trinityamps.com

Trinity Amps Guitar Amp Forum
It is currently Mon Jul 26, 2021 8:15 am

All times are UTC - 5 hours [ DST ]




Post new topic Reply to topic  [ 11 posts ] 
Author Message
PostPosted: Wed Dec 23, 2020 7:33 pm 
Offline
Friend
Friend

Joined: Tue Nov 17, 2020 2:48 pm
Posts: 10
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


Top
 Profile  
 
PostPosted: Wed Dec 23, 2020 9:46 pm 
Offline
Friend
Friend

Joined: Tue Nov 17, 2020 2:48 pm
Posts: 10
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


Top
 Profile  
 
PostPosted: Wed Dec 23, 2020 10:11 pm 
Offline
Friend
Friend

Joined: Tue Nov 17, 2020 2:48 pm
Posts: 10
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 :/


Top
 Profile  
 
PostPosted: Wed Dec 23, 2020 10:40 pm 
Offline
Friend
Friend

Joined: Tue Nov 17, 2020 2:48 pm
Posts: 10
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.


Top
 Profile  
 
PostPosted: Wed Dec 23, 2020 11:45 pm 
Offline
Friend
Friend

Joined: Tue Nov 17, 2020 2:48 pm
Posts: 10
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


Top
 Profile  
 
PostPosted: Thu Dec 24, 2020 10:02 am 
Offline
Friend
Friend

Joined: Tue Nov 17, 2020 2:48 pm
Posts: 10
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.


Top
 Profile  
 
PostPosted: Thu Dec 24, 2020 2:57 pm 
Offline
Novice
Novice

Joined: Wed Nov 20, 2019 12:22 pm
Posts: 50
Glad you got it working!

Regarding the value of those resistors: in general, you can't really measure components when they are in the circuit (unless you are absolutely sure one side of the component is open). Otherwise, as you observed, your meter will pick up whatever is in parallel with the component and give you unexpected readings.

Regarding the bias issue: do you happen to have 6V6 tubes you can test with? I believe the 6V6 tubes can withstand either setting of the bias selector switch; but the KT-66 tubes can not tolerate being set to the wrong position. In my Triwatt build, I had two problems with bias: the first one, I missed a jumper wire in the bias circuit. I looked at your pictures, and you do have the jumper wire that I missed. But I didn't check all your other connections. What I did to check all my connections was to make a copy of the Triwatt layout, and mark each connection or component with a highlighter as I checked it against my actual build.

My other problem was simply having the bias switch in the wrong position. I was (and still am) using 6V6 tubes, and with the bias selector switch set to the KT-66 position (i.e. in the wrong spot), the max bias setting was actually right at the minimum for my tubes. You seem to have the "mirror" problem as me, so it's possible you read the bias switch backward like I did. See also this post on bias switch clarification.

Good luck, let us know how it goes. We also need pics of the final build and your impressions of tone and sound quality! :)


Top
 Profile  
 
PostPosted: Fri Dec 25, 2020 12:56 pm 
Offline
Friend
Friend

Joined: Tue Nov 17, 2020 2:48 pm
Posts: 10
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!


Top
 Profile  
 
PostPosted: Fri Dec 25, 2020 11:53 pm 
Offline
Friend
Friend

Joined: Tue Nov 17, 2020 2:48 pm
Posts: 10
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


Top
 Profile  
 
PostPosted: Fri Dec 25, 2020 11:59 pm 
Offline
Friend
Friend

Joined: Tue Nov 17, 2020 2:48 pm
Posts: 10
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


Top
 Profile  
 
PostPosted: Sat Dec 26, 2020 11:51 am 
Offline
Novice
Novice

Joined: Wed May 22, 2019 4:26 am
Posts: 60
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!


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 11 posts ] 

All times are UTC - 5 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
Powered by phpBB® Forum Software © phpBB Group