parallel triode question

[joesatch]

can you parallel a triode with an LND for a boost? or will it blow up?

[kagliostro]

Parallel .... I'm not sure but think so

One other, may be, feasible way, I think it may be realized is a bootstrap

Franco

[kagliostro]

Ciao joesatch

I've just find this thing

https://www.tdpri.com/threads/i-finally-built-it-help-me-dial-it-in.772035/



I had no time to read the whole thread but may be of your interest


Other link with something you can be interested


https://www.diyaudio.com/community/threads/local-cfb-and-bootstrap-an-hybrid-12ax7-driver-with-55db-of-gain-and-cf-like-zout.403656/




Franco

[DummyLoad]

K, that LND 150 attached to the 12AX7 triode is a LFO for tremelo - It's cathode coupled and varies the bias on the 12AX7 gain stage for the trmrelo effect.

The second SIM schematic is a LND 150 cascade with bootstrapping - Very high gain - AV is about 560.

--Pete

[kagliostro]

Ciao Pete

I know, it was only to show that it can work without problems with B+ at 12a*7 levels (didn't burn as suspected)

Our friend Tubenit, some time ago, posted a proposal of paralleled  Triode+MOSFET but I remember there was a problem on the arrangement

Franco

[joesatch]

what i'm trying to accomplish is to add a clean channel to my amp but i only have one triode to work with. I have a splawn amp which uses one tube for clean but the triodes are in parallel and the cleans are great on that amp. Since i only have one triode to work with i thought of parallel'ing it with a mosfet to beef it up.

[sluckey]

what i'm trying to accomplish is to add a clean channel to my amp but i only have one triode to work with. I have a splawn amp which uses one tube for clean but the triodes are in parallel and the cleans are great on that amp. Since i only have one triode to work with i thought of parallel'ing it with a mosfet to beef it up.

This kind of info would be very useful to include in your original post.

[kagliostro]

Here you can find some advice about an LND150 used as "V1"

there are indication on how to obtain a high or lower gain

http://www.hawestv.com/amp_projects/amp_solid_tube/fetpreamp_200v1.htm



---

Here there is an article that talk about Super Triode (but it is too tecnical for my brain)

https://www.tubecad.com/2015/04/blog0321.htm

---

Here is an idea of our friend Tubenit which was not followed up

https://el34world.com/Forum/index.php?topic=22778.msg243512#msg243512




---

I'm not able to plan correctly a paralleled Triode + Mosfet

but, if I can suggest

Build your Triode Gain Stage + build an LND150 Gain Stage

(refer to the schematic and link I posted previously)



Each Stage must be independent

then use the VOX AC30CC2 link method to parallel the two different Gain Stage Families

Semplified path


Real VOX AC30CC2 Input with Channel Link Switch


Franco

[HotBluePlates]

can you parallel a triode with an LND for a boost? ...

Our friend Tubenit, some time ago, posted a proposal of paralleled  Triode+MOSFET but I remember there was a problem on the arrangement

Here you can find some advice about an LND150 used as "V1"
...
http://www.hawestv.com/amp_projects/amp_solid_tube/fetpreamp_200v1.htm


...

Here is an idea of our friend Tubenit which was not followed up

https://el34world.com/Forum/index.php?topic=22778.msg243512#msg243512

Looking back at Tubenit's thread, PRR gave the reason it does not work:
Triode needs its grid negative of its cathode
MOSFET needs its gate positive of its source

The basic arrangement of putting the triode & MOSFET in parallel connects the grid to gate, and cathode to source.  So the tube's cathode resistor biases the FET into cutoff, and it doesn't do anything.

EDIT:  Got to check the details of the FET being used.

[DummyLoad]

Looking back at Tubenit's thread, PRR gave the reason it does not work:
Triode needs its grid negative of its cathode
MOSFET needs its gate positive of its source

LND150 is a depletion FET, IRF820 is an enhancement FET, LND150 being depletion device so negative voltage on gate behaves like grid negative control attributes of tubes, however, depletion FET behaves more like a pentode - Gain structure (transconductance) being much greater. Bias a triode with a another device in parallel that has differing control and gain characteristics seems like would work asymmetrically rather than in unity. If you're looking for greater structure in gain, you'd likely see greater potential for success if you built a cascode with the LND150 as the upper device, a positive attribute being no worries regarding heater-cathode stress of the upper device since FET has no heater.


--Pete 

[joesatch]

Looking back at Tubenit's thread, PRR gave the reason it does not work:
Triode needs its grid negative of its cathode
MOSFET needs its gate positive of its source

LND150 is a depletion FET, IRF820 is an enhancement FET, LND150 being depletion device so negative voltage on gate behaves like grid negative control attributes of tubes, however, depletion FET behaves more like a pentode - Gain structure (transconductance) being much greater. Bias a triode with a another device in parallel that has differing control and gain characteristics seems like would work asymmetrically rather than in unity. If you're looking for greater structure in gain, you'd likely see greater potential for success if you built a cascode with the LND150 as the upper device, a positive attribute being no worries regarding heater-cathode stress of the upper device since FET has no heater.


--Pete

Thanks for the advice. I will cascade them with LND first stage.

[Willabe]

If you're looking for greater structure in gain, you'd likely see greater potential for success if you built a cascode with the LND150 as the upper device, a positive attribute being no worries regarding heater-cathode stress of the upper device since FET has no heater.

Thanks for the advice. I will cascade them with LND first stage.

Pete wrote cascode not cascade, different circuits.

[kagliostro]

Looking for a Cascode example of 12ax7 + LND150 I've find this (that seems interesting)

https://music-electronics-forum.com/forum/amplification/guitar-amps/theory-design/45971-understanding-fet-noise-curves



---

Then I've find this

https://www.diyaudio.com/community/threads/simple-building-block-for-high-gain-preamps-12ax7-with-single-lnd150-for-ccs.374622/



I didn't read the threads, so you must do it

Franco

[HotBluePlates]

Looking back at Tubenit's thread, PRR gave the reason it does not work:
Triode needs its grid negative of its cathode
MOSFET needs its gate positive of its source

LND150 is a depletion FET, IRF820 is an enhancement FET, LND150 being depletion device ...

Thanks for that correction!  That does make a big difference.

[kagliostro]

Ciao joesatch

Can you post the schematic of the amp you want to modify or, at least, a description of the signal path from V1 to the power tube ?

This will help a lot trying to suggest you something

Franco

[joesatch]

no schematic i'm just running a split off my input stage coupling cap to a relay'd clean channel with only one triode and plate driven tonestack. amp is something i put together based off a slo lead channel

[kagliostro]

Sorry, I'm not able to follow your description

please can you try to descript the circuit like I do now with the 5F2A




12ax7 (V1a) > Volume & Tone Control > 12ax7 (V1b) > 6V6 (Power Tube) > OT > NFB to cathode of V1b

Franco