VT-25 Class A1 Single-ended Power Amplifier

I introduce my first amplifier that I made in year 1999..
This amplifier is VT-25 Single-ended Class A1 stereo type.
Recently, I use ALTEC A5 “type” speaker driven by multi-amplifiers.
One is UV-845 A1 Single ended, another one is 2A3 A1 Single-ended.
So, this VT-25 amplifier has not been used for few years already.
I decided to lend this amplifier to one of my friend for few years,
Then, now checking this amplifier through N500C Network.

I attach the circuit diagram below.

About rectifier tube, you can see 2 types of different tube name, one is 5U4G(direct heating) another one is 5AR4(separated heating), but tube in my photo is 5Y4. Originaly I designed with 5AR4.
For the durability of power tube, I think better to use rectifier with isolated heater, but this time I wanted to use ST shape tube like 5Y4, then I used it after changing transformer tap to 360V.
This time I changed back transformer tap to 400V, and changed rectifier tube to 5U4G.
Charactors of this amplifier are
1) equip input transformer using High impedance tap (10k ohm), not low impedance (600 ohm)
2) Triode connected Pentode drives power tube(6V6G) through interstage transformer.
3) Interstage transformer (TANGO NC9) has limitation for DC cuurent (6V6’s plate current), then separete DC load and AC load.
Musical signal goes to transformer and DC is cut off by capacitor inserted to cathode side. DC goes to Resistor which is connected to B+ DC power supply.
4) Output transformer is TAMURA F2005 (Primary 7k ohm) , VT25 needs more high impedance load, then I connected 16 ohm speaker to 8 ohm terminal. Then from VT25, load will be considered as 14k ohm.
5)VT25 has 7.3V filament, I supply heating power in AC because hum noise level was ok for me.
In case my friend cannot take hum noise, then I will make small modification for heater circuit.
May be equip external rectifier circuit.
I used to use Electro Harmonics GT tube for 1st stage 6V6, I found G-tube with black smoked glass, then I changed it. I forgot about the maker of this G-tube 6V6. I attach photo.

VT25 is GE made.

Even I used very small chassis, equip interstage transformer, choke coil for rectifier circuit,
so, inside of chassis is very very crowded.

Now using BRIMER 5U4G, this tube used to be used in 2A3 amplifier, once lost contact and retired.
But looks still have enough getter, I tried to repair this tube. Use soldering iron, add some solder to the pins, then tube’s function was back to normal. I don’t know how long does it work properly, then still under observation.

Output power maybe slightly over 1 watt only. But I can enjoy music and also the glow of the VT-25’s thorium-tangsten filament.