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Just finished my Triwatt yesterday, no sound.

Info, mains voltage 116V. Tubes were in, 12ax7’s in all pre’s, 6v6’s for power. Heaters are all correct voltages, 6.4VAC, on all tubes.

Did the PT pre-hookup test, voltage was 680VAC on the secondaries.

1) Bias adjustment works backwards:

Tried the bias switch in both positions, same results either way.

Looking at switch as on layout, lever towards right (6v6 side so should be on KT66), starts at 22mV and goes down to 10.5mV as it is turned fully clockwise

Lever opposite, starts at 10.8mV and goes down to 2.3mV.

Bias pot is wired as on layout, which is opposite than in instructions.
I'm guessing that I need to rewire to match the instructions?



2) The following numbers are after I found that I had installed a diode in backwards on one leg off the off the center tap (

The amp had been powered up with diode backwards, voltages were little changed except V4, pins 1 and 6 and V5, 6 pins 3 and 4 all increased about 30V to what is listed below. When pulling the diode to re-orient I got a spark off the turret.

Since the caps are charging to about the correct values is the diode OK?

Pin voltages (DC):

V1 (P1) 150, (P2) 0, (P3) 1.1, (P6) 132, (P7) 0, Pin 8: .95

V2 (P1) 193, (P2) 0, (P3) 1.12, (P6) 118, (P7) 0, Pin 8: .7

V3 (P1) 272, (P2) 67, (P3) 72, (P6) 193, (P7) 0, Pin 8: 1.45

V4 (P1) 403, (P2) 72, (P3) 77, (P6) 405, (P7) 64.1, Pin 8: 77

V5 (P1) 0, (P3) 444, (P4) 418, (P5) 43, (P6) 43, Pin 8: 8.3mV

V6 (P1) 0, (P3) 444, (P4) 417, (P5) 43, (P6) 43, Pin 8: 8.2mV

Cap cans, ground to either positive leg:

Can closest to pots, 404VDC both legs

Can closest to tubes: 435VDC both legs

I’m getting a pop through the speakers when checking voltages on V4, pins 1 & 6, V5 & V6, pins 5 and 6. No pop when checking grids.

No guitar through the amp.

Components to V4, pins 1 and 6 look to be correct, don’t know why they are so out of wack.
I read that the 340 on V4, pin 9 is a typo on the instruction voltage chart, it is correct heater voltage.

Can I check the shielded runs by checking continuity of center core first, then see if I get a resistance reading from shield to center (reisitance meaning the core is shorted to the ground)?

Will be checking the circuit (again) tomorrow after a rest so I can give it a "fresh" look.

Suggestions?

And THANKS

Same thing happened to me. Turned out I had missed a jumper on the board. Can't recall which one it was - there's so many of them! But I still like the layout...much easier to work on, just more.

Don't tell me you were working on it without draining it!?

Revv, it was unplugged and draining the caps, I was just a bit quick on the iron Very small spark, about a good static zap, noticed it because I was staring at the joint.

Anyone have any comments on the out of wack V4 voltage or the "right" way to hook up the bias pot??

Edit:
Thanks to joeyvelour's idea, checked the shielded leads, found that the V1 to brilliant input jack and the V3 to Master leads were shorted

Also found that I'd left off the OT to board connection (orange lead)

Continuing to check rest of the connections

The orientation of the bias pot is a moot point, since as the bias voltage increases the bias current decreases.

Lack of sound is often caused by a missing link somewhere on the board. I'll have a look at your V4 voltages. That may also be a symptom of a link missing. Also, are you using a 12AT7 or a 12AX7 in V4. If you use an AX7, then the voltages will certainly be different.

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ZP, thank s for the reply

Pre's and the PI are 12ax7's.

I have to replace two of the shielded leads due to shorts (V1 to brilliant input jack and V3 to Master vol pot)

The OT (or impedance selector) to board lead was missing

Max I can get out of the bias pot is 22mV (ranges from 10.5mV to 22mV with bias switch one way, from 2.3mV to 10.8mV switched opposite).

Still checking rest of connections.

Again, thanks

Updated info after SOME corrections noted above
Info, mains voltage 116V. Tubes were in, 12ax7’s in all pre’s (including PI), 6v6’s for power. Heaters are all correct voltages, 6.4VAC, on all tubes.

Pin voltages (DC):

V1 (P1) 149, (P2) 0.1mV, (P3) 1.16, (P6) 130, (P7) 0.2mV, Pin 8: .93

V2 (P1) 189, (P2) 0.1mV, (P3) 1.11, (P6) 116, (P7) 0.1mV, Pin 8: .69

V3 (P1) 267, (P2) 66, (P3) 70, (P6) 189, (P7) 0.1mV, Pin 8: 1.42

V4 (P1) 293, (P2) 70, (P3) 72, (P6) 280, (P7) 62.5, Pin 8: 72

V5 (P1) 0, (P3) 439, (P4) 407, (P5) 41.4, (P6) 41.4, Pin 8: 9.0mV

V6 (P1) 0, (P3) 439, (P4) 407, (P5) 41.4, (P6) 41.4, Pin 8: 9.0mV

Cap cans, ground to either positive leg:

Can closest to pots, 400VDC / 410VDC

Can closest to tubes: 441VDC both legs

I’m getting a pop through the speakers when checking voltages on V3, pins 2, 6 and 7; V4, pins 2 & 7.

