I am looking to build a very very simple version of 300b SE with very few components. Is there any schematic that I can look at?
I had this discussion with Thomas Mayer a few times. Why do guys think they can build 300b on the cheap? Where does that idea come from?
Honestly. 300b is a bit of a beast to tame. Definitely not for any first build.
Honestly. 300b is a bit of a beast to tame. Definitely not for any first build.
Why? Wat is your reasoning. I'd love to help but need to know more what your are trying to achieve.... so I/we can help better.
"Make things as simple as possible, but not simpler" - Albert Einstein
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Being a DHT, 300B itself is simple enough. Driver can be simple, too.
But, for adequate performance, you can't get away with simple power supply, including filament supply.
Similar thing: http://www.diyaudio.com/forums/tubes-valves/172984-2a3-spud.html
But, for adequate performance, you can't get away with simple power supply, including filament supply.
Similar thing: http://www.diyaudio.com/forums/tubes-valves/172984-2a3-spud.html
Sorry… what's difficult about the filament power supply? 5 V at 1.5 A. The Western Electric manual says A/C or DC is fine, tho' I suspect that A/C direct would give a bit of hum. Or maybe not much, being that the grid needs to be about –60 volts in nominal operation, and the μ is 3.5 … The ±2.5 V of a balanced A/C filament (and the linearity of the tube's electron emission) ought to pretty much cancel out well.
http://home.versatel.nl/chiararomee/diy/triton/triton.gif, as a starting point.
Don't want the very nice and photogenic 6SN7? Use a 12BZ7: no one writes much about it, but I've come to like this little workhorse. Nice and linear, double the IK of a 12AX7, and dual like the SN.
Strictly speaking, the 300B filament balancing 100Ω pot isn't necessary. Just a pair of 50Ω resistors. Its not hard to locate 3 watt rheostats, these days. 774–026TB32R101B1A1 … mouser, $5.36 quantity 1. 5 watt.
Dunno. I respect your opinion Shoog, so … I must be missing something.
GoatGuy
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Many moons ago I built a version of this amplifier:
http://community.fortunecity.ws/rivendell/xentar/1179/projects/legacy/Legacy.html
I used a big ol' HP outboard regulator, though someone on the cheap could get away with a good CLC filter. Only one driver tube required.
http://community.fortunecity.ws/rivendell/xentar/1179/projects/legacy/Legacy.html
I used a big ol' HP outboard regulator, though someone on the cheap could get away with a good CLC filter. Only one driver tube required.
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A single ended DHT is pretty simple to begin with. 3 tubes, 2 transformers, a choke, some caps and resistors. Nothing complicated about that. But it won't be cheap, no.
Attached is the schematic of the amp that turned me ( and 1000s of others) on to SET DHT. You could make it simpler, but probably shouldn't.
Attached is the schematic of the amp that turned me ( and 1000s of others) on to SET DHT. You could make it simpler, but probably shouldn't.
Attachments
Nice diagram, but the screen grid (G2) of the WE310 has a capacitor whose value is not specified. Also, it seems (to me at least) that quite a few of the capacitor values are either cavalierly specified, or, just kind of wishfully over-specified. I'm sure it sounded quite nice though.
GoatGuy
It seems that people who build DHT are very particular about both their power supply and their filament supply, and you can well understand why when both are sources of hum and colouration. I think if you are going to go to the trouble of building with these valves then they deserve you go the extra mile to allow the extra investment to shine through.
Achieving a good driver implementation which doesn't saddle the final with distortion is another complex area - low gain triodes need good drive.
Remember the good old days when valve amps were synonymous with high levels of audible hum - thats what the old purist designs offer.
An interesting discussion of the issues involved in AC v DC heater, and for me 3-5mV of hum would be totally unacceptable from an AC heated 300B:
http://www.diyaudio.com/forums/tubes-valves/42104-ac-dc-current-300b-2a3-tube-filaments.html
I think a better bet if simple is your objective is to go with one of the excellent IHT where things like AC heaters are guaranteed not to be an issue. You still need to pay attention to your Power supply but this is not that difficult with chokes and a good quality final cap. remember the intrinsic value of most DHT like the 300B is there extreme intrinsic linearity making for a clean balanced sound. There are a few excellent IHT which can match them in linearity.
So its my opinion, but I think setting out with the intention of creating a minimal parts 300B amp is almost bound to end in disappointment and hum.
Shoog
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Those cathode bypass caps look marginal to me. Those old designs where constrained by what was available in a reasonable size rather than minimising phase shift and achieving low end extension. Again its another one of those compromises. Look at Allan Wrights 300B PP amp to see the size of bypass caps which take them completely out of the picture (8000uf back to back with 8000uf for an effective value of 4000uf).
Shoog
there is a lot of discussion on AC and DC heating DHTs in this thread:
http://www.diyaudio.com/forums/tubes-valves/38248-new-dht-heater.html
I was recently handed an SE 300B amp using centre tapped 5V windings to AC heat the 300B, it sounded dirty, congested and whilst it played tunes lacked any real fidelity.
I switched it to using DiyHiFiSupply DHT filament supply boards, and clarity, dynamics and resolution all appeared. These were then changed to TentLabs DHT filament supply modules, and there was a further improvement in tone and soundstage.
No other changes were made to the amp, but it was now beginning to suggest what a well implemented 300B amp can be capable of.
http://www.diyaudio.com/forums/tubes-valves/38248-new-dht-heater.html
I was recently handed an SE 300B amp using centre tapped 5V windings to AC heat the 300B, it sounded dirty, congested and whilst it played tunes lacked any real fidelity.
I switched it to using DiyHiFiSupply DHT filament supply boards, and clarity, dynamics and resolution all appeared. These were then changed to TentLabs DHT filament supply modules, and there was a further improvement in tone and soundstage.
No other changes were made to the amp, but it was now beginning to suggest what a well implemented 300B amp can be capable of.
As for the caps in that old design, it's just the first version of the schema I dug up. I will look for a more refined version. As for "over-spec'd", well that's Jean Hiraga for you. He never met a giant cap he didn't like. 😉 (see Hiraga Le Monstre amp)
Just showing that it can be simple, but you shouldn't bare it down to nothing. A pentode input, 300B output along with some caps and iron is pretty darn simple. You'd have to go to a 1 tube amp with an SS power supply make it simpler.
Just showing that it can be simple, but you shouldn't bare it down to nothing. A pentode input, 300B output along with some caps and iron is pretty darn simple. You'd have to go to a 1 tube amp with an SS power supply make it simpler.
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