Hiya,
Been posting some pictures here and there of a new project I have started on, might as well share the whole thing. The idea started in 2018 for a regular amp (speakers), but life happened and I lost track of audio once more. The good thing is that I already have some parts that I can re-use, so in today's thinking "they are free".
Goal:
Tubes:
As I want to tinker with the driver tube a bit, the power supplies will be setup to be universal for a 250V output tube and a 200V driver, current for each tube can be up to 50mA with headroom left.
4P1L will run at 225V/30mA/-19V initially (245V/30mA B+)
6E6P will run at 200V/30mA/-3.4V, 2P29L will be 6mA/-20V, so we have 30mA/-20V as worst cases for the PSU (225V/30mA B+)
As I am betting on the 2P29L, the rest of the info will focus on this combination so as not to have two projects in one.
Supply Chassis:
Signal Chassis:
Iron:
signal path
eTracer loadline on one of the 4P1L I have tested. 1.2W max with 10K.
Step 1: Concept
Step 2: Design PCBs for test setup
Step 3: Test
Step 4: Build chassis and integrated PCBs
Been posting some pictures here and there of a new project I have started on, might as well share the whole thing. The idea started in 2018 for a regular amp (speakers), but life happened and I lost track of audio once more. The good thing is that I already have some parts that I can re-use, so in today's thinking "they are free".
Goal:
- Headphone amplifier, 35 ohms
- Tube, single-ended,1000-1500mW of raw power power
- Daily beater, so no rare tubes, nothing end-game, just good music and a cool looking piece of kit
- Must fit on desk and desk must not collapse
Tubes:
- 4P1L
- 2P29L or 6E6P, might also look at other wee tubes like 6Z49, 6C4S, 5842 etc
As I want to tinker with the driver tube a bit, the power supplies will be setup to be universal for a 250V output tube and a 200V driver, current for each tube can be up to 50mA with headroom left.
4P1L will run at 225V/30mA/-19V initially (245V/30mA B+)
6E6P will run at 200V/30mA/-3.4V, 2P29L will be 6mA/-20V, so we have 30mA/-20V as worst cases for the PSU (225V/30mA B+)
As I am betting on the 2P29L, the rest of the info will focus on this combination so as not to have two projects in one.
Supply Chassis:
- Separate chassis for raw DC supplies to conform to the "must fit on desk" rule
- PCBs
- B+ will be SiC diodes, eChoke and MKP caps
- Filaments with SiC diodes and FW/KW caps
Signal Chassis:
- Filter for DH filaments, then Coleman regulator (current source) for DHTs
- LDO voltage regulator for IHT
- Passive B+ filter with RCRC to tune for both stages
Iron:
- 2x SE OPT 10K/50mA
- 2x Lundahl LL2763AM-40mA interstage
- 2x Toroid 250-210-0-210-250V/330mA, 12V/4A, 12V/4A
signal path
eTracer loadline on one of the 4P1L I have tested. 1.2W max with 10K.
Step 2: Design PCBs for test setup
Step 3: Test
Step 4: Build chassis and integrated PCBs
Attachments
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How big is your desk? 😉 Not sure you need any pcbs for this other than the 4 Coleman boards. There will be nothing much to fit on a PCB here. Also, at 1W dissipation, the 2K5 1/2W resistor will be very short lived. Better use 5W for cathode res. I would rather use a nice indirect heated tube like the 6e6p for the input stage and the 2P29L for the output stage. The 4P1L is too microphonic, at least in my hands. Not a very practical tube but maybe I did something wrong and I am going to try it again.
I looked quickly at the lundhal LL2763 and didn't find any Alt to get 1:1 ratio. What connection gives you that?
I looked quickly at the lundhal LL2763 and didn't find any Alt to get 1:1 ratio. What connection gives you that?
PSU will be on a shelf nearby, the signal section should fit in a 200x300mm chassis. OK, still not small. Mostly the signal iron taking up space.
PCBs: Yep, this will be all that goes into the signal chassis (2 of the longer ones). and yes, the holes for the large MKP caps are too small, new boards already ordered).
Supply chassis has six boards with rectifiers/caps: 4 of these for the filaments and 2 similar ones for B+ but with 500V MKPs.
When I have the test setup working (wood board) and all the right values etc, I will make a dedicated PCB for the headphone amp. That way I can use the seperate PCBs for future test setups.
Ah yep. there are some typos in there I see. Also the 2P29L has a lower rp. Thanks for catching that! I have a lot of 2W/5W Kiwames, so it was going to be one of those either way. I should just not place wattages, I never re-check them.
The LL2763 can be hooked up in 4:4 even though the datasheet does not list it, but I have to test that. Induction will drop. Else get another IT.
Yes, the 6E6P is already on my short list 🙂 Microphonics should be manageable and I have been used to this in older tubes I ran. There are no speakers to introduce noise, and I almost never bang my head on the table.
I also thought of just using the 6E6P as a spud, but past spud amps have never stayed around for long. The 5842 is also a really nice tube, I always enjoyed that one as a driver and even a spud. But don't get me started, I will never make up my mind 😀 The all-russian theme is pretty cool.
