Hi All,

To wrap up part of this discussion, Walt Cates' repair guide for the SR-160/SR-500, section 9.11, lists the changes needed to convert the SR-160 to an SR-500. Other than some component changes, the main change would be to change the power supply from the PS-120-150 (a 150 watt transmitter supply) to the PS-120-400 power supply. This supply has a higher B+ for the finals (800v vs 550v) and higher current capabilities. This is the same supply as is used for the SR-400.

In the case of the SR-500 (or converted SR-160), either the 8236 tubes or the 6DQ5 tubes can be used. The 8236 tubes are much more rugged (but in short supply), but the 6DQ5 tubes will work fine although I am in agreement with using a cooling fan in either case.

The SR-150 is a bit of a different beast, and while it could be modified to use different finals and power supply, it is not as straightforward and would involve a PA socket change and rewiring. There was a bit of a "how much peak power" can I get out of a given pair of tubes that took place during the 70s's. The sweep tubes provide high peak current capabilities, but with limited average power dissipation (typically 35 watts). In my humble opinion, I think it would be best to leave the SR-150 as it is rather than make significant modifications to obtain a few more watts of output. Remember, it take a 4x increase in power to provide a one "S" unit difference. If you are wanting more power, maybe a better solution is to look at using an external linear amplifier.

Just my two cents (oops, no more pennies) worth,

Bob,? K7DYB

On 2/20/2025 4:42 PM, HF via groups.io wrote: