Being there is a shortage of the 10M45S does anyone know of a replacement without my searching data sheets?
Thanks, I am old and lazy. Rather not hit the data sheets if someone already knows answer. But looking at both data sheets, 10m45s and 10m90 there are some questionable differences in specs. Not sure if it will work as replacement.
10M90's work fine though you should measure the current to verify about 10 mA. I used them in SSEs and TSEs several years ago when 10M45's got scarce.
I am going to assume you measure the voltage drop across R13 and use ohms law to find current in the circuit. Then adjust the value of R13, R23 to achieve 10ma.
Sorry to be a pest but newbie is still confused somewhat. I am now thinking you meant 10ma of current through the tube. Am I correct?
The 10M45 sets the amount of current through the tube. Neglecting the few microamps of possible grid current the tube current is equal to the current through the 10M45. Measure the voltage across the 220 ohm cathode resistor, R10 or R20. It would be 2.2 volts for 10 mA. To change the current you would change the value of the 330 ohm resistor connected to the 10M45, R13 or R23. You don't need exactly 10 mA, anything from 6 to 10 is OK.
Some users have put a 1 K or 500 ohm trimpot in place of R13 and R23 and adjusted for best sound, distortion profile, or whatever suits them. This is possible but one must be careful watch the current. 10 mA can be at or near the maximum plate dissipation for the 12AT7 on a board running at 400 or more volts.
Some users have put a 1 K or 500 ohm trimpot in place of R13 and R23 and adjusted for best sound, distortion profile, or whatever suits them. This is possible but one must be careful watch the current. 10 mA can be at or near the maximum plate dissipation for the 12AT7 on a board running at 400 or more volts.
Both 10m45s and 10m90s are non existent at reliable sources right now. Any problem using the SMD/SMT 10m45s other than dealing with the tiny size? Spec sheet says yes as far as I can tell.
The SMD version has the exact same die / chip inside. Electrically it will work fine. Depending on the tube it's feeding and the B+ voltage it will dissipate between 1 and 3 watts which requires a small heat sink. I have soldered an SMD part directly to a small piece of copper that's 1 to 2 mm thick, then soldered extension wires to the pins for use in a through hole board. The guys in the Pass Labs forum have created an adapter board that's made on a thermally conductive material for their LU1014D fets. There are also some clip on heat sinks that might be useful if leads are soldered to the SMD part.
You would surely need one of those adapters, my worry is heat dissipation. How do you attach a heat sink to one of those tiny things? We are probably in the neighborhood 60 milliwatts if my math is correct so we are not talking a lot. I seriously doubt anyone has tried using one of those things being the regular parts have always been available.
I will assume no one that has seen this post has tried one of the SMD/SMT 1045m45s'. After doing some searching of past post when the CCS were short in supply others used a DN2540N5 mosfet and as expected it is unavailable as well. Doing some looking at spec sheets it appears to me, from what little I understand about electronics, that a IXTP05N100 will work in place of a DN2540N5 with possible some adjustments of the K resistor. What do you guys think?
In order to use a mosfet in place of the 10M45S the mosfet must be a depletion mode, or "normally on" device. A traditional enhancement mode device will not work without circuit modification. The IXTP05N100 part is an enhancement mode mosfet, thus will not work in place of the 10M45S.
The easiest way to do this is to use Digikey or Mouser's search engine, choose mosfet, through hole, N-channel, and depletion mode, then hit search you could also specify a voltage rating of 450 volts or higher. Parts with more than an amp or two of current capability may have too much capacitance. Once you have a suspects list, click the "in stock" button and watch the choices vanish. I ran a search on both web sites this morning and there are a couple of possibilities. I'll look through my collection of mosfets and see if I have any that are in stock and try them in an amp, but the last time I picked some possibilities the stock was gone.
Thanks for looking and look forward to what you find. It just caught my interest on what others can use to keep building your two popular builds. Shame now 10M90S' are not available as well as the 10M45s'.
This one looks like it would work on paper unless there is something I am missing looking at the data sheet comparing it to the DN2540 others have used in the past, IXTP1R6N100D2. Price is real close to the cost of a 10M45s. I would certainly like George to take a look and see what he thinks before I purchase a pair to just play with on his design. From my little experience repairing and building SS equipment a CCS is always a plus on an input active device.