OK -
this amp is not pretty, BUT it is one of my absolutely favourite units. It is
found in the Concerto 2500 tube receiver and comes along with 2 of the
coolest audio tubes I know: the Telefunken ECC83 and the Telefunken round
plate EL84.
The circuit is very
simple and the unit sounds very nice in original condition.
The
output transformer is designed for 4 Ohms use only, so that the amp works
best (better bass and output power) with 4 Ohms speakers.
What you
should do for HiFi use:
1. Remove the equalization
PCB. Instead of it you should solder 10kOhms resistors in the
signal path (connector 1-2 and 5-6 - see picture below on the left).
2. Install an
input jack. The easiest way is to use a DIN jack as there is a hole provided
above the speaker connectors to install it.
3. Remove the
power connector for the radio/preamp section to avoid electrical shock.
(4. Add jumpers for correct
speaker connection next to the 10k R's as shown in the picture. Not
necessary in all units)
If you want more:
Disassamble the amp and
rebuilt it (using the same PCB and OPTs) on a bigger chassis with a bigger
power transformer. Use better filter caps and a choke in the power supply.
With a B+ of 320V you will get 5 watts of great sounding ouput power!
Watch
a modified unit here !!! |