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PostPosted: Sun Oct 25, 2020 8:47 pm 
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I just finished my build and I’m not getting the bias readings I should. I measure 4mv regardless of how I set the bias adjustment. I am also not getting any sound, hiss, or any kind of noise out.

I’ve checked connections, looked for shorts, tested continuity, I’m getting 350v from each side of the transformer, but after the first diode on each side the voltage is 146.

Any help or ideas would be greatly appreciated,

Thanks,
Kevin


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PostPosted: Mon Oct 26, 2020 11:58 am 
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K, Are your voltages (VDC) on all the test points for tubes close to correct or all showing voltage w/o the tubes in? Are you measuring voltage after the diodes using VDC range on multimeter? Can you post gut shot pictures using the upload attachment feature? I will look on the schematic again (haven't find the B+ test point, yet). According to docs, B+ should be around 442VDC (higher w/o tubes), so should be around 221VDC on each side after the diodes if those are correct spots for B+ voltages (it's my understanding that Hiwatt circuits are considered to be somewhat different than "normal" guitar amp circuits). If Mitch or Coco chime in, they would probably be able to help more. Hank S.

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PostPosted: Mon Oct 26, 2020 12:29 pm 
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Continued looking at your board photo and am wondering if you may have switched D5 (1N5355B) for D6 (1N4007)? The four diodes (D1-4; 1N4007's) should be feeding into D5 (1N5355B) in that 5 diode network near the right end of the board (looking at the layout). The lonely diode (D6) near the electrolytics a little farther up should be a 1N4007 diode. I really couldn't see the markings, but D6 looked fatter than the other 5.

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PostPosted: Mon Oct 26, 2020 4:54 pm 
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Thanks for your help, yes I did swap the diodes. I would not have caught that. I can wire up a guitar and do residential wiring, but this is my first time building an amp.

Thanks,
Kev


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PostPosted: Mon Oct 26, 2020 9:45 pm 
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You're braver than me! I would have picked a easier one for my first amp :thumbsup: Post if switching the diodes back to their correct locations makes any difference. I still haven't figured out where to measure B+ on the Triwatt. :hmmm:

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PostPosted: Tue Oct 27, 2020 1:47 am 
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It helps to get the right parts in the right places! Lots of diodes look similar.

Is the amp working properly now?

On a Triwatt, you can measure the main B+ where the three diode cathodes join together near the 2K5 5-watt resistor at the edge of the board.
This is also called HT1 and you can measure it at the positive terminals of the 50/50uF filter capacitor that's closest to the output tubes. The reading there depends on the setting of the KT66/6V6 switch, though. It will be lower than the main B+ if the switch is in the 6V6 position.

HT1 follows a somewhat convoluted path through the Standby switch and the KT66/6V6 switch. It eventually ends up at the 2K5 5-watt resistor at the edge of the board, then it heads to the center tap of the output transformer.

You can measure HT2 and HT3 at the positive terminals of the other 50/50 uF filter capacitor. HT2 is on the terminal that also has a 220K resistor. HT3 is on the terminal closest to the front of the amp.

This is all shown on the layout drawing.

The Triwatt looks like it's one of the more challenging amps to build. It's not that bad, though. As with anything, just take your time and follow the instructions. Make sure all the parts and wires are in the right places. Make good solder joints. Keep the wiring neat. Then check everything, double check it, then check it again.


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PostPosted: Tue Oct 27, 2020 10:11 am 
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Not yet, I’m waiting for parts. I tried desoldering, but it was taking way too long to heat up and I didn’t want to damage any of the parts near by. I wasn’t very good at reading schematics, I am much better now and I’ve learned a lot about tube amps, so I’m not disappointed or discouraged. I was meticulous about testing each part and triple checking each connection since I knew I would miss something. I’m just happy something didn’t burn up when I powered up. I’m hoping that after I change the diodes the amp will fire up and make noise, but I’m expecting there will be more work ahead. Once I get this amp working well, my next project will be an OSD.


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PostPosted: Tue Oct 27, 2020 9:07 pm 
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The OSD is a challenging amp to build with all the the relays and switches. It's good to get familiar with reading schematics and how they relate to the layout drawing. Once you know the symbols, it's actually easier to see what's connected to what and what the functions of the components are on a schematic rather than on a layout drawing.

While you are waiting for your parts, you can use the time to keep checking your wiring. I like to refer to the schematic and use an ohmmeter to make sure everything that's supposed to be connected actually is connected and there aren't any accidental shorts. Some people make a copy of the layout drawing and use a hi-lighter pen to mark the components and connections as they check them.

At Hiwatt, they used red ink to mark the actual turrets and the other connections as they did their checking. You don't have to go that far, though!


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PostPosted: Wed Oct 28, 2020 10:00 am 
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mitch m wrote:
Then check everything, double check it, then check it again.


