I'm leaving this information here for the benefit of others. An Artifact of what happens should you accidentally wire an ST-70 with pins 3-4 of the EL34 backwards on all 4 tubes as falsly documented in my notes and noticed whilst reading resistance plate to plate. This issue is since resolved.
During project turnup I noticed that a single channel could not produce more that 8VRMS into an 8 OHM resistor during testing before falling apart. Many overlooks have been done and one out layer is as follows on the following.
Consider as well the following:
That this effects BOTH CHANNELS in and around 8VRMS independently, under the same load.
Multiple rectifiers used to same effect
Stable mains
A particular test of interest is posted below where the input sine wave is 760mV
The following comparisons are some test points at idle/biased with grounding plugs in versus this sine wave
QUADCAP
rest load .760v
POS1 457 -> 434
POS2 445 -> 416
POS3 387 -> 362
POS4 302 -> 283
output from phase inv = 28.76v (one log to one el34, both outputs match)
output from EL34 71.36 into auto transformer
output into 8 ohm load = 8.2vrms
During project turnup I noticed that a single channel could not produce more that 8VRMS into an 8 OHM resistor during testing before falling apart. Many overlooks have been done and one out layer is as follows on the following.
Consider as well the following:
That this effects BOTH CHANNELS in and around 8VRMS independently, under the same load.
Multiple rectifiers used to same effect
Stable mains
A particular test of interest is posted below where the input sine wave is 760mV
The following comparisons are some test points at idle/biased with grounding plugs in versus this sine wave
QUADCAP
rest load .760v
POS1 457 -> 434
POS2 445 -> 416
POS3 387 -> 362
POS4 302 -> 283
output from phase inv = 28.76v (one log to one el34, both outputs match)
output from EL34 71.36 into auto transformer
output into 8 ohm load = 8.2vrms