[Heath] Plate voltage SAG in Heath 221

[John King]

I am  puzzled by the drop (sag)  in my SB221 when it is keyed up idling with NO drive. My Fluke 40 KV probe tells me that there is 2,970 VDC at the RF choke. When the rely jack is  grounded, the two NEW 3-500ZG tubes only draw 60 ma. which is one half of what they should draw when keyed up and idling.  The plate voltage drops to 2,250 VDC with only 60 ma. of idling current being drawn. Don't suspect the two tubes because I have installed a second NEW pair of tubes in the trouble shooting procedure with identical results.

I know that the metering resistor on the meter board of the SB 221 is off in value because it reads much lower than my fluke.

When keyed up resulting in the voltage drop from 2,970 VDC to  2,250 VDC there is no HUM or GRUNT indicating excessive current drain other than the 60 ma. of idling plate current. What is causint the plate voltage drop with only  60 ma of idling current being drawn.

Anyone had this experience with a Heath SB 220 or SB 221 ???? If you have suggestions based on your actual knowledge or hands on experience, I will appreciate your assistance. Asking me if it is plugged in or the obvious will not be of assistance because I have been  breaking and fixing radios for 56 years. Your considered answer will be greatly appreciated. Thanks and 73, John, K5PGW