Hi Guys
Sorry - i don't hang out on this forum very much as i must confess, i am a tube amp fanatic ;-)
The blue dots are where i removed the link wire and the green wire connects to the chassis ground.
One of life's great mysteries is why the only place i could find the schematic for a tube amplifier was on this - a solid state amplifier forum !
Anyway, sorry for the extremely late reply to this thread - i can always be found lurking on the freestompboxes.org forum or you can always email me (while i am still living) baja002steve@gmail.com
cheers to all
bajaman

.2V? My cheap meter probably.

Hey, Umlaut.
It's great that you've been able to breadboard and play it. Thanks a lot for all your input. It's going to save me, and possibly others, some time.
My parts came in this afternoon and I'm looking forward to breadboarding it myself, but it's going to have to wait a bit. Hopefully, no longer than two weeks.
Oh, and I found some BC550's the other day. I might give them a whirl too.

I also have a couple of questions:
1. Did you use the 2N5089 transistors?
2. Now that you have some hands-on (and ears-on) experience, how to would you describe the voicing of this preamp?

M.

Quote from: Randy Lahey on May 19, 2024, 06:35:53 PMTransistor pin resistance measurements:
Original Gate - Source: 550 ohms
Original Gate - Drain: 306 ohms
Original Drain - Source: 300 ohms

New Gate - Source: 11M ohms
New Gate - Drain: 320 ohms
New Drain - Source: 10M ohms

The Gate should measure like a diode to Drain or Source. If you measure from Drain to Source you should see the ON Resistance of the JFET (a couple of hundred Ohms). If you short the Gate to one of your meter leads while you are measuring resistance from Drain to Source, the resistance will go down slightly on one lead and rise slightly on the other lead. Those readings of 10M or 11M are probably just the resistance of you fingers across the leads.

From your schematics with the Volume pot at min and max it looks like the JFET is installed with Gate and Source reversed. It may pass a little signal but will have a gain less than one.

See my comments in this thread: https://music-electronics-forum.com/forum/amplification/guitar-amps/build-your-amp/debugging-your-build/20115-please-help-me-out-debugging-my-ruby-bassman-amp
about how to Ohm-check a JFET out of circuit. Note that with the vast majority of JFETs, the Drain and Source are interchangeable.

Transistor pin resistance measurements:
Original Gate - Source: 550 ohms
Original Gate - Drain: 306 ohms
Original Drain - Source: 300 ohms

New Gate - Source: 11M ohms
New Gate - Drain: 320 ohms
New Drain - Source: 10M ohms

Attached is the data sheet for the 2N5484 transistors I got from Mouser.  On the flat side of the original transistors, from top to bottom, the pins go Drain, Source, Gate.  On the new 2N5484 transistors, from top to bottom, pins go Gate, Drain, Source.  The original part was actually a TIS-58 but indicated on the schematic that 2N5484 could be used as well.
I've also attached a schematic with DC voltages measured with the gain pot at zero as well as at max.  These were all measured with a 1V AC 500 hz signal injected at the input jack.  I can also provide voltages of the AC signal throughout the circuit if that helps.
I should also mention that Q2 and Q3 have been swapped with new transistors.  I've also replaced C4, R7, C7, R8, and removed C5 and C6 for the meantime.
All voltages have been measured after all the new parts have been installed.  I've also verified conductivity of all the traces in this part of the circuit.

It would be better if you added your location to your personal info, there have been times when someone had one and was happy to send it if the recipient paid the postage.
I remember one time it turned out they lived in the same town so there was no need to send it in the mail.

I mean from the description of what caused a failure of the amp we have little to go on. What is the status of the main transistors? We have no idea what traces you bridged. With so little information I personally can't say go buy a transformer. With more information then I might have more of an answer.

What method did you use to make the conclusion that the transformer is shorted?

T4 collector connects to T6 emitter, so not sure why you are showing different voltages for those pins. (T4 and T6 are BCE pinout)