Fostex 600

[ScottulusMaximus]

Picture time!

Pre-clean, 30 years of dust but in remarkably good condition.



Power transistors, another 8 the other side 



The troublesome heat sinks, read here: http://www.diyaudio.com/forums/solid-state/81986-amplifier-bias-drifting.html that a guy in the UK suffered with these  sinks, John saved the day there too. As you can see these got fairly hot over the years and basically disintegrated.



The replacements, much bigger and properly bolted, the components will be much happier.



Post clean:



Busy testing the bias current now, channel 1 bang on and stable at 10mA, may drop it a bit but will get some advice first.

Oh yes and my biggest and most important change, FEET, my fingers couldn't take it anymore!!!!

EDIT: channel 2 also stable at 10mA, happy days!

[ScottulusMaximus]

Connected up some el cheapo speakers, no bangs or pops on turn on/off, completely silent even with gains at maximum.

DC offset of 0 for both channels when loaded.

That's all for tonight, may be on to a winner here.

[vleisman]

Have you amped them up yet?  When some come up in Durban I'll finally get my hands on a pair. (and not tell anyone before they are mine)

I think these deserve their own topic, will post some long winded waffle tomorrow...

[Kent Kassler]

Excellento! .....we have a winner!

[Kent Kassler]

I now look forward to some Tannoy waffling!

[ScottulusMaximus]

So I've spent some time slowly bringing everything online, did the tests last night then made up some RCA to XLR cables to get a signal into the thing:



My pre-amp is going to look like an amphenol groupie

Used my disposable speakers and an ipod, all good

Then connected up the Mars-pre with the ipod, all awesome! No bangs anymore at on/off, just slowly gets louder/softer. Still a big bang when switching to phono as the tubes get up to voltage, no speaker protection triggered so will have to watch that.

Then got it installed in it's home:



The word you're looking for is "headroom"... Lol, who am I kidding, the word is "overkill"

Quick listening impressions, very clean and precise, definitely more studio than hi-fi, which is perfect for me. There's also the feeling in the background that if you let loose it would throw the speakers across the room just for fun.

[Kent Kassler]

Brilliant result.....!Nicely done and enjoy!

[ScottulusMaximus]

Thanks Kentandre

Some stats for the beasty from the manual:

Power: 300W per channel minimum sine wave continuous average power into 8-ohm 20-20k at no more than 0.05% THD

Freq response at rated power: 10Hz-70kHz (+0dB, -0.5dB)

Square wave transient response: 1.5us

IM distortion: 0.05%

Damping factor: 150 minimum at 8-ohm

Weight: 18kg

And my favourite line from the manual:

[JonnyP]

Looks great, now you need a rack!

[ScottulusMaximus]

This amp is incredibly detailed, love it, can actually hear the bounce distortion on the kick in Bohemian Rhapsody, first time I've heard this on my system, even on YouTube!!! Haven't run a full test of all my tracks yet, maybe tonight...

Still to do:

Re-cap, incoming Nichicon PM series and original Chemi-con power caps from Mouser. There is a grand total of 14 electrolytics in this thing... But lol I'm spending as much on caps as I did on the whole amp

Vu-meter re-calibrate, will do it after re-cap but will need to borrow a decent voltmeter for this.

Re-bias, want to drop the bias to 7.5mA from 10, don't want to cook it while hosting one of my infamous rave parties with no air-con.

A shelf, Mars pre sits on the heat-sinks as it's feet are wider than the top. Got a steel plate from my GF's brother, need to paint and add feet to it.

[ScottulusMaximus]

A shelf, Mars pre sits on the heat-sinks as it's feet are wider than the top. Got a steel plate from my GF's brother, need to paint and add feet to it.

Done!

And caps arriving early next week

[Kent Kassler]

Now you just need some Fostex Laboratory Series drivers and Altec cabs.....

[ScottulusMaximus]

Caps caps caps!

[Kent Kassler]

Sjoe!....100volters sure ain't cheap!

[ScottulusMaximus]

Eh, not too bad... $23 each.

Rails are at around 70V, so have to use 100's