You can order O-netics direct. You'll have to write directly to Bud. He's a DIYaudio member with the handle BudP. Very nice guy. Also email: hpurvine@gmail.com
Doesn't have a web page that I'm aware. Here's some info from the web.
https://www.manta.com/c/mmswg19/o-netics-ltd
John
Doesn't have a web page that I'm aware. Here's some info from the web.
https://www.manta.com/c/mmswg19/o-netics-ltd
John
I can't find specs on those, but anything designed for a 300b SE should work. Just needs to be 3K to 5K and capable of 70mA current. That's many SE OPTs. Yes - 4P1Ls are much, much cheaper - buy a dozen and have tubes for many years to come! Use them in filament bias and preferably with a choke input filament supply. Regs from Rod Coleman. It's a great sound - clarity will bring a smile to your face.
Hi Andy
In my parts box I have some A470 Dynaco replacement transformers. 4.3K (suggested 80mA per side?)with 4, 8 and 16 ohm secondaries. Seem perfect and more importantly on budget at zero 2017 dollars.
If there is not a fatal flaw in this it will be my first crack at an SE amp.
Cheers
Grant
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Those Dynaco transformers will be "gapped" for a push pull amp which will have a very low net DC flux since it will cancel between the half windings but may saturate with the DC bias current of an SE amp. Maybe not a good fit although I've heard of folks using PP transformers for SE at much reduced bias currents.
You'd be better of selling those and buying a budget pair of single ended transformers.
Hmm, "better" assumes that selling and buying consumes no time and energy and postal costs from the antipodes will swamp material costs.
Better to leave them in the parts bin then and see if I can trip over some SE trannies with low freight costs.
You can think of a 4P1L as a 45 tube and a pair of them as a 2a3. Not far off, though different operating points. So 5K Sowter SE09 95ma would do for either 2 or in fact 3 of 4P1L.
The Dynaco push-poll transformers would do for 4 of 4P1L in PP - a pair either side. Think push-pull 2a3s. Filament bias isn't impossible in push pull - I have a half-finished amp exactly like this with a 6K OPT. I don't need PP, but it's an interesting experiment. I have loads of 4P1L.
The Dynaco push-poll transformers would do for 4 of 4P1L in PP - a pair either side. Think push-pull 2a3s. Filament bias isn't impossible in push pull - I have a half-finished amp exactly like this with a 6K OPT. I don't need PP, but it's an interesting experiment. I have loads of 4P1L.
How about PPP 4P1L's with your transformers but run them in pentode with plate to grid local feedback? Could use a CCS in the cathodes for good differential amplification. You might even also use the UL taps on the primaries to feed the driver stage for the local feedback aka e-linear.
Here's a nice PPP example using a 5k output transformer which isn't too far from the 4.3k of the Dynaco's. This one is triode connected 4P1L's. I expect you could make a very nice sounding amp.
4P1L Push-pull Amplifier – Bartola(R) Valves
John
Here's a nice PPP example using a 5k output transformer which isn't too far from the 4.3k of the Dynaco's. This one is triode connected 4P1L's. I expect you could make a very nice sounding amp.
4P1L Push-pull Amplifier – Bartola(R) Valves
John
Andy I like the flexibility of your setup. I'm going to build this, using your modular chassis. Are the threaded insert horizontal rails you're using something like this?
https://www.schneidersladen.de/en/sb-rail-19-ohne-kante.html
And, for the PSE 4P1L amp, are you in a separate chassis for the power supply?
Thanks!
https://www.schneidersladen.de/en/sb-rail-19-ohne-kante.html
And, for the PSE 4P1L amp, are you in a separate chassis for the power supply?
Thanks!
The horizontal rails are exactly like your link. They are 420mm wide which is 84 width on the subrack system. The height I use is "2U" on the rack system which is around 88mm. The threaded inserts are usually M2.5, though some units offer M3. The top plates I use are 4mm soft aluminium. It does mark a lot more easily than medium or hard, but it doesn't wear out my drills and hole saws. Much easier to work with. I use 50mm, 70mm, 100mm and 120mm plates and that seems to offer me enough flexibility. 50mm is wide enough for most tubes. 100mm is wide enough for most mains transformers and OPTs. 70mm is a nice in-between size and is needed to make the width up to 420mm. You need an extra 20mm somewhere.
I have ended up with loads of these top plates, which get recycled. They can end up a bit like Swiss cheese, but I can usually find a plate that's close enough to what I'm building. For fastening parts I use 15mm nylon spacers, female to male. I put a solder tag on the male end, fastened with a nylok nut which you absolutely need because heat softens the nylon and normal nuts slip. This is bolted onto the underside of the top plates with a screw which goes into the thread on the female end of the spacer. Used this for 10 years and the beauty is the more years you use it the more top plates you accumulate, so you end up building quite quickly.
As for layout I've tried all kinds of solutions. I have been using separate chassis for PSUs but lately tempted to put it on the same chassis as the amp - we have 420mm width after all and the depth of the top plates is 275mm which works very well. So the side pieces are 300mm or 1ft. The problem with filament bias and choke input is that you have chokes passing anything from 100mA to 630mA to 1.2A. As the current gets bigger, the hum can radiate round the choke and cause hum, so I put the filament supplies in separate boxes with 4 pole XLR connactors. Well away from the signal. I prefer to use choke input but others don't bother. I find it smoother. You don't want hum in these amps since you're probably using sensitive speakers.
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Attachments
Hi.
Some thoughts. Yesterday I wired a pair of 4P1L as PSE and hooked it up to me Lab Powersupply.
As I'm properly the only left who runs my 4P1L with 8R as Cathode resistor, build it a long time ago, and I'm very happy.
I fired them up, and gave them 1.2 Amps on but 8R and 16R as the cathode resistor and saw a huge different in the required voltage.
The 8R requires 11.8 volt and the 16R requires 21.8 volt + the 3.5 volt for Rod Coleman 7 boards.
Shouldn't it be possible to run it on 8R instead of the 15-16R I see on all schematics ??? It's a lot less heating to handle.
Some thoughts. Yesterday I wired a pair of 4P1L as PSE and hooked it up to me Lab Powersupply.
As I'm properly the only left who runs my 4P1L with 8R as Cathode resistor, build it a long time ago, and I'm very happy.
I fired them up, and gave them 1.2 Amps on but 8R and 16R as the cathode resistor and saw a huge different in the required voltage.
The 8R requires 11.8 volt and the 16R requires 21.8 volt + the 3.5 volt for Rod Coleman 7 boards.
Shouldn't it be possible to run it on 8R instead of the 15-16R I see on all schematics ??? It's a lot less heating to handle.
8R*0.6A= 4.8V
This is quite low bias, curve's operating points (for example about 115V, 30mA) not so optimal (below 4V bias the distortion is growing).
With double filament current (PSE), the op. points -about 9.6V bias- provides greater reserve (for example at about 140V, 30mA per tube).
First: what is the goal (operating point).
Second: how much bias voltage requiring to achieve around this op. point.