Millett "Starving Student" hybrid amp - Page 164

i'm guessing it should be possible to air wire the mosfet as well so long as we solder the correct resistor to the leg and then just wire it right?

It's probably a touch on lamp

well, I just powered up mine with the tubes and found that the voltage on pins 3 of the tubes I am getting 21.1V on one and full 48V on the other..

Any idea how this could be?

48v is source, the most direct route (and only) is from the transistor. Im guessing your not hooked up to the heaters. There is no way your putting 48v across a 19v heater and it surviving. The whole design is that the output is a ac signal with a 19v dc off set.

IN order to get the DC off set (the 19v for heaters) i believe it goes through a voltage divider from the 48v source to set the drain limit. so half the voltage divider is R13 and R2, and the other half is R4. So since r13+R2 is higher then R4 you get 19v out (if they were equal you would get 24v out, half the input). in other news i could be completely wrong. If you saturated the input of the transistor it could send full source (doesnt limit drain at all and "looks" like a short to the source) to the output, which would explain your 48v off set.

Thinking about it more, check R4.

http://tubes.mkdw.net/sheets/093/6/6J6.pdf

C1 value

Most of the caps I've scrounged so far are good quality Nichicon PLs but ran into a problem with the 680uF caps as they're only 35v. I remember Pete posting that C5 could be 1000uF but does that apply to C1 also?

IT looks like I might have saturated the transistor..there is almost full 48V on the gate of the transistor which could mean I fried the transistor....but also means the voltage divider is not working..or I have wired something wrong..pin 1 of the transistor could be shorted somewhere to full DC...Going to check it again..

Also, did a quick check and saw that I had gotten the wiring on the tube socket backwards..wired pin7 as pin 1 and vice versa ..

I have used the components in the original BOM except for 220uF for the input caps and 1000uF for the output caps.


Found another stupid mistake..had used 3.3k instead of 33k (really stupid of me..should remember not to do this stuff when I am groggy at 2 in the morning)..I replaced those now..But still the problem persists..

GOing to redo the network with the 220k/33k resistors again later and see what comes off it...

If i can get some thing backwards, i will get something backwards. I was double checking everything today, and the beezer vitamin q's and the .22 squares from beezer dont appear to have a polarity, but the schematic has them polarized. Are they polarized, and if so which side is what on the caps? Also can you dumb down the pins of the mosfet for me? I have no clue which is pin 1,2,3.

HI,

I assume you are asking about C2 and C4. I am using standard 0.1uF box film capacitors..so they are non polar...

Pin 1 of the transistor is the Gate...There is something seriously wrong in the input to the ate of the transistors if I have almost VDD on the gate..

Pin3 is the source and pin 2 is the drain...

Yes. If you are building P2P, you can pretty much put whatever you want in there, assuming you've met the minimums. However, 35V is too low.
Polarity is always shown on a schematic in case someone uses a cap that has polarity. The VitaminQ's don't care.

The first thing you should ever do when having a question about a MOSFET, transistor, opamp, tube, etc. - is to look at the data sheet. These are easily accessible when you order from Mouser or elsewhere. There are also a number of websites that provide data sheet lookup. For most parts, the pin arrangement is one of the first things detailed on the data sheet.

In the case of MOSFETs, the pins are usually labeled Gate, Drain, and Source. These correspond to pins 1, 2, and 3 on Pete's schematic. Here's a link to a datasheet for the IRF510:
http://www.diyforums.org/SSMH/mosfet/91015.pdf

EDIT: Oops - Sachu beat me to it.

Quickly checked Vgs..it is showing up as 0V..which is right as I seem to have 48V on both the gate and the source terminals..

BUt having 48V on the source is definitely wrong..and so is having 48V on the gate me thinks..

200v

Thanks. Forgot to mention the 1000uf were 200v.

3 legged piece of wire? pin 2 should be 48v on the mosfet. How you got 48v on the gate seems im possible since its a voltage divider if you simplify it, its only 3 resistors.

If you are as far as got the tubes wired correctly (not backwards as in 8 hours ago), id dike the lead to pins 1,2 (im assuming its the right channel) and the lead to c3. If you know the heater impedance when its hot, you can pop in a resistor in pins 3-4 and you will have a very simple circuit to trouble shoot without the tube.

It has a mechanical switch if that's what you mean?

It isn't a big deal, I can always unplug the lamp; just seems like a strange problem (and it only occurs in one channel).

It is strange, and I don't understand the subtleties, but it should occur in the tube closest to the lamp. Somehow the lamp is acting as an antenna and transmitting the 60 hz hum of the live wire to your tube.

Yes, it definitely seems to be a 60hz humming. I'll fool around with placement. For a while I was fooling around with the innards, thinking I had some kind of short or bad ground. I couldn't for the life of me figure out what would create the AC hum with the DC PS. Then I happened to turn the light on/off a couple times and noticed this was affecting it.

I'll have to find a lamp DIY forum.