Missing Build Docs / Schematics

alienas

New member
I don't like smd's with adapters because they must be soldered and are not removable. And transistors don't like heat.
About JFETs, is a JFET any good if it needs 100k drain resistor to be biased properly?
And are J201 and 2N5458 swappable?
Thanks
 

temol

Well-known member
About JFETs, is a JFET any good if it needs 100k drain resistor to be biased properly?
Value of the drain resistor depends on parameters of the particular jfet and other factors. Looks like 100k is a leftover from transfering tube amp schematics to jfets.
Below I attach screens from ltspice.
You can clearly see the difference between J201, 2N5457 and 2N5458 in terms of gain.

I only adjusted Rd value to get 4.5V on a drain of each transistor. Rs does not change (because people usualy adjust only Rd value. And often it's a trimmer).
Rd for J201 =34.3k
Rd for 2N457 =16k
Rd for 2N458 =11.95k
Rs = 3k

1632420337944.png
1632420461357.png

And are J201 and 2N5458 swappable?
It depends. As a source follower (buffer) - yes. In a gain stage - sometimes.
 

Feral Feline

Well-known member
I don't like smd's with adapters because they must be soldered and are not removable. And transistors don't like heat.
About JFETs, is a JFET any good if it needs 100k drain resistor to be biased properly?
And are J201 and 2N5458 swappable?
Thanks


IMO, it's the PCBs that have SMD pads that must be soldered and are not (easily) removable.
I like adapters because they are more easily removable.

When you've got a through-hole board and SMD-adapter daughterboards, you can socket the main board and solder the SMD bits to the adapters and shove the adapters in the main-board's sockets — if something goes wrong, remove the adapter with the toasted component and replace it — easy-peasy.

If an SMD-board's component goes bad, you can still remove it, but I would think it's more of a PITB to do so and especially so if the PCB has a mix of THD and SMD.
 

bowanderror

Well-known member
Value of the drain resistor depends on parameters of the particular jfet and other factors. Looks like 100k is a leftover from transfering tube amp schematics to jfets.
Below I attach screens from ltspice.
You can clearly see the difference between J201, 2N5457 and 2N5458 in terms of gain.

I only adjusted Rd value to get 4.5V on a drain of each transistor. Rs does not change (because people usualy adjust only Rd value. And often it's a trimmer).
Rd for J201 =34.3k
Rd for 2N457 =16k
Rd for 2N458 =11.95k
Rs = 3k

View attachment 16306
View attachment 16307


It depends. As a source follower (buffer) - yes. In a gain stage - sometimes.
Those look like quite useful LTSpice plots, how did you set up your command to step through 3 different transistor/resistor combinations?
 

bowanderror

Well-known member
I don't like smd's with adapters because they must be soldered and are not removable. And transistors don't like heat.
I use resistor leg cutoffs on my SMD adapter boards & they work great in sockets! Also never had a problem with SMD JFETs & heat, and I use a standard hand iron to solder them.
 

alienas

New member
Value of the drain resistor depends on parameters of the particular jfet and other factors. Looks like 100k is a leftover from transfering tube amp schematics to jfets.
Below I attach screens from ltspice.
You can clearly see the difference between J201, 2N5457 and 2N5458 in terms of gain.

I only adjusted Rd value to get 4.5V on a drain of each transistor. Rs does not change (because people usualy adjust only Rd value. And often it's a trimmer).
Rd for J201 =34.3k
Rd for 2N457 =16k
Rd for 2N458 =11.95k
Rs = 3k

View attachment 16306
View attachment 16307


It depends. As a source follower (buffer) - yes. In a gain stage - sometimes.
Thanks for these informations...
About the 100 k drain resistor, i mean that what if i have to turn the trimpot to 100k to get the correct voltage at the drain? Is the FET still good?
 

lfrank580

New member
Could we get the XB-MB schematic? I'm having issues with mine and would like to analyze the circuit and figure out what's going wrong. Thank you!
 

Barry

Well-known member

thesmokingman

Paid Hater
looking at the calendar and my email inbox and it's been over a month since the release of the acetylene and still no build docs ... got an ETA?
 
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