To build a 50Watt Hiwatt

[T-Rex]

I am slowly building a modified version of a 50watt Hiwatt. It is built to my taste of what I want this amp to sound like. I took my 36watt RS Overdrive amp apart for the donor chassis. After ripping it apart it looked like this:

 

[T-Rex]

It needed modified to add the can caps, so after reconfiguring and knocking out extra holes it now look like this:

 

[T-Rex]

Then I started a turretboard. I had ordered a set of Hiwatt boards from Modulus Amps in Scotland. Then some jerks took down the English postal system with a hack and the boards went to who know where. I decided to build a combo board. it has both the preamp board as typical Hiwatt and now has the single rail power section mixed in. it looks like this:

 

[T-Rex]

On this build, I took a 70's 4 hole preamp section and mated it up with a later date 50watt power section. I also added a choke, decided to try a pair of 6L6's instead of the typical EL34's, added a Marshall style adjustable fixed bias, in place of the typical non adjustable fixed bias. I also played with the preamp filtering a touch.

 

[T-Rex]

I should also mention that I flipped the typical turretboard to make the build more like a Marshall where when you look into the chassis, the input jacks are to the right

 

[syscokid]

Then I started a turretboard. I had ordered a set of Hiwatt boards from Modulus Amps in Scotland. Then some jerks took down the English postal system with a hack and the boards went to who know where. I decided to build a combo board. it has both the preamp board as typical Hiwatt and now has the single rail power section mixed in. it looks like this:

Very nicely done!

 

[T-Rex]

I am waiting on some parts to continue on with the turretboard.

 

[T-Rex]

A bit more progress. Got the cap cans, rectifier, switch, and fuses wired. Starting on the heaters next. It is a tiny bit messy at the moment, but there is a lot of stuff going on in here.

 

[Far Rider]

Adding in the power rail to the preamp board was a stroke of genius Terry. This might be your best build yet, among many, many others.

 

[T-Rex]

Talk about irony. My wife picks up the mail from Saturday on Sundays visit to the community center. In the mail are the two Hiwatt boards from Modulus Amps that were ordered the first week of January. Too late to use them now.

 

[T-Rex]

Adding in the power rail to the preamp board was a stroke of genius Terry. This might be your best build yet, among many, many others.

It has been the most challenging so far. I have not been able to find a matching set of schematics and layouts yet. The info on the Mark Huss site has errors in matching sets up. Then, add on an adjustable fixed bias with a pot, 1% resistors to read mV, and change the filtering. The worse was flipping the layout to a Marshall line up. I constantly found errors on my part until this final version. and the preamp tubes from right to left are V1, V2, V4, V3 which make things more confusing.

And on the board the far left components are for V3, with V4 components roughly around the area of the orange caps.

 

[Amp Mad Scientist]

Then I started a turretboard. I had ordered a set of Hiwatt boards from Modulus Amps in Scotland. Then some jerks took down the English postal system with a hack and the boards went to who know where. I decided to build a combo board. it has both the preamp board as typical Hiwatt and now has the single rail power section mixed in. it looks like this:

The problem I see is that classic hiwatt is a ridiculously clean amp, the way it's built it can't distort.
And so I couldn't put up with that...
The newer hiwatt (recent) sounds like a chainsaw on steroids...but it was obviously redesigned....but how?

 

[T-Rex]

I agree it is a clean platform. Although Ronnie Wood when with Faces used one to record his solos, and they sounded almost Tweed toned.

 

[bea]

The problem I see is that classic hiwatt is a ridiculously clean amp, the way it's built it can't distort.

Well, it can. I run a Mid 70s 4 input preamp in front of 4 KT88, and i can overdrive the 2nd stage even through the mixer. And that's the place where You can mod it for even more distortion:

• reduce the losses in the mixer (smaller decoupling resistors)
• maximize amplification in the 1st stage (larger anode resistor or even a mosfet constant current sink instead of the anode resistor - which will run the ECC83 at its maximum gain
  Both measures will maximize the output of stage one so that it can more easily distort stage 2.
  
  
• modify the cathode resistor of stage 2 away from the optimum. increasing it will give "colder" distortion and decreasing it will give "warmer" distortion with more compression. You can safely go down to 820 Ohms; for smaller values You must calculate the current drawn from the system and ensure not to overload it.
  If that's not enough, put an ECC82 (EC92) stage in front of stage 1. Or after stage 1 but in front of the gain pot. And/or run the signal through a Germanium (or valve) diode ... (which means that the amp cannot play clean anymore)

 

[Amp Mad Scientist]

I agree it is a clean platform. Although Ronnie Wood when with Faces used one to record his solos, and they sounded almost Tweed toned.

I had a hiwatt 50 head, I tried to make it overdrive...it won't.
The design deliberately prevents distortion. (quite remarkable I think)

You see Pete or Ronnie playing a Hiwatt, but it's obviously modified.
No stock Hiwatt sounds like that.

 

[T-Rex]

Ready to drop in the turretboard after swapping out the pots:

 

[T-Rex]

More progress:

 

[T-Rex]

More progress:

 

[T-Rex]

I decided to cancel this build and am going in a different direction. I'll up date after the new design is progressing.

 

[ibmorjamn]

I saw Be Bop Deluxe in the 70's and if I remember correctly he had 2 Highwatt amps . Not sure how distorted they got but he never was high gain player. He did have a sweet lead tone.

He normally had played Carlsbro amps and they are from what I hear are very loud and Fender like.