Hi Rod!
to be honest, I was intended to make something similar to what you have done. Double MOSFET, both on (+) and (-) filament side. But as soon as you have invested in this, there is no need for me to re-invent the wheel. I will place an order for your good thing.
LT devices sound bad as you mention, although the cap bypassing sounded much much better for the reason you mentioned. But again, distance to CM choke only solution was considerable. With your solution against the choke only solution, I would expect more precise and defined sound mainly on lower registers, but more articifial result due to electronics. But the choke-only solution is not a real solution after all, remember the voltage drifts way too much beyond tubes specs, so the dilema is only theoretical.
With my next project, the all Tenefunken amp, RE074N-RE074N-RS237 I will be able to get rid of all electronics on filaments of 1st & 2nd tube, except power tube where they are unavoidable. On RE074N I am able to use tube rectification with double pi filter and cm choke without any electronics because filament current is 65 mA! But 3,3A is something radically different.
CU soon!
Peter.
to be honest, I was intended to make something similar to what you have done. Double MOSFET, both on (+) and (-) filament side. But as soon as you have invested in this, there is no need for me to re-invent the wheel. I will place an order for your good thing.
LT devices sound bad as you mention, although the cap bypassing sounded much much better for the reason you mentioned. But again, distance to CM choke only solution was considerable. With your solution against the choke only solution, I would expect more precise and defined sound mainly on lower registers, but more articifial result due to electronics. But the choke-only solution is not a real solution after all, remember the voltage drifts way too much beyond tubes specs, so the dilema is only theoretical.
With my next project, the all Tenefunken amp, RE074N-RE074N-RS237 I will be able to get rid of all electronics on filaments of 1st & 2nd tube, except power tube where they are unavoidable. On RE074N I am able to use tube rectification with double pi filter and cm choke without any electronics because filament current is 65 mA! But 3,3A is something radically different.
CU soon!
Peter.
in case you want to look at the theory, see my presentation from 2003
http://tentlabs.com/Components/Tubeamp/Tubefilament/assets/Heatingmethods.pdf
best
Hi Peter, what do you suggest for an RCA #80 as 1st cap in a CLC arrangement?
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With the size of your tube rectified/choke filament supplies wouldn't you be better off just using a few deep cell batteries and /small choke, trickle charge/resistor divider network when its off?
Massimo, I think that 1st cap on a CLC arrangement must be limited to 4uF, exactly as in case of 274A/B rectifier.
Hi Gianluca, please tell us - what does it mean: THIS ^
How are your 'Water Babies' ?
'This^' means I fully agree with the previous statement (yours). LT voltage regulators are just something not to be considered for DHT's if end result is an objective. The difference vs chokes (and I mean a choke used in the last spot at the tube pins) is huge and there is absolutely no contest with your solution.
I could not test Guido's nor other complex current regulated heaters so my experience with current regulators is limited to 3 pins devices and your PCB but, yes, they do work better in current than in voltage mode. Explanations are given here and there in this thread and in Guido's presentation and somewhere else.
The best solution I could find is to filter the raw supply with an initial LC filter (as a minimum) plus your regulators. I have them running on my 211's pre (water babies) and also in a soon-to-be-finished-when-Ill-have-some-free-time-during-Xmas 801A spud amp. OH! Yes I might dismantle that preamp to recycle parts for a new line level xover ... a pity but I am reshaping my whole set-up.
DHT's are so sensitive to filament heating, that's a fact. In my bigger amp with 801A-75TL I do use LCLCL filters, there was no room for a bigger filament transformer to accomodate the extra voltage required by regulators.
In very short words the main difference between voltage regulated filaments and current sourced/high impedance filaments are 'accuracy and detail' you can hear in the music there is a sort of muddiness and fuzziness that goes away.
I am also reading with interest the other discussion on gyrators/CCS which I will try to use in the named 801A spud amp I am building, that looks like a good move too to clean up the sound.
Gianluca
One more surprised victim here 
Yesterday I finished the DHT regulators. Last stop was Rod's solution. I have tried crazy and out of this world ideas there, even tripple chokes, two differential and one monstrous common mode right before the filament.
Rod's circuit gave something I was missing till now. When switching back to common mode choke (22H of inductance!) I felt I missed a great part of immediacy and dynamism of music. I will try to replace 1-2 parts with better sounding ones, I think it deserves so because the result is fantastic.
I will be back with more news during the days ahead.
Yesterday I finished the DHT regulators. Last stop was Rod's solution. I have tried crazy and out of this world ideas there, even tripple chokes, two differential and one monstrous common mode right before the filament.
