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Page 3: Construction
January 4, 2007
Here you find a picture of the prototype Martin amplifier. I built the amp on a piece of wood as you can see and used an aluminum L-profile to mount the tube sockets, potmeter (right) and jack connector (left).
I built the following circuit on a piece of wood in order to be able to easily swap components etc. (click on the figure to enlarge it).
The amp worked immediately and the sound is not bad at all also. However, some resistors became very very hot and there is a slight oscillation, but that is probably due to the free cabling technique and the lack of housing.
At first I built the hole amp on a piece of wood, including a rather primitive power supply. It consists of a 12V/60VA transformer for Halogen lamps, a step up transformer (12-220V), 4 diodes 1N4007 and a capacitor. Strange enough, this works quite well for both ouput tubes, but the driver stage probably needs better filtering. For the moment an additional RC filter should do.
A little later, after hearing the amp was quite good sounding I decided to "invest" in better transformers. 2 transformers, one for heater supply (2x15Vac, 160VA) and another for the plates (2*115Vac, 120VA). Both are oversized (I know) but this will at least ensure I have enough power in reserve.
Now that I know that the amp works and it sound good as well it's time to look for a nice enclosure which is large enought to accomodate amp and the power supply. With respect to the last one I underestimated the whole power supply thing big way.
Resistors were much hotter than I expected, and also the power supply does nearly provide enough power for the amp. Filtering is not easy as both 832A tubes consume a lot of power.
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