| Posted by Ed Benway | September 22, 2014 - 09:11 am |
| Hey Dave, what wattage rating would be sufficient for the 5 k pot? I purchased a .5 watt PC board mountable trimmer pot. Is that going be hefty enough? |
| Posted by stephen zaneteas | September 19, 2014 - 09:20 am |
| OK....everything makes sense now..i should go your route for easier testing, of course. Just got me 4 matched MULLARD re-issues from Mother Russia for ...50$...that's a nice price. I purchased precision 1% MILLS 1 watt for the cathodes......... |
| Posted by Dave | September 19, 2014 - 07:23 am |
| Hi Stephen -- Some browsers require you to use the refresh feature to update the page so that you can see the information just posted. No doubt that has happened in your case, as your original post came through fine. In considering your question, an additional approach I thought of was to use a common spade terminal attached to a close tube socket mounting screw, and connect the 5 ohm resistor in each channel between terminal #3 of one output tube and the spade lug. You would likely have to use one spade lug for each amplifier board to make for an easy installation of both resistors. Then, simply run a lead connecting the two spade lugs together, and back to the regulator connection point. This approach works because the mounting screws for the output tube sockets are not grounded at all, but insulated from ground because the sockets mount directly to the circuit boards. Therefore, the socket mounting screws can also be used to mount a spade lug that will be insulated from ground as well. Dave |
| Posted by STEPHEN ZANETEAS | September 18, 2014 - 10:21 pm |
| hI...I did not see my post i wrote before so i will write it again. I need to know where else i can wire the 5 ohm cathode resistors. You chose to mount them, I just want to wire them into the board. What would be a good way to do it? |
| Posted by Dave | September 18, 2014 - 04:25 pm |
| Hi Stephen -- With a diy installation, no doubt you could solder one end of a 5 ohm resistor directly to pin 3 of one output tube in each channel, and use shrink wrap to connect/insulate the other end of these resistors to the lead coming from the regulator/regulator bypass cap/hum balance control connection. If you use this approach, be sure to use high stability 5 ohm resistors, since they will receive a significant amount of heat from the tubes, down through the tube pins, socket terminals, and through the leads to the bodies of the resistors. By mounting the resistors in a remote location away from the tube sockets, this concern is avoided, and stability of value is assured. The other down side of this approach, is that it makes the bias setting procedure more complicated, since there is no easy place to then connect your meter leads. Oh, it can be done. But you'll be forever having to remove the bottom cover to check or make the adjustment. With the resistors mounted topside, not only are they in a cooler location, but the T-strip they are mounted on serves as a meter connection point when setting the bias. Therefore, only the top cover needs to be removed. As to your other question regarding "how did you run your 5 ohm resistors", I'm not sure what you're asking here. If you can clarify your question, I'll be happy to address it. In terms of their operation, they dissipate just under .075 watt under sustained full power conditions in each channel, so a 1/2 watt rating is more than ample -- even when mounted close to a tube socket pin. Thanks for your interest, and good luck with your project! Dave |
| Posted by stephen zaneteas | September 18, 2014 - 12:28 pm |
| hi... just finished wiring the lm337 and 5k pot etc;..question... how else can i mount the 5 ohm cathode resistors to each output tube pair? you used terminal strips but i would rather not. can one end be soldered to the number 3 cathode pin and the other end to the cathode/ground return line?? Also, how did you run your 5 ohm resistors?? |