trinityamps.com

Hi, this is my first post to this forum. I've build a 5F2A and a 5E3 Tweed but this is my first 18 Watt project using the Trinity Kit. I would like to put screen resistors and grid resistors on my EL84 as Kevin O'Connor recommends in TUT-3. Could the forum confirm the best approach for this on the Trinity 18Watt sIII and and experience they have with resistor values. Kevin O'Connor recommends a 1K Screen Resistor on the EL34 and my 5E3 has a 1.5K on the Grid Stop Resistor. For the EL84 please confirm that the screen resistor should go on pin 9 and the grid stop resistor should go on pin 2. Looks like I can use pins 1 and 6 as supports to mounts these resistors.
Thanks from Newbie!

The sIII already has grid stoppers. They are the 8.2Ks on pin 2 . This is the "recommended" value for El84s. The screens are pin 9. So yes You could use pins 1,6,or 8 as "support pins" for the added screen resistors.
Some people will connect these resistors directly to the tube sockets with as short a lead as possible which is what I did with the screens but i wired the grids as shown in the diagrams.
Stew

The screen connection is technically a grid. I have heard that you should do the same thing you do with screen grids as control grids, with getting the resistor as close as possible to the tube. How much of a difference (if any) does it make? Try it and let us know...

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http://pdfelectronics.com

Lesson number one is not to believe everything you read in KoC's books. He's a *real* nice guy, but there are actually caveats to a number of things he says. A few of his statements are actually quite debatable from an Electronics Engineering theory POV. Now it so happens that he is quite right that grid resistors (including screen grid resistors) should theoretically be mounted right at the tube pins. However, the sIII is a proven working design, as are all the Marshall 18W variations, and there's really no need to change this aspect of it. Never forget one of the most important rules in electronics is the "If it ain't broke, don't fix it" one.

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Great tones come in small glass jars!

Thanks Stew
Thats exactly the advice I was seeking.
I really appreciate the input from the forum.
Thanks
Rags

Hey Gang,
Just wanted to let you know that I completed the Trinity 18Watt sIII this weekend.
What a great amp!
I did use 1.5K screen resistors on V4 and V5. I used the pin#1 as a support for the resistor.
The Trinity guide was handy for a couple of the areas on the layout that were confusing. Namely the wiring of the speaker jacks and the wiring of the input jacks.

Highly recommend the sIII for blues sound. The boost switch really lets you crank rock n roll when needed. My 1960 Reissue Les Paul never sounded better!

Until next time, keep sniffing that solder
Rags

Congrats Rags!!
Stew