The 2P29L (rp=4300) as output tube is a little on the weak side I think, but I should have some high Z OPTs around to test that out first. 2P29L driver and 6E6P output? 😀
PCBs: Yep, this will be all that goes into the signal chassis (2 of the longer ones). and yes, the holes for the large MKP caps are too small, new boards already ordered).
Supply chassis has six boards with rectifiers/caps: 4 of these for the filaments and 2 similar ones for B+ but with 500V MKPs.
When I have the test setup working (wood board) and all the right values etc, I will make a dedicated PCB for the headphone amp. That way I can use the seperate PCBs for future test setups.
Ah yep. there are some typos in there I see. Also the 2P29L has a lower rp. Thanks for catching that! I have a lot of 2W/5W Kiwames, so it was going to be one of those either way. I should just not place wattages, I never re-check them.
The LL2763 can be hooked up in 4:4 even though the datasheet does not list it, but I have to test that. Induction will drop. Else get another IT.
Yes, the 6E6P is already on my short list 🙂 Microphonics should be manageable and I have been used to this in older tubes I ran. There are no speakers to introduce noise, and I almost never bang my head on the table.
I also thought of just using the 6E6P as a spud, but past spud amps have never stayed around for long. The 5842 is also a really nice tube, I always enjoyed that one as a driver and even a spud. But don't get me started, I will never make up my mind 😀 The all-russian theme is pretty cool.
The 2P29L (rp=4300) as output tube is a little on the weak side I think, but I should have some high Z OPTs around to test that out first. 2P29L driver and 6E6P output? 😀
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I know the 4P1L well because I've built several amps with PSE 4P1L outputs, including my present daily amp. Amps, not headphone amps, though. What you need to know about the 4P1L is that it needs 35mA to sound its best, even 40mA. 30mA is possible but it gets progressively thinner in sound the lower current you go. Evan then, the sound is on the thinner side, but with good detail, treble and bass.
What the 4P1L needs is a driver tube with a full and rich sound to fill in the thinness. The 10Y, though very detailed, didn't quite provide the right synergy. The 26 is pretty good. The 27 mesh plate is a little fuller still. I'm using the 26 at present though I pull the 27 mesh out at times. This needs to be the Philco type of square mesh, not the RCA type of cylinder mesh with a pin holding it on one side.
I fully support an all-DHT solution, and the 26 is a bigger build so the 27 mesh driver was a cut-down alternative. It's one of a handful of indirectly heated tubes I like listening to, though it doesn't have the ultimate clarity of a DHT. I've used the 2P29L a lot also and I'd describe it as neutral rather than full or rich, so the end result might be on the thinner end tonally, though it will have plenty of clarity and detail. I don't remember this combination in my prototypes. So my contribution would be that 26 or 27 into 4P1L works nicely. 2P29L is a maybe. My guess is that you might want a slightly richer tone but I can't be sure of this without hearing it. It could also be a case of using headphones with a fuller tone.
What the 4P1L needs is a driver tube with a full and rich sound to fill in the thinness. The 10Y, though very detailed, didn't quite provide the right synergy. The 26 is pretty good. The 27 mesh plate is a little fuller still. I'm using the 26 at present though I pull the 27 mesh out at times. This needs to be the Philco type of square mesh, not the RCA type of cylinder mesh with a pin holding it on one side.
I fully support an all-DHT solution, and the 26 is a bigger build so the 27 mesh driver was a cut-down alternative. It's one of a handful of indirectly heated tubes I like listening to, though it doesn't have the ultimate clarity of a DHT. I've used the 2P29L a lot also and I'd describe it as neutral rather than full or rich, so the end result might be on the thinner end tonally, though it will have plenty of clarity and detail. I don't remember this combination in my prototypes. So my contribution would be that 26 or 27 into 4P1L works nicely. 2P29L is a maybe. My guess is that you might want a slightly richer tone but I can't be sure of this without hearing it. It could also be a case of using headphones with a fuller tone.
Andy,
You and Ale were my inspiration for trying these tubes, so. Thanks!!! 😉
Great little tubes that are perfect in terms of stats, price and availability. The US and european tubes are getting so expensive and rare, that all the russian tubes are perhaps a new lease on life for tube amp builders.
My all time favorite amp at the time was a 26/10Y/842, kind of at the peak of my hobby, but I burned out a year or so after that listening to components instead of music. I still have a bunch of nos euro/us tubes, but don't want to use them due to scarcity/price and the fact they will be burning 6 hours a day listening to spotify.
It's just a fun project to get back into audio a little, using tubes that I am not afraid to burn up.
Making all the PCBs is just a part that I like even though they may be over-engineered and not necessary in the way I am doing it. "Back then" I never used PCBs "because blasphemy", but now the final sound quality is not the only factor for making these amps, so lets have fun designing PCBs. The prices for making PCBs is so low now vs 20 years ago... just great fun.
Thanks for the current rating tip! I will definitely try it out!!! I take it the tube was running under 200V anode-cathode?
