If you are talking about the last bjt, emitter follower indeed, I wouldn't go above 10k unless I wanted to purposefully introduce "cathode follower"-ish distortion.
FWIW I breadboarded the 3-stage version of this circuit, not the 4-stage one, and there was plenty of gain and still some wiggle room to push it with a TS without turning into white noise. YMMV
Oh, and ref. biasing, nothing wrong with using 2 resistors in series to get to the right bias either.

Located in Toronto Canada. Thanks thus far...

Quote from: DrGonz78 on May 19, 2024, 12:19:47 AMWhat method did you use to make the conclusion that the transformer is shorted?

I watched a dlab vid. He shows how to check the transformer. I did his test and it failed. Also when I turned the amp on I could hear the transformer frying, bubling sound. Its toast.

Hi,

I have a Marshall Mosfet Lead 100 guitar amp (3210), and when I switch to the boost channel while playing, there's an audible pop (also if connected directly to a mixer from the DI in the back). The other way (boost->normal) there's no pop if I switch while playing. Also, normal->boost there's no pop if I'm not playing.

What I want to ask is, is this expected behaviour?

So, I did some breadboarding today to find collector resistors for my BC337's. I've found a set of 4 that bias very close to 4.5 VDC with a 22k in the collector.
I didn't bother to look for the 5th one because it's an emitter follower. Should I do it? Also, should I increase the value of the buffer stage's emitter resistor from 10k to 22k?
Next step is to put the whole thing together on the breadboard.

Just for the record, I'm attaching the datasheet for the TIS58.  It's pinout does not match the interfet 2N5484, nor the on-semi or centralab 2N5484.  So that's 3 possible pinouts for the Randall Fet's.   

From the voltages you listed, it would seem that T4 collector is connected to T6 base, as you have the same voltage listed for them.
But T4 collector should go to T6 emitter, so once again the voltages listed are questionable.

Thanks so much Loudthud!  I swapped those JFET leads and we now have audio!  Thanks to everyone who contributed to this thread!

Quote from: Umlaut on May 21, 2024, 03:18:58 AMGK schematics are an extremely useful resource on how to bias and design jFet gain stages, btw. Most if not all of their guitar amps from the late 70s on (and a lot of their bass amps) feature jfets in one form or another.

So much to learn, so little time... 

Yes, bipolar supply. Look for Gallien-Krueger 200RG model (and similar very early 80s models) schematics to see where that particular gain stage originates : ) they use J113, but for these particular applications, depletion mosfets behave like jfets.
That stage CAN be built to single supply, but then we'd have to tinker with an additional Vref, and since I am running the whole preamp on bipolar, there's absolutely no need to go down that rabbit hole.
GK schematics are an extremely useful resource on how to bias and design jFet gain stages, btw. Most if not all of their guitar amps from the late 70s on (and a lot of their bass amps) feature jfets in one form or another.