[elrod-tom]

Hi all:

I've now assembled my Millett tube amp, and I'm looking forward to seeing what this little gem is capable of. However, I'm having some problems.

I can actually hear some faint music, but not much...and what I can hear sounds crackly. When I turn it off, for a split second, it goes clear (though at a very low volume). When I turn it back on, it's clear (at a slightly higher volume) for about three or four seconds, and then it fades.

Any idea what the problem might be?? I'm brand new to this DIY stuff, so break me in gently. Thanks.....

 

[Dan H]

Kind of sounds like the pot is bad, did you check it with a VM?
What is the bias voltage at the two test points?
Do you have 24 vdc on the board?
Try swaping PF1 end to end, it maybe installed wrong?
I got a good quality PS like others here sugested a very worthwhile upgrade over the wall wart I started with.

 

[minya]

Quote:

Originally posted by elrod-tom Any idea what the problem might be?? I'm brand new to this DIY stuff, so break me in gently. Thanks.....

That sounds similar to the problems I had... I bet it's bad tube bias. Make sure your tubes are biased correctly. Try them at about 12 volts and steadily increase the bias until you come to a sound you're comfortable with.

BTW, Dan H: What power supply upgrade did you get?

- Chris

 

[Dan H]

I was reading others talking about a Condor HA24-0.5-A+ 24/28V 0.5A linear power supply and how much better it is. I just copied what they did and found it to be very worthwhile. This PS can be found on Ebay or other online electronic sales oulets.
Bias at 19 volts works great in my amp.

 

[elrod-tom]

Thanks for all the good advice. I will check all of these things this weekend, and report back ASAP. Interesting advice re) the upgrade in wall wart...I'll see if I can't run one of those down as well.

 

[Voodoochile]

Although I'm not a fan of the wall-warts, the amp should function just fine with a wall wart. Pete's does.

Do check the bias again. I have mine running off an open-frame 28v linear PS, and the bias is set to 18v. Mine went together and worked fine right away, so it might well be a bum part, if the bias is good.

Also, if you get nowhere this weekend, drop a line to Pete Millett. He's a super-nice guy, and is interested in this. He also answers his mail. I sent him my impressions, as well as an off-line rebuttal to the mail pubbed in Express regarding the compromises made in the design of this amp. The writer was wondering why the design was not more pure, etc.... I think he missed the point of this amp entirely. It's really a very very nice amp for the small outlay. Not intended to be out there kicking ass and taking names of hi-buck tube amps, but rather a nice, fairly simple-to-build introduction to tube amps for a tube novice, which is me!

It is a nice sounding amp, though. I like it. It might sound like crap compared to a Melos (I do not know), but what I like about it is that is has a different character from the SS amps.

 

[eric9201]

Hi guys,

I just received my Millett PCB from DIY Cable and I was wondering where the test points for the tube bias are. I'm sorry but I'm new to DIY electronics. Thanks for any help.

 

[n_maher]

Eric,

I'm not trying to be a wise guy but the test points are pretty clearly labeled on the board. The right channel is labeled R BIAS / TP1 and the left is L BIAS / TP2, each just to the right of the buffer heat sink for the respective channel. At least that's the way it looks on Pete's original board that is pictured on his site. The bias adjustment trimpots are also pretty clearly labeled.

I hope that helps.

Nate

 

[eric9201]

Thanks Nate!
So the +/- test probes go into the 2 holes of each bias/Tp point.
I hope to start assembly next week when the parts arrive.
Thanks again!

Eric