GAS son of ampzilla BIAS problem help needid

[JDRvintage]

Hello everybody,

i'm new here on this forum. I was recommendid this forum through members of audiokarma.org.

i'm a marantz collector and repair man for audio. I usually make everything in good working order and i rebuild with original components and high quality like panasonic FM and FC caps motorola/onsemi/toshiba transistors and the original types of casing, But i bought a GAS son of ampzilla, and it died on me last week. and it is quiet a different amp that i'm use to, all the transistors have patent GAS XXX number. you MUST need the manual to decode the numbers

problem is that the bias IC is broken and i do not know wich one i need to replace this broken one.

could anyone help me with the specs on this bias IC.

hear is a picture of the gas (hour later it died.....)




i usually repair different stuff




well i hope to get any reply.

thanks in advance,
Jon

[h_a]

While I can't help you with the IC itself, I can point you to the schematic which should help you to find a substitute:

http://www.audio-circuit.dk/Schemati...f_Ampzilla.pdf

Have fun, Hannes

[MikeBettinger]

Hi,
The bias IC is an MPQ6001. It is essentually two NPN transistors and their complementary PNP transistors in a 14 pin DIP package; with the IC package located and touching the heatsink between the output transistors.

You should be able to find a schematic on the SAE_Talk forum on Yahoo. I haven't looked recently so I'm making an assumption there. I can post one if necessary.

Regards, Mike.

[MikeBettinger]

The linked schematic does not show the bias circuit detail.

Mike.

[Bonsai]

Wow, some classic gear in those pictures. Brings the memories flooding back.

I think you will struggle to find a repacement part, and may need to make some adaptions to solve your problem - I'm wondering if something like a CA3083 (its a 16 pin device unfortunately) might not do the trick

http://www.intersil.com/data/fn/fn481.pdf

There are bound top be some Ampzilla experts somewhere on the forum - hopefully they can help steer you in the right direction.

Man, that Marantz looks good.

Reminds of when I was wondering around Buiwerwijk (I think I got the spelling right) a few years ago. There wa s one section where they had loads of 70's vintage amps and stuff. I wasn't able to buy anything - but some of th e stuff sure looked interesting.

[MOER]

I have repaired many Ampzillas from the early 70's and onwards. I always have replaced the bias IC with discrete parts. There is nothing fancy about the bias circuit. An NPN/PNP compound pair does as well. There is nothing fancy about the output stage. Simple darlington pair with 4 x Vbe drops in the bias path.

The new bias circuit lives between the two collectors of the VAS complementary stage.

Take any PNP capable of a few hundred mA collector current and connect its emitter to the positive VAS collector. Connects its emitter to the collector of the negative VAS collector.

Then solder a 620 ohm resistor Base to emitter of this PNP.

Then take an NPN TO-220 transistor (Beta >100) and connect its collector to the base of the PNP. Then connect the emitter of the NPN to the collector of the PNP.

Next solder a resistor of 1K6 between the emitter of the PNP and the base of the NPN.

Lastly connect a 220 ohm trimmer in series with a 430 ohm resistor between base and emitter of the NPN.

The thermal tracking of this circuit works well on the double Darlington output stage where you have 4 x Vbe drops.


Steve Mantz
Zed Audio Corp

[Original Burnedfingers]

The IC is available from ACK electronics. There were two different IC's used one was marked GAS100 I believe and if memory is correct the other was a GAS101.

Mike feel free to correct me on this.

Please don't cobble the damn thing up with discrete transistors and a cluster farce. The purpose on the IC was to have matched transistors in a package so it would track the heat correctly.

[Bonsai]

OK - so th e IC is still available. That's great news and I agree it s better to fit the original part than to improvise if it can be easily avoided.

[JDRvintage]

Originally posted by MOER
I have repaired many Ampzillas from the early 70's and onwards. I always have replaced the bias IC with discrete parts. There is nothing fancy about the bias circuit. An NPN/PNP compound pair does as well. There is nothing fancy about the output stage. Simple darlington pair with 4 x Vbe drops in the bias path.

The new bias circuit lives between the two collectors of the VAS complementary stage.

Take any PNP capable of a few hundred mA collector current and connect its emitter to the positive VAS collector. Connects its emitter to the collector of the negative VAS collector.

Then solder a 620 ohm resistor Base to emitter of this PNP.

Then take an NPN TO-220 transistor (Beta >100) and connect its collector to the base of the PNP. Then connect the emitter of the NPN to the collector of the PNP.

Next solder a resistor of 1K6 between the emitter of the PNP and the base of the NPN.

Lastly connect a 220 ohm trimmer in series with a 430 ohm resistor between base and emitter of the NPN.

The thermal tracking of this circuit works well on the double Darlington output stage where you have 4 x Vbe drops.


Steve Mantz
Zed Audio Corp

wich transistors should i use

[JDRvintage]

Originally posted by Bonsai
Wow, some classic gear in those pictures. Brings the memories flooding back.

I think you will struggle to find a repacement part, and may need to make some adaptions to solve your problem - I'm wondering if something like a CA3083 (its a 16 pin device unfortunately) might not do the trick

http://www.intersil.com/data/fn/fn481.pdf

There are bound top be some Ampzilla experts somewhere on the forum - hopefully they can help steer you in the right direction.

Man, that Marantz looks good.

Reminds of when I was wondering around Buiwerwijk (I think I got the spelling right) a few years ago. There wa s one section where they had loads of 70's vintage amps and stuff. I wasn't able to buy anything - but some of th e stuff sure looked interesting.

this is very helpfull, trhanks!!