[randomasdf]

Is there a link to a step by step or general overview of the equalizer's mod? I keep seeing it referenced, but not the actual mod itself.

 

[Lou Erickson]

Only the post in this thread. Use the web site and change a few resistors and wire the socket differently.

It's easy to miss things in this big thread, though.

 

[bmwpowere36m3]

Having built two Millet "starving student" amps, I'll be converting the old one (PnP) to run on SR7GT tubes like Logistic did. I just ordered a couple tubes and sockets off eBay, should be easy enough with a few resistor changes.

 

[the_equalizer]

Quote:

Originally Posted by dsavitsk /img/forum/go_quote.gif Well, you should be able to make a reasonable approximation from the 12au7 curves. Even without detailed curves, you can make an educated guess -- for instance, pick an operating current, say 1mA. Then, try to split the voltage between the load and the tube -- thus, 24V/1mA leads to a 24K load. If you look at the curves, ~-2V grid bias is the half way point on this line, so that puts the cathode resistor at 2V/1mA = 2K. You may need to adjust from there, but that gets you pretty close. You can also look at the 12U7 curves which are pretty similar at low voltages (12U7 is to the 12AU7 what the 6GM8 is to the 6DJ8). Oh, remember that since the tube sides are || that you need to double the current scale on the plate curves.

That post contains so many pieces of useful advise and wisdom that I don't even know where to start.

Indeed I printed a nice big plate curve graph for the 12AU7 and I was able to succesfully draw a load line with your indications. The fragment about splitting the voltage between the load and the tube answered a question I had had for a long time about how to set an initial value for Rp.

Thank you very very much for sharing this knowledge!

cheers!

 

[Lou Erickson]

That keeps happening around here. Some really smart guys who are happy to share. I'm glad dsavitsk mentioned how to meter tubes in the circuit. It's making it possible for me to stop looking at all the shiny tube testers on eBay...

I'm probably going to have to buy a new DMM, and that'll use up my tools budget for a bit, at least if I break down and get a good one. I thought I bought a good one last time and it only lasted ten years. Now Sears/Craftsman is giving me a useless run-around trying to figure out if it's covered under warranty. Not happy with them today.

I am, however, happy with TomB! I got a box from him, full of parts. Beautiful packaging job, and the custom case and board are both very pretty. I wish I could start in on it right now, but that would be silly. It'll probably be next Friday (weekend after Thanksgiving!) before I can build this pretty amp.

It is smaller than I thought it would be!

 

[nkk]

So...two stupid questions:

Tomb: Is there a power supply with this kit? I am thinking not, but wanted to check before I bought one and paid for expedited shipping (this amp is my thanksgiving break project).

So, any good sources for an acceptable power supply? Amazon.com sources preferred, because I have free 2 day shipping with my amazon prime trial (a rip off IMHO, but for free trial for 3 months, I took it).

Thanks
Nkk

EDIT: There is also no consequence for not wiring in the tube LED, right? If I just want to skip it, I can? I looked for a circuit schematic to make sure it was in parallel and not a vital connection (do not know why you would do it otherwise), but I cannot find one that has them included.

 

[tomb]

Quote:

Originally Posted by nkk /img/forum/go_quote.gif So...two stupid questions: Tomb: Is there a power supply with this kit? I am thinking not, but wanted to check before I bought one and paid for expedited shipping (this amp is my thanksgiving break project). So, any good sources for an acceptable power supply? Amazon.com sources preferred, because I have free 2 day shipping with my amazon prime trial (a rip off IMHO, but for free trial for 3 months, I took it). Thanks Nkk EDIT: There is also no consequence for not wiring in the tube LED, right? If I just want to skip it, I can? I looked for a circuit schematic to make sure it was in parallel and not a vital connection (do not know why you would do it otherwise), but I cannot find one that has them included.

Yes, each kit included a power supply.

No, there is no consequence for not wiring in the tube LEDs.

Yes - the questions are moot because the kits are sold out.

