diyAudio

diyAudio (https://www.diyaudio.com/forums/index.php)
-   Solid State (https://www.diyaudio.com/forums/solid-state/)
-   -   Metaxas Solitaire III Bias (https://www.diyaudio.com/forums/solid-state/330269-metaxas-solitaire-iii-bias.html)

Depaj 21st November 2018 07:33 AM

Metaxas Solitaire III Bias
 
Hi Guys,


A few weeks ago a friend brought me his two mono blocs from Metaxas (Solitaire III). A previous tech plugged them in to a 230V mains outlet when they were configured for 110V mains so... lets just say there wasn't much left of the fuse and most of the small signal transistors shattered to pieces.
I changed most of the small transistors, replaced the main caps that vented and all the power transistors (2 were shorted so I replaced the whole bunch with MJW 1302/MJW3281) and drivers (MJE15030 ans MJE15031). All the other transistor are original references. I powered the amp up with a dim bulb, and it puts out a beautiful clean sine wave, voltages are spot on and I measured 1mV DC offset.

There is some service info available but some are contradictory and a suppose they vary between the 3 versions of the amp. One of them says to adjust bias for 50mV across the 0.51ohm emitter resistors which would get about a 100mA bias current per output transistor, does this sound right ??

AKSA 21st November 2018 08:49 AM

These amps tend to self-destruct. Once you have it together, I suggest increasing the lag compensation on their voltage amps. I received this information from a good friend who was a hifi tech who fixed quite a few of them.

HD

Depaj 21st November 2018 09:31 AM

That is indeed what I have heard as well although the mk3 seems to have fixed a few issues.
What do you mean by that and how exactly do I proceed ?

Any suggestions on biasing these, maybe from that same tech ?

Depaj 25th November 2018 09:02 AM

:o Anyone ?

RM 25th November 2018 09:35 AM

I used to work on these many years ago. I totally concur with Hugh`s findings.
As the heatsinks are somewhat piddling, I would settle for quite low quiscent current. Don`t let them exceed 30-35 degrees C in a noload condition.

Regards
RM

Depaj 25th November 2018 09:38 AM

Hi RM,

Thanks for your help, do you remember what kind of bias voltage would keep them at that approximate temp (the emitter resistors are 0.51ohm).

RM 25th November 2018 11:07 AM

Its been more than 15 years since I worked on them, so please forgive me for not remembering all the details. `

Start with 5-10mA/transistor and work your way upwards until you reach that temp.
The quiscent current will not be very high.

R

adason 25th November 2018 11:56 AM

Depaj, can you post schematics, just for completness of the thread?

Depaj 25th November 2018 12:11 PM

Adason, schematics are not available unless for sale on ebay but they are not even complete and from the wrong version so... The part of the service manual that I do have says to adjust for 0.05V on the emitter resistors but that means 100mA and event at 30mA (approximately what it was reading when I first powered it up on the dim bulb tester) it already gets warm, than again it's supposed to be a class A amp for the first 15W.

RM, I really feel comfortable following your advice but won't this affect the working in class A mode ?

RM 25th November 2018 12:29 PM

Class A!!! Are you joking? The class A region will be in the order of milliWatts with those heatsinks.

Get it lukewarm and enjoy is my final advice.

R


All times are GMT. The time now is 02:29 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2021 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 17.65%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2021 DragonByte Technologies Ltd.
Copyright ©1999-2021 diyAudio

Wiki