Hiwatt Dr201 Build

[danfrank]

Hi All,
Time for another build thread from me. This time it's a Hiwatt DR201 build, the six EL34 version. Again, it's not gonna be an exact replica but the circuit will remain true to the DR201. So, here goes...


Above is the main circuit board. No turrets! Guess how long it took me to put it together?!? Not as long as if I used turrets on the board. LOL! Most resistors are 1W carbon film with a few 1/2 watters also. All capacitors are polyester film & foil, except for one.


Above is the power supply board and power transformers... There are 2 PTs, one for HV & bias, the second one for the tube filaments. This build, like my others, use parts that I have collected throughout the years so it will not be a total exact replica but will have the same electronic circuit as the original.
There are two HV supplies stacked on top of each other to get the required B+ voltage. Bias supply uses a full wave bridge rectifier so the amp will be very quiet when operating. For grounding, I am using a 12ga piece of solid copper wire attached to the chassis at one point, in the center.


Above is the bias and preamp power supply board, on the other end of the chassis. With six EL34 output tubes, getting all six to match up current-wise is not as easy as a 50 watt amp with 2 power tubes. I am using two 10 turn pots to adjust bias in each set of 3 EL34s in the push pull output circuit. All HV wiring is to the left at the back of the amp while the yellow bias wiring is to the right in the picture.

 

[danfrank]

Here's the 6 capacitors that connect the P.I. to the EL34s. One cap per EL34. I am using old stock ceramic octal sockets for the EL34s as there is over 600 volts going to the plates of the output tubes. Good quality sockets are mandatory!

 

[danfrank]

Here's the back of the amp. I'm using a stainless steel chassis which is a total PITA to work with but it was the right size and free, so I used it. From left to right are:
IEC socket with mains fuse holder.
Plate HV fuse holder
Screen HV fuse holder
Male XLR for 600 ohm D.I. output to board
1/4" speaker jack
Speakon speaker jack with 1/4" jack in the center
4/8 ohm selector switch


The top of the amp. Clockwise from top left is the OT, filament transformer, HV & bias transformer, and choke. This amp will be heavy!

 

[ampmadscientist]

El34 I think is rated 500V max plate 450 screen....so, it sounds like a wild ride.

 

[danfrank]

The front of the amp. Got the faceplate from Modulus Amplification. He's a super nice guy to work with and does an excellent job! He made the "CUSTOM 200" label at no extra charge to me.
More to come...

 

[danfrank]

El34 I think is rated 500V max plate 450 screen....so, it sounds like a wild ride.

Hi!
Yeah we'll see what happens... The screens only have about 350 volts on them so chances are that the screens won't overload. There's no way I'd use the high plate voltages on this amp if the screens received the same high voltage. Using a dual B+ supply is much safer than the way Marshall goes about it by using one high B+ voltage for everything. So with a dual supply, I can get very high power outputs and the output tubes don't stress too much. The down side is that with 650-700 volts on the plates of the tubes, the output tubes wear out quickly.
Oh! And 6550/KT88s can be substituted for the EL34 tubes. The power transformers are definitely beefy enough.

 

[danfrank]

A pic of the "guts"... The preamp circuit board will attach vertically to the 2 metal posts in the lower center of the picture, right above the six output tube coupling caps. I configured it this way so the wires going to the preamp tube sockets and control pots will be very short. I like keeping signal wiring as short as possible.
Yes, no Harry Joyce style layout here. LOL! But I'm willing to bet that this amp, when completed, will sound as it should and be very quiet also.

 

[liontato]

Beautiful! A work of art and skill for sure!

 

[Stych]

I compliment you on your use of lacing cord vs. cable ties!!!

 

[jensvonbustenskjol]

Wow! That looks great!!
Nice work!

 

[danfrank]

I compliment you on your use of lacing cord vs. cable ties!!!

Thanks! Yeah, that's actual lacing cord from the early 1970s that was used on the flight simulators for the NASA Apollo Missions. My dad had several rolls of it and I ended up with one of them. I have no idea how to do proper lacing; I just tied double knots on each one. Truth be told, I am currently running short on cable ties so I got out the lacing cord! LOL!

 

[johnfv]

Wow nice! Are you going to play guitar through it? A friend has an original Hiwatt 200 that he uses for bass and it always sounded fantastic. One day I may have to breakdown and add another Hiwatt (likely a clone) to my collection. I have an '80s 50 watt that is relatively high gain (more like a 2204 gain wise) - a great amp but not the same as the originals.

 

[danfrank]

I have a bass player friend and if he likes the way it sounds with his setup, he'll probably buy it. But it could be used for guitar also!

 

[Stych]

I wish I could show you the traditional way to use lacing cord! I's SO easy and quick. My airplane is over 60 years old, and all the original wiring bundles are done like that, and holds up incredibly well over time. AND it doesn't cut into the insulation or scratch you with sharp ends. Sadly, it's becoming a lost art. Newer isn't always better....

 

[Crunchifyable]

The board you use in place of a turret board, is it fiberglass? Where do you get it? Hardware store?

I'm interested in trying your method because I always end up having to shoehorn new things into a board.

 

[johan.b]

About lasing string. ..i'm always struck by the similarities in appearance between the lasing on seventies amps and dental floss. ..just an observation...
J

 

[danfrank]

About lasing string. ..i'm always struck by the similarities in appearance between the lasing on seventies amps and dental floss. ..just an observation...
J

Lol! They're very similar but the lacing string is quite a bit thicker.

The board you use in place of a turret board, is it fiberglass? Where do you get it? Hardware store?

I'm interested in trying your method because I always end up having to shoehorn new things into a board.

Yes, it's 0.125" G10 fiberglass board. I used to be into amateur rocketry years ago and this type board is commonly used for fin material. Somebody was selling a lot of it on a forum board a long time ago and I bought it thinking I'd use it for something one day. I'm down to my last piece and I don't think I've used any of it for rocketry. Lol!

 

[danfrank]

Finished!



I will test it out tomorrow... I gotta go over it and retrace all connections before I plug it in. Doing a quick 15-20 minute circuit retrace saves a lot of time later if something is miswired.

 

[johnfv]

NICE! I didn't understand from the description previously how you were going to mount the board - clever. I hope it sounds fantastic like the originals!

 

[liontato]

Artistry of the highest order!