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PostPosted: Wed Dec 23, 2020 7:33 pm 
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Hi everyone,

Just completed the assembly of my Triwatt kit. Did all the tests as per the manual. Everything seemed ok but I get no sound and the bias seems off and I get no sound at all.

Here are my voltage readings:

Main: 125.6 VAC
B+ (Tubes installed): 454 VDC

Tubes:
V1: P1 151.5v; P2 0V; P3 1.2V; P6 131.4V; P7 0V; P8 0.9V.
V2: P1 195.8V; P2 0V; P3 1.1V; P6 124.7V; P7 0V; P8 0.6V.
V3: P1 274V; P2 66.6V; P3 70.7V; P6 187 8; P7 0V; P8 1.5V.
V4: P1 270V; P2 70V; P3 73V; P6 273V; P7 64V; P8 74V.

I have KT66 tubes and the bias switch is set to the KT66 position.

I checked all my ground routes and all the board jumpers for continuity and everything is good.

My bias readings are as follows: when the 10K pot is all the way counter clockwise, I get 56mV. When the pot is all the way clockwise I get 39mV on one side and 36mV on the other side (the KT66 are paired). I am not sure how to see this. It is not like my other amps where I get my lowest readings on the counter clockwise position.

Another awkward item is with 3 resistors. I checked all the values of the installed resistors and 3 are off. The color code for the value is right and I checked all the resistors with my ohmmeter when I installed them. But the values of these 3 are now off:

The 560k reads 400k;
The 620k reads 132k;
The 180k reads 140k.

They all look ok (not burned) and they have no weird smell like bad resistors can have. Can this be normal after installation?

And... I get no sound at all. Checked the guitar, speaker, cables, guitar volume, etc. No sound.

Any suggestions would be very much appreciated.

Cheers,

Juan


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PostPosted: Wed Dec 23, 2020 9:46 pm 
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Here are some pics of the wiring. Sorry, not sure how to make the links show the pics.

http://imgur.com/gallery/H6QadHz

http://imgur.com/gallery/0apzJFV

http://imgur.com/gallery/YtYa5Js

http://imgur.com/gallery/CLgsekx


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PostPosted: Wed Dec 23, 2020 10:11 pm 
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Just noticed I was missing a ground connection on the speaker output jacks. It is in the guide but not in the layout. That makes sense. But I still don't get sound. I do get a slight hum at very high volume, almost max volume, which seems pretty normal with any tube amp.

But still no guitar sound :/


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PostPosted: Wed Dec 23, 2020 10:40 pm 
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After checking all the connections I checked for potential short circuits with the coaxial cables. I actually do have 3 short circuits to ground on the input jacks and on the OD pot. Will correct those and revert back.


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PostPosted: Wed Dec 23, 2020 11:45 pm 
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It seems like the coaxials on the input jacks and the OD pot were ok (not a short) but at least they have a cleaner connection now. Now there was a short circuit to ground on the coaxial cable from the volume pots. I corrected that and... I got sound! :)

Noise seems ok. Will check better tomorrow. But sounds pretty good :)

I would still be interested in getting some views on the bias (it is set at 40.7mV and 39.6mV. That is the minimum I can get to.

I would also appreciate any feedback on the resistors with a lower value reading. Could any of these affect the amp's tone?

Thank you!

Juan


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PostPosted: Thu Dec 24, 2020 10:02 am 
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So I have been reading and it seems the lower value on the resistors is normal because of the circuit's parallel resistance. Sorry for the newbie question.


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PostPosted: Fri Dec 25, 2020 12:56 pm 
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Thanks a lot Matt for the advice!

I got a pair of matched 6V6 to test as you suggested. I will try them out later today.

So far I really like the tones. I really like how you can tweak the tone using the link input and setting the volumes of the normal and bright channels.

I tried the OD with a 12AT7 on V4 and compared it with a 12AX7. The OD is much better with the 12AX7 as you would expect. The amp is very sensitive to touch. Playing with a guitar with humbuckers and picking hard can get to a slightly dirty clean (no OD). I have not tried louder volumes with single coils (which is what I really want this amp for).

I will post some pics in a bit.

Thanks again for the tip!


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PostPosted: Fri Dec 25, 2020 11:53 pm 
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So I tried the pair of 6V6s and I could check the bias switch. It seems to be in the right position. It is not bad at all actually, testing back with the KT66s I get 36.7mv and 38mv at the lowest setting but that is within the range of the acceptable measures (30 to 40). I still get the lower readings turning the pot clockwise vs higher counter clockwise but the readings are good.

Thanks again Matt for the tip!

Cheers


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PostPosted: Fri Dec 25, 2020 11:59 pm 
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Here are some pics of the finished amp:

http://imgur.com/gallery/Rax0d28

http://imgur.com/gallery/UaZn4gm

http://imgur.com/gallery/4QWOHLV

http://imgur.com/gallery/eSTF6Ga


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PostPosted: Sat Dec 26, 2020 11:51 am 
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Location: The Netherlands
Great build mate!

Glad that you got it working!

Next thing to try is a big muff and single coils, tonal heaven!


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