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Millett "Starving Student" hybrid amp
Jan 26, 2009 at 9:09 PM Post #2,012 of 7,277
I'm going to check the circuit again in a bit. The tubes are not lighting up but the transistors do start to warm up (I haven't been leaving it on that long).

I'll see what I can do about a picture in a little while.

I checked the voltages again with it running and they're not fluctuating as hugely as I thought, they're jumping between almost 0 and 4 or 6 volts. I'm going to look through the circuit in a few minutes.
 
Jan 27, 2009 at 1:36 AM Post #2,015 of 7,277
Dsavitsk and I agreed that perhaps it was a good time to show where we're at with the SSMH PCB. Dsavitsk has designed the PCB, of course, with some comments from n_maher and myself. I've provided the CAD file layouts of the component parts in the second post below.

The board is designed to be mounted upside down, with the sockets soldered on the bottom of the board and the remainder of the parts hanging down from the other side. This will become clearer with the next post, but suffice to say the ground plane is on top. In order for you to see all of the components of the board, I've included two images, one with the ground plane turned on, and one without:

SSMH-layout-1.jpg


With the ground plane layer turned on:
SSMH-layout-2.jpg


The MOSFETs are designed to be bolted to the case lid, from the inside. This prevents any exposure to the voltages inside the case.
 
Jan 27, 2009 at 1:42 AM Post #2,016 of 7,277
Below are a couple of examples of how the board would fit in the proposed case - either the Hammond 1455L1201 (preferred) or the Hammond 1455N1201 case. The parts clearance in the "L" case is a little more than 20mm. There are several selections of the most used power-type capacitors that will fit - UPW's and FC's, for instance, are available in 470uf 63V at 20mm high.

If boutiques are desired, which are quite a bit taller (the Nichicon Fine Gold at 470uf 100V comes to mind), then the "N" case provides more than adequate clearance. While the headphone jack and pot shaft line up rather high in that arrangement, one can air-wire both parts if desired.

Hammond 1455L1201 case:
SSMH-layout-L1201.jpg


Hammond 1455N1201 case:
SSMH-layout-N1201.jpg


Note that the PCB mounting holes are intended for other case choices. The strategy with the Hammonds is to slide the board into the top slot. I don't have them drawn in, but the tube sockets would be soldered into the board on top, and would stick up slightly through the case's top plate.
 
Jan 27, 2009 at 2:56 AM Post #2,019 of 7,277
the pcb looks great guys, i'm sure i can speak for everyone here and say that we appreciate your hard work


based on the mosfets bolted to the case i'm assuming that the case will act as the heatsink and that the stand alone to-220 ones won't be required?
 
Jan 27, 2009 at 3:01 AM Post #2,020 of 7,277
I got a message from Tube Center a week ago that they were out of stock (I will assume you were inquiring about 19J6s?) and that they expected more shortly.
 
Jan 27, 2009 at 3:09 AM Post #2,021 of 7,277
I've got another question pertaining to the PCBs and the tube sockets. I noticed on every single tube socket that I've seen that the terminals you solder wires to are flat, rather than round like the pins on the bottom of the tube itself. Will the PCB account for this, or will the holes where the socket is to be soldered in still be round?
 
Jan 27, 2009 at 4:20 AM Post #2,022 of 7,277
Quote:

Originally Posted by wiatrob /img/forum/go_quote.gif
I got a message from Tube Center a week ago that they were out of stock (I will assume you were inquiring about 19J6s?) and that they expected more shortly.


Oh well. If they don't reply by midday tomorrow I am going to send another email their way. It is a bad business practice to ignore your customers.
 
Jan 27, 2009 at 4:46 AM Post #2,024 of 7,277
Quote:

Originally Posted by iareConfusE /img/forum/go_quote.gif
...I noticed on every single tube socket that I've seen that the terminals you solder wires to are flat, rather than round like the pins on the bottom of the tube itself. Will the PCB account for this, or will the holes where the socket is to be soldered in still be round?


7 pin ceramic pc board mount sockets should be available...
 
Jan 27, 2009 at 11:59 AM Post #2,025 of 7,277
Quote:

Originally Posted by MoxMonkey /img/forum/go_quote.gif
the pcb looks great guys, i'm sure i can speak for everyone here and say that we appreciate your hard work


based on the mosfets bolted to the case i'm assuming that the case will act as the heatsink and that the stand alone to-220 ones won't be required?


Yes, Dsavitsk says the case itself is enough to dissipate the heat. That was with the "N" case, I believe, which has more metal than the "L" case. In any event, if the "L" case runs hot by itself, we can put one of the half-circle type heat sinks on the top - there's plenty of room.

Quote:

Originally Posted by iareConfusE
I've got another question pertaining to the PCBs and the tube sockets. I noticed on every single tube socket that I've seen that the terminals you solder wires to are flat, rather than round like the pins on the bottom of the tube itself. Will the PCB account for this, or will the holes where the socket is to be soldered in still be round?


As wiatrob indicated, the sources for PCB-type tube sockets are as numerous as tube dealers:
Beezar.com
SILVER Plated 7 PIN Ceramic Tube Socket PCB - 2PCS - eBay (item 270336166337 end time Jan-28-09 01:33:12 PST)
Cascade Surplus Electronics
7 Pin PC Mount Socket
http://www.partsconnexion.com/catalog/tubesockets.html (scroll down the page)
etc., etc., etc. ...
 
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