[miniman82]

The sulphide tubes were the ones where red turned more orange when driven to high beam currents, but it was less objectionable to viewers than a tube with correct NTSC gamut that could only be viewed in a darkened room because it was so dim (like the 15G). The 21AXP22 tubes can provide pretty decent brightness, but you have to have a stout HV power supply for that. That's why sets like the 21-CT-55 and CTC-4 work so well, and the CTC-5 was such poor performers. My CTC-4 produces a picture that can be seen just fine in normal room lighting, where with my 5 you'd have to draw the drapes and dim the lights.