As output transformer has been choiced the Lundahl LL1627/185mA
with secondaries connected in B configuration to have a primary load
of 2.3K on 8ohm load. so each EL34 will have a load of only 2300 * 4
have a primary
of 9H and the EL34 have a nominal plate
resistance about 910ohm
and four 910 / 4 = 227.5ohm so in theory the low frequency cut-off will
be egual to Ra / ( 2 * pi * 9H) = 4Hz (-3db).
Using the LL1627/185mA each EL34 will be set with a bias about 185 /
4 = 46.25mA that produce at 430V an anode power dissipated of Pa = Va *
Ia = 430V * 46.25mA = 20W that is very less than EL34 max power.
You could request without any problem to Lundahl a custom
LL1627/220mA or a 240mA to increase the Ia to 55mA or 60mA per each
EL34 but there is no advantage.
Before to insert the EL34 tubes in the sockets switch on the
amplifier with only the two little tubes (12AX7/ECC83 and 5814/ECC82)
and set the trimmers to get about -50V from the grids of the EL34 and
After switch off insert the EL34 and switch on the ampl. to set the correct bias.
This amplifier, like the my other designs, should be connected
directly to a CD Player or to a DAC without use pre-ampl. and the
sensibility should be enougth in any combination.
The interstage capacitor should be a 0.33uF 630V Jensen Copper film
paper in oil or a 0.33uF 450V Auricap from Audience
All the audio transformers used in this project are Lundahl products:
|The input stage is a 12AX7 / ECC83 Mullard or Jan Philips|
|A valid alternative to very
expensive Caddock is to use a parallel of
two normal 1% metallic oside resistor with inverted phase to compensate
some of their inductance.
Here is show the connection of two resitors to create a parallel.
|I am using a DACT stepper attenuator instead of the normal ALPS or NOBLE solution, because the the sound is clearer.|
About wire; forget the teflon ! Use only stranded tinned copper wire with pvc insulator, and for loudspeakers use the same.
A very good quality stranded tinned copper wire could be bought
directly from E-Z-HOOK that
carries an extensive line
of fine stranded and extra flexible wire.
The layout of the EL34 of only one channel and the input stage per both channels.