[amphead]

Quote:

Originally Posted by tomb /img/forum/go_quote.gif Don't know about that. Maybe you meant something else, but the Bijou is not affiliated with the MAX, the Millett, Colin or myself. EDIT: Your post count looks good, though!

Yeah, its not a Millett in any way shape or form. Don't know how it sounds in relation to the MAX. Edit: All tube sometimes = mid hump, good star grounding is needed to avoid 60 hz hum, and it runs at 300v B+, therefore the lethal voltages need to be dealt with. I have been hit with 480v, and my body was convulsed violently...need we say more?..........There are careful high voltage amp builders and then the are the.......dead.

Thanks for noticing my graduation!

 

[willisv]

Quote:

Originally Posted by amphead /img/forum/go_quote.gif Yeah, its not a Millett in any way shape or form. Don't know how it sounds in relation to the MAX. Edit: All tube sometimes = mid hump, good star grounding is needed to avoid 60 hz hum, and it runs at 300v B+, therefore the lethal voltages need to be dealt with. I have been hit with 480v, and my body was convulsed violently...need we say more?..........There are careful high voltage amp builders and then the are the.......dead. Thanks for noticing my graduation!

LOL, congrats on the post count!

 

[slowpogo]

Another probably-already-answered question...what are the negatives of using 1" heatsinks for the BJT output or power supply, as opposed to 1.5"?

Obviously the shorter ones won't dissipate as much heat, but what does that mean in terms of what you hear? I do want to bias the power transistors as high as I can.

My main concern is that I wanted to put some screening under the vent holes on the top panel, but the 1.5" sinks will literally scrape the top panel--no room for metal screening. The screening will allow big fat vent holes, so I'm wondering if the excellent ventilation will offset the need for a bigger heatsink.

 

[tomb]

Quote:

Originally Posted by slowpogo /img/forum/go_quote.gif Another probably-already-answered question...what are the negatives of using 1" heatsinks for the BJT output or power supply, as opposed to 1.5"? Obviously the shorter ones won't dissipate as much heat, but what does that mean in terms of what you hear? I do want to bias the power transistors as high as I can. My main concern is that I wanted to put some screening under the vent holes on the top panel, but the 1.5" sinks will literally scrape the top panel--no room for metal screening. The screening will allow big fat vent holes, so I'm wondering if the excellent ventilation will offset the need for a bigger heatsink.

The base configuration is supposed to be with 1" high heat sinks.

I have had my BJTs up to 60ma when using the rollbars - they tend to enhance the heat transfer effect, but I'm sure another 10-15ma is possible with care. 50ma with no ventilation whatsoever is a reasonable build. It will get a little toasty, but nothing more than that.

I have not cased up a MAX yet with anything other than 1" sinks and 1" parts.

 

[Hubbard0]

I've got another question too. I'm building an Alien to go along with this and on that board there are 2 capacitors that do not need to be populated if the amp has input DC protection. Does the Millet have this?

 

[slowpogo]

Quote:

Originally Posted by tomb /img/forum/go_quote.gif The base configuration is supposed to be with 1" high heat sinks. I have not cased up a MAX yet with anything other than 1" sinks and 1" parts.

Great, no worries then, I will add some 1-inchers to my mouser order. My kit from Jeff has 1.5" heat sinks, so I wasn't sure. If it weren't for my obsessively crafted top panel I wouldn't even have asked.

 

[tomb]

Quote:

Originally Posted by slowpogo /img/forum/go_quote.gif Great, no worries then, I will add some 1-inchers to my mouser order. My kit from Jeff has 1.5" heat sinks, so I wasn't sure. If it weren't for my obsessively crafted top panel I wouldn't even have asked.

Yep - my use of the phrase "supposed to be" may be a bit strong. Jeff's kits are a primary build option - it's just that 1" sinks don't work well with the giant KZ's that Jeff uses in his kits. ES caps or Black Gates will get you down to the 1" maximum part height.

 

[rhester]

tomb, where do those sporty rollbars come from? Add a nice touch to the build.

 

[tomb]

Thanks! Believe it or not, they are standard cabinet wire pulls from Home Depot or Lowes. I use 3" or 3-1/2". They are typically brass and plated with another color - brushed steel or black. The brushed steel are very common.

They have plastic ones, too, but they wouldn't do much except add some protection for the tube tops. The metal ones add heft and ruggedness to the amp and most importantly, improve heat transfer from the case.

They are about $2.50 or $3 ea. and come threaded for 8-32 screws. However, you'll need to purchase some of your own screws. The ones that come with them are sized for 1/2"-3/4" wood thicknesses and will never screw far enough to clamp down on a 1/16" case lid.

