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New 845 amplifier - version 2
by Andrea Ciuffoli - starting in the September 2007

BEWARE! This is an expert-only project because the high power supply voltage, about 900V. Be careful, it can kill you!
Keep always one hand (better if it is the left hand) behind your back.


This project is born to be simple and secure but with high electrical performances and great sonic results.
The sound quality has been obtain using the best components on the market and a good circuit.
All the test on first version confirm a very sonic high performances and I consider it like one of my best amplifiers.
The use of normal diode bridge instead of common vacuum tube diodes give a many advantages and the sound is always good.
This project use only common vacuum tube in current production because I don't like old stock items difficult to find and with short life time.

These are the characteristics of this design:



Very cheap and good chassie created with these componentsç

  1. 2 marine plywood 19 mm 38 x 38 cm
  2. aluminium 3mm 37.5 x 37.5 cm
  3. aluminium 3 mm 37.5 x 23 cm
  4. stainless steel studding M12


All the audio transformers used in this project are Lundahl products and the distributor list is available here

items models description price (euro)
2 LL1620/90mA Lundahl output transformers (148 euro each) 300
2 LL1671/20mA  Lundahl interstage transformers (68 eur each) 140
2 LL1638/8H 200mA  Lundahl power supply inductances (64 euro each) 130
1 Custom R-core  ECU Electronics Industrial co.,ltd (price about 70$ + 150$ shipment) 170
3 159 ZJ Hammond inductances 60
2 43 20Kohm Spectrol multiturn cermet trimmer 2
2 534 2Kohm Spectrol precision wire wound multi-turn potentiometers  20
2 845 vacuum tubes   Golden Drangon or Valve Art (from 120 to 400 euro per pair) 120
2 EL34 vacuum tubes Svetlana 52
2 12AX7 vacuum tubes Jan Philips or Mullard 50
2 100uF + 100uF 500V Jensen Electrolityc Dual (price about 44 euro each) 90
2 100uF 500V Jensen Electrolityc (price about 32 euro each) 96
3 220uF 500V  Jensen Electrolityc (price about 36 euro each) 108
2 0.22uF 600V Jensen Copper film paper-in-oil (45 euro each) 90
6 10000uF 16v Panasonic HA serie 30
    Varies components + connectors 250
    Total price about 1700

to add input cables and DACT stepper attenuator cost

Lundahl is one of the world´s leading manufacturer of audio transformers used in many professional studio recording and radio stations so it has great experience and all these products use a custom audio C-core.

About passive components types,  I don't leave many choices:  Caddock resistances on the signal path, Sanyo OS-CON capacitors on cathode and Jensen AudioGrade electrolytc capacitors on power supply.

You can find many components of this project at Audiokit online shop.

I am using a DACT stepper attenuator instead of the normal ALPS or NOBLE solution, because the the sound is clearer.

The Custom R-core has been custom design with 2 secondaries 6.3V 5A necessary only if you want to use the SV572-3 instead of the 845.

About wire forget the teflon ! use only stranded tinned copper wire with pvc isulator.

A very good quality stranded tinned copper wire could be buy directly from E-Z-HOOK that carries an extensive line of fine stranded and extra flexible wire.

I have used the model 9506 with WVDC (Working Voltage Direct Current ) of 5000V for all the main power supply connections, the model 9504 for the signal and the model 9510 for the output loudspeaker connections.

All the wires near the tube socket have been cover by Sterling tubes in order to avoid that the high temperature will destroy them.

As visible in the photos to fix some components I have used some good PTFE Insulated Twist Eye Terminals by Grennan Audio.

After my big experience with the cables published on "Cable test" I can assert that the quality of cables is very important.
So like internal input cable I have used a good Q-Audio Tao

For the R-core power supply transformer contact:

ECU Electronics Industrial co.,ltd
NO. 669 Changjiang West Rd,
Huadian Building Hefei, Anhui, 230031 P.R.China
Tel:0086 551 5311411
Fax:0086 551 5324417






Here are some plots generated with my Clio system by Audiomatica.

With a driver stage of this type (107Vrms with only 0.18% THD) I expected a great performace.

The distortion spectrum is perfect driving with this amp. a
5 ohm load until 11-17W and the output impedance is less than 1.5 ohm.

So the result is a perfect amp. and I am sure there are very few 845 amp. around with this performances.