In case you are not aware of the interesting work done a few years back with the 2P29L over at bartola.co.uk.
https://www.bartola.co.uk/valves/?s=2p29l
Below, is one of their headphone/line amp diy designs for the 2P29L
https://www.bartola.co.uk/valves/?s=2p29l
Below, is one of their headphone/line amp diy designs for the 2P29L
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Thanks Ken - Ale is a fan of the 2P29L. He's a friend of mine and we did a big preamp shootout some years ago which you can see on his site. The 2P29L did very well on that. I've stopped using SIC diodes in the cathode and I also prefer a resistor load, so that particular design isn't for me.
You’re welcome, Andy. I‘ve been checking in on Ale’s interesting DHT work from time to time. The 2P29L, in particular, appears to offer a unique combination of benefits. Sort of a sweet spot amongst low-power affordable DHT triodes. I have it earmarked in my mind as the valve I would utilize should I ever build a DHT linestage.
Hi Fla
This is all about finding something which pleases your ear. Request you to try:
1. Filament bias, I tried everything, liked filament bias the most
2. Put 1uf - 2.2uf cap as first cap before the choke and adjust/reduce 500r to get right voltage
3. You may try 10k:600r line transformer (4:1 voltage ratio) as parallel feed. Can buy within $30 budget for the taste of it first.
Congratulations for your DHT pre, this is the best to my liking. I built and use, as you know, 3a5 pre for many years and a I am really happy.
Regards
This is all about finding something which pleases your ear. Request you to try:
1. Filament bias, I tried everything, liked filament bias the most
2. Put 1uf - 2.2uf cap as first cap before the choke and adjust/reduce 500r to get right voltage
3. You may try 10k:600r line transformer (4:1 voltage ratio) as parallel feed. Can buy within $30 budget for the taste of it first.
Congratulations for your DHT pre, this is the best to my liking. I built and use, as you know, 3a5 pre for many years and a I am really happy.
Regards
@minhaj
I do want to try filament bias sometime. This 2P29L preamp design was only breadboarded, though, I never built it. During that breadboarding process I tried about 10 or 12 different tube types and I found I preferred the 1626 but the 2P29L and the 6V7G were really nice too - those were the 3 that stood out.
Here's a link to a thread about the "Boogie Factor 1626" preamp I built, if you're interested.
https://www.audiokarma.org/forums/index.php?threads/1626-preamp-build.931276/
I do have another preamp build in mind but I'll likely be breadboarding some amps first. But, eventually, I do want to build a pre with some type 10 tubes I have. Not sure if filament bias is possible with them. I've heard that some tubes are better candidates than others for filament bias. I need to research it more.
I'm also interested in the 3A5 as an input tube, though, not in a separate preamp. My most recent project was an "inverted SET" (iSET) which I call the Nuance. iSET is a concept that Andy pioneered. I used 26s on the input and 6N6G outputs. Here's a link to that build:
https://www.audiokarma.org/forums/index.php?threads/the-nuance-my-inverted-set-diy-project.990205/
Anyway, I've thought of building a mini iSET using the 3A5 on the input and another 7 pin mini, the 6AQ5, for the output tube. The 6BQ5 would also be a possibility. That's not likely to make its way to the bench soon, though, as I've got some DHPs I want to try.
I was thinking of using 1626 as a driver in my 2a3 amp instead of the 6SN7, if I put a 2P29L in front of it. Right now it's just the 2 stages but if I add the 2P29L I could maybe do with less gain in the driver tube. Looking at the curves it seems possible with a resistor in anode and cathode and cathode bypass cap. By all means go a bit OT and tell me how the 1626 worked out.
The 10Y can be used with filament bias. The tubes that work well in filament bias are those with low bias voltage. The 10Y could fit that. Once you get to a bias of 20v or more, combined with the current drawn by the filament, you're looking at big filament transformers and a big wattage cathode resistor. It all gets very impractical. Type 46 is maybe on the cusp, but that would be a big demand. Read about that on Bartola valves.
The 10Y can be used with filament bias. The tubes that work well in filament bias are those with low bias voltage. The 10Y could fit that. Once you get to a bias of 20v or more, combined with the current drawn by the filament, you're looking at big filament transformers and a big wattage cathode resistor. It all gets very impractical. Type 46 is maybe on the cusp, but that would be a big demand. Read about that on Bartola valves.
The ‘Boogie Factor’ preamp schematic shows level adjustment pots. at both the input and output. I presume, this is a one or the other option, but not both, correct?
