Has anyone had any experience with using 6080's in a common cathode linestage?
Was curious of how it would sound. Had some 6080's lying around and threw one together this afternoon.
Running 60mA through each 6080 with a plate voltage of around 180V.
B+ 280V.
cathode resistor: 1000 K (bypassed with 220uF and 0.1uF)
Plate resistor: 769 ohms (Had to stack quite a few as they are running some power)
The reason for building this was to use a common cathode amp for its dynamic feel but be appropriate to use with a SS power amp.
My other triodes had just too much gain. The 6080 has just x2.
CF's sounded ok but didn't give me the sound I was looking for.
Was curious of how it would sound. Had some 6080's lying around and threw one together this afternoon.
Running 60mA through each 6080 with a plate voltage of around 180V.
B+ 280V.
cathode resistor: 1000 K (bypassed with 220uF and 0.1uF)
Plate resistor: 769 ohms (Had to stack quite a few as they are running some power)
The reason for building this was to use a common cathode amp for its dynamic feel but be appropriate to use with a SS power amp.
My other triodes had just too much gain. The 6080 has just x2.
CF's sounded ok but didn't give me the sound I was looking for.
Have you seen Pete Millett's Low-mu preamp project? I built one once, but I could never get the 6080 quiet enough.
Thxs. Interesting use of the EL34.
I might try this but with some SV83's I've got hanging around.
His output cap is kind of high. 10uF?
Any CCS should be fine.
IIRC, the article explains that he had this hooked up to several power amps, thus the large cap.
QQ:
Do I need a 1M to ground just before the grid stopper?
Got the pot grounded of course but then I thought maybe I need a 1M to ground between the pot and grid stopper.
Do I need a 1M to ground just before the grid stopper?
Got the pot grounded of course but then I thought maybe I need a 1M to ground between the pot and grid stopper.
In theory no. However it is possible that as you turn the pot the wiper might break contact with the track for a split second, leaving the grid without a path to ground. Also the pot may fail. For both reasons it seems sensible to include a resistor where you have noted. However I do not know if 1M is the *right* value.
Thought it was common practice to add grid stoppers.
Any reason not to add it to a 6080?
Can I do without it?
Any reason not to add it to a 6080?
Can I do without it?
Seems mad overkill to me. The 6080 is not reputed for its linearity in this configuration. Also gain is unlikely to be better than unity (in my experience , mu is not gain).
A Jfet source follower seems a better bet to me.
Shoog
A Jfet source follower seems a better bet to me.
Shoog
Actually it's not bad with a CCS load (an EL34 in this case):
THD + noise (800Hz – 80kHz bandpass):
1kHz, 1V RMS out, 100k load 0.15%
20kHz, 1V RMS out, 100k load 0.12%
1kHz, 1V RMS out, 10k load 0.16%
20kHz, 1V RMS out, 10k load 0.13%
1kHz, 2V RMS out, 100k load 0.18%
20kHz, 2V RMS out, 100k load 0.24%
1kHz, 2V RMS out, 10k load 0.33%
20kHz, 2V RMS out, 10k load 0.27%
Frequency response (using 250k pot – see text):
2V RMS in, 1V RMS out, 100k load: 20Hz: -0.05dB 20kHz: -0.40dB -3dB @ 65kHz
2V RMS in, 1V RMS out, 10k load: 20Hz: -0.11dB 20kHz: -0.43dB -3dB @ 65kHz
2V RMS in, 2V RMS out, 100k load: 20Hz: -0.08dB 20kHz: -0.60dB -3dB @ 55kHz
2V RMS in, 2V RMS out, 10k load: 20Hz: -0.12dB 20kHz: -0.56dB -3dB @ 55kHz
Output impedance: 324 ohms
Noise: -55 Dbv (mostly 60 Hz)
Voltage gain: 1.92
(Low-mu preamp)
Pete
Peter,
I see your implementation has a CCS load which is an entitrely different beasts. It also makes a hugely inefficient design even more inefficient. I know your results are good and you are happy with the preamp - but I'm certain you could just as good results with a more efficient design.
Shoog
I see your implementation has a CCS load which is an entitrely different beasts. It also makes a hugely inefficient design even more inefficient. I know your results are good and you are happy with the preamp - but I'm certain you could just as good results with a more efficient design.
Shoog
Shoog,
Could you point me in the right direction for an efficient but simple CCS load for this type of design?
Possibly with SV83 pentode?
Could you point me in the right direction for an efficient but simple CCS load for this type of design?
Possibly with SV83 pentode?
Peter Millets design is fully worked out and would be a good place to start.
As I said I wouldn't do it. I built a similar 807 based SE design for a power amp but couldn't live with the inefficiency, and your idea about matches it for just a preamp.
Shoog
As I said I wouldn't do it. I built a similar 807 based SE design for a power amp but couldn't live with the inefficiency, and your idea about matches it for just a preamp.
Shoog
It's ABSURDLY inefficient. That's part of the charm 🙄
There are lots of ways to build a line stage. This just happens to be one using a 6080, which the original post was asking about.
If efficiency were a big concern, I'd use silicon!
Pete
Just tried out a CCS as in Petes design BUT with some SV83's.
Never tried a CCS before.
😀
Very nice indeed. I tried this design without any CCS, just a plate resistor and it ok ish but with loads of noise.
Hooked up this CCS for the plate load and it went absouletly dead silent. The quietest I've had.
I have only 60 ohms on the cathode of the SV83 CCS, and only getting 140 Volts. I have 300V on the B+.
I want to increase this to 200V.
Am I safe decreasing the cathode resistor on the SV83 here to get the required voltage to supply the 6080 anodes?
Never tried a CCS before.
😀
Very nice indeed. I tried this design without any CCS, just a plate resistor and it ok ish but with loads of noise.
Hooked up this CCS for the plate load and it went absouletly dead silent. The quietest I've had.
I have only 60 ohms on the cathode of the SV83 CCS, and only getting 140 Volts. I have 300V on the B+.
I want to increase this to 200V.
Am I safe decreasing the cathode resistor on the SV83 here to get the required voltage to supply the 6080 anodes?
6080's are more than happy running down as low as 100V plate to cathode.
In my last amp, and my next project, I have run them and will be running them again at 100V and 100mA, a very sweet sounding operating point.
So I wouldn't bother increasing the voltage - theres very little to gain.
Shoog
In my last amp, and my next project, I have run them and will be running them again at 100V and 100mA, a very sweet sounding operating point.
So I wouldn't bother increasing the voltage - theres very little to gain.
Shoog
Thxs Shoog.
Got to increase the 6080's current. Only running them at 45 mA.
Now I need to understand the CCS a little more.
Is the 45mA in this case from the 6080, also being pulled through the SV83 CCS?
I'm a noob when it comes to CCS's.
Got to increase the 6080's current. Only running them at 45 mA.
Now I need to understand the CCS a little more.
Is the 45mA in this case from the 6080, also being pulled through the SV83 CCS?
I'm a noob when it comes to CCS's.
Yes the CCS is also pulling 45mA so for a EL84 varient that probably quite hot, Notice that Peter is using a EL34 which is a considerably beefier Valve than the SV83. My preamp only pulls 8mA and that plenty enough drive for my valve amp, so I doubt that you need extra current. Think of valve life been the upside.
If you could lay your hands on one an EL36 might make a good low voltage CCS.
Shoog
If you could lay your hands on one an EL36 might make a good low voltage CCS.
Shoog
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