[MASantos]

I decided to start a new thread because I couldn't find the answer here or in any of the other forums.

I finally finished my millett hybrid. I am using a steps PS at 25V, pretty much standard parts list with wimas, elna silmic II and blackgates of the output. Using the BUF634 right now for testing.

I wired everything correctly, steps works flawlessly but there is something wrong with the amp. The Vdc at the tube bias test points is about 1.8Vdc in each channel. I started going through the circuit and noticed that the fuse on the board, the yellow round one is getting burning hot after a few second of power up. Could the part be damaged? It is not polarised right?

Any thoughts or sugestions are welcomed.

Thanks in advance!

 

[tomb]

Quote:

Originally Posted by MASantos /img/forum/go_quote.gif I decided to start a new thread because I couldn't find the answer here or in any of the other forums. I finally finished my millett hybrid. I am using a steps PS at 25V, pretty much standard parts list with wimas, elna silmic II and blackgates of the output. Using the BUF634 right now for testing. I wired everything correctly, steps works flawlessly but there is something wrong with the amp. The Vdc at the tube bias test points is about 1.8Vdc in each channel. I started going through the circuit and noticed that the fuse on the board, the yellow round one is getting burning hot after a few second of power up. Could the part be damaged? It is not polarised right? Any thoughts or sugestions are welcomed. Thanks in advance!

It sounds like you've got a short somewhere on the board. The PF1 polyfuse is not polarized, but the P6KE (D1) is. I'm assuming that you mean you can't adjust the bias any higher than the 1.8VDC, right? Maybe the CCS's are misoriented. There's really not that much to the Millett, except for getting a few parts mis-oriented, perhaps.

You know the drill

... pics, please. We'll try to help.

 

[MASantos]

problem solved after a blown capacitor that was reverse mounted. THe big pop sound of the exploding cap scared the **** out of me

So I installed a crapy cap in its position and it is working now. I'm letting the tubes run for a bit( those "test" ones you sent me, Tomb) and will install the diamond buffers in a few moments.

Ones question, I measured the dc offset at power on and it goes high and then comes down as the tubes heat. I've read about this sometime ago but can't remember right now. Is it safe to have the headphones plugged in during power on if there is no music playing?

 

[n_maher]

Yes, it's probably just fine to have headphones plugged in when you turn the amp on. What you're observing is the output coupling caps charging. If you're really worried about it you can either build an e12 or unplug your phones before you turn the amp on.

Also, shoot me a PM if you need help finding a replacement cap.

 

[ruZZ.il]

edit: I guess what I'm thinking of may be of little concern. in fact, I'm really uncertain how this effects the rest of the circuit, etc.. since I don't have much experience with amps,.. nate's likely to be right

I'd guess not, since its not the music thats problematic.. it may be the lack of the electron cloud around the heating element (cathode) that puts the tube in a more steady state kind of.. state. at this point you'd have random electrons flying out and with nothing to immediately slow them down they'd smack into the cathode and right round through the circuit they go, creating random spikes of current. Once there are enough electrons out and around the element, they slow down the other ones that come out.. in this state, its the field created by the source thats needed to excel them into anode.. ie, while initially heating up, the tube is the furthest from steady state that it could be.. exactly what you're trying to avoid.

 

[tomb]

Um ... with a 25V power supply, you'll see 12.5VDC to Ground at the Left and Right channels, until the output caps charge up. Typically this takes about 5 seconds.

That amount of voltage is enough to kill headphones, I think. The admonition has always been: Don't plug in your headphones until the thing has warmed up for at least 10 seconds. Same for turn off - get the headphones unplugged before you turn it off or they'll see killer offset.

 

[vixr]

I saw some really high DC readings for a few ticks on my MH...more than enough to damage the phones. I installed the e12 with about 22 seconds of delay.

 

[n_maher]

Has anyone ever actually had headphones damaged this way?

I've had continuous exposure to DC offset nuke a set before, but I've used my Millett for a good long time and never had it hurt a pair of phones when I left them plugged in.

 

[ruZZ.il]

ahh. makes more sense..

 

[vixr]

Quote:

Originally Posted by n_maher /img/forum/go_quote.gif Has anyone ever actually had headphones damaged this way?

I have heard some very un-pleasant sounds coming out during the first few seconds of turn on... couldn't have been good. The phones seem to be OK though.

 

[fran]

I added a e12 to my board. Works fine and gives about 10-12 seconds of mute. There are simple instructions on ambs site about how to wire it so that it cuts instantaneously on power off - and that works too!
The parts for my diamond buffer just arrived today so I hope to get soldering in the next few days.

Does anyone have extra diamond buffer boards?

Fran

 

[tomb]

Quote:

Originally Posted by fran /img/forum/go_quote.gif I added a e12 to my board. Works fine and gives about 10-12 seconds of mute. There are simple instructions on ambs site about how to wire it so that it cuts instantaneously on power off - and that works too! The parts for my diamond buffer just arrived today so I hope to get soldering in the next few days. Does anyone have extra diamond buffer boards? Fran

Did you purchase Nikongod's? I thought I saw your post on his For Sale thread. He was asking $6 ea, I think and his last post says they're available. Those are the only ones I've seen lately.

 

[fran]

Yep, but he won't ship outside the US.

Fran

 

[amphead]

Hmmm......I wonder if Amb would ship you one?

 

[fran]

I'll ask him if he has any. Shipping won't be a problem as I've already bought stuff from amb.

Fran