50 Watt Plexi and Zero Loss Loop

[TheFullNelsons]

As a new member I wanted to say hello to the forum. I will be pulling the trigger on a 50 Watt Plexi in the near future with a PPIMV and effects loop. I have never built an amp before so I have been trying to do my homework here on the forum and with George's instuctions. I already owe a significant debt to the wise veterans here as I have learned a ton from reading your responses to other struggling newbies like myself. I was wondering if someone could have a look at the photo at the above URL and let me know if I am on the correct track regarding installing the loop in the 50 watter.

http://www.huronoc.ca/images/50%20Watt%20Loop%202.jpg

I wasn't sure if I should post this here or in the Mods section?

Thanks for your help

David

[SDM]

Hello David, welcome to the forum.

Your drawing is correct (except for switch location, goes near the other loop jack). The loop installs just the same way in a Metro JTM 45 kit as it does in a Metro 50 watt kit, almost the same way as it does in a Metro 100 watt kit . Just as in a Metro JTM 45 though, feeding the loop from the blue circled turret in your drawing (that you will attach the loop kit decoupling resistor too) means you will be feeding the loop it's B+ from the screen supply B+ node rather than the PI B+ node. These B+ nodes, screen and PI, are just swapped around/at opposite ends of the board compared to a 100 watt kit. That said, attaching the loop decoupling resistor to the screen node is 100% fine to do, but you'll simply need to omit step 15 in the loop instructions too.

So drawing is good, just omit/skip step 15 as it is not needed when the loop is fed from the screen node. Went over the same thing for a Metro JTM 45 install the other day, and what I wrote there applies directly to the Metro 50 watt kit as well: http://forum.metroamp.com/viewtopic.php?f=15&t=29858" onclick="window.open(this.href);return false;

Now that all said, and this last bit depends on your power transformer, but the B+ at the blue circled turret in your pic you may find is above the voltage chart range in the loop instructions for your particular 50 watt kit build. If your voltage at the blue circled turret is only a bit above the chart range, say 440V or less, likely you'll be fine to ignore this paragraph here and still use the blue circled turret to connect loop decoupling resistor to, loop board B+ should still be below 320V. If your B+ is higher than that though, above 440V, then you can alternately connect the loop decoupling resistor to any of the turrets circled below in green instead. These are all PI node B+ turrets now, so all three will read the same and a much lower B+ then the blue circled turret. If this turns out to be the case for you, you need to use one of these green circled turrets instead, then you'll just want to include step 15 again of the loop instructions.

Hope that made sense. Ultimately was/am hoping to do individual instructions for Metro 45 and 50 watt kits, but so far have not had either in hand to properly document a loop install. If any questions arise during loop install (or any time during your build), can simply ask again here or shoot me a PM. This probably seems more complicate than it really is, should be a piece of cake to understand and install the loop once you've got the kit up and running first.