The only "trick" that I can think of right now is the voltage doubler but that is only possible if the winding is specified for about 2x the current the filament is currently demanding. If not, you will get less or much less than 2x voltage depending on the specifications of the transformer.
The standard voltage regulation does not solve the intermodulation distortion issue. The Coleman's regulator is both current and voltage regulator with intrinsic soft start. You will need to use a dedicated toroidal with screen. The specifications and recommendations you can find them here:
https://www.lyrima.co.uk/dhtreg/dhtRegIntro.html
The standard voltage regulation does not solve the intermodulation distortion issue. The Coleman's regulator is both current and voltage regulator with intrinsic soft start. You will need to use a dedicated toroidal with screen. The specifications and recommendations you can find them here:
https://www.lyrima.co.uk/dhtreg/dhtRegIntro.html
Hello elac310,
I also have built such an amp with about the same configuration than yours, but as a push-pull version. Phase inversion is done by the input transformer (Sowter, 1:1+1), followed by a PCF200 - Triode input amplifier, Pentode voltage driver for the 211. Followed by a PL508 (former vertical deflection output in color TVs) adding the necessary current needed for operation into the positive grid range of the 211 (galvanic coupling), so I can use quite a low plate voltage of 750V. The PL508 do not only have a cathode resistor (820 Ohm), but also a choke formed by the 8kOhms primary winding of a small PP output transformer - to reduce the loss of AC driving power. Biasing of the 211 (actually on 70 mA) via the grid bias of the PL508. Output transformer 8 kOhm, 100W from Experience Electronics. I am using the Psvane 211 (the pair at ca. 300€) which have already about 3000 hours (counter) - and are still in perfect shape. Really good quality. Heating by two Meanwell switchmode supplies (adjustable) 12V 10A over thermistors and additional RF filter chains. The amp is dead silent, I mostly use it as home cinema amp due to its power and dynamics. Friends of mine love its smooth performance with classical music.
Salut de la Moselle, best regards
Uli
I also have built such an amp with about the same configuration than yours, but as a push-pull version. Phase inversion is done by the input transformer (Sowter, 1:1+1), followed by a PCF200 - Triode input amplifier, Pentode voltage driver for the 211. Followed by a PL508 (former vertical deflection output in color TVs) adding the necessary current needed for operation into the positive grid range of the 211 (galvanic coupling), so I can use quite a low plate voltage of 750V. The PL508 do not only have a cathode resistor (820 Ohm), but also a choke formed by the 8kOhms primary winding of a small PP output transformer - to reduce the loss of AC driving power. Biasing of the 211 (actually on 70 mA) via the grid bias of the PL508. Output transformer 8 kOhm, 100W from Experience Electronics. I am using the Psvane 211 (the pair at ca. 300€) which have already about 3000 hours (counter) - and are still in perfect shape. Really good quality. Heating by two Meanwell switchmode supplies (adjustable) 12V 10A over thermistors and additional RF filter chains. The amp is dead silent, I mostly use it as home cinema amp due to its power and dynamics. Friends of mine love its smooth performance with classical music.
Salut de la Moselle, best regards
Uli
I get the sense that some of the arguments around things like that really derive from people stating that the circuit in question sounds bad when in fact it's just not the sound they were looking for.
You might look into what Bottlehead did years ago with their FC-1 filament choke. I don't recall exactly the details other than that it was a rectified voltage taken from a power transformer winding specified for the AC voltage of the filament . ie 2.5V for a 2a3/5V for a 300B , into a dual bay bifilar wound choke designed to have enough leakage inductance to do the job.
There's a post here that mentions it and in the attached schematic, another way.
The FC-1 was discontinued (though for the 211 you would have to have a different one custom wound anyway) but I don't know whether they decided it wasn't effective enough or whether perhaps it had something to do with their customers trying to squeeze them into a preordained form factor that was already pretty tight. You'd need to do some probing.
Yes. It's not a lot of feedback, but helps to overcome part-to-part variations in the driving stages, and slightly reduces the source impedance driving the output valves. This is actually a pretty well designed circuit.
All good fortune,
Chris
I would suggest that those seeking knowledge begin by ignoring the pronouncements of Gurus and other self-proclaimed Experts who try to reduce a complex discussion to some cookbook formula.
Real cooking is a process, not just a list of ingredients, and so is a technical design. Seeking knowledge, we must begin somewhere, but we must not be distracted by shortcuts that substitute questionable simplifications for real knowledge. "Feedback is bad" is a modern example of poor understanding amplified by the echo chamber of modern discussion group thinking. Question all assumptions, and as you progress question the assumptions beneath those.
If this comes across as harsh or uncharitable to Gurus and Experts, please forgive me, but it's been a dark night in America.
Always good fortune,
Chris
Real cooking is a process, not just a list of ingredients, and so is a technical design. Seeking knowledge, we must begin somewhere, but we must not be distracted by shortcuts that substitute questionable simplifications for real knowledge. "Feedback is bad" is a modern example of poor understanding amplified by the echo chamber of modern discussion group thinking. Question all assumptions, and as you progress question the assumptions beneath those.
If this comes across as harsh or uncharitable to Gurus and Experts, please forgive me, but it's been a dark night in America.
Always good fortune,
Chris
A friend of mine with a long experience in tube amp construction has built the Uesugi 211 1971 for me. The heating of the 211 was changed to vdc but for the rest we sticked to the original schematic. With the exception of a very slight hum it’s a very lively and high resolution amp which surprised me for its ability to deal with a pretty complex load (2x15” bass each channel, comp drivers for mid and high, with variable impedance). Even the bass is surprising and my reference is a Crown 1Kw+ transistor amp…. The slight hum could be caused by some stress on the power supply: although we used toroid transformers the HT amperage in the schematic is somewhat underrated as the 2x211 alone already consume 100-120 mA
Hi Chris, couldn't agree more.
Unfortunately, it appears to be an uphill battle.
It is always easier to believe the gurus instead of educating yourself; that's hard work so is seldom undertaken.
Jan