27-01-2018, 11:10 AM
The January Mr Dopey award goes to AW Scredington : ). Firstly Ik should be halved as the 2C34 has a common cathode and 12 ohm sense R, so Ik is 16.5mA. Secondly I boo boo'd with the grid R's on the 2C34, I had two 47k R's, one on each grid, the ends connected to -15v, so no reference to ground. I've put them as per the schematic.
A mistake I saw whilst drawing the schematic is the OP from the CF should be from the 10k/1k5/470k junction, not the cathodes themselves. The circuit was thrown together so caps and R's arn't optimum for frequency response. room for improvement.
Followed Jeffrey's suggestion, scoped one anode of the 2C34. There's a load of high frequency crap on there as well as 50hz. It looks like a 33khz signal modulated by 50hz. 50hz from the heaters I guess. Will try bigger stoppers and ferrites.
The main problem seems to be crossover distortion. I monitored the common cathode of the 2C34. It's 33mA (both) at rest, rises to 37mA then drops to 30mA at full OP. Xover dist occurs soon after Ik starts to drop.
See oscillograms below. Top trace OP , bottom one anode of 2C34.
A mistake I saw whilst drawing the schematic is the OP from the CF should be from the 10k/1k5/470k junction, not the cathodes themselves. The circuit was thrown together so caps and R's arn't optimum for frequency response. room for improvement.
Followed Jeffrey's suggestion, scoped one anode of the 2C34. There's a load of high frequency crap on there as well as 50hz. It looks like a 33khz signal modulated by 50hz. 50hz from the heaters I guess. Will try bigger stoppers and ferrites.
The main problem seems to be crossover distortion. I monitored the common cathode of the 2C34. It's 33mA (both) at rest, rises to 37mA then drops to 30mA at full OP. Xover dist occurs soon after Ik starts to drop.
See oscillograms below. Top trace OP , bottom one anode of 2C34.
