SR-160 to SR-500 MOD
The SR-160 is the predecessor of the SR-500. They took the SR-160 made a few ckt changes to improve the overall performance and used different final tubes. Then they replaced the PS-150-120 power supply with the PS-500-120, PS-500-DC, P-500-DC or the P-500-AC.
The factory change used the 8236 carbon block plate tube. However the 6DQ5 is a direct replacement for the rare and expensive 8236. If you use the 6DQ5 you will absolutely need to use a fan for cooling. I use a 12 volt computer muffin fan powered by a 12v wall wart simply placed on the top of the case over the final tubes. The fan should draw hot air out not blowing cold air in. If at all possible go with the 8236, it is indestructible and will last forever. But you need a MATCHED PAIR.
PART CHANGES required for proper operation.
REF DESIGNATOR STOCK SR-160 MODIFIED SR-160
C11 * 47uuf 22uuf
C12 * 8.2uuf 6.8uuf
R53 47K 6.8K
C65 47uuf 150uuf
R92 180K 220K
C100 1000uuf 750uuf
C104 470uuf 220uuf
C107 1000uuf 750uuf
R96 ** 56K delete
C119 680uuf 620uuf
C120 430uuf 250uuf
C121 510uuf 300uuf
* These changes did not have anything to do with the PA mod. They were Factory directed changes to improve the receiver operation.
** Resistor R96 was removed for proper bias for either the 8236 or 6DQ5 final upgrade.
Making the change from the 12DQ6A to the 6DQ5 or the 8236 will require rewiring the cathode, screen and the filaments.
Best Regards, Walt WD0GOF.