Tube or SS Preamp?

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#62
Hi Guys,

I tried reworking the circuit so I could try the 6N1P tube. Can one of you look it over and see if I've got it right? I added the resistor and cap to the cathode side. Can one of you verify that this is the correct way to proceed? Also, this circuit uses a 170V rail and the schematic I have for the 6N1P is 200V. Do I need to change any resistors to allow for the 30V difference?

Thanks, Terry
 

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#63
I found some errors in the last one so I have reworked it some. I didn't mention that I am also feeding the heater direct with 6.3VAC as I found that the L7806 over heated when feeding the heater circuit and the relay circuitry. On the ECC88 circuit I fed the heater from a separate transformer winding but I though I would try feeding the heater and the L7806 both from the same windings here and see if it will work.

Please have a look and see if you find errors.

Thanks, Terry
 

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#64
Hey guys,

I have it singing now with the 6N1P. Very similar to the ECC88. It's nice with lots of gain. If anyone wants to build it let me know and I'll share the file.

Blessings, Terry
 

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#65
still4given said:
Hi Guys,

I cut the traces to the heater pins on the tube and added a jack so I could feed 6.3vac directly to the tube. Now the L7806 runs cool and the tube heats up more quickly. Further testing with the 6N1P shows that it doesn't settle to 0V offset. It stays at about 20mV. That is too much for a preamp so I can't recommend this tube. The ECC88 settles to +-1mv and stays there.

Blessings, Terry
Click to expand...

Since this appears to be a cap coupled design it seems impossible there would be any DC on the output, regardless of tube. Unless I'm missing something here...
 
#66
Yes I can't explain it either I just know what I read on the meter. Regardless, I couldn't gt the 6N1P to work as is. It is working perfectly with the changes I made. I added two caps and two resistors and changed the values of a couple of other resistors. I also feed the heater directly from the 6.3Vac on the transformer. I am attaching the value changes and the new layout. The only other issue is that with 47u in C7 the relay would not switch. I tried 10u and it would switch on but still took a log time. I now have 2.2u in there and it is better but still takes a full 13 seconds. This may be because I am using 6.3vac to feed the L7805. I might try an L7806 and see if that can speed things up.
In the attached schematic Ra = R22, R23 and Ca=C18, C19
Blessings, Terry
 

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#68
😀 Spent some time with bespoke 12a... Pre circuits in several variants.
Even did the 6n.. route.
Happy with the results.
One day I assembled a simple Stepped attenuator /line stage (gawd that's a Pompous name for a pot in line 🙂 gizmo.
Wayy better in some cases and in the worst case; Every bit as good as my years long Tube Contraption Build.
Bit of an Epiphany. Simplicity Has advantage 😉
Try it ??
 
#69
Bare said:
😀 Spent some time with bespoke 12a... Pre circuits in several variants.
Even did the 6n.. route.
Happy with the results.
One day I assembled a simple Stepped attenuator /line stage (gawd that's a Pompous name for a pot in line 🙂 gizmo.
Wayy better in some cases and in the worst case; Every bit as good as my years long Tube Contraption Build.
Bit of an Epiphany. Simplicity Has advantage 😉
Try it ??
Click to expand...

what do you mean by " Stepped attenuator /line stage (gawd that's a Pompous name for a pot in line 🙂 gizmo"?

Do you have an easier to understand description?
 
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