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[SripBoard Design] Starving Student Millett Hybrid Vacum Tube Amp - Page 18

post #256 of 269

Unfortunately they only had like 5-6 tubes and only 2 of the same brand. The radio museum is driven by a few pensioners who have worked with or designed radios in the past. I told them it was rare and how lucky I was to find them, I highly doubt they would jack the price :). But next time I swing by I will ask them if they would know of a place to get some more. My guess is they will  probably know if there is any place to find more in Sweden.

post #257 of 269

So very ammatureish question, But I am indeed an amature.  

 

So I will be using a proto board like the one above however there are no strips.   The boards I have are literally just a bunch of independent holes I can solder to.  SO I guess this means I will have to run a wire from each component to the ground individualy correct?  I wish there was a way to connect a whole strip on my protoboard as ground.

 

And even more basicly,  How do I ground this?  This is my first expererance ever needing to ground something.  Do I simply attach it to the case or what.

 

Thank you for the help. this thread has been great so far.  

post #258 of 269
Quote:
Originally Posted by audi0lurker View Post

So very ammatureish question, But I am indeed an amature.  

 

So I will be using a proto board like the one above however there are no strips.   The boards I have are literally just a bunch of independent holes I can solder to.  SO I guess this means I will have to run a wire from each component to the ground individualy correct?  I wish there was a way to connect a whole strip on my protoboard as ground.

 

And even more basicly,  How do I ground this?  This is my first expererance ever needing to ground something.  Do I simply attach it to the case or what.

 

Thank you for the help. this thread has been great so far.  


Don't use that protoboard, it is a huge pain. You definitely want stripboard. If you flip through my pictures, I built a regular old millett on stripboard. I can send you the board layouts.

post #259 of 269

Hello there,

After studying the stripboard layout, it is quite unclear to me where the Q1/Q2 Mosfets go.

Are they connected to the R2, and R8 resistors in series?

post #260 of 269

In the middle of the right half of the board picture, there are two rows of 3 black dots. This is where the mosfets go. If you look lower, bellow the board, there is the pinout of the 3 dots rows along with the pintout of the mosfet.

 

Actually, the mosfets are supposed to be mounted on heat sinks. You then wire them to the board.

post #261 of 269

Okay, thanks a lot :) Now I finished soldering, waiting for PSU to arrive. By the way, I saw that the Cisco 48V one is more or less precise to 0.1 Volts. Is that punctual enough for hi-fi use?

post #262 of 269
Quote:
Originally Posted by ricardobayes View Post

Okay, thanks a lot :) Now I finished soldering, waiting for PSU to arrive. By the way, I saw that the Cisco 48V one is more or less precise to 0.1 Volts. Is that punctual enough for hi-fi use?

 

The output voltage isn't really relevant to it being hi-fi or not. The important thing is it needs to be a clean and stiff voltage. I think the recommended PSU proved its worth by now. wink.gif

post #263 of 269

Hello everyone. Managed to assemble everything, but hearing no sound from the amp.

I'm measuring 13V between pins 4 5 on one tube, nothing on the other. However, the 0V tube doesn't heat up.

Another measurement between the MOSFET gate and source: 3,43V on the good side, 48V (!) on the other one.

Any suggestions?


Edited by ricardobayes - 7/18/13 at 2:04pm
post #264 of 269
Sounds like a blown MOSFET, Vgs should always be around 4V for standard fets. Then again the gate should be at about 17-18V not 48V so recheck the warning on that side, in particular the voltage divider that biases the MOSFET and if you have a spare there's no harm in replacing the MOSFET.
post #265 of 269

Question. Should pin 1 and 6, 2 and 7, etc. be connected at both tubes?

I wired the thing as pin 1,2,3,4,5 to one tube and 4,5,6,7,8 to the other.

post #266 of 269
Quote:
Originally Posted by ricardobayes View Post

Question. Should pin 1 and 6, 2 and 7, etc. be connected at both tubes?

I wired the thing as pin 1,2,3,4,5 to one tube and 4,5,6,7,8 to the other.

 

the 12au7 is a twin-triode. This mean it's got two triode in each tubes. In the MSSH, each triode is connected in parallel. To parallel them, we connect pin 1 and 6 together, 2 and 7 together... etc. 

 

Note that the amp will still work if you only use one triode, but it won't be working at the operating point that it was designed for.

 

The way you connected it is using half of both tubes for a single channel... so what did you do with the other channel?

post #267 of 269

Just left them floating :)

Now I'm rewiring the tubes

post #268 of 269

Hi, it's me again. Managed to rewire the tubes and now there is sound on both channels.

However, it is not amplified and it is quite distorted and the lower frequencies are missing completely.

Any pointers on where to start debugging?

I have a 10k pot as the volume knob. Measured resistance on pin 2 of tubes, they both go up till 10k if I turn the knob.

Also should the tab of the FET be connected to Drain?


Edited by ricardobayes - 7/19/13 at 3:08pm
post #269 of 269
Quote:
Originally Posted by ricardobayes View Post

Hi, it's me again. Managed to rewire the tubes and now there is sound on both channels.

However, it is not amplified and it is quite distorted and the lower frequencies are missing completely.

Any pointers on where to start debugging?

I have a 10k pot as the volume knob. Measured resistance on pin 2 of tubes, they both go up till 10k if I turn the knob.

Also should the tab of the FET be connected to Drain?

 

No, the tab is already connected to drain, internally. This is why we need to electrically insulate the tab from the heat sinks.

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