Hello Simon. I have several 300b amps, with OPTs by O-Netics (Wright Sound and Level 1), NP Acoustics amorphous, and Lundahl LL1664/70 (3K) and LL1682/50. I'm particularly fond of the LL1682/50mA. On paper this isn't the "correct" match for a 300b, but in reality it sounds extremely good and I would urge others to consider it as long as they don't need the full power of the 300b. Like you my speakers are 89db sensitive and I listen at around 2 metres in a medium/small room.
I use a triode driver with a large amorphous plate choke and Russian teflon FT-2 coupling caps. No doubt a pentode is another option. For the rest of the parts, Lundahl do a LL1668 plate choke and Hammond do PSU chokes and mains transformers. Suppliers in the UK are:
Hammond: KGA Transformers Price List - Hammond Manufacturing
Lundahl: Blore Edwards 01685 882 043, Brett
For the cathode bypass on the 300b I would recommend DC Link Kemet C4AQ capacitors from RS Online, 40uF.
C4AQLBW5400A3FK | KEMET 40μF Polypropylene Capacitor PP 500V dc +-10% Tolerance C4AQ Series | RS Components
A DC Link is also a good capacitor to use as last PSU cap, but 15uF is OK there.
You will need pair of regs from Rod Coleman for the 300b. Lyrima online. To feed these I use a 50VA 9+9 transformer, but Rod can give you some instruction with this. He supplies all the backup you need.
Good luck with the build. This - a SE 300b - is probably the best amp I can think of building.
I use a triode driver with a large amorphous plate choke and Russian teflon FT-2 coupling caps. No doubt a pentode is another option. For the rest of the parts, Lundahl do a LL1668 plate choke and Hammond do PSU chokes and mains transformers. Suppliers in the UK are:
Hammond: KGA Transformers Price List - Hammond Manufacturing
Lundahl: Blore Edwards 01685 882 043, Brett
For the cathode bypass on the 300b I would recommend DC Link Kemet C4AQ capacitors from RS Online, 40uF.
C4AQLBW5400A3FK | KEMET 40μF Polypropylene Capacitor PP 500V dc +-10% Tolerance C4AQ Series | RS Components
A DC Link is also a good capacitor to use as last PSU cap, but 15uF is OK there.
You will need pair of regs from Rod Coleman for the 300b. Lyrima online. To feed these I use a 50VA 9+9 transformer, but Rod can give you some instruction with this. He supplies all the backup you need.
Good luck with the build. This - a SE 300b - is probably the best amp I can think of building.
Thanks Andy for the data! Some great stuff there and shows I have alot to research.
I see Rod posted thoughts too so what are the regs you are refering too please as I am not clear?
EDIT: - found it Rod Coleman DHT Filament Regulator
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In case anyone is interested in building this, I uploaded a BOM and the final schematics.
I have no doubt there are other and likely better ways to build a 300B amp if you have the extra funds. But for someone on a tight budget I think you could do a lot worse than this one turned out. It sounds very pleasant to me 🙂
Skunkie Designs 300B
I have no doubt there are other and likely better ways to build a 300B amp if you have the extra funds. But for someone on a tight budget I think you could do a lot worse than this one turned out. It sounds very pleasant to me 🙂
Skunkie Designs 300B
Finally got around to doing a final tweaks video, found an issue using the Audio Analyzer Suite and it was a simple fix. It really turned out sounding amazing!
300B DIY Budget Tube Amplifier Build DHT Final Tweaks and Wrap up. - YouTube
300B DIY Budget Tube Amplifier Build DHT Final Tweaks and Wrap up. - YouTube
Hey Stephe, you were right about the Douk board drive clip. I don't know where I miss-measured it.
Any way, I will try to implement your driver mod to it and document it as an option in addition to mine for people who purchases the board and want to improve it.
Steven
Any way, I will try to implement your driver mod to it and document it as an option in addition to mine for people who purchases the board and want to improve it.
Steven
i watched your video, it was awesome....
there was a thread here long time ago about cascodes, and from what i gathered in that thread, the bottom triode is high gm for gain and the top triode is for supplying the bottom triode, constant plate voltage....
so i wonder is a 6dj8 bottom triodes and 6sn7 top triodes will make good combinations..
high gm of the 6dj7 and drives a vertical load of the 6sn7....what do you think?
I have a question - could the 47K resistor on the top anode of the cascade be replaced by a plate choke? Reason would be if there was less HT available, e.g. if the outputs were 2a3s.
Has anybody tried a cascade with a plate choke on top?
Has anybody tried a cascade with a plate choke on top?
This looks like a pretty unconventional idea and maybe not a very good one, but a pentode with a plate choke has been discussed here...
Pentodes and Choke Loading
With limited HT, I guess you just have to choose the input tube more carefully.
Patrick Turner loved doing that, there are a lot to pick up from his webpages...
afaik, the choke will have a series resistor also in order to speed it up and to establish idle dc conditions..
gain is gm x Rl, where gm is the gm of the lower triode, and Rl is the impedance provided by the choke is paralleled with the upper triode plate resistance and the next stage grid leak resistance...