I can't imagine the carbon plate would make a huge difference in ham radio
service where people will often transmit for a minute or two at a time. It
might help somewhat, but it would not be the huge improvement in power
handling that you would get in pulsed service.

That's OK. Nevertheless, in the 8236 data sheet, Tung Sol claims "Its carbon
anode and hard glass bulb permit continuous operation at 50W plate
dissipation". Conversely the 6DQ5 (electrically identical to the 8236) has a
24W plate dissipation. Actually, in the SR-500 the two 8236s draw 500mA at
750V, whilst in the SR-160 (identical to SR-500 except for output power) the
two 6DQ5s draw 200mA at 575V



I would consider the EL509, since it's currently manufactured and pretty
reliable. Maximum ratings including the power dissipation are all MUCH
higher. Socket will have to be changed, or you can make an adaptor, but
it's a far more advanced tube design.

Yes, the EL509 would be the most appropriate substitute. Its plate
dissipation it 35W but, looking at it, it is hard to figure out why it has a
lower plate dissipation than the 8236.

73

Tony I0JX
Rome, Italy