Millett "Starving Student" hybrid amp - Page 169

If you're using a DMM to figure out "which pin is which" how are you not able to determine which is the positive one? It's also written right on the power supply.

Hey Nate, I think what he's asking is on the dc jack as to which ground pin he should use -- there's the middle positive pin and also 2 potential ground connectors

Fuzzy, I use the one close to the jack edge and seems to work fine, not the one close to the middle/positive pin. That one is unswitched when the ps male jack is plugged in.

zk

I found the positive. I'm not sure whether to put the ground pin to the ground plane or the negative pin to the ground plane.

EDIT: Thanks zkool. Use the negative pin for the dc jack.

There is no "ground pin" on the DC jack. As zkool said, it's a switched jack and once the plug is inserted you have one positive and one negative "pin". If you don't connect the negative pin to the GND terminal I'd wager you'll be unhappy with the results. GND in this example is zero voltage potential and the power supply's negative pole is the reference that we want to set at 0.

Ok, that makes a little more sense.

i got some of my order delivered today but it seems like they sent me 2k2 resistors instead of 2k ones i ordered. are those ok to use?

also zcool great work on the case can we have bigger pics with more closeups of your handy work please

Hello,
I've seen that the 19J6 tube is very hard to find, so I've a question

Is it possible to use other type of tubes with 12.6v filament like ECC82 or ECC83 ?

They need 150ma like the 19J6, so if I add a resistor I can use these filaments with a 19V supply

For the original 19J6 : 19V / 0.15A = 127 ohm

For the ECC82/83 : 12.6V / 0.15A = 84 ohms

So a 43 ohm resistor in series to the 12.6V filament can do the job and the mosfet load doesn't change.

What do you think about that?

Sounds like a good solution to me. I have my doubts that the 12AX7 will overcome the fet's gate capacitance, and the gain is likely too high, so I think the 12au7 is the better choice here. AT7, AY7, and AV7 are all worth looking into as well depending on your needs. You'll want to fiddle with the Rk and Rp values most likely. Also, if you have sufficient heatsinking, no reason not to just bias the mosfet at 13 volts and drop the heat across it rather than adding a resistor.

Just finished mine and it is quite amazing for the size and price.


Somehow I even managed to have it working on first startup, a rare situation.


[EDIT]: The only problem I am having is microphonics, any light touch to even the desk it is on causes a sound. Is there any way to mitigate it?

All tubes are different. My Sylvania tubes need a good flick to make a pinging noise. No problem in normal use.

Thanks Yaka, sorry about the previous pics I only had my phone cam with me at the time. Anyway, it's not quite ready but I managed to get most of the sanding done today. All it could use now is a fresh coat of paint. I'll try to post some more pics after I decide on a color

note: Bottom plate is made of frosted acrylic/plexiglass, the LCDs should make the bottom plate 'glow' in the dark (hopefully).

zk

Awesome build. Wish I could do that

What would be a good match with this unit for a source for 128kbs mp3's? Right now i have a nano2nd gen (cant imod). Should i get a pcm2702 based usb dac for $40 instead?

Yes it is another solution, I think that the results are the same
I don't know what tube can be a good replacement for the 19J6

Now just some case feet and a bit of tung oil - should look sick!!!!!!