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That's some heavy-duty shielded cable you used!

The wiring looks OK. As you said, just check several times to make sure everything is connected properly and there are no accidental shorts. Then follow the start-up procedures in the manual.

A good tip that has been mentioned lots of times is to make a copy of the layout drawing and use a highlighter pen to mark the wires and connections as you check them. On original Hiwatts, they used red ink to mark the actual connections as they did their checking. You don't have to go that far, though.

Looks like the secondary side of your output transformer is wired properly. There should be four wires - a black one going to the ground lugs on the speaker jacks and the green, yellow and orange ones going to the impedance selector switch. The primary could have five wires. The red one goes to B+, brown and blue go to the output tubes. The blue-white and brown-white are a different impedance winding on the primary. They aren't used, so just cap their ends with heat shrink tubing. You can coil them up out of the way or tie them to the brown and blue.

No problem. I knew what you meant. Good luck with the check out and mounting the amp in the cabinet. It should sound good with the Reeves Vintage Purple speaker.

Make sure all the resistors are the proper values in the bias circuitry for the output tubes. Did you check them with an ohmmeter before installing them? Sometimes brown, red and orange color bands on resistors can look similar.

With the output tubes removed can you measure the bias voltage and see it changing as you rotate the bias pot?

Was a speaker attached when you did the testing? Could be the amp is oscillating and you would hear it on the speaker. If so, reverse the connections from the output transformer to the anodes of the output tubes.

Yes, without the output tubes installed there should be 0 volts at the bias test points

But you should see about -54 volts at the junction of D6/R45/C22 and it should be steady.

At the junction of R45/R46/C23 the voltage should be closer to -45. It should vary with the setting of the bias pot, but once set it shouldn't tend to go towards 0.

If your multimeter checks diodes, make sure D6 is OK. Also make sure all the connections in the bias circuitry are good. Check them for continuity with the multimeter probes on the actual leads of the components, not the turrets.

Glad you found the problem. That little jumper is hard to see on the layout drawing. It would pretty much shut down the bias circuit if it's not there, though.

The voltages look good. Close enough to not indicate any problems.

You could try changing the 180K resistor in the bias circuit. If you want to run KT66 tubes the bias will probably be low for them too.

As an experiment, if you have a 1Meg resistor you could clip or tack-solder it in parallel with the 180K and see what that does. That will reduce the 180K down to about 150K so you should have more bias range.

Sounds like you are having lots of fun with the Triwatt! Congratulations on a successful build.

The pictures look great. The cabinet looks very authentic with that tolex and grill cloth.

I built a couple of Hiwatt clones a few years ago - a very authentic reproduction of a 50-watt DR504 with EL34 tubes, and a 30-watt version with 6V6 tubes something like the Triwatt. They have lots of clean headroom and can sound very "precise" as you said. But to really get the full effect you have to crank them up! I thought they sounded good, then one day a guitar player a lot better me played my 504. We cranked it and it sounded fantastic! It was a totally different amp compared to how it sounded with me playing at "polite" levels. So with these amps, volume and playing style play a big part in their tone.

Here's a picture of the chassis for my 504.



I have a Large Beaver and a Silver Pony too, and they work well with my "Hiwatts."

It's good to have an assortment of the common values for resistors and capacitors on hand. You can start with the parts for the mods suggested in the manual.

Congrats on the successful build.

For the bias, make sure your switch is set to 6V6 position (lower B+ & Bias voltage position incorporating the Zener diode and 180K bias resistor, and the correct bias resistor. If it is still low, you can make the voltage MORE negative by adjusting that resistor to say 150K. Just Remember that the KT66 position puts the two (180K//620K == 140K) in parallel to obtain a higher bias voltage.

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

The voltage at the cathodes of the preamp tubes is very low, around 1 or 2 volts. So electrolytic capacitors rated at 50 volts would be suitable.

The way I read it, the mods suggested specify what goes on the cathode of V1.

V1 Pin 8 -Townshend/Who CP103 1k5 + 64uF
This looks like it's the existing 1k5 plus a new 64uf in parallel.

