New transformers for front-end arrived from Poland. These are 49V secondaries instead of 46V.
Lock is now down to 197V, which is a hair-breadth's away from 15%.
If you recall, it's regulating at ~54V (vs SPICE's predicted 52V), so I can lose a volt or two there to get the full 15%.
I tried increasing the bottom of the voltage divider from 6K to 6K8: output 51V; lock down to 185V.
Something in between ought to be about perfect.
(This is one area where my OCD is a bit of a pain: paralleling 2 resistors will bug me, so it's back to Mouser for a 6K49....)
Lock is now down to 197V, which is a hair-breadth's away from 15%.
If you recall, it's regulating at ~54V (vs SPICE's predicted 52V), so I can lose a volt or two there to get the full 15%.
I tried increasing the bottom of the voltage divider from 6K to 6K8: output 51V; lock down to 185V.
Something in between ought to be about perfect.
(This is one area where my OCD is a bit of a pain: paralleling 2 resistors will bug me, so it's back to Mouser for a 6K49....)
It lives....
I have no idea yet if it makes music or not, but it's offset adjusts easily and it (more or less) biases easily.
(The more-or-less part is that even after carefully planning it in SPICE my bias voltage divider isn't well-centred: I need to turn the pot to about 98% to reach the design point bias.)
I have no idea yet if it makes music or not, but it's offset adjusts easily and it (more or less) biases easily.
(The more-or-less part is that even after carefully planning it in SPICE my bias voltage divider isn't well-centred: I need to turn the pot to about 98% to reach the design point bias.)
It makes music.
But it also makes hum. I can decrease the hum by moving the output wires away from the output stage transformer. I can eliminate the hum by disconnecting the feedback.
Does the later suggest I need to get the outputs even farther away, or is something else going on?
(The transformer hums a bit even without speakers connected, and even with the feedback disconnected. I assume that's a bit of DC on my mains?)
But it also makes hum. I can decrease the hum by moving the output wires away from the output stage transformer. I can eliminate the hum by disconnecting the feedback.
Does the later suggest I need to get the outputs even farther away, or is something else going on?
(The transformer hums a bit even without speakers connected, and even with the feedback disconnected. I assume that's a bit of DC on my mains?)
Sometimes it can be useful to connect a scope probe ground lead to the tip so as to create a little loop antenna. One can then wave it around transformers and such looking for magnetic fields cutting the loop. Perhaps a rough measurement, but it can sorta help map out where fields are stronger and weaker.
One might also use the feedback wiring as an antenna to see what its picking up. Might need a preamp before the scope if the signal level is very low.
One could possibly also experiment with a 1/8" plate of soft steel as a shield between transformers and sensitive circuitry...
One might also use the feedback wiring as an antenna to see what its picking up. Might need a preamp before the scope if the signal level is very low.
One could possibly also experiment with a 1/8" plate of soft steel as a shield between transformers and sensitive circuitry...
Toroidy 1.5KVA "audio grade"; 2 x 35V secondaries. Impregnated core; copper tape between windings.
My F5 (also with Toroidy "audio grade") is quiet both at transformer and through speakers.
My Rogue Audio Cronus Magnum does hum a bit (EI transformer), but only at the transformer (not through the speakers).
My F5 (also with Toroidy "audio grade") is quiet both at transformer and through speakers.
My Rogue Audio Cronus Magnum does hum a bit (EI transformer), but only at the transformer (not through the speakers).
