Too late now, Hiwatt DR103 Gilmour-spec build

  • Thread starter Thread starter SpiderWars
  • Start date Start date
SpiderWars

SpiderWars

Well-known member
This amp has had several failed iterations but none were a Hiwatt build at all. But it just never sounded good no matter what I did. So I decided I'm just going to gut it and start over and make a Gilmour-spec DR103. The existing PT is a Merren Marshall style that delivers about 500-510vdc at idle. That stays. The OT will be a new Mercury Hiwatt/Partridge clone. I'll keep the PEC pots, only two need to change. Getting some red fiberboards and using Takman REX 1W carbon-film resistors just for the hell of it. They look similar size and color to the old Hiwatt pics. Vishay MKT caps but V1a and b will get Mustards.

Took a while too yank all the old crap out and still have to clean it up. This is with the old OT which is a custom Merren 2xKT88 U/L 100W OT. I've given up on it. Going straight 4xEL34 and Partridge-style OT. New sockets too. All the cans are good though.

Freshly gutted carcass.
624289-D1-E496-4-C71-BFDB-6985-B2986-B3-A.jpg


Former life
IMG-20220323-162626.jpg
 
Look what Santa left. Those elves are fast.

633-A6107-DBEA-41-DF-AFA9-658-A8-C95-C15-A.jpg


I requested no universal mounting bracket like the original Hiwatts had. The PT looks like a Marshall PT so I wanted the OT to match.

Mark Huss' Hiwatt page is my main source of info. It's so awesome to have sites like his. AFAIK, Gilmour's DR103 was stock early 70s circuit except for linked inputs. The fourth input was plugged. I intend to put a Bright switch in the fourth input and switch that 47n cathode cap in/out.
DR_PreLinkedInput_v1.gif
 
Last edited:
SpiderWars said:
This amp has had several failed iterations but none were a Hiwatt build at all. But it just never sounded good no matter what I did. So I decided I'm just going to gut it and start over and make a Gilmour-spec DR103. The existing PT is a Merren Marshall style that delivers about 500-510vdc at idle. That stays. The OT will be a new Mercury Hiwatt/Partridge clone. I'll keep the PEC pots, only two need to change. Getting some red fiberboards and using Takman REX 1W carbon-film resistors just for the hell of it. They look similar size and color to the old Hiwatt pics. Vishay MKT caps but V1a and b will get Mustards.

Took a while too yank all the old crap out and still have to clean it up. This is with the old OT which is a custom Merren 2xKT88 U/L 100W OT. I've given up on it. Going straight 4xEL34 and Partridge-style OT. New sockets too. All the cans are good though.

Freshly gutted carcass.
624289-D1-E496-4-C71-BFDB-6985-B2986-B3-A.jpg


Former life
IMG-20220323-162626.jpg
Click to expand...
I need a replacement PT for a Sovtek MiG-50. Two EL-34, 550v B+. Currently have a PaC Trans 100w British Trainwreck spec but it only gets 480v or so. This is for a cathode bias monster. Where would you recommend?
 
Nigel said:
I need a replacement PT for a Sovtek MiG-50. Two EL-34, 550v B+. Currently have a PaC Trans 100w British Trainwreck spec but it only gets 480v or so. This is for a cathode bias monster. Where would you recommend?
Click to expand...
I usually pony up the dough and buy Mercury. But I wouldn't replace that PT with a 550vdc replacement. 480vdc with modern tubes is a nice compromise so unless I really thought it needed extra voltage I'd leave it and adjust it elsewhere to get it where I wanted it.
 
Got almost everything. Just need the three boards which have been shipped. Takman REX 1W carbon film resistors and Vishay MKT 630v caps with Mustards for V1. Power resistors from Mouser. And bear traps.

736-E2845-E15-D-4-D7-D-94-A9-03-EC7-D5333-C7.jpg
 
Takman Rex are nice.. Beefy 1 Watters that will make your build stand out..
 
Are the partridge clones as big as the real partridge? Those are huge.
 
mooncobra said:
Are the partridge clones as big as the real partridge? Those are huge.
Click to expand...
I don't know. The original Partridge had those universal-mount brackets on them where you could mount them in any orientation you wanted. So they looked bigger. And the PT is definitely bigger than the OT pictured above. When I look at pics of old Hiwatts they look about the same. I ordered mine without the universal-mount brackets just because the existing PT (a Merren 100W Marshall PT that puts about 500vdc on the plates which is perfect) doesn't have them. But Mercury usually puts them on.
 
It’s cool to hear Mark Huss notes are still the standard. Two of my Hiwatts are in the pics. I also owned the subject amp of the blocking distortion article with my Canadian distributor master volume mod that totally sucked.
 
Searay said:
It’s cool to hear Mark Huss notes are still the standard. Two of my Hiwatts are in the pics. I also owned the subject amp of the blocking distortion article with my Canadian distributor master volume mod that totally sucked.
Click to expand...
I was going to build a different, later version but when I read that part I decided that early 70s with the linked input was the direction I would go. As far as I know that’s the only ‘Gilmour-spec’ that’s not stock.
 
This is cool but my wuestion is how can you service the radials underneath all that if it's covered up. I understand you can decouple the leads from further out but are u able to get to the mounting hardware if you have to pull them out for replacement?

Btw, what's that pot underneath near the incoming ac?
 
Last edited:
Exo-metal said:
This is cool but my wuestion is how can you service the radials underneath all that if it's covered up. I understand you can decouple the leads from further out but are u able to get to the mounting hardware if you have to pull them out for replacement?

Btw, what's that pot underneath near the incoming ac?
Click to expand...
If you look between the big resistor and big black bias cap there is a red wire connected between the two can caps. That's all you have to unsolder in order to replace them from the top side. I left enough wire on the other connections to get them out that way. Good question tho, after seeing it with that preamp cap under the board in some Marshalls it was definitely a concern.

That's not a pot its just a knob I was using to help hold something in place. Sometimes you need a wedge that is just 'THAT' big.
 
That looks really good. Nicely done turret board is my favorite method of amp building. Awesome blend of craft and serviceability.
 
SpiderWars said:
I think I might be done…I think. I’m gonna look at this picture for a while and have a beerand if I don’t see anything I’ll start ignition sequence.

A3-BA46-D5-5-DD3-47-E1-B4-AA-9-E1-FDA17-C47-B.jpg
Click to expand...
Wow man, I can't wait to hear it!!!!!!
 
japetus said:
Wow man, I can't wait to hear it!!!!!!
Click to expand...
Thanks! I really hope I got the OT primaries right. It's pretty much 50:50...and if it's wrong the amp will instantly howl at full volume when you flip the Standby switch with tubes installed. It's jarring.
 
You must log in or register to reply here.
Back
Top