One of my alltime favourite tubes is the RV218, this direct heated Triode is powerful and smooth in one glass, she is the little sister of RV258 which can do more Volts but in soundstage and electrical structure they are the same. Both of them need an outputtransformer of around 10k, mine here is made from Piemme Electra factory in Italy and is really a good choice. First of all i had built an only mainstage amp and used different driver stages. But now as there had been two extra sockets for changing to RS241 which has same OPT and also quite same anode Voltage, i decided to leave the RS241 changing opinion and changed the european socket to octal sockets and so the way was free for 6SN7 Triode. As I have quite a nice collection of them and never built anything with them i was curios about the outcome.
Surprise, the 6SN7 was not able to drive the RV218 formerly. There was only small sound coming on my 97dB speakers.
What to do?
Phoning with a in this matters most expierienced friend we came to the conclusion to try 6J7G pentode as she has the same socket almost same heater, just the pins and the electrical fitting has to be changed.
In time of Corona is enough time to handle this even as I am already in retirement.
Drilling a hole for the wire to the Grid Cap, connecting and finding right resistors for Anode and G2 Voltage, Kathode Resistor...
I can tell you this was a great Moment starting the amp, he is completely silent and sounds great. and the best is that I had some very nice 6J7G´s like Mullards you see on the pictures, but also Westinghouse and even the EF37a and the 5A/157D from STC are fitting well. This tubes are so similar that they can be changed without any problem.
After all I put in also an Alps Poti.
The RV218 can be changed to RV258, in the middle you see RGN2504 and the Mullard CV1935 with the Grid Cap.
The knob for Volume control can be changed easily.
The Trafo comes from Toroidy in Poland and the OPT from Piemme Electra.
The wooden chassis and the copper plate of 2 mm Copper is my work. It is always the first way to find the size of the amp, get the plate, look how is the position of the parts. I always go more to smaller size, which makes it mostly not easier but the result is possible to carry and to place on the board.
The Transformer brings 360-0-360V AC, and the outcome is around 400V on the Anode of RV218.
The Katode resistor is 500 Ohm and the tube has 22V on the Kathode.
The 6J7G is running with 120V on Anode, 70 Volts on G2 and 1,7V on the Kathode.
Kathode resistor is 900V Rosenthal.
The amp has no hum and is really a fun to play music with him. The music comes so direct and livly that I am always again fascinated even with different kind of music.
thanks for looking.
