Back at the beginning of the year I purchased a pair of Emission Labs 300B for my new amplifier version (still working on it). I own several 300Bs but was keen to try these out given their reputation.
Jac from JacMusic sent me a matched pair which I traced them with the eTracer:
Lovely linear curves as expected. Here is the Spice Model I developed if you’re interested in playing with it:
You need about 140Vpp to push the 300B to full output power. Here is the operating point I worked out on my previous implementation:
Yes it’s rather hot at 35W. With a Monolith Magnetics OPT of 3K2, you should get 8W when driven with 140Vpp. You can use this excellent driver:
The D3a in triode mode is probably one of the few valves which can do 250Vpp without any issues and very low distortion. Below is a THD plot for 240Vpp which is impressive. You won’t get this level of performance if it’s not with a hybrid mu-follower. Here is the amplifier circuit:
If you are interested in less gain and adding a pre-amplifier stage (e.g. like an 01a) then you can look at implementing the 6e6p-DR (or a 6e5p) like in my original design:
I really like the sound of this valve and has a lower H3 component when driving large volts. See below:
Here is a plot of the frequency response of the driver. Less gain of course (i.e. 30dB) but with great performance:
Alternatively, if you need more gain, one of my favourite drivers is the 6SF5GT. This one can give you 40dB in sterling performance with a hybrid mu-follower (a.k.a. gyrator) topology. You need to bias the valve a bit higher than the D3a and similar triode-strapped pentodes. Therefore the HT has to be increased to 450V. You can add a drop RC to feed into the 300B output stage (R3 and C2 below):
Here is the frequency response of the driver stage:
There are so many options to work on. Even the lovely Russian 6C45P triode (which is a wild oscillation beast) can be used at a gain of 32dB:
Amazing response as well. You need to set the anode voltage to 200V and the cathode resistor (un-bypassed) to 120Ω.
For me this time round, I will build the 300B output stage separately so I can play with different drivers. Yes, I want to experiment as usual.