Rod's circuit gave something I was missing till now. When switching back to common mode choke (22H of inductance!) I felt I missed a great part of immediacy and dynamism of music. I will try to replace 1-2 parts with better sounding ones, I think it deserves so because the result is fantastic.
I will be back with more news during the days ahead.
I think I have come to the end of this story...
Replaced R1 resistor with a DIY graphite rod. Copper lead firmly wrapped on one side, permanently glued with cyanoacryllic glue (like logo, etc). Other side was wrapped quite loose and moved back and forth till the desirable amount of resistance was achieved. Then firmly wrapped and glued as well.
Replaced the small plastic capacitor 0.22uF with a Sprague Vitamin Q of same value.
If you consider yourself a real DIYer, Rod's circuit sound amazing, like NOTHING whitnessed so far. And I have tried many... Performance lift with those two mods is amazing to my ears. I think I have come to the end of story of DHT heating and will never look back. Nothing has ever given me this upgrade of performance. And if you have the skills, you can perform those simple two mods and you will gain double its performance.
Well done Rod!
Replaced R1 resistor with a DIY graphite rod. Copper lead firmly wrapped on one side, permanently glued with cyanoacryllic glue (like logo, etc). Other side was wrapped quite loose and moved back and forth till the desirable amount of resistance was achieved. Then firmly wrapped and glued as well.
Replaced the small plastic capacitor 0.22uF with a Sprague Vitamin Q of same value.
If you consider yourself a real DIYer, Rod's circuit sound amazing, like NOTHING whitnessed so far. And I have tried many... Performance lift with those two mods is amazing to my ears. I think I have come to the end of story of DHT heating and will never look back. Nothing has ever given me this upgrade of performance. And if you have the skills, you can perform those simple two mods and you will gain double its performance.
Well done Rod!
I have not available the cord of my digital camera and I cannot upload a pic. The rod is taken out of a Duellund resistor, it is around 3mm, but you can use a 2mm rod. Some mechanical pencils are equipped with this kind of rod.
The improvement in sound quality is so big that is hard to believe! At least in my system. I was never prepared for this kind of shock!
Rod,
carbon comp resistors do not sound that good like carbon/graphite resistors. The mechanism of resistance generation in various materials os totally different. For audio signals, you should look nowhere except carbon film or graphite resistors. For frequencies in magnitude of MHz they produce excessive noise and are not suitable.
Metal film resistors is a real disaster for music. Like plastic caps. These all sound terrible.
Replace ALL metal film resistors in your regulator, I mean everything! Use nice and cheap carbon films and you will see... Regarding the caps, Vitamin Q and russian K40-Y9 are the best. And do not forget to get rid of this crap of metal in R1, it takes half of the sound!
I have experimented with everything I could imagine, regarding DHT heating, I heard better things with your regulator but it did not make me fly. As soon as I replaced the cap and the R1 crap my mind and soul flew away.
Today I plugged my RV258 Telefunken oldies and I have to admit that Rod's circuit drew me inside the performance of these fantastic tubes as I have never felt before.
I have to give Rod my congratulations once again. The performance with graphite rod and Vitamin Q cap makes your soul fly to paradise! Trust me!
Nicoch58
IME the graphite rod resistor is no better or worse than a MOX resistor. I believe the placebo effect does its job here... The more money or time we spend on so called improvements or tweaks the greater things we hear...
Try this: listen to the first 15 seconds of a track three times. Did you notice exact the same things in this record? Nope... The 3rd time is best due to our lack of good acoustic memory...
Back to topic. It takes a very good DHT regulator to outperform ac supply. I've done experiments with classic and exotic 3-pins voltage regulators and they suck the life out of music. I'll try tentlabs DHT supply in the future. Rods solution looks nice too!!
IME the graphite rod resistor is no better or worse than a MOX resistor. I believe the placebo effect does its job here... The more money or time we spend on so called improvements or tweaks the greater things we hear...
Try this: listen to the first 15 seconds of a track three times. Did you notice exact the same things in this record? Nope... The 3rd time is best due to our lack of good acoustic memory...
Back to topic. It takes a very good DHT regulator to outperform ac supply. I've done experiments with classic and exotic 3-pins voltage regulators and they suck the life out of music. I'll try tentlabs DHT supply in the future. Rods solution looks nice too!!
You're right about the 3-pin regulators - they are useless for filament heating. But ac-heating is also bad-sounding, compared to the possibilities of Direct-Heated Triodes.
The first test to make with a filament regulator is to compare to ac. If your new regulator does not sound better in every possible way than ac, then you have a failure.