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DIY-Projekt / Integrated TUBE-Amplifier / RIAA Preamp CLASS-A / 'Single-END' FEATURES 4x 12AX7 preamp/riaa and 2x 6L6/5881 final |
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INDEX
Updated
2012.10.02 Designed some PCB layouts for the filter / rectifier circuits, also made a board for rectify / filter / regulator use.
The first card is used with B+ High voltage up to about 300-500V - The idea is to mount 4x 1N4007 diodes and one (or two) pair of 220-470uF/200-250V electrolytic filter capacitors in series. The card can also be used with external rectifier or rectifier tube '5U4G' +/- lead from external rectifier or tube is hocked up to the card DC+/DC- point.
Rectifier / Filter card 1
The second card is also amed for use with B+ High voltage, above 500V - This time with 4x 1N4007 diodes and up to tree(3) 220-470uF/200-250V electrolytic filter capacitors in series. The card can also be used with external rectifier or rectifier tube '5U4G' +/- lead from external rectifier or tube is hocked up to the card DC+/DC- point.
Rectifier / Filter card 2
The third card is a universal rectifier, filter and regulator card. The idea is to use it with 4x 1N400x or 1N540x diodes + a sutable electrolytic filter capacitor. If needed one can also add a regulator from 78xx series, if supply needs is more than 1Ampere there is also place for one additional MFJ3055 NPN output transistor, this gives up to about 10Ampere maximum current drain possibilities. (External heat-sink is then needed)
- For use without regulator / transistor simply place a 'jumper' wire from 'C' to 'E'
- For use with regulator only (No output transistor) simply place a 'jumper' wire from 'B' to 'E'
Rectifier / Filter / Regulator card
I'm going to use the universal rectifier, filter and regulator card with 4x 1N5408 diodes, one 2200uF/25V electrolytic capacitor, a 7806 regulator and a MFJ3055 NPN output transistor. This is then hocked up with the filament heater supply for the four ECC83/ECC88 preamp tubes.
2012.06.19 Working with the front and back panels, using 5mm aluminium sheet metal. Now i'm also able to make the holes for the RIAA preamp tubes. Finaly also got two KT88 final tubes to test with.
KT88 final tubes and RIAA preamp tubes in place
2012.05.27 Winding choke coils this evening. Using standard IE-60 iron core with 0.30mm enameled copper wire in 1500 turns. Testing the coil with ohm meter, the resistance of the coil is 41ohm. Calculated inductance is 6,56 Henry. Starting with making only one in order to get it tested with sufficient instruments, my own LC-Meter 'Velleman DVM6243' goes only up to 2 Henry.
Making HV-Chokes / Testing ready made choke
Absolute inductance value is not important, however it needs to be at least above 5 Henry in order to give the intended LF blocking on the B+ HV supply line - Recorded a .wmv video, I'm cranking the winding machine by hand when making the choke coil, click on the image to view the video.
choke coil in the winding machine
2012.05.26 Made a 'shield' box to shield and protect high voltage parts on the amplifier chassi top. The box shields the rest of the amplifier from AC interference and prevents contact with lethal voltage. .
ventilated Sheeld box on rectifier tube and power transformer
2012.05.20 Made a wooden frame for resting the chassis top plate on, the frame is made for support and protection when starting the actual build inside the amplifier. The wood frame will later be covered, using teak-wood side panels and aluminum front and back plates.
Drilled holes for the tube sockets, transformers and for wire feed thrue, using rubber grommets to protect the wires.
The wood 'Chassi' in place / Wood parts is made with the wood jointer / planer machine
2012.05.19 Working with the amplifier 'layout' - Trying to get everything to fit together nice on the chassi top.
 First 'lineup' - With everything in place |
  Right Click 'View image' for closeUp |
This layout is made to 'accommodate' the different amplifier parts in separate schassi 'compartments' - The compartments is: Left channel amplifier compartment, Power supply compartment, Right channel amplifier compartment, RIAA amplifier compartment and input compartment.
Chassi dimentions:
Top plate 383 x 262 x 2 mm (Anodized Aluminium)
Sides 262 x 64 x 14 mm (Wood)
Front / Back plate 383 x 68 x 5 mm (Brushed aluminium)
Side panels 274 x 68 x 14 mm (Teak wood)
2012.05.15 The project is now on 'halt' for the summer.
2012.05.17 Can't realy let go, made the secondary windings on the power transformer this evening.
Transformer making 'in progress'
Transformer making 'in progress'
Description
Main design characteristics/features: The amplifier is made using doubble mono amplifier design, with one seppatare amplifier per channel. Single-end output stage in Class A operation, using Hi-End Hammond 15W output transformers.
Preamp in two stage using 2 tubes per channel. First tube is preamp with second tube acts cathode follower for wide band matching from preamp stage to final tubes, this makes 'tube-rolling' possible with less final tube impedance matching problems. Shielded input tubes in 'Balanced' circuit design. Simple / Straight signal path using hi-end audio capacitors only.
Final tubes is 'self biasing' with circuit using current regulator ic LM317, one for each tube, they are also feedback loaded up to 45% to secondary grid in order to increase stability and reduce distortion. The cathode on our final tubes is to be connected to 'testpoints' on chassi top via 1ohm pressission resistors (1%) to signal earth, in order to monitor and adjust BIAS when 'tube rolling'
150VA Hand-made power transformer, Full wave electron-tube rectifier 5U4G(5U3C) and Hand-made 10H chokes on HV-Power, one for each channel. Also using 6,3V regulated / filtered DC supply for tube filament heater. Separate 6,3V DC supply for each channel.
