My 300b driven by 4P1L is now alive, and fortunately there's more volume in my smallish room than I expected. Speakers are Alpair 10M. I'm listening flat out but I'm getting a good moderate background listening level. Some CDs are quieter, some are pretty much OK. Needs a bit more gain, maybe 1:2 but where to put it...at the input I should think.
Sound is smoother than the PSE 4P1L. I have cathode bias with a big polypropylene 47uF. I only have about 300v through the 300b stage and I can ramp that up. It's also a LL1682 which is 5K at 5R. I'll try it out with the NP Acoustics 3.4K OPT. The smoothness is promising. Could turn out nice.
Sound is smoother than the PSE 4P1L. I have cathode bias with a big polypropylene 47uF. I only have about 300v through the 300b stage and I can ramp that up. It's also a LL1682 which is 5K at 5R. I'll try it out with the NP Acoustics 3.4K OPT. The smoothness is promising. Could turn out nice.
The 4P1L can handle 30mA, even 35mA. I have a nice amorphous plate choke at the moment, NP Acoustics, and the alternative interstage i have is LL1660/18mA. 18mA is a bit low for a 4P1L which likes 20mA or over, and the LL1660 as an interstage has never sounded as good to me as the NP plate choke. But everything's possible, and there will be tradeoffs.
Since the LL1682 OPT is gapped for 50mA, my theoretical operating point is 290v a-k, 50mA, -60v. That could be increased with my second build with a NP Acoustics amorphous 3.4K OPT. If I'm going back to the 300b as my main amp, which seems likely, I'll have to try out a variety of operating points to find the sweet spot. Now that's a procedure which has probably launched a good number of threads and comments!
Since the LL1682 OPT is gapped for 50mA, my theoretical operating point is 290v a-k, 50mA, -60v. That could be increased with my second build with a NP Acoustics amorphous 3.4K OPT. If I'm going back to the 300b as my main amp, which seems likely, I'll have to try out a variety of operating points to find the sweet spot. Now that's a procedure which has probably launched a good number of threads and comments!
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Moving on, I've been happily listening to just the 4P1L into 300b two stage amp for a few days. I really, really like it. Very smooth and detailed. Just about enough volume for background listening.
Today I started experimenting with output transformers for my AK4490 DAC which outputs something like 2v with a NE5532 at the end of it. First off was a Lundahl LL1540 connected in 1:2. I could live with the volume of 1:2 though 1:3 might be better to cover quiet sources. Well, sound was pretty terrible - harsh and just generally yuk. All the smoothness was gone. So that one failed. Disappointing. The OPT will have to be considerably better than that one.
Today I started experimenting with output transformers for my AK4490 DAC which outputs something like 2v with a NE5532 at the end of it. First off was a Lundahl LL1540 connected in 1:2. I could live with the volume of 1:2 though 1:3 might be better to cover quiet sources. Well, sound was pretty terrible - harsh and just generally yuk. All the smoothness was gone. So that one failed. Disappointing. The OPT will have to be considerably better than that one.
I developed a simple circuit to prevent tube current runaway.
If the peek (or increasing DC) voltage on sensor resistor exceed setting limit, the first relay switch on, the first contact energised the second relay, which break off B++. The second contact set steady this condition, pulling up first transistor basis.
It can be realize with comparator too (better hysteresis adjustment).
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The driver for my first 300B with 26 + 45 + IT + 300B has been changed using an inexpensive old tube as a driver for 300B
use 2 stages InHT + DHT + IT + 300B (OT 2.5K)
I use: REN904 + B403 + IT (1: 2) + 300B.
does not disappoint, have a good sound
before:
20190724_165714.jpg - Google Drive
after:
20190802_115535.jpg - Google Drive
20190809_125218.jpg - Google Drive
20190802_152732.jpg - Google Drive
20190802_113340.jpg - Google Drive
use 2 stages InHT + DHT + IT + 300B (OT 2.5K)
I use: REN904 + B403 + IT (1: 2) + 300B.
does not disappoint, have a good sound
before:
20190724_165714.jpg - Google Drive
after:
20190802_115535.jpg - Google Drive
20190809_125218.jpg - Google Drive
20190802_152732.jpg - Google Drive
20190802_113340.jpg - Google Drive
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euro21 - is that your daily amp, the 300b with 801A input? Very nice circuit. Congratulations on making 2 stages work with a triode driver. Are you happy with the Sowter 9063 in 1:4? I just discovered I have a pair of LL1544 - amorphous core. They're something I'm keen to try.
I just spent 2 days building a complete duplicate 4P1L line stage. Line stage chassis + PSU and choke input filament supply chassis. This way I can leave my present 4P1L setup intact and experiment on the bench. I'll be trying out pentode mode to see if that will give me more gain without destroying the sound I'm getting in triode, which is really nice.
suwanned - wow, that's really high class building. One day I'll build myself a really good looking amp. Problem is I keep changing stuff in the search for perfection. I'm always recycling top plates, since all my stuff is modular. 3 triode stages is a way of relaxed building, avoiding all the challenges of getting 2 stages to work into a 300b and still sound good. I'm determined to crack this puzzle! I haven't even started on solid state stages out of my DAC, but that's another way of doing it. 8 volts out of my DAC would be just perfect.
