Alpha shows a minimum dielectric strength of 500V.
LND150 replacement options
Moderators: pompeiisneaks, Colossal
Re: LND150 replacement options
1M send should go before 22nF ofcourse, ground pin to the ground like master volume, and then from the viper 22nF to IRF to existing schematic.
also there is 100k gate stoper on that IRF which is making more bad then good. it is easy to understand why, need to dig little bit about , enjoy
also there is 100k gate stoper on that IRF which is making more bad then good. it is easy to understand why, need to dig little bit about , enjoy
Re: LND150 replacement options
So then with a 450V B+, you would have 250V across the MOSFET to get 750mW. At 300V B+ you would have 166.67V across the MOSFET to get 500mW. Neither of these scenarios are even remotely similar to the example you quoted. The example you quoted has 20V on the Source, so a 300V B+ puts 280V across the MOSFET. The 2mA idle puts the dissipation at 560mW. 560mW is what a 740mW device derates to at 55.4 degrees celsius.
Re: LND150 replacement options
If you put the 1M Send pot there, then the load presented to the tone stack will vary from 157.33k to 1M. Not desirable.bepone wrote: ↑Mon Jan 23, 2023 8:51 pm 1M send should go before 22nF ofcourse, ground pin to the ground like master volume, and then from the viper 22nF to IRF to existing schematic.
also there is 100k gate stoper on that IRF which is making more bad then good. it is easy to understand why, need to dig little bit about , enjoy
100k gate stopper is appropriate. What bad do you see?
Re: LND150 replacement options
What safe operating area is that? It is certainly not anywhere near the SAO's of the four devices I suggested.
3mA is the peak AC voltage. The idle current is 2mA. 2mA is what you would use for power dissipation.
Re: LND150 replacement options
tehnically you dont even need send, only CF bottom part just to reconstruct.
if you want send then you can put it there (in CF bottom part divider, then send can be 10k pot)
100k gate stopper can be a big problem, already this mistake is rolling 15 years from forum to forum, from VVR schematic to every other...do some tests and you will find out.
Re: LND150 replacement options
Like this?
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Re: LND150 replacement options
I have thoroughly tested it. It works correctly. Maybe you had better just tell me what the big problem is.
Re: LND150 replacement options
yes, maybe little bit fine tuning, i would go like this, serial loop classic p.s. before i was commenting schematic with IRF fet
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Re: LND150 replacement options
actually i was reffering to gate stopper 100k it is not the same for LND/IRF. for LND you can leave 100k , for IRF to be reduced..also huge difference is material composition, but i'm sure that you know which one you need to take.
Re: LND150 replacement options
Let's throw some numbers at the IRF820.
The total input capacitance on the data sheet is 360pF.
The reverse transfer capacitance is 37pF, so the Gate-to-Source capacitance is 360pF - 37pF = 323pF.
The Gate-to-Source capacitance for a source follower is reduced by the factor (1 - A) where A is the gain at the Source.
The gain at the Source is around 0.99, but to be conservative we will use 0.98 for the reduction factor.
323pF x (1 - A) = 323pF x .02 = 6.5pF = effective Gate-to-Source capacitance.
The effective input capacitance is the sum of the reverse transfer capacitance and the effective Gate-to-Source capacitance.
Cin = 37pF + 6.5pF = 43.5pF
fc = corner frequency = 1/(2 x pi x R x C) = 1/(6.283 x 100k x 43.5pF) = 36.6kHz
In testing, the frequency response was dead flat through 30kHz with a 100k Gate stopper. The response was down 0.15dB at 20kHz and 0.3dB at 30kHz with a 220k Gate stopper. Obviously, the corner frequency with 100k is somewhat higher than 36.6kHz. This is because the data sheet is quoting at 25Vds and we are running at around 130Vds and because we used a conservative gain. The input capacitance falls with increasing Vds.
Attached is a mathematical derivation of the effective input capacitance for a vacuum tube cathode follower. The same math holds true for a MOSFET source follower.
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Re: LND150 replacement options
It is not about input capacitance..think more, you dont need any math, only logic.
Maybe some experience with HF circuits
Maybe some experience with HF circuits
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Re: LND150 replacement options
Also 40 years of age on an IC doesn't mean much, the 555 timer was invented in 1971 and still used to this day on circuits all day long.
I'm 52, that 555 timer is 1 year younger than me
Vacuum tubes are a LOT older than that and we still love them.
~Phil
tUber Nerd!