One more Hiwatt 50 Build

[marooned.echo]

So I decided to built a 50watt Hiwatt with a few twists. My initial plan was to go after one channel of the DR504OL ( http://www.hiwatt.org/Schematics/DR504OL.gif ) with a switchable gain stage and a FX Loop. On the way I changed my mind and I will follow the original version of that design (DR504) which has one gain stage less.

The project is moving very slow but today I managed to finish the first version of the layout. I have attached the layout because I need some feedback from experienced eyes on any mistakes I have done. The chassis will be 600x250mm and on the right is the PT. Some standard wiring is omitted in order to keep the layout clear.

One question I have is about the signal going from the output tubes to the OT. In this configuration I will run long wires towards OT. Should they be shielded? Is their length a problem or should I just be careful not to run them close to other wires that can give them trouble ?

[Structo]

I usually twist the OT secondaries that go to the impedance switch.

[alvarezh]

As far as I can see you could do two things:

First, place the bias circuit on a board so it seats low on the chassis and move it closer to the PT. BTW you have too big a cap there, it calls for a 100 mF @ 63 volts which is way smaller than the one you have there now.

Secondly move V1, V2 and V3 to the left, I believe you should have enough space now to place the OT between V3 and the PI. Place the speaker out jack to the left of the OT but to the right of the EFX loop.

All the best.

[marooned.echo]

As far as I can see you could do two things:

First, place the bias circuit on a board so it seats low on the chassis and move it closer to the PT. BTW you have too big a cap there, it calls for a 100 mF @ 63 volts which is way smaller than the one you have there now.

Secondly move V1, V2 and V3 to the left, I believe you should have enough space now to place the OT between V3 and the PI. Place the speaker out jack to the left of the OT but to the right of the EFX loop.

All the best.

Alvarez you are right , I should put the bias on the board. Concerning the cap I have to go with it as I made a mistake in the order and got that big one. Maybe down the line I will change it into something smaller. Your suggestion about the OT will put the amp head out of balance , but I guess that the wiring and hum benefits will surpass this inconvenience , right ?

Thank you for your tips guys

Aris

[alvarezh]

It won't be as balanced as per your design no, but most amps are built that way with both transformers on one side. Remember, their primary function is to play well, a short lived inconvenience while moving it, is of little importance. Furthermore, when you move your preamp tubes to the left the signal leads to the board are much shorter which is another big plus.

Understood on the cap issue. Never-the-less, try to find it locally, that small a value is common as is also used on modern transistor equipment. I just bough some 150mF @ 63 volts for an old transistor amp here locally and we are a third world country, a far cry from being one of the cradles of civilization. The purpose is to keep the components low close to the chassis to keep a safe distance between it and the fuse carriers.

Nice work on the layout drawing BTW.