I should have probably measured across those resistors, because I noticed that OPS pulls a bit of current even with the bias adjusted to 0.00v so the drivers must be drawing a pretty good load. I guess with the added load of the IPS it was just too much. The CF-CET has only been used through the Tubsumo OPS so far. I guess I had better test how much it draws too. Anyway, here's a pic.
Attachments
I just checked and the drivers are shorted. For some reason the CF-FET is not a good match. I'm going to have to investigate why that is.
I said I was done for the day but I couldn't stay away. I replaced the drivers and R17-20. I checked the OPS with 15K resistors and everything looks fine. So I dialed the bias all the way down and hooked up the IPS again it looked good. I ran sine waves and square waves through it and all looked good. So then I hooked it up to a CD and played music through it. Looked good for about 5 minutes when the 2SA shorted and R19,20 went up in flames again. So now I'm thining there is definitely something amiss in the CF-FET. I repair it again and try other Slew IPS's.
Any ideas what is causing the drivers to short out?
Blessings, Terry
Any ideas what is causing the drivers to short out?
Blessings, Terry
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I questioned that earlier but you seemed to defend it. I thought I'd try it since it is a nice small package. If you would rather we only talk about your designs I'm cool with that.
Blessings, Terry
I'm not DX ?? Much more open to a deviation in the design.
Mistakes are great learning tools. If everything worked , what would
we learn ?
I would prefer we fix any design than to discount it !
OS
post the voltages (schema) before you "blow" it ...
edit - what is the "CF-FET" ?
OS
I use a variac and a light bulb. Once everything is working I then by-pass them so I can raise the bias. I doubt even the light bulb will save a 1/2 watt resistor when a transistor shorts.
Hi Borys,
You've got my attention. Can you post a silk mirror for those when you get a chance.
Thanks, Terry
Oh , it's brother Val's creation.
Looks like he tested on both his VFET/LFET output stages , but not on a
BJT OPS.
Just like the infidel and the first "kypton V" , there are certain IPS's that do
not interact well with the EF3.
Lack of VAS cpacitance and other factors have to be simulated with the
original slew OPS.
Typically , any that work with the BJT will work with the FET OPS's.
Sometimes , the opposite might not be true. Hard to accurately sim
the MOSFET OPS's ... build it and cross yer' fingers ... 🙄
OS
I'll try to simulate/investigate what happens with EF3 BJT over the next few days.
Pete, you're right - I tested only with VFET/LFET ones and those ran smoothly for weeks.
IRF610/9610 VAS is rather high-current (20 mA) - better linearity in this region - and the whole thing is rather fast. Something causes the current shoot-through in the OPS...
Pete, you're right - I tested only with VFET/LFET ones and those ran smoothly for weeks.
IRF610/9610 VAS is rather high-current (20 mA) - better linearity in this region - and the whole thing is rather fast. Something causes the current shoot-through in the OPS...
He would have to run the FET VAS in a non-linear region to get <10ma
VAS I. At 20ma , I'm not sure you could even bias the EF3 ?
Another factor ... that looks like Borys's OPS (burned up) ??
OS
Yep. Terry, can you please drop the link to Borys's OPS "as built" schematic or the schematic itself. Can't find it now.