Building the 6S45P amplifier part two

Here are all the links to this story:
The simplest amplifier obsession Part 0
Breadboard amplifier Part 1
Chassis building Part two – this one
Assembling the 6S45P amplifier Part three
Finalizing the 6S45P Part four

The summer vacation is over and the weather is turning grey and rainy again here. Time to start making a finished version of the 6S45P breadboard prototype I built in April. My follow through ability has been too low, there are several projects floating in limbo right now. We´ll see what the winter brings.
The plan with this amp is to do a couple of new things, at least for me. I want to build the chassis in the traditional style of using an aluminum sheet for mounting all the components, and then fixing the sheet in a wooden frame. The second thing I want to try is to use the 5Ц4С as a hybrid rectifier bridge. this uses an octal socket so if it does not work I have several other options.

For output transformers I am still using the Edcor GXSE 10-6-5K transformers from the breadboard, but for the power supply I decided to buy a transformer with all the necessary supply’s rather than to patch together something with several simple power transformers I already have. I decided to take a chance on a no-brand transformer from China, sold through on Ebay.
Type nr. PT190.2i: primary voltage 220 or 240V, secondary 190-0-55-190 centertapped, 6.3V x 3A, 5V/6.3Vx2A filament winding.

Edcor GXSE 10-6-5K, 6 ohm output. Painted all white.

Musical Power Supplies PT190.2i:

190-0-55-190 Centertapped Output 120mADC, 220 or 240Vac in,  (1) 6.3V x 3A, (1) Combo 5A/6.3Vac x 2A filament winding, I painted the transformer white and polished the Zinc Plated finish

For materials I found some scrap aluminum at work, which was painted white with a clear finish and of-cuts of beech, which were cut and finished like this:

There are several considerations when planning an amplifier layout.
First you should make sure the power transformer is far from the sensitive input signal. Then the magnetic field of the power transformer should be far from the output transformers, and preferably oriented 90 degrees to avoid inducing noise in the output. All the components should be arranged around a star ground, preferably with a sub star for the noisy power supply. And then there is the issue of routing the filament wires away from the signal wires and positioning things to make it easy to do point to point wiring. Finally the design should be visually pleasing and the controls should be placed in a position were they are easy to reach and see.

Finally the design is starting to take shape! I will have the power transformer in the front left with a  rectifier tube behind it. The output transformers are in the middle and right rear and create a symmetrical space in front for the tubes and the mA meters. In the middle front is the volume control. Power switch and fuse is on the rear panel left.

More to come…
Update11 october 2011: Another two months passed by before I managed to continue the project. In the meantime I have painted parts. The only part left now is the back panel so its time to mount all the hardware and see what I have created. Before I show all the pictures, Yes, I know I didn’t turn the power transformer 90 degrees like I said. It didn’t look good and took room from the rectifier. Since its pretty far away, I´m taking my chances. Here is the eye-candy!

One of the screws for the amp meter is missing this is the hole for adjusting current.
Volume knob is temporary, but black works pretty well, I think.
power transformer is slightly out of line – on the to-do list


7 thoughts on “Building the 6S45P amplifier part two”

  1. Make provisions for adjusting the current of each tube separately, and heating them in parallel not in series like I did in the breadboard, because tubes vary quite a lot, some warm up quicker, and some conduct more current than others for the same cathode resistor value.


  2. Congartulations on a nice design! I love the textile finish, and its reference to classica guitar amps. Also you builta really compact design


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s