I have a similar 2P29L linestage using Coleman Regs , 305V HT and 10k non-inductive resistors as loads . I have played with filament bias (which I always find inconvenient) and stacked schottky diodes but have settled on a 5 ohm cathode resistor and fixed bias . I'm running this with 0.022uf teflon caps on the inputs for midbass upwards and taking the sub out from the 2.1 output of my DAC . Bias is a very basic and cheap setup : unregulated 15V DC , LN150 CCS-fed LM4040-4.1 voltage reference IC with the bias taken via RCRC network . I may experiment with other voltage ref chips , as the LM4040 was a 60p jellybean part . It works well , sounds good and is dead-quiet , may be worth trying this bias arrangement if you already have a cap on the input
Andy, I don't know if there would be any difference running the 1626 as a driver but I'm loving it as a preamp. I very much agree with your assessment of its sonic attributes, which I documented in my build thread. The gain is minimal, which is what I was looking for, since I don't really need any gain. But, unlike a passive, it really livens up the sound. Everything just swings more, yet it's not particularly overt about it.
I mostly use it with tube amps, such as a Pilot 260 (PP EL34). It works especially well with the PP Magnavox 175 console amp that I modded to use 6N6G outputs and the little Magnavox SE 6BQ5 that I modded to use 12BH7 outputs.
https://www.audiokarma.org/forums/index.php?threads/magnavox-175-185-build-with-a-twist.934198/
https://www.audiokarma.org/forums/i...0-or-8600-conversion-to-12bh7-outputs.824135/
The output impedance is low enough that it even works well with SS and Class D. I recently picked up a little Aiyima A-07 to power the bass using an active crossover. This little amp has been getting lots of praise, so while I was breaking it in for a few weeks I listened to it full range. It's quite good on its own but with the Boogie Factor in front it's even more impressive.
I'm guessing it would complement the sound of the 2P29L nicely.
The pots are all functional.
I use the two mono PEC pots to adjust the left / right balance, which is important to me because I have a couple of listening positions, neither of which is centered between the speakers. The stereo stepped attenuator allows me to adjust the overall volume without changing the left / right balance and its channel to channel balance is perfect, so adjusting it doesn't affect the left / right balance.
I presume that the additional (up to) 25K of output impedance hasn’t caused any problems?
Converted the 2P29L stage to filament bias with Rod's regs. It's really good - it reminds me strongly of the 10Y. The same kind of lively yet refined sound, very involving. Good on everything - bass, mids, treble. Great piano sound, but same for the drumkit, vocals and everything else. I'm loving it - going through all my demo tracks with a smile on my face.
Right now it's acting as the front end of my 2a3 amp. So 2P29L > 6SN7 > 2a3. FT-2 teflon coupling caps. It would certainly improve all those Chinese 300B Sun Audio circuits with 2 stages of 6SN7. It would lift them to the next level.
Right now it's acting as the front end of my 2a3 amp. So 2P29L > 6SN7 > 2a3. FT-2 teflon coupling caps. It would certainly improve all those Chinese 300B Sun Audio circuits with 2 stages of 6SN7. It would lift them to the next level.
It's most probably 9V + 9V in Parallel.
9V rms gives around 12.5 - 13.2V DC, depending on the diode types, resistances, load current &c...
It's a 9+9v transformer. So it has 2x outputs of 9v giving 12.7v into Rod's regs. Seems to work OK.
I could tart it up but it sounds fine right now. It could be optimised, of course.
I could tart it up but it sounds fine right now. It could be optimised, of course.
Andy, what’s your assessment of the sound impact of leaving the 30R cathode resistor unbypassed? I realize that it’s low value makes capaitive bypassing impractical without resort to eletrolytics.
The whole idea of filament bias, as introduced to most of us by Thomas Mayer, is to get rid of the cathode bypass cap. I don't think there's a problem with 30 ohms. No need to bypass it, surely? In any case I use DC Link caps as bypasses, but not with filament bias.
https://www.monoandstereo.com/2014/12/interview-with-thomas-mayer-vinlsavor.html. Interview with Thomas.
The 2P29L has a rated gm of 2.15mA/V; this amounts to an intrinsic cathode 'resistance' of 465Ω. Adding a 30Ω external resistor makes very little difference - but there is a little linearisation from the Rk feedback.
The low filament current makes for low dissipation in the cathode resistor too - making this DH tube an excellent candidate for filament bias, to the point that there can be few reasons not to bias it this way.
I also removed the aluminium shield. But funny thing is that, I cannot see the flame of the filament and all the measure are not quite right. Can you see the flame of the filament? Maybe I am not lucky enough and bought some flawed tubes.