SIII build from scratch

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colossal
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Re: SIII build from scratch

Post by colossal »

Interesting, thanks!
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AussieTim
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Re: SIII build from scratch

Post by AussieTim »

Hi Guys
Starting to assemble my turret board and found I don't have a couple of resistors that I need. The question is can I substitute 1 watt resistors for .5 watt ones how important is the wattage?
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Re: SIII build from scratch

Post by Daviedawg »

Yes you can use 1 watt resistors. Never ever use lower than half watt on a valve amp build. Never use lower wattage than the schematic calls for. Generally using a higher wattage is not a problem and you may get better accuracy of value and a more substantial look to the build.
There are exceptions to the half watt use such as a discrete board with solid state build where you can use lower wattage for space benefits. But only for low voltage sections.

Dd
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Re: SIII build from scratch

Post by AussieTim »

Siii Complete board.jpg
Hi Guys
I have finished populating my turret board as per Trinity 18Watt v6 Layout v7.
Any positive criticism appreciated I know my soldering is not as neat as it should be and for some reason I couldn't get hold of any 200k resistors so I have joined 2x 100k in series
I,m still working on the chassis cutouts so that is why I have left wire sticking out everywhere
I hope I haven't made too many obvious mistakes
Tim
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Re: SIII build from scratch

Post by colossal »

Tim,

I am away from my graphics tool at the moment so cannot mark up your photo, but you have two green wires coming off the power amp and phase inverter ground bus. You are going to want to remove a section of that bus bar, so that the Phase Inverter ground is its own node...if you follow me. If not, I'll get back with a marked up photo so it is clear what I mean.
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Re: SIII build from scratch

Post by JMPGuitars »

What colossal said. Review the sticky post regarding ground schemes for more info.

Also, the 2 spots where you put 100Ks in series to make 200k, is probably supposed to be 220K, so maybe that's why you couldn't find them?
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Re: SIII build from scratch

Post by AussieTim »

Trinity 18Watt v6 Layout v7(3).pdf
Trinity 18Watt v6 Schematic v8(1).pdf
Trinity 18Watt v6 Schematic v8(1).pdf
Hi Guys
Thank you for your feedback
I built the board exactly like the above layout, working through the layouts and schematics is teaching me how these things work although I am not sure where you want me to cut the bus wire.
M Huss,s original siii had 470k resistors where the 200k resistors are, as do other versions of 18watt amps so I am wondering if this is a deliberate value or a typo.
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geoff 1965
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Re: SIII build from scratch

Post by geoff 1965 »

hello Tim,
one area i can see on the board that might cause problems is the bias caps laying on top of the bias resistors,those resistors get hot and the caps above are going to absorb that heat,idealy you want air to be able to flow around the resistor so they might be better fitted over the caps with a gap between.
also check your B+ wires running underneath the board are clear of the turrets,so in future if you replace any components the heat in the turret won't touch the wires,i used a little epoxy on mine to keep them in place.
regarding the 270/200K grid leaks i would of thought they would just use 470K's for both 6V6 and EL84's but maybe it relates to the lower phase inverter 470R & 22K tail "almost plexi"values? passing through the 270K will lower the signal into the EL84 grids and with 200K leaks your going to have some clean headroom whereas with the 6V6's you've got them in series giving you stock 470K.
i like the look of this amp,some cool features and can't wait to see you finish it!
good luck
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Re: SIII build from scratch

Post by AussieTim »

Thank you Geoff
The bias resistors are going to have to stay where they are, as I chopped the legs too short to change them around but good advice for my next build Ill file that information away for then. I was thinking of maybe putting a hole in the chassis under that end of the turret board and a small piece of mesh on the opposite side in the back of the combo to allow airflow around the inside of the amp. Heat does worry me a bit as I live in a fairly warm climate and jamming tends to become a sweaty affair, but the vent idea is a bit of an Occam,s razor thing with reasonable amounts of beer consumed when the instruments are brought out and as evenings progress sometimes beer does get spilled.
Thank you also on your thoughts regarding B+ soldering there may be some tweeking to get the noise I want out of the thing so point taken, the resistors may just be one of the things that will need to be tweaked
Siii under turret.jpg
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Re: SIII build from scratch

Post by JMPGuitars »

AussieTim wrote:
Mon 10/14/19 6:47 pm
Trinity 18Watt v6 Layout v7(3).pdfTrinity 18Watt v6 Schematic v8(1).pdfTrinity 18Watt v6 Schematic v8(1).pdf

I built the board exactly like the above layout
Ah, I see what they did there. Those resistors can be anywhere between 220K to 470K for EL84s. I have them at 220K on EL34s, and 330K when using an EF86 preamp and EL84 power tubes.
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Re: SIII build from scratch

Post by AussieTim »

Hi Guys
I am picking back up this project after it being unceremoniously pushed onto the back-burner by a couple of health issues that have absorbed a lot of my time in the last year or two,
This is a sIII v6 - Dual Power Tube with Boost rev 8 from Trinity amps
So far I have
Built the turret board and populated it
Bent up the chassis
Come up with layouts for the switching knobs etc and rear panel with the tubes
Sourced and acquired the majority of the parts
Started building a cabinet
Now a couple of questions
What is the usual layout of the lettering on the front panel of a top rear placed chassis on a combo?
Is it so the letters are the right way to read when standing in front of the amp? or are they laid out so that the reader is standing behind the amp.
Are there any problems with mounting the boost and output tube cathode switches on the front panel so they are accessible when playing as opposed to delving around the underbelly of the amp?
Looking forward to hearing from you and getting back into the build
Tim
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Re: SIII build from scratch

Post by geoff 1965 »

Hello Tim,good to see you are back on track.
I used the trinity plexi mk2 preamp on my 6V6 amp and mounted the boost switch on the front panel for ease of access.”but” i’ve just removed it because I was’nt impressed with the the level of boost and it made a very loud pop when switching on or off with the amp on.it simply put in parallel a .68uf cap with the 820R cathode resistor but in comparison yours is different so you might find yours better.
good luck
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Re: SIII build from scratch

Post by zaphod_phil »

Yes, I would prefer to keep that .68uf cathode cap permanently connected - maybe even make it 1uF for a fuller sound.

For a real boost, you would need to add in an extra gain stage. Check out schematics for the Trinity SIII One to see how that could be done.
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Re: SIII build from scratch

Post by AussieTim »

Thanks Phil I am pretty well committed to this version as I have already made up the turret board etc and once I get a head of steam up I want to keep going. I am assuming that I can mod this retrospectively which I will do if I dont like the noise that the thing makes. Being my first Marshall style build and only my third build I want to build it standard for starters.
I am curious why Stephen has gone back to separate channels rather than switched channels as in the first version.
I still would like some feedback on my questions on my last post.
Finalizing my face plate layout this week, at this point going for laser engraved anodized aluminium with a underlying black layer so that the numbers and labels will show up
https://www.trotec-materials.com/engrav ... amark.html black
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Re: SIII build from scratch

Post by AussieTim »

Hi Guys
Getting serious about the layout of the faceplate ready to laser engrave
Does anyone know the diameter of where the numbers sit? I suppose the diameter of the base of the numbers is what I need as I have not got anything I can measure off.
Thank You in Advance
Tim
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