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New 845 amplifier - version 3
by Andrea Ciuffoli - starting in the May 2008

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.

INTRODUCTION

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:

and in this last version:

COMPONENTS

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

items models description price (euro)
2 LL1620AM/90mA Lundahl output transformers (350 euro each) 600
2 LL1671AM/20mA  Lundahl interstage transformers (237 eur each) 400
2 LL1638/8H 200mA  Lundahl power supply inductances (64 euro each) 130
1 Custom double R-core  - 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
1 100uF + 100uF 500V Jensen Electrolityc Dual (price about 44 euro each) 44
6 220uF 500V  Jensen Electrolityc (price about 36 euro each) 216
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 2200

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.

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
The power supply transformers are 2 custom made created on my specifications by:

ELETTROMECCANICA F.E.R. snc
di GIUSEPPE FERRI & C.
40064 Ozzano Dell'Emilia (BO) - 16, v. Matteotti
tel: 051 798008
fax: 051 796593
email: 
fertrafo@tin.it

 
 
 
 
Primaries
    2 x 115V

Secondaries first transf.
    2 x 340v 0.4A
    1 x 230v 0.2A
    1 x 200v 0.2A
Secondaries second transf.
    1 x 6.3v 4A
    2 x 10v 4A

Magnetic flux 70% of normal (13000 instead of 17000 gauss)

Internal electromagnetic copper shield.

SCHEMATIC

MEASUREMENTS

see prev release

CHASSIE