[Amps] Clipperton L - GI-7B

[Roger Parsons]

I have been occupying myself during this lock-down rebuilding an old Clipperton L. This came without tubes so I have modified it to take a pair of GI-7Bs. It seems to work quite well and even looks pretty neat.

Now comes the rub: Carl has suggested that I should be 'drawn and quartered' if I should dare use it on SSB as 'The low mu GI-7B is about as IMD dirty it can be for SSB'. I will probably avoid that terrible fate as I only use CW, but I started to wonder about the linearity of the GI-7B.

Many people have said how well the GI-7B worked in their constructions, but I could not locate any specifications for the tube that includes linearity details. This is not surprising as it was primarily intended for pulse operation, and in fact the only thing I have been able to find is:

https://www.ac0c.com/attachments/SB200_Sleeperv3a.pdf

Apparently the measured IP3 was -26dB relative to either one of two tones which corresponds to -32dB relative to PEP. That's not a wonderful result but it's not terrible either, especially as some of the distortion may be due to the driver. (Part of the discussion in Jeff's paper seems to suggest that the 6dB numerical improvement should be added twice which I don't think is correct.) Jeff obviously spent a great deal of time and effort doing the work on the SB200, and it's a shame that it didn't work out in the end. But I would be most interested in comments.

73 Roger
VE3ZI