Strange Custom Hiwatt 100 layout

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sonicmojo
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Strange Custom Hiwatt 100 layout

Post by sonicmojo »

I recently came across this old Custom Hiwatt 100 and am trying to figure out what exactly it is. I assumed an early 70's DR103 with a few mustard caps changed to orange drops until I started comparing to layouts online. This one has a longer middle standoff row than what I can Google and appears to possibly have some extra caps in the extended area - four .022uF. There is no serial plate as there is an additional jack in back where that used to be so no help there. Has anyone seen a Custom Hiwatt 100 with this layout? Any ideas what this might be otherwise?

[img:1632:1224]http://www.sonicmojo.com/hiwatt/hiwatt100.JPG[/img]
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martin manning
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Re: Strange Custom Hiwatt 100 layout

Post by martin manning »

Seems to be a unique variant. Do you have any pictures of the front and back panels?
Stevem
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Post by Stevem »

Unless I am mistaken , I do not recall those 4 holes in the front of the chassis on other amps?
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martin manning
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Re: Strange Custom Hiwatt 100 layout

Post by martin manning »

I asked Mark Huss (Hiwatt.org) to take a look. He thinks it's a Hiwatt that has been heavily modified by someone, noting a "totally different" PI.

Does it play? What does it sound like?
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sonicmojo
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Re: Strange Custom Hiwatt 100 layout

Post by sonicmojo »

martin manning wrote:I asked Mark Huss (Hiwatt.org) to take a look. He thinks it's a Hiwatt that has been heavily modified by someone, noting a "totally different" PI.

Does it play? What does it sound like?
Thanks for the feedback! I tend to agree it is modded but probably was a weird variant to start too since I think the center tag strip is factory. There is no nut scuff on the extra middle hole in the chassis indicating anything other than that long thin strip was ever there.

It sounds pretty good! It is the first HIWATT I have played around with so I don't have any other reference. Very slight 60Hz hum probably due to an old cap going bad. It is very bright, even on the normal side. When I got it, the indicator light was missing and I also replaced the two power switches. I thought to restore it to stock but I think that is not really possible given the existing layout. The extra jack where the serial plate would be looks to be a line out or something but I have not analyzed it yet.

Here are more links to pictures.
http://www.sonicmojo.com/hiwatt/5.jpg
http://www.sonicmojo.com/hiwatt/12.jpg
http://www.sonicmojo.com/hiwatt/4.jpg
http://www.sonicmojo.com/hiwatt/1.jpg
http://www.sonicmojo.com/hiwatt/2.jpg
http://www.sonicmojo.com/hiwatt/3.jpg
http://www.sonicmojo.com/hiwatt/6.jpg
http://www.sonicmojo.com/hiwatt/7.jpg
http://www.sonicmojo.com/hiwatt/8.jpg
http://www.sonicmojo.com/hiwatt/9.jpg
http://www.sonicmojo.com/hiwatt/10.jpg
http://www.sonicmojo.com/hiwatt/11.jpg
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sonicmojo
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Re: Strange Custom Hiwatt 100 layout

Post by sonicmojo »

I traced this a bit more and found that one of the PI output coupling caps was a .01 instead of .047 so I corrected that and the hum went away - it must have been unbalanced quite a bit. The PI tube was 12AX7 so I put in stock value 12AT7.

It's mostly DR103. On the other side of the .047 PI output caps are two of those .022 mustards in addition before going to the sockets. The major mods occur on the board around V3 (far preamp tube in this amp since the V4 PI is next to last). I'll have to figure out what has been done there later but it sounds really good. I replaced the 100uF bias cap for good measure and added a quick and dirty bias trimpot. I may do the voltage doubler thing to get it more adjustable later as the Partridge bias taps don't allow for much downward adjustment - I was able to move down from 50mA to about 43mA at around 462V or so.
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sonicmojo
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Re: Strange Custom Hiwatt 100 layout

Post by sonicmojo »

And maybe Dave Reeves built this weird one himself! Sure looks like a big "D" in that signature....

I'm also wondering about the power transformer. It says Surrey on it but it's not the same color as the OT definitely marked as a Partridge.

Also the pots are different than a lot of the pictures I see online although I see some with this type. What kind are these and when were they used? I don't see any dates on them.
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martin manning
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Re: Strange Custom Hiwatt 100 layout

Post by martin manning »

Thanks for the additional pics. It all looks very well done, definitely not a hack-job. I agree the long tag strip looks original, especially since its one piece. I asked Mark about the signature, and he said he didn't recognize it. Interesting piece for sure!
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sonicmojo
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Re: Strange Custom Hiwatt 100 layout

Post by sonicmojo »

Thanks again for asking around. The amp isn't mine yet but I may trade something for it. I like the weird factor plus it sounds very good! I'll be replacing those OJs for mustards as I can grab them and trace out all the changes. I can't understand why there is additional .022 uF caps in serial on the extended tag board. Maybe this was some sort of prototype to experiment with the PI output values without modifying the main board. Who knows....it's a mystery.
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Post by Stevem »

Hiwatts bussing of the grounds if kept original make for 120 hz hum as does bad filters , if you have 60 hz hum try moving the early stage grid wires up off of the heaters!
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!😊

Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
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sonicmojo
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Re: N

Post by sonicmojo »

Stevem wrote:Hiwatts bussing of the grounds if kept original make for 120 hz hum as does bad filters , if you have 60 hz hum try moving the early stage grid wires up off of the heaters!
The low frequency hum is all gone now for some reason. Probably just using it a bit helped, or it was one of the caps I replaced. There is one can cap with a bulge but perhaps just using it a bit woke things up. It is dead quiet without signal unless I really crank the volume up and then some normal sounding white noise.
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