Tag: 47

300B SE Amp: 47 Driver

Going DHT end to end

As previously mentioned, I played around with the 46 driver.  I love it sound and is a great valve. However, there were 2 reasons that pushed me to switch to the 47. Firstly, I wanted an extra tad of gain. Secondly, I have a nice stash of RCA 247 globe which measure extremely well. I’ve been reserving it for a 47 PP amp with local feedback (a la Pimm) and hopefully will get to in the future. Anyhow, the 47 in triode mode has a mu of about 8 which in combination with the SUT, gives me good gain to drive my 300B. After tweaking on the bench the stage for optimal swing and distortion performance, I ended up with the following circuit:

Continue reading “300B SE Amp: 47 Driver”

Flexible HT supply

The return of the Jedi

Time has come when breadboarding and HT is not longer an option. With a baby around, I was forced to remove most of the valve equipment. However, the return of the Jedi is closer than you expect. With very little time, albeit at continuous pace when I get a free 30min here or there every weekend, I keep very focused on my objective. The 814 SE monster amp is close to retirement (probably before Christmas) and although I have a fantastic LME amp already working, I need to get the valves back on the scene providing I can prove I’ve complied with “heath and safety” – as my wife well put it.

Well, I had a nice attempt of a wooden frame made out of pine wood. Yes, I’m really bad at woodworking but I’m getting better. The top plates are 4mm thick. I have added a nice set of 2 100mA meters at the front of the frame. A 300VA custom-wounded multi-tap HT transformer from JMS which gives me full flexibility from 100 to 500V in 25V steps. The supply is choke input (LL1638) and filtered with a set of nice 50uF oil caps and 20H chokes. Damper valves used with some nice SiC to form a hybrid rectifier.

Top plates are protected with paper before drilling!

This looks to be quite neat in my view!

The idea is to use this supply for my new 4P1L PSE, 300B and DHT Schade experiments with 6P21S/47 and 1624 valves. A lot planned and so little time for this unfortunately.

Cheers, Ale

 

 

 

 

THD benchmark

I’m still in the process of testing valves, here is how the ranking is coming up so far. This is a mix of driver and output valves. All tested at Vo=+22.22dBu:

THD analysis of different valves

Looking at the chart above a couple of interesting points to highlight:

  • 4P1L is the most linear valve I’ve found so far.
  • 6e5P and 6C45 are expected to be on the top five anyway.
  • 12P17L despite of having similar characteristics as 4P1L is not that linear
  • 6N6P and 6N6P-I disappointed me. I thought the would be more linear..
  • 46 and 47 in triode mode are superb drivers

Have so many other ones to test, but limited time….

Expect this chart to be updated in the future, so stay tuned 🙂