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Hiwatt mod

6/5/2000 7:27 PM
Hiwatt mod
How would I significantly increase the gain on a handwired hiwatt dr 504? I like all the stocks sounds but want more face tearing action on the brilliant channel.
6/6/2000 3:25 PM
Re: unused preamp gain stages?
A good question....anyone with Hiwatt experience out there?  
i don't have your answer but my Hiwatts have 2 types of overdrive when plugged into Brill....  
First type:brill is cranked and master turned down for "face tearing"overdrive.Normal has no effect on brill(when plugged into brill.)  
Second type:both normal and brill interact and can be cranked for an excellent ballsy overdrive which has more gain on tap than the first type.  
Both of these preamp od's get better the more you crank the master(live i'm usually around 2-4)  
The second type involves using one of the unused halves of the existing preamp tubes(v4?)and can really send the head over the top.While i've seen some posts on other boards touch on the subject,i've never seen a really good explanation,let alone schematic.  
All of my heads give excellent overdrive(1-74,2-75's,2-76's,1-78)when the preamps are cranked(imo) ...i use a Menatone KOB for a boost(THE best od for my Hiwatts!)...the '78 seems to be the highest gain of all(a trend like Marshalls...later heads have increased gain?)  
6/6/2000 4:08 PM
Glen H.

I have had (and still have) a few (late 70's) Hiwatt Custom 50 and 100 heads which were all modified for cascading gain in the preamp stage. It is a simple, reversible procedure. But I can not remember the exact details of this mod. My Hiwatt's only have 2 inputs, in which the brilliant and normal gain(s) can be combined for intense, saturated distortion (when plugged into the brilliant i/p), and the normal gain i/p functions with a mild distortion output (via the normal preamp gain ctrl).  
All the Hiwatt's I have seen, in western Canada, from the late '70's have this mod. I guess Hiwatt wanted to put out higher gain amps, as this was the trend among British amps (and some American amps too! RE: Mesa/Boogie) during this period.  
As for tonality, I enjoy the cascaded gain sound, but it can be a bit grating at times. I prefer to roll the preamp gains back to about 1/2, and let my Boss OD-1 pedal finish the job! Result: smoother, cleaner distortion, and really nice lead tones that really cut through!:D  
6/6/2000 3:47 PM
Ray Ivers
Re: Hiwatt mod
I'm speaking only for myself (although I suspect that many people on this board may agree with me), but even in my hacking days I never could quite bring myself to disturb the mil-spec wiring grace of a Dave Reeves Hiwatt. There is one place I would add a jumper, though (carefully soldering away from the gold paint dabs); across the 1K series dropping resistor in the bias circuit. This brings the negative bias up just a few volts, and the bias current down from 'old-Mullards-only' range to something much more acceptable for modern tubes. A Menatone Red Snapper pedal may help out a lot; the Hiwatt tone controls seem to me to operate in ranges more appropriate for a hi-fi amp (high treble, deep bass), which is not a problem when overdriving the Hiwatt power amp (quite the reverse, it's a big part of the Hiwatt sound), but can become one when using a distortion pedal in front of the amp. The Red Snapper is more of a gain/mid booster, and may complement this Hiwatt characteristic well.  
Ray Ivers  
R.A.G.E. Electronics
6/6/2000 5:30 PM
Re: wiring?
I've often wondered,but glenn's comment tends to support this,that the heads sent to Canada had this mod factory installed at Dave Reeves assembly plant after he received the mil-spec chassis from Harry Joyce...maybe a little tweaking involved here before final assembly? It seems most amp manufacturer's were headed down that road at the time anyway.(Mesa,Marshall,Dumble, and of course Fender's hopped up offerings...their first boost switches..yech!)Hiwatts became more and more gainy until in the early 80's it became incorporated on the main panel as a overdrive knob.Getting the classic Hiwatt clean on my mid to late 70's Hiwatts ,however,is simply a matter of plugging into normal and dialing back the normal volume while upping the master.  
I once e-mailed Steve Gibbs of Audio Bros.(an outstanding fellow and a wealth of info. on Hiwatts)about output transformers and he replied "there are more variations in Hiwatts (and their wiring) out there than most people would have you believe" sounds like the vintage Marshall scene...just not as well documented...  
I've compared several chassis photos from the internet with my amps and one irregularity stands out...wiring on my heads goes directly from the brill jack to V2,and then back to V1...most photos of standard Hiwatts i've seen has brill jack wiring going directly to v1...  
I also agree with Menatone OD.does an outstanding job boosting my Hiwatts...the tone is preserves the sound of my hiwatts,and gives me tons of gain when i need it...they seem to be a perfect FDII is now retired...  
john roeger

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