...and check again! :)


Twixpickups wrote:
so I’m not disappointed or discouraged.


That's the most important thing! Once you get it all worked out, you'll be rewarded with a fantastic amp that you won't want to stop playing.

I was in a somewhat similar situation as you when I built my Triwatt. I had done a number of DIY audio electronics, but all of it solid-state. The fundamentals with a tube amp are the same, but it certainly "felt" different than anything I'd previously done.

I checked everything countless times; I even made a copy of the layout diagram, and highlighted connections on it as I checked them against the actual build. And yet I still managed to miss one small connection in the bias circuit, which caused the power tubes to red plate immediately. I somehow managed to overlook this countless times previously, including during the layout-highlighting exercise!

And even after I had it up and running for a while, did I realize had the kt66/6v6 bias switch in the wrong position!

But I think it's all good now. I find this amp has quite a bit of tonal versatility. The EQ controls offer a lot of control. And I find that when using the "link" input, there's a surprising amount of tone-shaping available by simply adjusting the normal and bright volumes. The boost stage adds another dimension to the amp's capabilities. Throw in output tube flexibility, and you've got an amp that really covers a tremendous amount of ground.


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PostPosted: Thu Oct 29, 2020 8:27 pm 
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I got the parts today, put them in and the amp worked surprisingly well. It even sounded pretty good with the crappy tubes I had laying around.

There are still some issues:

1. The presence control doesn’t seem to do anything.

2. The treble control makes a hum when it’s turned all the way up.

3. The overdrive control board doesn’t turn on the overdrive. The led lights up, but there is no increase in volume. The diodes are in correctly and are the proper ones. The capacitors were installed with the + leg on the +. I am likely going to remove it and see if the overdrive works then.


Thank you Hankules, Mitch, and Matt for your help and advice.

Kev


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PostPosted: Sat Oct 31, 2020 6:05 am 
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Glad you got the amp more or less working.
According to the layout drawing, the treble control has a couple of long wires heading to the board. Try moving them to different positions to see if that reduces the hum.
The presence control has a shielded cable running to it. Make sure there aren't any shorts from the center conductor to the shield.
Same with the wiring to the relay board. Can you tell if the relay is clicking on and off? If so it's probably just a wiring problem between the relay board and the overdrive control. Good idea to see if the overdrive works with the relay connections removed and the push/pull switch is wired as shown on the main layout drawing.


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PostPosted: Sun Nov 01, 2020 3:46 pm 
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So I disconnected the overdrive board and wired the overdrive switch as shown in the diagram. The overdrive switch worked almost as expected.

1. When the overdrive potentiometer is turned past about 9:00 it has an extremely high pitched squeal. There is also a low hum also only when turned past 9:00. While I would expect some noise as the potentiometer is turned up, this comes on suddenly. Moving the wires does not eliminate the noise.

I reconnected the overdrive board as pictured.

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The way I have it hooked up is not the way it is on the overdrive board diagram. The foot switch only works when the overdrive switch on the amp is pulled out. The foot switch then turns off the overdrive. I have no idea why this works, but unless there is an issue with wiring it this way, I’m inclined to leave it.

The presence control seems to be doing something, but it super subtle.

The treble buzz seems To be greatly reduced with wire position. I still find it odd that it only happens when the potentiometer is all the way up.

Would shielded wire make a difference?

Thanks,
Kev


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PostPosted: Tue Nov 03, 2020 12:17 am 
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I changed the wires from the overdrive board to v2 to shielded wire and moved the other shielded wires to the top of the board and the amp worked perfectly. That was until I installed the tube effects loop, now there’s quite a bit of noise and when bypassed there’s no guitar signal and a loud hum.


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PostPosted: Sat Nov 07, 2020 1:40 pm 
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So I am a little frustrated, with the overdrive board and effects loop removed, the amp is fantastic. I can’t get the overdrive board to work properly, it’s squealing at higher gain settings. I’ve tripple checked the wiring and construction and can’t find anything contrary to the diagram. It sort of works when I have it wired as pictured. When the overdrive knob is pushed in the foot switch boosts the signal when the overdrive switch is pulled out the foot switch boosts the overdrive signal.

The tube effects loop is super noisy and super loud. If the board is tapped with a chop stick you can hear it through the speaker. The board was pre built all I had to do was solder in the jack and variable resistor for the loop level. It’s hooked up correctly and the bypass works great. Only when the effects loop is engaged is it very noisy, even when turned all the way down.

I appreciate any help or advice.

Thanks,
Kevin


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PostPosted: Mon Nov 23, 2020 12:07 am 
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All done!
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PostPosted: Wed Nov 25, 2020 11:56 am 
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Looks great! Did you get all your technical issues worked out? Everything now working reliably and consistently?

What kind of cab/speakers are you running it into?

What's your take on the tones?


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