If this combo ends up sounding thin then I will just have an excuse to try other tubes 😉
You and Ale were my inspiration for trying these tubes, so. Thanks!!! 😉
Great little tubes that are perfect in terms of stats, price and availability. The US and european tubes are getting so expensive and rare, that all the russian tubes are perhaps a new lease on life for tube amp builders.
My all time favorite amp at the time was a 26/10Y/842, kind of at the peak of my hobby, but I burned out a year or so after that listening to components instead of music. I still have a bunch of nos euro/us tubes, but don't want to use them due to scarcity/price and the fact they will be burning 6 hours a day listening to spotify.
It's just a fun project to get back into audio a little, using tubes that I am not afraid to burn up.
Making all the PCBs is just a part that I like even though they may be over-engineered and not necessary in the way I am doing it. "Back then" I never used PCBs "because blasphemy", but now the final sound quality is not the only factor for making these amps, so lets have fun designing PCBs. The prices for making PCBs is so low now vs 20 years ago... just great fun.
Thanks for the current rating tip! I will definitely try it out!!! I take it the tube was running under 200V anode-cathode?
If this combo ends up sounding thin then I will just have an excuse to try other tubes 😉
I'm fully with you for using tubes you can happily burn out. I have 40 of 4P1L, all tested and graded. I also have plenty of 26 tubes. They're not rare, thankfully. I have plenty of 2P29L as well. And some backups of the 27 mesh, which actually is quite rare though still available.
I only briefly used a single 4P1L in my amp output but I do remember it sounded better than 2 in parallel. As outputs I run them at 240V a-k and 35mA. A very useful tube - worth buying up a few while they're cheap. 6C4C have gone up a lot recently.
I only briefly used a single 4P1L in my amp output but I do remember it sounded better than 2 in parallel. As outputs I run them at 240V a-k and 35mA. A very useful tube - worth buying up a few while they're cheap. 6C4C have gone up a lot recently.
Not a fan of paralleling tubes myself, same with the internally paralleled tubes like that 6C4C. Too bad the single plate 2A3 is hard to find now, the Sovtek ones back then looked really nice and were super affordable.
At some point I made a few spud amps using the 5842, 6S45P, 437A, EC8010 for a single stage amp powering my 108dB speakers (just the AER full-range unit). You would say a single stage would beat a multistage amp, but my 3 stage DHT amps were still a night and day improvement over the spuds. I think the indirectly heated filament has such a large influence on the sound that it will just never be the same experience. Even one IHT and then a DHT will leave it's mark. Not saying it can't sound absolutely gorgeous, just that a full DHT amp will sound more gorgeousererer.
BTW: I have always hoarded tubes, so have quite a stash of nos EU/US tubes. Even 25 years ago the number of tubes was dwindling, and their prices inflating. I bought a ton of nice DHTs back then. Lets just say you could get VT25/801A tubes at $10-15 each when buying in bulk, as no one wanted the 10/10Y variants because they had a high rp.
Also a very nice tube is the 842, a lesser known and really rare variant of the 801A. Most people have probably heard of the 841, well the 842 has about half the mu and rp of an 801A. Those were expensive back then, $50-60 each, I found about 10-12 pieces in 15 years of collecting. Pfff. today a chinese 2A3 replica costs $300.
I bought a box of 50 of the 4P1L and the 2P29L as well, about $3 each with shipping. Can't go wrong buying bulk, a lot of the dealers are open to lower bids if you buy a bunch at the same time. Same with the 6E6P-DR, I think I paid $4 each back in 2018 and I see them going for $8-10 each now.
At some point I made a few spud amps using the 5842, 6S45P, 437A, EC8010 for a single stage amp powering my 108dB speakers (just the AER full-range unit). You would say a single stage would beat a multistage amp, but my 3 stage DHT amps were still a night and day improvement over the spuds. I think the indirectly heated filament has such a large influence on the sound that it will just never be the same experience. Even one IHT and then a DHT will leave it's mark. Not saying it can't sound absolutely gorgeous, just that a full DHT amp will sound more gorgeousererer.
BTW: I have always hoarded tubes, so have quite a stash of nos EU/US tubes. Even 25 years ago the number of tubes was dwindling, and their prices inflating. I bought a ton of nice DHTs back then. Lets just say you could get VT25/801A tubes at $10-15 each when buying in bulk, as no one wanted the 10/10Y variants because they had a high rp.
Also a very nice tube is the 842, a lesser known and really rare variant of the 801A. Most people have probably heard of the 841, well the 842 has about half the mu and rp of an 801A. Those were expensive back then, $50-60 each, I found about 10-12 pieces in 15 years of collecting. Pfff. today a chinese 2A3 replica costs $300.
I bought a box of 50 of the 4P1L and the 2P29L as well, about $3 each with shipping. Can't go wrong buying bulk, a lot of the dealers are open to lower bids if you buy a bunch at the same time. Same with the 6E6P-DR, I think I paid $4 each back in 2018 and I see them going for $8-10 each now.