Common cathode linestage with 6080

[Brit01]

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.

[dsavitsk]

Have you seen Pete Millett's Low-mu preamp project? I built one once, but I could never get the 6080 quiet enough.

[Brit01]

Have you seen Pete Millett's Low-mu preamp project?

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?

[dsavitsk]

Originally Posted by Brit01

Thxs. Interesting use of the EL34.
I might try this but with some SV83's I've got hanging around.

Any CCS should be fine.

His output cap is kind of high. 10uF?

IIRC, the article explains that he had this hooked up to several power amps, thus the large cap.

[Brit01]

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.

[Gordy]

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.

[rdf]

Does a grid stopper do anything on a 6080?

[Brit01]

Thought it was common practice to add grid stoppers.

Any reason not to add it to a 6080?
Can I do without it?

[Shoog]

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

[pmillett]

Originally Posted by Shoog

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).
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