V1 Pin 8 -Jimmy Page amp 2k2 + 100uF with additional parallel 1k5 resistor
This looks like it's the existing 1k5 plus a new 2k2 and a 100uF all in parallel. You could use an 890-ohm resistor, but that's not a standard value and even if you got one it would be harder to go back to the original configuration if you don't like the mod.

V1 Pin 8 -SAP DR 103 2k2 + 100uF (no additional resistor)
This looks like the 2k2 replaces the 1k5 and there's a parallel 100uF.

V1 Pin 8 -Late '70s, Late '80s and OL/Lead 1k5 + 150uF
This looks like it's the existing 1k5 plus a parallel 150uF.

The rule of thumb with tube amps is the voltage can vary + or - 10%. If it's 20% over at V4 pin 6 that's starting to get on the high side. The voltage at pin 1 of V4 is good so it's just variance with the tube and not a problem with your circuit. You could try a different 12AT7 there if it bothers you, but the higher voltage isn't exceeding the tube's specs so if it sounds good I wouldn't worry about it.

Thanks for the compliment about my DR504. It was actually my second tube amp project. The first one was a Trinity TC-15 I built about a year earlier, but I had been building electronic projects for over 30 years by that time. The assembly work for the original Hiwatt amps was contracted out to an outfit in England that also did work for the British Navy. The wiring was very neat and close to military specifications. I tried to emulate that as closely as possible when I built mine. Also I started with a fairly big chassis, like the originals had, so it was easier to keep the wiring from looking cluttered.

Here's a picture of the outside of the chassis.

Mitch, did you loom the wiring on the mains and power transformer wiring or are those cable ties? Curious minds (mine) would like to know . In any case, sure is "priddy" (Okie for pretty).

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"The only problem with being retired is you never get a day off"

Thanks, Hank. The original Hiwatts used cable lacing and plastic tubing to bundle the power and transformer wires, so I did that too. Also like the originals, I attached all the fly-off wires to the underside of the circuit board. It sort of looks like the board isn't wired to anything yet in the photo of the chassis interior I posted earlier, but that's the completed amp.




I'm happy to answer your questions, but this is sort of hijacking Matt's post about his successful Triwatt build. I have lots more pictures of my DR504 project and I can post some of them in the Dressing Room section if anyone is interested in seeing what a Triwatt's big brother looks like.

Sorry, Matt I just wasn't sure from Mitch's first pic and couldn't tell what I was seeing. Mitch, YES! Always looking for techniques

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"The only problem with being retired is you never get a day off"

Looking at the schematics, a TC-15 is pretty close to a DC-30 running at half power. So it should sound pretty much like your Dizzy 30 with two of its output tubes shut off. I still have my TC-15 and I really like it, but I haven't played it too much lately. I also have a Trinity Tweed Deluxe that I play most of the time.

The metal piece between the output tubes and the filter capacitors on my 504 is a heat shield like the original Hiwatts had. A couple of EL34 tubes get fairly hot so it helps to keep the capacitors from getting too warm. Some Hiwatts have four EL34s so they would get even hotter.

Hey Matt,

I am very glad to hear that my pictures helped you out.
Ultimately, that was the reason for me to document all the different steps with high-res pictures.

Enjoy your amp!

It's most likely just normal component variation that's reducing your bias range rather than a problem upstream or downstream of R43.

I helped Mark (rotorcraft230) recently with a mod to increase the bias in his Triwatt so he could run EL34 output tubes. The thread is five down from this one if you want to read it. We found that to increase the bias range he had to increase the value of R43. He ended up using 220K.

Thanks for the clarification, Matt. Don't worry, you aren't the first one to get confused due to incorrect switch settings!

So these are the readings you get at the bias test points?
KT66 setting: -9mV to -15mV
6V6 setting: -15mV to -23mV

If so, that means 6V6 gets higher bias current than KT66 and Stephen's comment makes sense. For some reason I thought it was the other way around, too.

It's great to hear that everything looks okay, but double-checking connections and guarding against accidental shorts is always wise. agar io

Your approach to double-checking connections and using a layout MapQuest Route Planner drawing is excellent.