Hi Russ,
Yes. All things have risk. But let's say a tube melts down (has never happened to me in over 50 years messing with this stuff), - and let's say we get a full ~350V on the cap coupling the tube section to the MOSFET section, - if the cap holds up, all we will get across the speakers is .9X of the residual power supply hum. Could happen. Would potentially sound ugly. And iif it draws too much current, the protection circuit will trigger. Likely the 3A fuses will also blow.
For this very reason, I do not trust Hybrid Amps where tubes are coupled directly to the MOSFET section. Tubes do blow out. But with a good quality cap between the tube and transistor section, not a great deal of stuff can go wrong.
If you do not like caps, try transformer coupling:
https://www.audiodesignguide.com/Hybrid2021/index.html
Yes. All things have risk. But let's say a tube melts down (has never happened to me in over 50 years messing with this stuff), - and let's say we get a full ~350V on the cap coupling the tube section to the MOSFET section, - if the cap holds up, all we will get across the speakers is .9X of the residual power supply hum. Could happen. Would potentially sound ugly. And iif it draws too much current, the protection circuit will trigger. Likely the 3A fuses will also blow.
For this very reason, I do not trust Hybrid Amps where tubes are coupled directly to the MOSFET section. Tubes do blow out. But with a good quality cap between the tube and transistor section, not a great deal of stuff can go wrong.
If you do not like caps, try transformer coupling:
https://www.audiodesignguide.com/Hybrid2021/index.html
Hi Denis - Is there any reason this differential SRPP input cannot be used with your version 10b design? As well, have you tried the Exicon lateral FETs in lieu of the 1058/162?
Thanks,
Gary
No reason at all. That is the fun part: you can cook up any tube driver amp section you want. Some like SRPP. Some like plate followers. And so on.
The Exicon's are direct replacements for 1058/162 and should work fine. The only tricky bit is that as the tubes warm up, they can send a low refrequency current wave to the output transistors. No DC - as the gates are capacitor coupled to the tube section. I use 3A fuses in the rails. And yes, I have had them blow on ocation. If this happens, use an extra relay to ground the gates for 20 seconds or so (driven by the protection circuit).
Or you can use a cathode follower as the last stage in the tube section. In fact, my very first hybrid was a 6SL7 plate loaded driving a 6SN7 cathode follower before we hit the MOSFETs. Works well and sounds good. You need to shoot for 20X to 25X amplification by the tube section - and there are many ways to get there. It is all a matter of your personal tastes. - But hey, is that not why we all love this hobby? We can have it our way. Experiment. All without it costing a furtune.
Good luck! 😎
The Exicon's are direct replacements for 1058/162 and should work fine. The only tricky bit is that as the tubes warm up, they can send a low refrequency current wave to the output transistors. No DC - as the gates are capacitor coupled to the tube section. I use 3A fuses in the rails. And yes, I have had them blow on ocation. If this happens, use an extra relay to ground the gates for 20 seconds or so (driven by the protection circuit).
Or you can use a cathode follower as the last stage in the tube section. In fact, my very first hybrid was a 6SL7 plate loaded driving a 6SN7 cathode follower before we hit the MOSFETs. Works well and sounds good. You need to shoot for 20X to 25X amplification by the tube section - and there are many ways to get there. It is all a matter of your personal tastes. - But hey, is that not why we all love this hobby? We can have it our way. Experiment. All without it costing a furtune.
Good luck! 😎
In the schematic above, one of the BIAS arrangement 22K resistors can be replaced with a 15K resistor and a 10K trimpot for OFFSET adjustment.
Or do it this way:
BIAS should be set to ~200mA and OFFSET should be set to +/- 10mV (it will drift a bit). All adjustments should be made after the amp has warmed up a bit (20 minutes or so).
Have fun.
Or do it this way:
BIAS should be set to ~200mA and OFFSET should be set to +/- 10mV (it will drift a bit). All adjustments should be made after the amp has warmed up a bit (20 minutes or so).
Have fun.