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Messages - Luthier Vandros

Quote from: g1 on March 04, 2023, 06:35:33 PM
Quote from: Luthier Vandros on March 04, 2023, 12:31:48 PMonce the new silicon is in, I'll try to align voltages between green and red, along with biasing these little jerks.
On another forum J202 fet was working as a drop-in replacement for the 2N5485/TIS58 with no adjustment required.

TY, G1. I found a broken trace under the board. The 3819's are passing signal, but cery attenuated compared to the green channel. I imagine I'll have to tweak the drain resistors. Is there a rule of thumb? I have a solid 24v on the source rail (thanks to a 24v zener. More on that below.

Btw the schematic posted must be of a more recent model. My circuit board has several variances, such as no 24v zener off the E supply. Instead that tap is supplying 34v. Both the cap and dropping resistor have been replaced, so as a test, I tacked in a 24v zener. 

Sorry for the delay; not getting notifications. That is the correct schematic. I really appreciate the comments and once the new silicon is in, I'll try to align voltages between green and red, along with biasing these little jerks.
Amplifier Discussion / 1980’s Randall RG80-112 SC
March 02, 2023, 10:17:16 AM
Hi, all. Long time lurker/first time caller.

I've got the aforementioned amp on the bench and I'm knee-deep in the doo-doo, as it were. I generally don't take on vintage SS amps, but a good customer asked for help.

The amp arrived with a dead red channel that wasn't passing signal. All voltages check out after replacing a few drifted resistors, so I removed the three transistors and replaced them with a set of 2N5484's from an eBay seller. Obviously there are issues with counterfeit obsolete parts and maybe I fell victim. I then tried a set of BF245's with the same result, except it passed the signal almost inaudibly. I made sure to reorient the legs to respect the pinout. Thankfully, I've been refunded on both occasions, but I'm giving this one last try with a more generic, albeit branded, transistor — 2N3819's. General purpose parts should do the trick, but if these fail I'm at a loss.

I don't have an o-scope, but an audio probe/sig-gen that I use for this type of troubleshooting, but solid state gear isn't in my wheelhouse. From time to time, I'll take these on to help financially strapped customers that can't afford to have their gear go down. Can anyone weigh in with any direction should these 3819's fail to resolve the issue?

Much appreciated!