building an amp question

[lerxst88]

Well i found myself with a crappy sounding crate 15 watt combo and a half working Kalamazoo model one and I figured I could use the chassis, speaker and cabinet from the crate and use the transformers and tubes from the kalamazoo and build my Mark IV a little brother!

The kalamazoo uses a 6x4 rectifier tube and the socket is falling apart and I dont want to deal with drilling more holes and running a tube rectifier so i want to use silicon diodes. From my research I just need a beefy low ohm resistor (100 ohms? 10 watts) to lower the voltage getting to the amp.

I also tested the PT and I'm getting 550 volts! according to the schematic the tubes should be seeing around 260 volts i believe. So how did this thing work without blowing itself up?

 

[J.J]

The transformer will be center tapped giving 275-0-275 or so. A tube rectifier will usually eat about 100 volts or so which would amount to 260 or a bit more volts DC.

You will need to build a half wave rectifier with two solid state diodes, but you need a hefty voltage rating. I would probably use 2x1000V (4 in total) diodes like 1n4008 in series for each side to make sure it will cope for the long term.

You will then need to drop the 100 extra volts. Without doing the maths properly, the resistor value will be something like 1000Ohm
and 10watt min, but a 20 or 25 watts would be much better.

 

[lerxst88]

Great! I ended up buying 1N4007s and a 250 ohm 10 watt resistor as per a schematic from a kit i found online from a reputable builder. Thanks for the tip!