All,
Newbie here. Hoping you can help me. Had my first Dynaco 10 years ago, sold it (stupidly). Now I have a friend's ST70 that was "rode hard and put up wet" - a total rat's nest.
I totally rebuilt it (stock). The only things original are the sockets, driver board, chassis and transformers.
Went to fire 'er up last night and the right channel didn't work.
Biased to 1.56VDC. No change.
Swapped the inputs, same problem (confirming my source is working properly).
Swapped the outputs (speakers), same problem.
Swapped the EL-34s in various ways, same problem.
Checked the voltages on pins 3 and 4 with the EL-34s out and got ~510V (confirms output transformers OK).
Also verified negative VDC on pin 5. All show range of -24 to -36 VDC. (confirms bias supply OK).
Voltages at terminal 19 = 300VDC, terminal 20 = 375VDC
Voltages from the 7199 sockets themselves (double checked voltages by swapping tubes between sockets):
Right channel (good)
pin 1 = 257
pin 2 = 101
pin 3 = 37
pin 4 = 3.1
pin 5 = 3.1
pin 6 = 1.2
pin 7 = -
pin 8 = 110
pin 9 = 101
Left channel (not working)
pin 1 = 338
pin 2 = -0.5
pin 3 = 13
pin 4 = 1.9
pin 5 = 1.9
pin 6 = 0.8
pin 7 = -0.02
pin 8 = 30.1
pin 9 = -0.5
Thoughts? Suggestions? Help? Where do I go from here?
Chris