No guitar through the amp.

Bias adjustment works backwards:

Tried the bias switch in both positions, same results either way.

Looking at switch as on layout, lever towards right (6v6 side so should be on KT66), starts at 9.0mV and goes down to 2.3mV as it is turned fully clockwise

Lever opposite, starts at 20.2mV and goes down to 8.0mV.

Getting closer Voltages are in the right ballpark except for bias adjust.

So it looks like the signal is getting lost between V2 and V3. So that's where you need to check some more. Also you will need a 12AT7 in V4 to come up with meaningful voltage readings.

_________________
Great tones come in small glass jars!

Found two more errors:
Had the lead from the 3k3 resistor on the presence pot going to the 81k carbon comp (R31) instead of the 100n cap (C13)

also had the jumper between 2k2(R25) and 7k5(R36)

I now get noise when I check voltage on V4, pins 2 and 7, V3 all pins except heaters and V2, pins 1, 2, 6 and 7

Still no output

I assume my problem is now between V1 and V2

The voltages with the 12ax7 are real close to the voltage chart, V4, pins 1 and 6 are a bit high but I assume that's the 12AX7 instead of the 12at7

Any idea why my bias voltage is so low? I've gone over that a few times including comparing parts visually with your board and I can't see a difference.

Again, thanks

IT'S ALIVE

Only one problem left, bias range is still way low

Figured out the final issue from yesterday

Triple checked all the connections again this morning, couldn't find anything else THEN I remembered that the last one who played my guitar I was using ('56 Dano reissue) was my nephew, who ALWAYS TURNS THE VOLUMES COMPLETELY OFF WHEN HE'S DONE

DOH!!! Turned up the guitar volume and IT WORKS!!!

Now if anyone has any ideas about the bias issue????

Congrats on getting the TRIWATT to work. Way to hang in there.

The bias current looks low (you said mv but sure you mean mA actually

What is the bias negative voltage inside the chassis at the diode feeding the two bias range resistors?

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

Thanks Stephen

Voltage at the juction of D6 and R43 / R44 is 121.7VDC, mains is still 116 VAC.

Can't believe how quiet this thing is compared to the SIIIv6.
I can already tell my nephew is going to want one , the reason he always turns the guitar volume down is that he doesn't like the hiss on his sIII (it's not bad, it just bothers him for some reason.)

I had the same problem with the bias voltage. I think I mentioned it in my build thread. Don't recall what I did to fix it...

Found it. From my build thread...

"I have the biasing issue fixed. It was the bias cap ground. It was there & had continuity. Guess it was a bad solder job on my part. Biasing perfectly now. "

Emohawk, thanks
I'll check on that tomorrow! I've checked that everything was there and that there is continuity (it was and there is) so it has me a bit stumped so your idea is what I've been looking for.

Hope it works for ya bro. Don't know for sure if the problem with mine was with the amp or the guy biasing it!

Reflowed all of the joints, no improvement.

JV suggested that I check my voltages against what is listed on the schematic.

On the 6v6 setting, bias pot adjusts from 3.0mV to 11.0mV
On the KT66 setting, bias pot adjusts from 10.4mV to 23.3mV
Mains voltage is 116.8VAC

Junction of D6/R45/C22, schematic says should be -54VDC, I have -50.3VDC

Junction of R45/R46/C23, schematic says should be -45VDC, I have -39.6VDC

These look to be about right with the mains voltage being 116V

Any chance that the adjustment pot may be off? Any way to check it?

If I unsolder the connections, what shoould the pot range be?

I'm not planning on using KT66's for now so I can use the switch in the KT66 position to dial in the 6v6's, but I'd like to get to the bottom of this.

Just checking- what are tre values of the bias range resistors we supplied? 620K & 180K?

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

That's what I measured before I put them in.
Color codes are:
180K resistor is marked brown, gray, yellow with gold band.
640K resistor is marked blue, red, yellow with gold band.

Want me to lift the leads off the bias pot and get a measurement?

If you measured them, they should be OK.

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

The mV you measure at the test jack points depends on the power tubes themselves, and will vary somewhat between individual tubes. When working on the prototype Triwatt we tried out as many different types of 6V6s we could get our hands on, as well as some different types of KT66s, and tweaked those resistor values, so that the tubes would bias somewhere near centre travel on the bias pot. The bias circuit itself is also a well-known and proven one. However, there's always the possibility that some tubes may bias nearer one end of travel or the other. If you're worried at all in the case of your amp, you can always slightly alter the bias resistor values yourself. The 180k resistor provides bias voltage for the 6V6s. Using a higher value will give lower bias voltages - hence more mA current and mV on the test jacks - and vice-versa. The 620k resistor in parallel with the 180k gives the higher bias voltage required by the KT66s, and the same principle applies with that one. Larger value = warmer (more mA/mV), lower value = colder (less mA/mV).

_________________
Great tones come in small glass jars!