Introduction

            In this last part five projects based on tubes 6C45, 6H30, 6C46 are presented. I will don’t show in-depth  descriptions since this could require more space. However the audio experimenter can extract useful informations both for  a duplication and elaboration.

            The Single Tube Single Ended 6C45-PE Amplifier

            This compact amplifier summarizes the enormous potentialities of the russian triode

 6C45-PE, Fig. 1 and 2.

                        I report the main specs in Tab. 1.

Looking at the schematic in Fig. 4, you can observe a relatively high plate load (5kW): sound quality and tonal imprint are more important than output (although in this project the theoretical maximum power is truly low...).  Low power amplifiers tend to have abrupt saturation phenomena. Nevertheless I have noticed an unsuspected capacity of this amplifier with my 87dB loudspeakers with overloading effects very smooth.

The Single Ended 6C45-PE/211 Amplifier

            The best use of the 6C45-PE triode is as driver for power triodes with high voltage swing requirements as trasmitting varieties but also 300B or the new Svetlana’s SV572-XX.

High s tubes remove the need of a three stages architecture (gain stage+driver stage + output stage) allowing easy building of more performing, more good sounding two stages amplifier.

A SRPPed 6H30 Line Preamplifier

I have essayed the wonderful 6H30 in a classic context, with top results.  

            The more impressive quality of this preamp is the easy driving of any complex load. The schematic reveils a very simple project and I invite you to experiment with different topologies as Mu-Follower and balanced structures.

Thanks to the low voltage requirement for the 6H30 (plates of uppers triodes have only 120 volts) I use toroidal units  as power transformers obtaining a compact building.  I don’t show the power supply, but any HV unit with 80..120V- 60..70mA well filtered is good. Heaters require 6.3V-1.8..2A.

A 6H30 Low voltage OTL SEEP Stage

High s tubes can be the fuel for the freak audio experimenter. In the recent past I have designed a Class  AB₂ SEEP Stage with a low voltage power supply. The fundamental driver stage is designed around a Compound N-MOS source follower.

The 6C46 integrated PSE Amplifier

At the moment this amp lies inside a piece of PSPice code, but results are confortable:

A low voltage integrated PSE amplifier (only 100V) with 2W of maximum power, Fig.13.

            A plate load of 1000..2000 ohms is good. The output transformer can benefit of a low cumulative plate resistance r_p but its building is slightly complicated by the current requirements of the output stage (120mA). The low load for the SRPP reveils the application in this design of the  THD cancellation technique.

            Conclusions

            High g_m vacuum tubes have always divided audio experimenter in two factions:

a)     Enthusiasts, tickled by their unique electrical specifications;

b)     Opposers, twarthed by a supposed Solid State like sound, costs and apparent unreliability.

As any other product of technology you has faced with merits and defects. Surely designing with this tube family requires a lot of caution but the greatest results are in the corner.