[SripBoard Design] Starving Student Millett Hybrid Vacum Tube Amp - Page 3

are 4 tubes necessary? couldn't a dual mono 2-tube be made by splitting the ground planes? or isn't dual-mono the same as balanced?

Quote:

Originally Posted by TestSubject 

So:

 

1) The 12AU7 tubes can handle 2 channel per tube

2) The amp from the link you gave me only uses one of those channel so two tubes (plus the reciprocal of the circuit) would be needed in order to output stereo

3) The SSHM must be the same because it uses 2 tubes.

 

Thanks for the help you are supplying.

1) Yes.

2) & 3) The SSHM uses 1 tube per channel, and that 1 tube per channel has both triodes (within the 1 tube) both paralleled. The other designs given here only use 1 tube, and just use 1 of the 2 triodes per channel.

http://www.nj7p.org/Tube4.php?tube=19J6 Data sheet for 19J6

 http://tdsl.duncanamps.com/show.php?des=12AU7 Data sheet for 12AU7

Part of the reason for the dual triode per channel in the SSMH is because of the unique heater voltage/current, and the fact that it is used in series with the output mosfet, along with the 48V power supply. It is trying to get the most amp, using the very least amount of parts possible... almost.

If no one has suggested this before, sit yourself down and take a good long look at the schematic. Got it? Okay, now draw out that schematic using real life parts. That means drawing capacitors, resistors, the mosfets, the tube sockets, the potentiometer, input/output jacks, the whole shebang. I suggest getting several pieces of paper and a pencil and just doing this for like an hour or so. Eventually you'll get good enough at reading the schematic that you know where everything is and how you should go about laying out the components in whatever enclosure you decide to put it in. This is how I put together my 12AU7 SSMH. When you've come up with a layout that looks ideal, post it here and we can tell you if there are any problems with it.

It took me about a month of planning to put together this SSMH as my first full project, but if you're willing to put in the time it's very rewarding. If you're not willing to put in the time, then why are you considering DIY?

^That is what I do. After drawing the layout maybe 20 times, then I will try to make the actual parts fit into my selected enclosure. 

Have you tried to see if you can get the tubes, or the 48V power supply?

Be careful about the mosfets - the schematic refers to it in numbers 1, 2, and 3, where 1 is gate, 2 is drain, and 3 is source. These numbers correspond to the pins like so: http://wb5rvz.com/sdr/components/irf510.gif

So pin 2 of the mosfets (drain) should connect to each other and the resistor should be connected to pin 1. Several people have burned out mosfets by connecting them incorrectly, so it'll save you a couple bucks to make sure you have them properly hooked up.

Furthermore it looks like you drew the schematic for the 19J6 original. I don't know about you, but I had a hell of a time trying to find 19J6 tubes last summer, so I gave up and went for the 12AU7 variant instead. That schematic can be found here: http://diyforums.org/SSMH/variants/SSMH-12AU7.gif

There are not many changes, just a couple resistor swaps and a reassigment of the pin socket numbers.

Otherwise the drawing looks good. I'm not too familiar with the 19J6 schematic so I'm not looking carefully for errors. If you want some guidelines on how to build a P2P 12AU7 you can look through the main SSMH thread for Beftus' build pics (search for his name and find some of his earlier posts), and mine as well. My album can be found here: https://picasaweb.google.com/submergence/StarvingStudentMillettHybridSSMH

As for the single-tube alternative, I've never looked into it, but I did see a similarity between that and the cheap chinese "open" tube hybrids you find on eBay. One of them had a single 12AU7 driving two channels and IRF510 mosfets, so I figured the schematic was probably very similar. I have no idea how they sound, though.

Good luck building! The main SSMH thread is a great resource and a lot of pertinent info can be found in it if you search around a little bit. It can be daunting at first but take it slowly and eventually you'll know the project like the backside of your hand.

You can get stripboard with any number of connected pads. http://www.futurlec.com/ProtoBoards.shtml

You could also use a terminal strip or turret board.  http://angela.com/connectors.aspx

I use euro strips a lot for prototyping.  http://compare.ebay.com/like/350115300106?var=lv&ltyp=AllFixedPriceItemTypes&var=sbar&_lwgsi=y

Most of the optional components are, in some people's opinions, necessary (like R14/15, 16/17). The main one you can do without is C7/C8, since that doesn't necessarily improve SQ very much. You can try searching for info but I don't think there's very much about it besides the fact that they increase gain (by reducing feedback, I think). You could probably do without C3a/5a but those are film bypass caps so will probably improve the sound. You can find a BOM on the DIYForums page, making sure to swap out the necessary changes for 12AU7 (resistors). http://www.diyforums.org/SSMH/SSMHbom.php

Quote:

Originally Posted by Aflac 

The main one you can do without is C7/C8, since that doesn't necessarily improve SQ very much. You can try searching for info but I don't think there's very much about it besides the fact that they increase gain (by reducing feedback, I think).

 

These caps reduce internal feedback in (around?) the tube and frequently result in more gain, but more importantly adding them reduces distortions. Kind of paradoxical, since people normally think of feedback as the great distortion destroyer.

In any event, putting them in/taking them out is just a few solder joints away. Experiment!

do the newer additions work/benefit with the original 19j6 tubes?