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Hi All, new to the forum and just finished building my 18 watt sIII. Fired it up yesterday following the instructions and got it going just fine. Did some tweaking with tubes and its running with a JJ Rectifier, NOS Telefunken EL84s with a mix of Mullard,RDF and Telefunkens in the Pre-amp stage. Pics to follow.

Here’s how my voltages came out

V1 P1-160 P3-.85 P6-160 P8-.82
V2 P1-178 P3-1.56 P6-261 P8-178
V3 P1-205 P2-47 P3-70 P6-202 P7-49 P8-70
V4 P3-10 P7-341 P9-329
V5 P3-10 P7-344 P9-329
V6 P1-302 P3-354 P7-303

Boost Mod problems when it’s engaged and the gain is close to maxed the amp becomes unstable, it appears to pushing the amp into cutoff. Did a double check on everything and all the resistors, caps and wiring appear to be in order. Did anyone out there have a similar problem.

Second concern is the amp seems to have quit a bit of hiss when the volumes are pushed past 6-7. Is this normal? Up until around the 6 position the amp is really quiet. When compared to my Allen Accomplice when its maxed out the sIII is allot noisier. Just looking for a bench mark here.

Conclusion after a short time of playing around with it. When maxed it has probably enough gain on either channel to suit my style of music. Right now it pumping through a Crate Speaker I took out of an old amp I had since I really haven’t decided on a speaker yet. Out side over the hiss even with the Crate speaker it sounds great. It’s got the Marshall roar without blowing out my hobby room walls. Outside of the hiss at higher volume it just seems to blossom as you turn it up, not so much getting louder as it gets bigger, amazing for a single 12 speaker. Great Amp even with the few bugs I still have.

JGK

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JGK

Hiss is a characteristic of carbon comp resistors. Some is normal & you'll hear it but not above the roar of the amp at those levels!

Unstability at max gain, boost on - I havent heard about this. Is it oscillating, howling or what are the symptoms?

You can try it without either the boost resistor or the boost cap.

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

When its on an I push the gain on the TMB side the amps starts cutting out which I assume is the tube getting too much voltage? Although the voltages I took seem close to trhe ones in the instuctions. JGK

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JGK

try bypassing the switch in case that's the problem

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Thanks

I'm just getting going here and I will check out the switch. I'm sure I will be doing some fine tuning in the future but I'll out of town for the next week before I get too involved. Overall I am very happy with what I've heard so far. I've aways been a fender guy for 35 years anyway and playing on the sIII I'm getting a whole new world of great sounds. JGK

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JGK

Hey, no problem. Post some pics if you can. (just link to them)

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Here's some pic's
http://s183.photobucket.com/albums/x228 ... tt%20SIII/
While it fired up and I've been playing it now I have found another problem which is the tone stack in non funtioning on the TMB side. I would assume that I have a bad ground somewhere in there or a wire in the wrong place, this also is probably part of the boost problem. Thanks for the feedback I will trouble shoot tomorrow. JGK

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JGK

Went through the wiring today redid some connections that looked questionable. Traced all my wiring with the diagram, the switch and played it somemore. The boost is still screwed up I'm not sure why as it works great until it hits the 8-10 possition then its begins to squeal and cut off, so its only at very high gain that this happens. I've changed tubes both new and NOS and its still the same although I did try a 5751 which gave the amp some improved headroom and did not squeal when the boost was maxed.

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JGK

When you get a squeal with high gain, it is sometime the OT polarity.
Try reversing the secondary leads going to the tubes & see if that makes it better or worse.

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Thanks I'll give that a try over thanksgivng since I will be out of town for a while. Thanks for the input. JGK

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JGK

Hi all just got around to sitting down and do some trouble shooting and testing the amp out. I'm still getting the squealing on the boost and the tone controls still don't work I can set them at 0 or 10 and they have no effect yet everything else works fine. I checked the voltage on the pots as per the layout diagram and have 0 there. Not sure where to start with this again.

I checked all my wiring and it appears correct when referenced to the diagram. I removed and rewired the tone controls to in case I had problems from wiring them underneath the lip. I switched the OT polarity wires and it was worse than before so I put them back as they were. Changed and compared pre-amp tube again all 12ax7s some seem to let me kick up the gain a little higher befor it starts cutting out. The boost goes into a high pitched squeal around 8-9 and then cuts out.

additionally I changed power tubes with a set of sylanias and a set of Hamond el34s I had laying aound my voltages on P& dropped a little 337 and 341 with the hammonds (amprex made in holland) I'm assuming and I left them in as they sounded really great so left them in.

In closing I'll get the bugs worked out as time goes on and I am by no means unhappy since the amp sounds killer with the screwed up tone stack and the boost. I would have to say the plexi side cops a great grind with considerable sustain while the other channel is a bit more bluesy. I dug out my HB equiped tele and was amazed at how quiet it stayed even at higher levels its quit a bit nosier with my single coil Strat but they are unsheilded. I'll try and post some more pics tomorrow JGK

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JGK