Vox AC30 + EF86 channel in a different way

[kagliostro]

Usually the amps that has an EF86 as V1 didn't have a TS, at least there is a rotary switch with some capacitors

Adding the EF86 input to an AC30 schematic usually mean to do something like in the Weber 6d30

but what about to use the CF of the TopBoost as to be able to take advantage of the existing TS ??

in red my idea, what do you think about ? Have you councils ?

Thanks

K

[darryl]

When your triode/pentode switch is in the EF86 position, the cathode follower grid has no ground reference - the cathode follower gets its bias voltage from the anode of the preceding triode.

It might work if you removed the .01mfd coupling capacitor between the EF86 anode and the switch. However, operating the switch might generate a substantial bang in the amplifier output because of voltage differences on the switch contacts.

[HotBluePlates]

... It might work if you removed the .01mfd coupling capacitor ...

Or add a coupling cap and 2 resistors to have a self-biased cathode follower in both switch settings.

[kagliostro]

There is no intention to switch between channels during a play session

---

This can work ?

47K resistor + 1N4007 diode are there for arc protection (Merlin docet)

---

Thanks

K

[jojokeo]

Kag,

I personally like the EF86 going into the full CF stage just as the other 12ax7 does (and am doing that in a current amp as well as past ones). Leave the arc protection in the CF stage too. No need to install a triode/pentode switch to EF86 since you already have a 12ax7 stage to use (it will perform similarly) unless you simply want to have it. If so, then use the 100R/1M resistors Merlin likes on the switch as it's better than nothing but still gets a little pop.

BTW, your inputs aren't going to give you the "hi/lo" if you wire them up the way they are in the schematic. Also, you can lose the mixing resistors the way you have them and input the first triode straight into upper pi point and then input the lower two stages into the lower pi input since it doesn't look like you're using any NFB or Presence control.

[kagliostro]

Thanks Jojokeo

BTW, your inputs aren't going to give you the "hi/lo" if you wire them up the way they are in the schematic. Also, you can lose the mixing resistors the way you have them and input the first triode straight into upper pi point and then input the lower two stages into the lower pi input since it doesn't look like you're using any NFB or Presence control.

My fault, I didn't specified that the schematic was found on the web and used by me only as to expose the idea about the EF86 + CF, don't look to other details of that schematic

use the 100R/1M resistors Merlin likes on the switch

the 100R resistor added to the CF has grid stopper purpose, no anti-pop, I don't think of a use of that switch during playing session, but to add a pair of 1M resistors as to mitigate possible pops is a good idea

K

[sluckey]

BTW, your inputs aren't going to give you the "hi/lo" if you wire them up the way they are in the schematic.

Yes they will.

[jojokeo]

Yes they will.

Thanks, on re-check it does. Not used to seeing the "hi" input on top.