EDIT: I've attached a PDF CAD layout of the top plate incorporating the rollbars. I'll try to get this posted on the MAX website sometime today. 3" rollbars are used in the center, while the option to use 3-1/2" are on the sides. Again, this was mainly due to availability at HD/Lowes in Atlanta. The black ones are only at a couple stores and only at 3". There are online places where you can order different colors and lengths and are not too expensive, however. This is one that I bookmarked recently, but I haven't ordered anything, yet:
865 - Wire Pull, Contemporary Cabinet Pulls Amerock, www.knobsandhardware.com

Layout/PDF Template: MAXtopPlate-rollbars.pdf

 

[jerrygp]

Want to wish everyone that celebrates Christmas, a Merry Christmas...and to all, a creative new year. Thank you everyone for this forum over the past year...

 

[xmokshax]

so i've finished stuffing my MAX board, and so i went right on to biasing, but encountered a problem immediately. i plugged in the wallwart and flipped the switch, and the fuse blew immediately. i've seen quite a bit of discussion regarding fuses blowing earlier in this thread (which i'm wading through as we speak), and i'm not sure if i should just bypass the fuse and continue with testing, or if the fuse blowing on first startup should be an indication that something is wrong. any thoughts?

the fuse is the one that was supplied in Jeff's kit - i'm not sure if he's still supplying fast-blow fuses or he's switched to slow-blow.

 

[tomb]

Quote:

Originally Posted by xmokshax /img/forum/go_quote.gif so i've finished stuffing my MAX board, and so i went right on to biasing, but encountered a problem immediately. i plugged in the wallwart and flipped the switch, and the fuse blew immediately. i've seen quite a bit of discussion regarding fuses blowing earlier in this thread (which i'm wading through as we speak), and i'm not sure if i should just bypass the fuse and continue with testing, or if the fuse blowing on first startup should be an indication that something is wrong. any thoughts? the fuse is the one that was supplied in Jeff's kit - i'm not sure if he's still supplying fast-blow fuses or he's switched to slow-blow.

Yep - if you size the fuse to handle the inrush current it won't blow, but then it won't protect anything on the board, either. Better to go without it, IMHO. Screw your AC leads into the first two terminal positions and bypass the fuse, instead.

Bump the amp on and off while checking for minimum DB bias on the left and right channel. When you're comfortable those are at minimum, then turn it on for good and start measuring the PS and set the voltage as desired. If all appears well, then go on to biasing the DB's carefully using the procedure outlined earlier. (I'll try to post it on the website right now.)

 

[xmokshax]

thanks for the reply, tom. by the way, thanks also for the package that i received on friday.

i bypassed the fuse and checked the DB biases - at maximum RB12L/R, i read 25.8 and 26.5 mV for the two channels, well below the estimated 50mV. is this cause for concern? in light of some other results, it seems like it should be.

after finding the DB biases to be very low, i quickly set the PS voltage to 27V. so far, so good. however, when i measured the tube biases, both clocked in at around 24V. i played with the trimpots, but they didn't seem to make much difference. i think i've read some other posts about this problem, so i'll go back and look. the odd thing is that if i leave the amp on for a few seconds, the bias voltages plummet (not sure how far down they go, because i shut the amp off when this happened). i figured this might be a thermal shutdown of the LM317, but both the chip and the sink feel cool to the touch. any idea what might be going on?

 

[tomb]

Quote:

Originally Posted by xmokshax /img/forum/go_quote.gif thanks for the reply, tom. by the way, thanks also for the package that i received on friday. i bypassed the fuse and checked the DB biases - at maximum RB12L/R, i read 25.8 and 26.5 mV for the two channels, well below the estimated 50mV. is this cause for concern? in light of some other results, it seems like it should be.

No, that sounds good. As a matter of fact, it shows that you have well-matched JFET's. I'm pretty sure they are what govern the actual minimum voltage through the DB's and difference. That difference is very small in your case - 0.7mV. I've had as much as 20mV difference in mine.

By the way, I finished posting that blow-by-blow on DB biasing on the MAX website:
MAX Setup and Bias Settings

Quote:

after finding the DB biases to be very low, i quickly set the PS voltage to 27V. so far, so good. however, when i measured the tube biases, both clocked in at around 24V. i played with the trimpots, but they didn't seem to make much difference. i think i've read some other posts about this problem, so i'll go back and look. the odd thing is that if i leave the amp on for a few seconds, the bias voltages plummet (not sure how far down they go, because i shut the amp off when this happened). i figured this might be a thermal shutdown of the LM317, but both the chip and the sink feel cool to the touch. any idea what might be going on?

Did you install R1, the heater resistor? The tube heater circuit is open if that resistor is not installed or jumpered - the tubes will never conduct. It almost sounds like that's what's going on.

I'm not sure if that's a reason for the bias voltages to fall - can't answer that one. However, you are correct to conclude that without lots of heat, chances are the LM317 is not shutting down. It sounds like you are in the safe range for the DB's - let's see if you can get those tubes to conduct.

BTW, be sure you're not mixing up the trimmers - I've caught myself a couple of times trying to adjust the DB trimmers, thinking they were the tube trimmers. Also, be sure you're measuring the proper test points - the key is on that same "MAX Setup and Biasing" page referenced above.

All I can think of so far ...

 

[heatmizer]

edit found the answer on the other forum
Have quick question about the max in bjt configuration. Why does qb1 require such a higher idss than the original rev db.