Hi,
I have a Musical Fidelity B1 Mk1 and I have just noticed that the 4 2n3055's closest to the front panel have less bias than the front ones and that I cant get the pairs to show the same mV across the resistors. They all warm up, but I noticed after hard driving the higher mV set run hot whereas the lower mV pair (nearer to the front of the case) run lukewarm
eg: R63 and R64 show a potential difference of ~12mV but R65 / R66 only get 4mV. If I adjust the bias I get large increases for the transistors next to R63/R64 but only minimal changes for the R65/R66 transistors.
The following has been done:
Jonathan
I have a Musical Fidelity B1 Mk1 and I have just noticed that the 4 2n3055's closest to the front panel have less bias than the front ones and that I cant get the pairs to show the same mV across the resistors. They all warm up, but I noticed after hard driving the higher mV set run hot whereas the lower mV pair (nearer to the front of the case) run lukewarm
eg: R63 and R64 show a potential difference of ~12mV but R65 / R66 only get 4mV. If I adjust the bias I get large increases for the transistors next to R63/R64 but only minimal changes for the R65/R66 transistors.
The following has been done:
- Renewed the 4700uf caps
- Replaced the TL072CP opamp with a 4562
- Replaced the 50K Vol pot with new original one (no space to fit better one )
- Replaced all 10 BC550C and BC 560C transistors
- Replaced 2x BD139 and 2 x BD140
- Replaced all 3055's with matched ones
Jonathan