By Enzo Grazioso
Over the past 10 years I have focused on Russian tubes from the era 1960-1980 and have discovered numerous types with very interesting characteristics. Signal tube like 6n6p, 6j51p, 6j9p, the high gain planar triode 6s17k, the strong, linear driver as 6e5p, power tubes like 6c4c, 6c33c, 6s18s and 4p1l. This last DH ( direct heated ) pentode has the reputation of amazing performance and low distortion in triode mode. After many days of breadboarding,…
A LCR phono stage is probably one of the most challenging circuits to build in audio.There are several approaches to low noise tube RIAA stages. 1. Negative feedback RIAA. I think 90% of the phono preamps in the hi-fi market are configured this way: an RC network in the feedback loop implement the active RIAA filter. Low cost solution = poor performance. 2. RC type: a RC network between two gain stage achieve the RIAA…
The beating heart of this project is the 12B4-A. This 5.5 W single indirectly heated triode an amplification factor μ of only 6.5, coupled with a plate resistance of a only 1kΩ , is the ideal candidate for a great linestage. Due to low μ I opted for a plate CCS ( Constant Current Source ) A CCS presents an ‘infinte’ AC load to the tube, maximizing gain. This high resistance load to the plate,…
Macbeth…the ULTIMATE Line Preamplifier. 16dB gain, zero feedback, active load DHT tube stage. Double power supply: Tube rectifiers, CLCL regulator plus dual mosfet stabilized stages for HV anode and SLA battery PSU for DHT filaments. LED Display for battery check, internal battery charger. Polypropylene and oil filled polypropylene capacitors in PSU. 6 NOS tubes ( two 4P1L, two E810F and two 6AX4GT ). Only one copper polypropylene coupling capacitor in the signal path. Macbeth…the ULTIMATE Line…
For a RIAA preamp it’s very important keep a short path for audio signal from input to output. Otello is a tube phono preamplifier, zero feedback circuit with an ultra low noise tube-hybrid power supply. Otello use a passive RIAA network, only one high quality coupling capacitor in the entire signal path and a star ground circuit with separate path for signal and power supply. Two choices are available for gain: 42 dB for MM cartridge…
A terrific line all tube preamplifier fitted with NOS Philips ECC186SQ as voltage amplifier and 5687 for low impedance high current output buffer. Power supply is a fine all tube Shunt Regulator. ECC186SQ is the best ECC82 family tube ever made. The crucial mid range ( male/female voices ) is astouning but unfortunately …this tube now It’s very expensive !! All capacitors are MKP or Paper in oil, carbon composite resistors in the signal path,…