Noice-free 24 step 250K logarithmic attenuator for gain controle (No potentiometer) Relay controlled input selection, input connectors inside separate shield.
The Chassi 'body' compartment is divided into five(5) sections: Left / right amplifier section, psu section, input section and riaa amplifier section. Al sections are shielded from each other with aluminum 'walls'
Since the amplifier is 'Single-END' (Using only one output tube per channel) it's possible to use unmatched tubes, it's also able to use a number of different tubes s.a. 6L6 / 6p3s(6n3C) / 5881 / EL34 / KT88, with anode on top-hat one can also use 6P31S(6n31C) / EL36. In the drive one can also use other tubes s.a. ECC83 / 12AX7 / 6N2P(6H2n) and ECC88 / 12AT7 / 6N1P(6H1n) / 6922 - I like experimenting with Russian tubes, they are often of good quality and none expensive.
The amplifier is quite a heavy piece, in al there is six(6) different IE ferrite cores in transformers or chokes giving the amplifier a total wight over 12Kg.
Bygget
Materials
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Resistors
100 0,5W V1 Catode resistor (150)**
V3 G2 Feedback (150)**
390-470 2W V3 Catode resistor (470)**
1K 0,5W V1 Catode resistor
6.8K 0,5W V1 voltage supply devider
10K 0,5W V1 voltage supply devider
100K 0,5W V1 Voltage supply devider
Capacitors
0,22uF V1 Signal path **
Electrolytic capacitors
2x 47uF 450V Voltage supply devider **
1x 47uF 500V Supply filter **
1x 100uF 500V supply filter **
2x 470uF 100V V3 Catode resistor **
2 pcs 8pin OCTAL tub socket
6 pcs 9pin NOVAL tub socket
2x 5H 180mA DC Volatge choke
1x HV rectifier tube 5U4G
Transformer data
Primary 240V prefabricated
Secundary
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2x 6,3V 1,15A (Eqval 18,94/19 turns each)
1x 5V 3,4A (Eqval 14,8/15 turns)
1x 290-250-220-0-220-250-290
taps @ 0 / 118 / 207 / 858 / 1510 / 1598 / 1717 turns
Power Transformer
This is the ready made power transformer. The core is a standard IE-108, rated for 150VA, the core and bobine is purchased as a 'kit' from SVEBRY.se[L4] - Primary winding is 'readymade' from factory, and all the secondary windings is by myself.
 Transformer - Layout |
  Ready made transformer |
The transformer is made to meet the following supply needs:
- Section A is for anode supply for the ECC83/ECC88 preamp tubes and the 5881/6L6 final tubes.
- Section B and C is anode and low voltage supply for the riaa / phono preamp (400VDC/12VDC)
- Section D is fillament supply for the 5U4G¹ rectifier tube.
- The 6,3 volt sections is for fillament supply of ECC83/ECC88 and 5881/6L6 tubes.
The 'A' section is made for use of full wave rectifier, using the tube 5U4G¹ witch also need a 5Volt fillament supply @3 Ampere - The Anod voltage is 'selectable' by selecting sutable 'taps' on the winding. Rectified voltage (No load!) is calculated to: 295 - 335 - 388Volt (DC)(Selectable)
Note¹ 5U4G Rectifier tube data sheet in 342Kb .pdf format
First testing the new made transformer for short sircuit with the ohm meter, hocked up and ampere meter in series with the primary, applied some AC voltage and cranced it up to 240Volt. The transformer works fine!.
Checked output voltage with volt meter, no load is applied, the voltage is calculared to drop about 20% when max load is connected. (The next test is with load)
HIGH VOLTAGE section - Voltage output (with NO load!)
LOW VOLTAGE section - Voltage output (with NO load!)
Testing the 6,3V @3,9Ampere windings. Simulate load with two russian 6n31c (EL36) tubes, current drain on fillament (pin2/7) is 1,3Ampere each. Leaving total drain to about 2,6 Ampere, with this load the voltage drops from 7,47 to 6,74 Volt, this equals 9,77% drop @ 67% of max calculated load. (Uf for the intended tubes is rated to 6,9V max)
2x 6n31c tubes makes up the fillament load / Tubes glowing in the dark...
HV PSU Circuit drawing
RIAA/Phono preamp
The plan is to use a RIAA/Phono preamp stage with 'tube only' design. Purchased a ready made PCB for the simple yet well designed 'Matisse Reference' preamp.
RIAA Preamp schematics / PCB
The RIAA preamplifier uses only two tubes, one 12AX7(ECC83) and one 12AT7(ECC81) - RIAA correction is made thrue 'active' feedback over a 'Linsley-Hood' equalisation RC network. RIAA accuracy is stated to be within 0,3dB. The input is 'MM' only and output level is sutable for direct feed in to main amlifier preamp stage.
PRE AMP preamp
Preamp schematics
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Referenser / Länkar m.m.
Honors to the brains behind - 'Äras den som äras bör' - som talesättet säger. Som vanligt så är det inte jag som kommit på allt detta. Här hittar ni länkar till referenser och leverantörer.
[L1] ELFA.se
[L2] ELECTROKIT.se
[L3]
[L4] SVEBRY.se
[R1] InLine Inductance calculator
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