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I see you've put the Overdrive control in the same place it was located on Biacrown's OL/Lead models. http://mhuss.com/php/pix.php?p=OL103 Is that to make it more historically accurate?

I may be wrong but I think the reason they were originally done that way was because the Overdrive stage was built kind of like a mod on these amps, and that was the simplest way to fit the extra control without having to completely redesign the amp's layout. In the case of the Triwatt we effectively had a clean sheet of paper for the layout, and so we were able to place the control IMO where it was more logical in terms of its function and also helped keep the lead dress tidy.

http://mhuss.com/php/pix.php?p=OL103OverdrivePot
http://mhuss.com/php/pix.php?p=OL103Mod

Although, we have more gain in the Triwatt Lead amp than in a regular Custom Hiwatt DR, I doubt that you'll experience noise issues provided you're careful with the lead dress. I think the smaller Triwatt chassis was a greater challenge with all that gain and the two transformers in closer proximity, and Stephen will remember how nervous I was about the first prototype. In the end we got an amp that's exceptionally quiet. With all the extra space you've got, and with the transformers mounted at the rear of the chassis, I doubt you'll have problems.

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LOL.... that's funny! You're right, they probably put it there because there was already a hole there. I put it there because I think there might be an issue with clearing the board. I am not married to it btw, and I am not ordering my faceplate until it's up and running! Right now, I am thinking of running the leads around the board, instead of over it.....




I think it'll be fine.... I am really looking forward to using this amp!

I've been sidetracked by my GTO. I am gonna do some work on the car today, and then give it a rest for a few days, and get back to the amp. It's like hell with palm trees down here this time of year, and you'd think I'd learn to do the outside stuff in the winter when it's nice, but I'm not the sharpest knife in the drawer.

It'll be nice to crank the AC and smell some solder fumes again!

For a variety of reasons, car, work and band related...... I am back at it!


I populated the board last night, and will finish the chassis wiring tonight.

I have been giving the PS for the relays some thought. I have a 12V PS and a few DPDT 12v relays, that I am gonna try. I can also run the Red Box on 12v.

Pics later.......

Welcome back. Been hoping you'd get back into this build soon!

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

Me too! Where does the time go?

My GTO is running perfect, and I've been spending a lot of time with my kids wife and dogs!

Back to amps!

Sounds like you've got your priorities in the right order.

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Great tones come in small glass jars!

Populated board.....

Very Sexy.

thanks! It's a nice clean design. The lack of jumpers is a nice touch!

Well, I FINALLY got around to finishing this thing (well, almost)! It's been a busy summer around here.

This was a fairly labor intensive build, mainly due to the fact that I changed the layout considerably. The good thing is I was forced to double and triple check a lot of stuff with the schematic to be sure I was getting it right.

I fired her up and she works, but has a few minor issues that I will get to tomorrow. I only played at low volume due to the hour, but it definitely sounds like a Hiwatt! With the boost engaged, it sounds like a Hiwatt on steroids...... I ran it with all 12AX7s in the preamp, even the PI. I didn't have a cheapo 12AT7 handy for the PI, and I didn't want to risk a Mullard on the first start up. I can't wait to crank it tomorrow.....

With the boost engaged, it plays at normal volume. If I disengage the boost, the volume cuts in half and I get a noticeable hum, that isn't there with the boost engaged. Probably a missed ground or a cold solder joint. I'll deal with it tomorrow....


Instead of the extra jack for the linked inputs, I used a mini switch. It works as advertised.....

No squeals at all, but let's see what happens when I get it working right. I left some extra wire on the shielded leads to allow me to move them around. I also moved the boost switch from the end to where it is shown on the layout to keep the leads as short as possible.

All of the controls work, but I am not sure about the presence. Presence is pretty subtle in Hiwatt circuits, but it doesn't seem to be doing anything at all. I'll play with it some more at volume tomorrow.

I am getting 450V on the plates. I set the bias at around 17... I can't remember what I used when I was running these JJs in my Hiwatt, but I think it was around 21 with 500V on the plates. I need to run the numbers again......

Overall, I am psyched..... I'll post some pics tomorrow. It needs a little clean up dress, but it's not too bad.

Now, to build the power supply for the footswitch!

Thanks for a great design guys.....

We found this can also be sensitive to squeal if not done right. Use coax to go to V2. Bacically V2a is bypassed in non-boost mode. I'm sure you'll figure it out. The schematic is correct.

Yes, the presence is very subtle as you've noted. Dont forget the 100R to ground and the 3K3 to the board!



We set ours to 21 ma FWIW. (15-23 ma rec'd)



For the Power supply. I recommend a seperate one from the heaters. A regulated one ideally. See seperate post on the footswitch. We did try to one on the schematic, but it was too noisy. You could try a regulator off the heater .

Looking forward to the comments & pics.

Congrats on the build!

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

I played around with thing all afternoon. I have gone over everything twice, and still can't figure out the reduced volume problem. With the boost disengaged, I can dime it and sit right in front of it. It has a pronounced 60 cycle hum that varies depending on where I touch it or where I stand.

The hum goes away completely with the boost engaged, and volume is normal.

It's got to be something in V2A, but I'll be darned if I can figure it out. there simply aren't that many components in there, and it is something common to both normal and bright channels.

I tried different tubes and remelting the solder joints. I also lifted the grounds from the coax trying to isolate it, but nothing I do makes a difference.

I know the answer is staring me in the face.......

I'll keep pressing on!

