Just wondering if anyone has actually built a 6DJ8 preamp with moderate B+ of say 150V or so. It appears like it should work OK. Thinking input stage with plate to grid FB followed by an active tone control. Perhaps 60-70V on the plate with 3 or 4 mA plate current.
Sure, the 6DJ8 will work at relatively low voltages. Been there, done that. However, it would work better (more linear) at higher voltage.
If you need low voltage, you might want to look at tubes aimed at operation in battery powered radios and the like. I recently looked a the 3S4, 3V4 and 3C4 DHT triodes, which are superbly linear at low voltages.
https://www.diyaudio.com/community/...card-for-the-vfet-diy-amp.371158/post-6636693
https://www.diyaudio.com/community/...card-for-the-vfet-diy-amp.371158/post-6642149
If you need low voltage, you might want to look at tubes aimed at operation in battery powered radios and the like. I recently looked a the 3S4, 3V4 and 3C4 DHT triodes, which are superbly linear at low voltages.
https://www.diyaudio.com/community/...card-for-the-vfet-diy-amp.371158/post-6636693
https://www.diyaudio.com/community/...card-for-the-vfet-diy-amp.371158/post-6642149
Thanks. I have some transformers that would give well over 300V which seemed like real overkill but I also have a 117V that I thought might be useful for this one. I do have one more transformer that I haven't checked yet so it might be better. Initially I had planned on 250V B+.
P.S. I just rechecked and 300V may not be too ridiculous. It looks like with 56k plate resistor and 105-110V on the plate we get about 3mA. Seems reasonable. I think any 6DJ8 variant should be OK with 110V.
P.S. I just rechecked and 300V may not be too ridiculous. It looks like with 56k plate resistor and 105-110V on the plate we get about 3mA. Seems reasonable. I think any 6DJ8 variant should be OK with 110V.
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I've enjoyed Mr. Broskie's self-contained 12VAC boards. Just need a 12 or 18VAC supply to run either 6DJ8s or 12AU7s (respectively) at 100VDC or 130VDC (again, respectively).
https://glass-ware.stores.turbify.net/aikido12vac.html
https://glass-ware.stores.turbify.net/aikido12vac.html
Suggest trying this load line calculator .
https://www.vtadiy.com/loadline-calculators/loadline-calculator/
For an ecc88 , with a plate voltage of 150 Vdc , linearity looks good with a bias of 10mA or even 12 mA .
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Don't trust that calculator over a datasheet! Va max for 6DJ8 is 130Vdc and I think that's pushing it.
I should be able to keep the Va at 100-110 even with 300V B+ except for the direct coupled CF at the output but I should have enough heater supply to use a 6N1P in that spot.
Yes I used it at 150 V in an SRPP circuit: the anode voltage of the lower tube is 150 V, same for the upper tube. B+ is 300 B. Linearity is excellent.
Sylvania has a good data sheet for a 6dj8 .
https://datasheetspdf.com/datasheet/6DJ8.html
Recall the heater voltage should not be left floating and there should be a DC path between the heater voltage and cathode .
The max heater voltage w.r.t. the cathode is 150 Vdc . Are you referring to this ?
Also note how the small signal parameters change with the bias current .
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I've been running these at 24V (Vb+) as a MC pre-preamp since forever. They sound good, but have to be sorted for noise.
Note that the expected output is only about 50mV in this case.
Note that the expected output is only about 50mV in this case.
Start with a 6DJ8.
Use a fairly low B+ voltage.
How can you preserve most of the B+ voltage to run the 6DJ8?
Load the plate with Either a plate choke, Or an Interstage transformer.
The DCR of the choke or interstage transformer typically drops much less DC voltage than an SRPP, a CCS plate load, or a resistor plate load.
Lots of tradeoffs here.
Use a fairly low B+ voltage.
How can you preserve most of the B+ voltage to run the 6DJ8?
Load the plate with Either a plate choke, Or an Interstage transformer.
The DCR of the choke or interstage transformer typically drops much less DC voltage than an SRPP, a CCS plate load, or a resistor plate load.
Lots of tradeoffs here.
I did some experiments with the MF X10 clone buffer. It was designed to run from +-24v but results were better on +- 35 to +-50 volts.
I found the best measured results were using a PCC88. (the 6DJ8 is same as UK ECC88, the PCC version has 7v heaters.)
It runs on 84v with 6.3v DC heater supply. I haven't tried an ECC88/6DJ8
https://www.diyaudio.com/community/threads/x10-clone-tube-buffer-with-6n1p.402747/
I found the best measured results were using a PCC88. (the 6DJ8 is same as UK ECC88, the PCC version has 7v heaters.)
It runs on 84v with 6.3v DC heater supply. I haven't tried an ECC88/6DJ8
https://www.diyaudio.com/community/threads/x10-clone-tube-buffer-with-6n1p.402747/
Roger Modjeski built his Music Refrence RM5 preamp with a B+ of 160 V.
The plate voltage on the first two triodes was about 60V, on the third about 80V if memory serves me right.
The plate voltage on the first two triodes was about 60V, on the third about 80V if memory serves me right.
Plate voltage in datasheet it is what it is , the voltage on the plate to ground ( cathode ) , not B+ . You can use 550V B+ as long as the voltage across the hot tube is below 130V .
I use the 6DJ8 as MC preamp with +24Vdc B+. Cathode directly to ground and plate load with DN2540.
Real cool and sounds so good.
Johnny
Real cool and sounds so good.
Johnny
It would indeed seem like an ideal tube for choke loading. Having had to quit working early due to health problems however I will need to work with what I have on hand. 🙂
I still have a MF X-can V2 headphone amp: an hopelessly bad design, only the box is worth keeping.
With 150 volt supply I would shoot for 75-90 volts at the plate. 6DJ8 works well around that region if you keep sufficient plate current.
Just from checking my notes with a 150 volt filtered supply-
A good starting point is 75 volts at the anode, 12k plate resistor, 6.25mA and ~1.7 volts bias (or cheap modern red/green LED) Is a pretty good spot to run them- distortion is almost all 2H at this operation point.
You can drop down to a 10K plate resistor, 75 volts at the anode, 7.5mA, ~-1.6 volt bias or so for a smidge (~10%) lower distortion, but also a smidge lower output swing.
Just from checking my notes with a 150 volt filtered supply-
A good starting point is 75 volts at the anode, 12k plate resistor, 6.25mA and ~1.7 volts bias (or cheap modern red/green LED) Is a pretty good spot to run them- distortion is almost all 2H at this operation point.
You can drop down to a 10K plate resistor, 75 volts at the anode, 7.5mA, ~-1.6 volt bias or so for a smidge (~10%) lower distortion, but also a smidge lower output swing.