Hi All
The CARY SLI-80 is a great amp, except the 520V on the KT88's can stress some KT88's and make it hard to bias matched pairs to run equivalent idle currents.
I had a look at the bias configuration, and modified the bias circuit to accept a bias balancing pot. After some adjustments, it works like a dream.
Take a few things in consideration when you work on the CARY. If you have only one pair of KT88 in the circuit, the B+ is a bit higher at 550V and the tubes run hotter than you would expect from their standard bias setting for all 4 tubes in circuit.
I removed the 10K resistor from the bias pot.
I had to increase the bias voltage to reign in the JJ's to a 50% dissipation. That is why the 10k resistor bridges the 47k.
On the KT88 side, I added a 10k balancing pot and two 22k resistors to ground.
Now the tubes can be balanced to perfectly identical idle currents.
The CARY SLI-80 is a great amp, except the 520V on the KT88's can stress some KT88's and make it hard to bias matched pairs to run equivalent idle currents.
I had a look at the bias configuration, and modified the bias circuit to accept a bias balancing pot. After some adjustments, it works like a dream.
Take a few things in consideration when you work on the CARY. If you have only one pair of KT88 in the circuit, the B+ is a bit higher at 550V and the tubes run hotter than you would expect from their standard bias setting for all 4 tubes in circuit.
I removed the 10K resistor from the bias pot.
I had to increase the bias voltage to reign in the JJ's to a 50% dissipation. That is why the 10k resistor bridges the 47k.
On the KT88 side, I added a 10k balancing pot and two 22k resistors to ground.
Now the tubes can be balanced to perfectly identical idle currents.