Bonehead move #1.......

If you run V2A through a 100k resistor, it really lowers the volume....

I had the 100k and the Pin 2 lead reversed on the OD switch....

Problem solved!

It sounds great....


Now, I need to redo all the shielded wires I removed while troubleshooting......

Now we're talking. That sneaky 100K resistor and OD switch!

Looking forward to the Tone Testing now!!

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

Hey, I'm psyched by this too! I love the way you're doing this Triwatt (your "second" one) in that big vintage style Hiwatt chassis. I just can't wait to see this cool amp build of yours finished.

I guess it's time for the 12AT7 now. That will tame down the amp a bit - well, except when you kick in the Biacrown overdrive stage.

Once you get everything fixed, you will also find that the Presence works the same as on a DR103. We A/B'ed the prototype Triwatt against bgroup's own DR103, and found the tone and presence controls worked pretty darn near identically.

Have you got the 18V zener there in the power supply? You should be getting 440V on the anodes, 430V screen and biased to around 20mA, give or take a couple. With KT66s you bias to around 40mA.

We really need to thank Dave Reeves (RIP) for most of that design. Stephen also did a really fantastic job on the board, layout and mechanical design (ie all the hard stuff).

Please post those pictures!!!

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Great tones come in small glass jars!

Phil,

i'll get some pics posted asap. I am flying today, maybe tonight. The tone controls do work just like my dr504s etc. The presence is more subtle than any of mine. On the hiwatts. Any change below 3:00 is inaudible. This one is similar.

As for the voltage...... My wall voltage pushes 125ac. I use a variac with my vintage amps to get it down to 115. It's amazing how much difference a few mains volts make in these things! My dr504 and Jimmy Page noth run at around 500v on the plates, which is higher than most folks are reporting with these amps. I am using the zener. In the 6v6 position, it averages 445-450. In the kt66 mode, its aroumd 460-465.

I've just accepted it as a fact of life. I haven't had any major tube or other issues.

I'm a little confused. So you're saying this Triwatt's Presence control works like other Hiwatts', but not like your own 504's, or....???

Yes, I've seen how the voltage really affects them too. The Custom Triwatt Lead is designed to work at 120V AC. So you will get the best Hiwatt tones from it at that voltage (and using a 12AT7 in the PI). With lower voltages it will break up a little too early, and if you go too low, will start to get somewhat mushy, as opposed to the classic Hiwatt tightness. If you go too much higher OTOH, 6V6s will start to sound shrill, although KT66s will still sound fine.

With KT66s in their biased to 40mA, the voltage in KT66 mode should again drop to around 440V.


I've just accepted it as a fact of life. I haven't had any major tube or other issues.[/quote]

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Great tones come in small glass jars!

Sorry, I was typing from my iphone in the jetway!

On all of my Hiwatts, the presence doesn't seem to do anything until you hit about 3:00 on the knob, then it adds more uppper everything, but it's not a huge change, just a little extra "keraaanggg". It seems similar, but even more subtle on the Triwatt. Clear as mud?

FWIW, the rest of the tone stack is very close if not identical. It feels and sounds like my '78 2 holer, except I can turn the master up quite a bit more before it gets too loud. A lot more preamp gain than a 4 holer, and less headroom than a 50 watter, of course. I like it. I am looking forward to trying it out at band rehearsal this week..





My clones both have 120V primary windings, and definitely sound the best with 120 going in. My '78 gets real sterile and microphonic at 125ish, which is why I use a variac with it. On my gigging amps (which the Triwatt will likey be), I don't want to deal with the variac for a variety of reasons, so I just set the bias with the higher voltage and go with it. They still sound great.

After initial fireup, I put one of my Mullard ECC81s in there. I still have my lousy Sovteks/Chinese 12AX7s in the rest of the preamp and it sounds great. I can't wait to play with some of my good glass!




I've found the same thing with the variac. I have tried running lower voltage, like around 100, but the amps turn to mush. Not my style at all, plus it runs the heaters outside of their range. I've played with My Twin, '78 DR504 and '69 Traynor YBA1 all sound shrill when wall voltage is used, in addition to running the heaters higher than I feel comfortable with. Also, on my '78 in particular, the high mains voltage makes just about every one of my NOS preamp tubes microphonic. At 115, they are fine.




I don't have any KT66s. I need to order some tubes for another project. I'm gonna get a pair of KT66s too. Any brand preferences?

One of these days, I'm gonna build a box with a 6/12 bucking transformer in it. I have 2 of the transformers, I just haven't gotten around to sourcing enclosures for them.....

That subtlety factor should be the same, since it's the same circuit. We've even tweaked it slightly to compensate for the Triwatt's having an 8k OT compared with a regular Hiwatt's 4k or 2k OT.

It's actually the very same tone stack.

I presume you mean with a 12AX7 in the PI and/or the Overdrive engaged... With a 12AT7 in the PI and the Overdrive switched out of circuit, the preamp *is* the early 70s 4-hole preamp with no extra gain added. OK it's the Dave Gilmour 3-hole version of the 4-hole preamp, but that's it. I'm afraid there's very little new design in this amp.

Cool. Keep us posted. I'm itching to know how it goes!

We've run both Shuguang Golden Dragon Retro KT66s and New Sensor's Red Lion RI KT66s. And both sounded mighty fine. Just a bit darker than the 6V6s, with more headroom. Probably the Red Lions were the nicer sounding of the two varieties.

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Great tones come in small glass jars!