I really wanted to build a push pull amp for myself. I tried it once and I posted it here, the design, if you can ever call it, was just pasted TubeCAD results. It did put out a sound and Wayne spent some time with me privately optimizing it. Thanks again Wayne.
I know that there is another EL34 PP amp project where Wayne is again involed, but that talk of CCS, long tail with negative supply, and all that parts, just doesn't inspire me. I'm lazy
I was browsing the Lundahl site when I saw this LL1660S SE to PP interstage transformer. I haven't made an interstage project yet! Yes!
The LL1660S Alt-B connection has max of 18mA and I suppose my favorite driver tube at 10mA load *and* LED bias will just be perfect.
I drew up this schematic on our whiteboard and took a pic.
I think I might have screwed up on the output tubes' cathode.
Do you guys think this will work?
I know that there is another EL34 PP amp project where Wayne is again involed, but that talk of CCS, long tail with negative supply, and all that parts, just doesn't inspire me. I'm lazy
I was browsing the Lundahl site when I saw this LL1660S SE to PP interstage transformer. I haven't made an interstage project yet! Yes!
The LL1660S Alt-B connection has max of 18mA and I suppose my favorite driver tube at 10mA load *and* LED bias will just be perfect.
I drew up this schematic on our whiteboard and took a pic.
I think I might have screwed up on the output tubes' cathode.
Do you guys think this will work?
Attachments
I'm looking at the tap on the driver side of the interstage xfmr. Aren't you shunting the B+ to ground there?
lndm said:
Right. Big smoke involved there 😉
Remove that connection between the primary of the interstage xfmr. and ground. IIRC that tap should be used when using a pentode as driver (to have some NFB, aka Ultralinear operation).
Pins 13 and 18 are the electrostatic shield.
They should be grounded.
In alt B, the primaries are in parallel, so there is no center tap on the "c" windings.
In other words, "That dog don't hunt" 🙂
HTH
Doug
They should be grounded.
In alt B, the primaries are in parallel, so there is no center tap on the "c" windings.
In other words, "That dog don't hunt" 🙂
HTH
Doug
Thanks Doug. I revisited the PDF and indeeed they're the shield, hence my schematic is wrong. I should have a dotted line between the windings that goes to ground.
I finally prototyped this project 😀
Since I don't want to blow up my 417A/5842 tubes, I decided to use my Hitachi 6SN7 as the driver for the prototype, just to know whether this thing will sing or not. And it did 😎
I wanted it to be a monoblock so I made separate power supplies in the same chassis. Here's what it looks like.
Since I don't want to blow up my 417A/5842 tubes, I decided to use my Hitachi 6SN7 as the driver for the prototype, just to know whether this thing will sing or not. And it did 😎
I wanted it to be a monoblock so I made separate power supplies in the same chassis. Here's what it looks like.
Attachments
And this is the current schematic.
I'm using two orange LEDs to bias the paralleled 6SN7 driver. Currently my power transformer HV is low, as I haven't asked my winder to make a suitable one. The rectification is solid state and using a bridge W02M (warning! the W02M is rated *only* for 200V, do not do this even if I did ) to put out a B+ of around 280V. As I said, just want to know if this will put out a sound.
At this weird operating point, I'm surprised at the sound it does- smooth and heavy. The all important "tone" is good to pursue this project further. It does not sound like the ST-70 (note! personal bias here- I never liked the ST-70) or the push pull EL34 monoblock I was loaned before (sounds balsy and impressive at the start then becomes boring and fatiguing in the long run). I don't know if I should attribute the sonic to the LL1660S, as this is the first time I've heard this specific one.
Where would be the best place to put in a CCS? 😀
I'm using two orange LEDs to bias the paralleled 6SN7 driver. Currently my power transformer HV is low, as I haven't asked my winder to make a suitable one. The rectification is solid state and using a bridge W02M (warning! the W02M is rated *only* for 200V, do not do this even if I did
) to put out a B+ of around 280V. As I said, just want to know if this will put out a sound.At this weird operating point, I'm surprised at the sound it does- smooth and heavy. The all important "tone" is good to pursue this project further. It does not sound like the ST-70 (note! personal bias here- I never liked the ST-70) or the push pull EL34 monoblock I was loaned before (sounds balsy and impressive at the start then becomes boring and fatiguing in the long run). I don't know if I should attribute the sonic to the LL1660S, as this is the first time I've heard this specific one.
Where would be the best place to put in a CCS? 😀
Attachments
Hmmm, since my ultimate driver is the 417A/5842, maybe a shunt regulator to feed that section...
CCS loaded VR150 + VR105 for 255 something volts...
CCS loaded VR150 + VR105 for 255 something volts...
how does using an inter-stage transformer differ from using a "traditional" inter stage? does one or the other out and out sound better?
Hi alex, if you mean LTP or split load- it's hard to explain but it's very smooth sounding without being slow or suffering from dynamics.
Cost can be a stumbling-block where interstage trannies are concerned. A good one costs plenty and for maany years they were considered poor. However, there are good ones available these days and Lundahl has the best reputation, to my knowledge.
With ~250V at the plate and ~4V bias (2xLED) wouldn't that indicate a lot of current drawn in the 6SN7?
alex, the Lundahl 1660S will cost you some $200 so you compare that with tube phase splitter, it will be much higher. But it's your call. For me, I haven't done one like this, so there 😀
jane, maybe so. My mind is still thinking 417A perhaps so the paralleled 6SN7 maybe getting more than what they need.
jane, maybe so. My mind is still thinking 417A perhaps so the paralleled 6SN7 maybe getting more than what they need.
arnoldc,
why not push-pull it all the way? the ll1660 can be hooked up as such, a 6sn7 push-pull driver in a differential mode instead of paralleling them.😀
why not push-pull it all the way? the ll1660 can be hooked up as such, a 6sn7 push-pull driver in a differential mode instead of paralleling them.😀
Tony, I thought of it using 5842 pairs, ala Amity.
Although I have several pairs of 6SN7, I dont like them (prejudice) in this amp. I don't know why 😀
edit:
However, why would I limit myself 😀
It will be driven by a preamp anyway, so I can avoid using an input transformer. What do you think?
Although I have several pairs of 6SN7, I dont like them (prejudice) in this amp. I don't know why 😀
edit:
However, why would I limit myself 😀
It will be driven by a preamp anyway, so I can avoid using an input transformer. What do you think?
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