I just spent 2 days building a complete duplicate 4P1L line stage. Line stage chassis + PSU and choke input filament supply chassis. This way I can leave my present 4P1L setup intact and experiment on the bench. I'll be trying out pentode mode to see if that will give me more gain without destroying the sound I'm getting in triode, which is really nice.
suwanned - wow, that's really high class building. One day I'll build myself a really good looking amp. Problem is I keep changing stuff in the search for perfection. I'm always recycling top plates, since all my stuff is modular. 3 triode stages is a way of relaxed building, avoiding all the challenges of getting 2 stages to work into a 300b and still sound good. I'm determined to crack this puzzle! I haven't even started on solid state stages out of my DAC, but that's another way of doing it. 8 volts out of my DAC would be just perfect.
https://www.diyaudio.com/forums/attachment.php?attachmentid=837371&stc=1&d=1587748669
https://www.diyaudio.com/forums/attachment.php?attachmentid=837376&stc=1&d=1587748669oq6hpAUiRuWiKoZsUdNFhvU[/IMG]
link my YT:
YouTube
https://www.diyaudio.com/forums/attachment.php?attachmentid=837376&stc=1&d=1587748669oq6hpAUiRuWiKoZsUdNFhvU[/IMG]
link my YT:
YouTube
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eduard has been emailing me a mouthwatering series of photos of European broadcasting equipment. Style is utilitarian and mostly grey, but I just love it. Amplifiers that look like naval warships. Very "un-Asian" I suppose. Asian hifi can be very pretty, of course.
310a/b eh? I'm not going to shell out for exotic tubes - 10Y is as far as I go. I used to have a few RE tubes, not sure the numbers, but I sold them no doubt for a lot less than they're worth today.
Nearly ready to hook the 4P1L up in pentode mode. I have 2P29L as well, but I've always preferred the 4P1L.
310a/b eh? I'm not going to shell out for exotic tubes - 10Y is as far as I go. I used to have a few RE tubes, not sure the numbers, but I sold them no doubt for a lot less than they're worth today.
Nearly ready to hook the 4P1L up in pentode mode. I have 2P29L as well, but I've always preferred the 4P1L.
Hi Andy,
No, it's only a plan.... for years ago. I haven't found appropriate SUT.
My daily used amp is CCS loaded D3a, source follower, 300B, 5k SE in my living room.
In my work room living the monster: breadboarded 841, 10Y cathode follower /or sometimes SiC source follower/, 801a PSE with -at least- 15kg PSU for each monoblock. It's more heavy than my -another- 211 amp.
This SUT is very fine -better than Lundahl SUTs I have-, but I wouldn't dare using it with 350V between primary-secondary.
I'm not sure that Brian (Sowter) developed it for this extreme challenge.
Hello,
The line pre amp is connected and at its final location. 21,2 kilo.
The vt25a amp will be one level under it with its 45 kilo. Just have to check if it fits. Of course it does!!
Now have to move it to my diy table to wire the input transformer and to connect the loudspeaker terminals with solid core silver.
At first i will use the old kimber pbj as symmetrical interconnect because that is the one i use for my el84 French broadcasting amps. So will install the xlr chassis parts temporarily on the vt25a. Later the kimber will be replaced by a home made symmetrical cable with 3 0,5 mm solid silver and one lemo 6 contacts connector.
Greetings, Eduard
P.s Andy these tubes can have a very long life. In my choke input supply for my old line preamp i have been using the same 5T4 metal housing tube rectifier for twenty years! Of course with choke input so easy life but because of shunt supply 70 mA current all the time
The line pre amp is connected and at its final location. 21,2 kilo.
The vt25a amp will be one level under it with its 45 kilo. Just have to check if it fits. Of course it does!!
Now have to move it to my diy table to wire the input transformer and to connect the loudspeaker terminals with solid core silver.
At first i will use the old kimber pbj as symmetrical interconnect because that is the one i use for my el84 French broadcasting amps. So will install the xlr chassis parts temporarily on the vt25a. Later the kimber will be replaced by a home made symmetrical cable with 3 0,5 mm solid silver and one lemo 6 contacts connector.
Greetings, Eduard
P.s Andy these tubes can have a very long life. In my choke input supply for my old line preamp i have been using the same 5T4 metal housing tube rectifier for twenty years! Of course with choke input so easy life but because of shunt supply 70 mA current all the time
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Well, here we have my present working 4P1L pentode stage. This took a lot of trial and error. The sound is rather disappointing. The basis of the 4P1L sound is indeed mostly there, but it's somewhat rough sounding. Can't really describe it except to say it isn't smooth like the triode version.
The output 300b stage now needs more power - I need to increase the B+ quite a bit. the OPT is gapped for 50mA so I need more volts. The volume is plenty loud enough.
The pentode operating points right now are surely not optimal. Would any of you guys suggest something better?
The output 300b stage now needs more power - I need to increase the B+ quite a bit. the OPT is gapped for 50mA so I need more volts. The volume is plenty loud enough.
The pentode operating points right now are surely not optimal. Would any of you guys suggest something better?
Attachments
