eBay 300B PC board kit

[popa marius]

I think the 300b tube has an interesting property in the sense that the spread between H2,H3,H4 is kept relatively constant at 20dB between 3-8w at least on the amplifier designed by me and only at 10w it drops to 10dB with THD of 5%

 

[TheGimp]

I think I have finally sorted out my distortion issue.

After losing one of my Electro Harmonix GL tubes I pondered a replacement. After much reading I decided on JJ 300B matched pair from Tube Depot.

After comparing them to the remaining EH tube and the LinLai, and Psvane tubes, I have come to the conclusion that (1) I wasn't biasing the tubes hot enough, and (2) I just had lousy luck on the previous tubes.

The JJ are capable of under 0.5% THD at one watt when pushed to 36W dissipation. The rest are near 1% (or over, LinLai) except the remaining EH tube.

 

[euro21]

My CCS loaded D3a, SF, fix biased EH gold grid (70mA, 28W Pd), 5K OPT has 0.35/0.32% at 1W.

 

[TheGimp]

I found a problem with my regulator for the driver tube. Ok, I blew it up by pulling a "TubeLab" and had been cranking B+ up to 500V+ on 450V caps.

Once I rebuilt everything, I find my distortion at one watt is running well below 0.3% with the JJ tubes.