[Toni Rambold]

… These are the Biasing Instructions:






the bias adjust potis on the boards are the outer ones. the inner ones
are called offset trim - you have to ask my old master of electrical engineering
what that means.


hope i could help - Regards Toni

[avahifi]

When you replace those old power supply electrolytic capacitors, you are going to have to be creative.

The problem is that new electrolyics have gained vastly in volumetric efficiency over the years.  A capacitor of the same capacitance and voltage rating is now MUCH smaller physically than the ones made 30+ years ago.  This is a good thing, except in your case.

The Model 2 was designed for specific physical size capacitors to provide support for the audio circuit boards.  These capacitors are now long gone.  You will find the right value and voltage ratings at DigiKey or Mouser, but you will need to add connection wires to get their terminals to the audio boards as they will be much smaller.

Frank

[dB Cooper]

Wow, this thread was started almost ten years ago....

[Toni Rambold]

  ... no, it started almost 40 years ago, when a magazine in his January 1979 issue

introduced the three van alstine components:



... sorry for the cutout !

Remember the good old days:

A pair of Magnepan Tympani 1D for $1395, a Model Two for $800 and a Model One for $600 -

and you could live happily ever after !

[depaj]

Hi guys,

Sorry for the delay, I didn't get a notification for your replies (strange because I got them for the first ones).

Thank you Toni for the info on the biasing procedure 

Anyway, I bought the new caps, 100v 22000µF Nippon Chemi-con with exactly the same dimensions except for a little less high. I will place something underneath them to get them to the right height.

Is there something I should absolutely check before turning on the amp with the new caps, waht they call the "monistor" for example, or the triac ? Are those prone to failure ? I ask this because when I first turned on the amp without the dim bulb the circuit breaker was "cracking like hell before stabilizing after a few seconds and well next of course the cap blew so... (again voltage across the cap was 76V.

Also I noticed the thermal sensor that is in parallel with one of the resistors in the fan circuit is reading open circuit, which means I guess that the fan is always going to be in the high position right ?

[depaj]

Well, I answered my own question partially, the triac is dead, any advice on what part to replace it with ?

[depaj]

I was wrong about the thermal sensor for the fan speed control. Its open below 63°C and when heating it above that point (with a hair-dryer) it closes, makes perfect sense now that I look at the circuit again.

So only thing to replace would be the triac, I saw a previous post mentioning the Q6015L5 as a replacement that has now been replaced by the Q6015L5TP from littlefuse.
I will order one and keep you posted.

[Toni Rambold]

Triac and Movistor work as a switch-on current limiter.






part no. triac: Q6015L5

part no. movistor: 2502 GEKB



There are thermal sensors on both boards, e.g.:




so the fan operates in two speeds:

under 63°C low speed - over 63°C high speed

thermal cutoff is at 85°C:

[charmerci]

Remember the good old days:

A pair of Magnepan Tympani 1D for $1395, a Model Two for $800 and a Model One for $600 -

and you could live happily ever after !

There are inflation calculators - they really aren't such bargains when you add that.

[Pineappledave]

Hello Toni,

Can I get a copy of the service manual please?

[Tone Depth]

I have a Model 2 Amp that I would sell at a fair price to a good home, I am the original owner of it. One channel cut out some years ago, and a local high end repair shop was able diagnose and fully repair it. Anyone message me if you're interested in it.

[danielgk]

75v capacitors on 75v lines was probably not the best choice to make way back when these guys were designed and built.  Capacitor technology has come a long way since then, the next step up in voltage back then probably made the capacitors too big to fit in the box.  All is not lost though:  a reasonable over voltage on a capacitor will not blow it immediately, it will merely reduce its expected life.  So the 2000 hour capacitor will become a 1900 hour capacitor, no big deal.

There are also some interesting theories about how it is NOT good design practice to use capacitors that are too high in voltage, like putting a 200v capacitor on a 75v line.

Dan

[opnly bafld]

There are also some interesting theories about how it is NOT good design practice to use capacitors that are too high in voltage, like putting a 200v capacitor on a 75v line.

Dan

Good post dank.

I recently replaced some caps in an older 6973 tube amp to reduce some noise and also because the previous owner went a little crazy on the voltage ratings.

[Pineappledave]

A scan would be a lot more readable but I still doubt AVA would touch them. And understandably so. Where would you get the potted active parts for instance.

Hello Toni,
Is it possible to get a copy of the service manual please.
my email is discodabs@hotmail.com

[Foxy]

Hello, I am introducing myself. Sid from Seattle. I have been a long time music and technology lover. I happen to have a Model 2 that I acquired a number of years ago. It’s been laying dormant for a while and I have renewed interest in restoring the amp.

I recall several years ago when I used it regularly to power house DJ parties and in my own setup. I love the gobs of power and the “dark” sound. I remember I had to tap the amp just right to get one of he channels to engage and it seemed to run hot.