Transcript 5687-based preamp

Simple EL84
Basic layout
DIY Paradise
13 June 2003
“EL84 doesn’t sing without feedback.”
“EL84 has no bass.”
These are comments I gleamed off the World Wide Web from various
places.
The truth is, if the circuit is done CORRECTLY, then all the above points
are moot. This circuit uses NO GLOBAL FEEDBACK and it has BASS!
Listening is king. But you can’t listen to one until you have built one right?
Note that the layout shown in the following pages are specific for
• this implementation wires the EL84 in ultra-linear configuration.
• this implementation has filaments of 4-0-4V, meant for 8BQ5. Use 3.150-3.15V for 6BQ5 or use a resistor to drop the voltage to 6.3V.
• Hammond output transformer, particularly the 1650x series.
• using one half of ECC99 for each channel. You could, of course, opt to
use one tube for both channels, or use some other tube, say 5687. Wiring
will be different then.
Schematic
Signal circuitry property of
diyparadise.com
Schematic
Power supply circuitry property of
diyparadise.com
Wiring the Simple EL84 is just a tad more complicated than the Simple
5687. If you can understand the wiring of the Simple 5687, the Simple
EL84 shouldn’t be too difficult.
Basic rules still apply. If you have forgotten them, please read the Simple
5687 layout file again.
Layout of the Simple EL84 is slightly different. We are dealing with very
hot components here. The EL84 is one hot tube! When planning the layout,
please ensure adequate ventilation between tubes. 1.5-2” between each
tubes should be okay.
Please note that I didn’t show wiring of volume pot, input RCA socket etc.
If you have built the Simple 5687, then I don’t want to repeat myself.
As usual, safety first.
SAFETY FIRST: REMEMBER TO SOLDER IN BLEEDER
RESISTOR! REMEMBER TO “EARTH THE CHASSIS”!
Input RCA
jack
Speaker binding
post
IEC socket
Power
transformer
Choke
EL84
EL84
Output
trans
ECC99
Chassis Layout Top View
Output
trans
ECC99
EL84
Stereo
volume pot
EL84
Input RCA
jack
Speaker binding
post
IEC socket
100uf/
450V
Choke
Ground
Signal lines
run from
RCA socket
to volume
pot.
Chassis Layout Bottom View
Ground Layout
Stereo
volume pot
240-0-240V
100uf/
450V
Ground
100kohm 5W
Bleeder resistor.
Very important!!!!!
Tap B+ from here
Colour-coded Wire from Hammond
Output Trans
Chassis Layout Bottom View
Power supply circuitry layout
Colour-coded Wire from Hammond
Output Trans
Bias network
Goes to B+ (be careful!)
23kohm / 4W
0.33uF
390ohm / ½ W
470uF/10V (optional)
9
1
8
2
7
3.15-0-3.15V
9
3
6
5
4
1
8
9
2
7
3
6
5
4
1
8
2
7
3
6
5
4
ECC99
EL84
220kohm / ½ W
Stereo
volume pot
4-0-4V
Chassis Layout Bottom View
Signal circuitry layout (One channel only)
EL84
In case this isn’t clear enough, pot center tap goes to YHLMCCS,
while the other 2 ends, go to both cathodes (pin 3) of EL84.
15 ohm / ½ W
500 ohm pot / ½ W
Current sensing resistor
1-1.2 ohm / ½ W
YHLMCCS
Current sensing resistor
1-1.2 ohm / ½ W
9
1
8
EL84
9
2
7
3
6
Ground
5
1
8
2
7
4
Chassis Layout Bottom View
Bias network (One channel only)
3
6
5
4
EL84
YH’s Lazy Man Constant Current Source
Using LM317, TO-220
package, preferably with
heatsink.
Vin goes to pot (bias network)
center tap.
Vout goes to GND.
Resistor between ADJ and
Vout determines current.
For Simple EL84, 40mA per
EL84, use 16 ohm 1W.
Chassis Layout Bottom View
YHLMCCS (One channel only)
Build the YHLMCCS on a
small protoboard to make life
easier for you.
0
4 ohm
Colour-coded Wire from Hammond
Output Trans (secondary side)
Chassis Layout Bottom View
Output section (speaker binding post)
8 ohm
Very easy to build.
Start with the grounding scheme first, followed by heaters. The heater center
taps, you could bring to GND or elevate it to some potential.
Then build the power supply, followed by the signal circuitry.
Check wiring, again and again and again. Oh yeah, please fit in 5A fuse
before powering up.
Power it up, check all the voltage points are within 10% of the schematic. If
they are different, check for incoming AC and/or heater voltage.
After tubes are warmed up (say after a minute), check voltage on current
sensing resistor. It should read ~40mV. Both tubes on each channel should
draw the same amount. If current draw is different, adjust 500 ohm pot. Be
careful that you don’t touch any high voltage points.
When both tubes conduct same amount of current (+/-5mA), you are ready to
play!
By the time you reach this point, you should be having a truly wonderful
musical machine.
This amp has surpassed all my expectations. It delivers 10W and oh! What a
sweet beautiful 10W!
10W can drive lots of speakers, but it’s no slouch either with high sensitivity
speakers. In other words, this amp should be able to last for a while as you
change your speakers. Just don’t give it power hungry speakers.
I’ve talked too much.
Enjoy your music.