent some time matching up transistors using my cheesy component tester. I figure if it reads hfe consistently on the same part it should match things closely enough. I got the MPS8099/MPS8599 quad matched between 200-210 hfe.

 

[dapbmw]

Hello all,

I am currently planning a complete restoration on my Son of Ampzilla. I have decided to replace all of the capacitors and semiconductors, so the rectifier, diodes, transistors etc are being sourced.



I'm trying to decide on what the best currently available parts are to replace the following:

GAS101/GAS102: These are the original output transistors. Mine looks to have a mix of Sanken and original GAS parts. My plan is to replace the whole set with MJ15003G/MJ15004G from ON Semi.

2N6316/2N6318: ?? Maybe MJE15030/MJE15031 ??

GAS 107/108: Looks like they cross to MPSU06/MPSU56. Any modern equivalent for these that would work? Only source for originals seems to be Ebay at nutso prices.

GAS116/GAS117: Should just be a direct cross to MJE15028/MJE15029, but I am always interested in an upgrade or suggestions

MPS 8099/8599: These should be matched pairs. I see matched sets from China on Ebay, but I always worry about what I am getting when I order parts from overseas. If I replace these what is the best modern equivalent, and is there a good source for matched pairs?

MPS6001 Quad complimentary pair transistor IC: Should I even bother replacing these? Is there a better modern upgrade?

I will continue to do my own homework here, and I will update the thread with what I come up with, but appreciate anyone's suggestions on any or all of this. The amp powered up, and did not blow fuses, and there are no signs of any heat or failed components except for a couple of 1/4W resistors on the driver board that look to have some discoloration from heat.

Would you happen to have the BOM parts list?
Cheers!

 

[Joe Kraft]

I would be interested in that parts list also. Thanks

 

[ivandezande]

Well if we’re digging up threads….

I like to use MPSA56/06 for the inputs and BD139/140 for the limiters. Done three and no issues.

BU-00282 for binding posts and RCJ-031 for RCA’s.