What is so special about the Hiwatt phase inverter

[timrichter9]

I have been wanting a 50W Hiwatt for a while. My brother builds amps and has built me an awesome 18w and has some great single ended 6V6 examples too.
He is about to start a 40-50W project for me and I asked about the Hiwatt (as an old Who fan, that Townsend thump kills me!).
He made a comment that the phase inverter is funky and he would have to do some research on it.

Anyone out there familiar with it can dish out some knowledge?
He has built many of the Fender/Marshall style PIs.

Thanks
Tim

[Enzo]

A circuit is a circuit. If you want him to build a clone of something, then duplicate its circuit. If he wants to redesign parts of it for whatever reason, that is fine, but you no longer have the thing being cloned, you now have something different. You may or may not like it better, but that is the decision to make - clone or something different.

[loudthud]

One feature of the HiWatt circuit is that the Presence control will boost or cut high frequencies as opposed to the boost only of the typical Presence control. The way the DC operating point is derived for the phase inverter will give a small bit of compression with a long time constant.

[Gingertube]

Here is a circuit trace I did some years ago whan I restored one of these things.
http://www.webphix.com/schematic%20h...watt_sa412.pdf
Note the DC level shifted input to the cathode follower which drives the PI. This cathode follower also acts as an impedance buffer inside the feedback loop which provides the treble boost/cut prescence control which loudthud refers to in the post above.
What else is unique to Hiwatts - the Partridge Output Transformer, you probably won't (totally) get the Hiwatt sound unless you source a similar tranny. What else ? - Well 4 x 12" Fane Speakers will help, maybe someone can recommend something similar or do a search on "Hiwatt Spares" and see what turns up.
Cheers,
Ian

[Gtr_tech]

The Fane speakers were prob'ly a bigger part of the fabled Hiwatt sound than the output transformer. Those old Fanes were pretty dark sounding and quite ineffecient, so you could run the amp harder and get less fizzy noise from the cab.

[timrichter9]

Thanks

One feature of the HiWatt circuit is that the Presence control will boost or cut high frequencies as opposed to the boost only of the typical Presence control. The way the DC operating point is derived for the phase inverter will give a small bit of compression with a long time constant.

[HTH]

The Fane speakers were prob'ly a bigger part of the fabled Hiwatt sound than the output transformer. Those old Fanes were pretty dark sounding and quite ineffecient, so you could run the amp harder and get less fizzy noise from the cab.

^ +1

You need Fanes with a Hiwatt, they just sound 'right' together. Celestions are too trebley with Hiwatts, imo.

[Sowhat]

Fanes are the right speaker for a Hiwatt although I have restored one recently and Fanes are a little hard to get here. I found that 4 Eminence Governors came real close to that Fane sound.

[Ramsay]

This is a typical negative feedback mid controller.
Marshall JCM800 uses something similar.

[Tage]

This is a typical negative feedback mid controller.
Marshall JCM800 uses something similar.

Not quite, you should have another look at the schematic... it is arranged very differently than marshall or fender feedback. The Phase Inverter is not the same long tail style, as it's bias is derived from the second triode of the third pre-amp tube rather than "cathode bias". Yes the feedback is still applied into the "tail" section of the PI
, but the control also rolls off treble before the PI when it is rotated counter clockwise, kinda like a very noticeable presence control.

It may be a variation on the usual presence control but it unique to Highwatts and I think it's very much a part of their sound.


With regards to the OP the PI is not too "funky" only the way it's bias is derived and the way the presence control is set up, but if your Brother can read schematics then he should have no problem working this out.

This may be a good route for you, or at least an idea for a good layout,

https://taweber.powweb.com/store/kits_60b.htm#6H50

Weber also does a Fane speaker clone, the FC12 model. I have never used it but I agree that Fanes will be an important part of the formula

Best of luck with this project, Keep us posted.
Tage