 

[nkk]

Quote:

Originally Posted by tomb /img/forum/go_quote.gif Yes, each kit included a power supply. No, there is no consequence for not wiring in the tube LEDs. Yes - the questions are moot because the kits are sold out.

You just saved my life. And no, they are not moot, as I bought a kit and only now thought of the power supply. I am the annoying person who took the chance to ask you about a kit without the case and PCB. I bought a kit anyway

I figured I will make another one later, and maybe sell it or give it to my sister depending on how quickly she descends into audiophilia. Really any excuse to make more than one will do.

-Nkk

 

[getllamasfast]

I have a two questions before I buy my parts.

In the 12AU7 version of this amp, R2/R8 ≈ 390Kohms, right? Does it have to be exactly 390Kohms? I'm ordering R2 as a 1.5Kohm and R8 as a 590Kohm which equates to ≈ 393.3Kohms, so is that okay?

My second question is: Are the heatsinks in this picture are good enough for the extra load the 12AU7 puts on the mosfets?
http://imageups.com/files/131/DSC_1944.jpg

Thanks.

 

[kuroguy]

Get within 10%; anything between 350 and 430 ohms should work.

 

[tomb]

Just an FYI, but all kits have shipped except for two and those will go out on Monday.

It looks like there are enough tubes to do another run of 25 kits. However, I've sent a note to Hammond asking for a slight mod on the case design. We may try to do something special for this last run.

 

[revolink24]

If it involves a gain switch, I might just kick myself

 

[tomb]

Quote:

Originally Posted by revolink24 /img/forum/go_quote.gif If it involves a gain switch, I might just kick myself

No - I just thought we might try Stackpole resistors and Muse Fine Gold caps on the output.

There's nothing to stop you from adding a gain switch already, though - simply wire a DPDT switch with your resistor choices into the input resistor pads.

 

[the_equalizer]

Quote:

Originally Posted by getllamasfast /img/forum/go_quote.gif I have a two questions before I buy my parts. In the 12AU7 version of this amp, R2/R8 ≈ 390Kohms, right? Does it have to be exactly 390Kohms? I'm ordering R2 as a 1.5Kohm and R8 as a 590Kohm which equates to ≈ 393.3Kohms, so is that okay? My second question is: Are the heatsinks in this picture are good enough for the extra load the 12AU7 puts on the mosfets? http://imageups.com/files/131/DSC_1944.jpg Thanks.

CAUTION!! My writing may have caused this confusion... when writing R2/R8 I did not mean the ratio of R2 and R8; rather it was shorthand for meaning R2 and R8. Thus you should be ordering two 390Kohms resistors, one for the R2 position and another for the R8 position.

Now, each individual resistor may indeed be 10% around 390Kohms without a hitch.

cheers !

 

[swedishhatfaction]

So these are some pictures of my Millett Starving Student Hybrid amp. It's the second amp I've ever built (the first being the Cmoy). The outside looks alright but as you can see the inside is an embarrassing mess. I really need to work on my cable management skills. It works but there is a significant amount of buzzing and hissing in it. It is also very susceptible to stray EMR (on my desk, I can even hear the electrical pulses my keyboard gives off when I type).

I'm thinking that I screwed the nuts too tightly on the MOSFETs and it could have ripped through the thermal pads -- making the back of the FETs touch the heatsinks which aren't grounded. If replacing the thermal pads doesn't fix the issue, I may just redo the internals on perf board to make troubleshooting a bit easier and make it look a great deal cleaner. A larger case may make things easier to work with too.

Something strange I've noticed is when I touch the right heatsink and the case at the same time, the buzz decreases considerably; touching anywhere on the case (which also isn't grounded) by itself or attempting to do the same with the left heatsink, however, the buzz increases. Also, the noise increases when I move my hand closer to the blue 1uF film caps -- it feels like I'm playing a theramin or something! I don't have any idea what any of that implies.

I could definitely use some feedback from a pro.