Very nice!
Another MAX lives!

good work ferds (no need for air/cooling holes?)

I'm currently burning in my 12FK6 tubes (did a while with the 12AE6, but their gain was too high for my NAD C542/MS2i-combo)

the AE seem to have a bit more bass than the FK, but I still think the FK's provide a good low-end in the Max. Just listened to some Boris & Sunn O))) and it was clean and punchy but at the right times almost rummmblin' deep

Will the 12FM6's be somewhere in the middle? (they are gain-wise, I believe, but what about sound?)

At the moment my NOS 12FK6's are still slightly unstable in their bias voltage (even after being on for 6 hours straight, each evening this past week)

Congrats Ferds! Another MAX Lives!

Hows your sound?

Maligayang bati sa iyong pagtatapos! he he

Quote:



You describe the quality of the different tubes exactly. There are tradeoffs and advantages with each one. Yes - the 12FM6 is in the middle.

Yep for the bias voltage, too. As they break-in, the bias will become more or less rock-solid (after an hour or so)

Thanks guys..

I will surely put some holes on top.. it runs a little hotter than i expected..

hey amphead nice to see another pinoy here (are you?) hehe

bout the sound? hmmm i still used to the sound of my PPAv2 (637 +627) but definitely loving it..

No, but I thought I would congratulate you in tagalog.
Not exactly a graduation but almost.

Pabbi, I have decided to get as far as I can on the bad board before the replacement DBs arrive. So far with those parts removed, I have plugged your board into my power supply. Its showing signs of life. The fuse does not blow. The tubes and leds light up (nice green glow). I adjusted voltage from 27.9V to 27V on the power supply. I biased left tube to 13.7V. Checked bias on left DBs/channel and currently its at 30mv. I won't bias left DBs, until I can bias the right channel. I am going to listen to the left channel alone with my phones. More info to come. If all goes well as I expect, I want to get your amps back to you in good working order as soon as possible.

Pabbi, update: So there is a bit of nice music eminating from the left channel, even though it is still supremely underbiased at 30mv on those DBs. That means I can concentrate on getting the right channel up to spec. - more info later. Edit: I need some information on setting up the 2 Maxes in a balanced configuration. Anybody?

I'd guess feeding them from a balanced source, + to one channel, - to the other.. or whatever the terms are with one amp L, one amp R.. but I haven't done anything balanced yet, so my guess is as good as a fleas

Quote:




For balanced, both channels on both boards should match - I'll use R as +, and L as -, which is all the magic there is to this. I have dual leads from the outs that will go to Neutrik combo jacks, following Ti's guidance (though he is referencing Beta22, the concept is the same) here, under 'Other Options', using the 'Combined Balanced / Unbalanced' diagram:

Balanced / Unbalanced wiring

The balanced input to the boards is coming from the Twisted Pear OPUS dac.

I am using Denon AH-D2000 (with the markl mod) balanced, so I doubt there needs to be more bias than the bottom end of the range, especially with the 12AE6A. I also have 12fk6 (my real preference in the Millett, as determined with my prioor Millett), which will be my permanent tubes.

Much love to Amphead - without you, this is a heap of parts headed for the recycle bin.


So, for the $64k question - do the buffer biases change with different tubes? If so, how does the buffer bias change when changing 12ea6a to 12fk6?

Quote:



NO. The buffer bias is absolutely unaffected by the tube bias. We have had a couple of reports where the reverse has happened - biasing the buffers has had an effect on the tube bias. Neither should be the case, although I would believe it sooner in the case where the DB's may be able to suck current out of the CCS and perhaps drop the voltage slightly on the tubes.

Neither should happen, however. That's one reason I changed the parts recommendation for the CA4 and CA5 caps to 1000uf minimum. I've actually used 1800uf FM's except for 1200uf FM's in the 1st proto - never had a problem with either situation.

EDIT: Colin would probably say either case is impossible, but hey - it's only a few pennies for some extra uf's and they look better bigger, anyway.

Quote:



As I had hoped - I will be really gun shy abiut touching buffer bias...

I have to change out one of my tubes later today. At least I think it's a tube issue. If I tap on my desk or tap the amp, I get nasty static in the left channel. But, if I do it enough, like tap on my desk for 5-10 seconds, it slowly fades away not to return. The only thing I can think of is that I got a funky tube.

This happened after I switched out a couple of orange drops for wimas in CA9, but touched nothing else. I thought maybe it was a grounding issue and wired the ALPS to ground, but it still happens. It's the fact that the static goes away after some tapping that makes me think it's a tube thing.

Quote:



It's possible. One way to know for sure is to swap the tube out or switch the tubes from one channel to the other.

If that doesn't stop it, it's possible that you might have something shorted to ground if it was case up. Sometimes taking one apart and putting it back together is enough to short something that wasn't shorted before, perhaps.

If the tube is microphonic - which is what one normally thinks of when a tube reacts to tapping on an adjacent surface - it usually manifests itself in ringing or echoing in the sound output. 99 times out of 100, it's very, very obvious.

My first foray into Black Gates on a Millett MAX:

[size=xx-small](click for a larger pic)[/size]

Panasonic FM's all around, Wimas, etc.
1" or less parts all around
1000uf 25V BG NX's in CA2
680uf 35V BG NX's in CA7
BJT's - 2SC2238/2SA968's

27VDC, for the PS, DB biasing was straightforward - started out at about 40mV and worked up to 110mV (50ma) in about an hour - everything stable. LM317 is running at about 42deg.C. on the plastic, about 50deg.C on the metal tab. The sink is very hot - almost burning hot to the hand, but more like automobile-door-in-the-sun hot. It should run like that indefinitely. DB's are considerably cooler - 37deg. C. on the plastic, about 42deg.C. on the metal tabs (the 2SC2238's have metal tabs).

It sounds OK so far - it's obvious that the frequency response on the BG's is very extended - both extended highs and bass. However, things sound a bit metal and harsh for the time being. I haven't decided whether to put film caps on the output - have some Russian PIO's I'm itching to try, but will probably let it run this way for a week, at least.

EDIT: The relay is sounding pretty harsh in the left channel, but I've measured both turn-on and turn-off and the offset is within previously seen values - it just sounds bad. Maybe the caps need to break-in some more. If it continues like that, I may replace the smaller electrolytic with a 10uf 25V tantalum - something Amb recommended over on Headwize in the E12 thread - and see if that helps. I may have a not-so-good relay.

EDIT2: Wow - it doesn't take too long for those things to start smoothing out - sounds very good!