On the workbench: the legendary

Peavey EVH 5150

The amplifier in wich Eddy van Halen was involved in developing.
Yes… A top-notch tearaway… but this particular amplifier has a bit of history.

History.

Recently, the owner had a small modification made by your truly to the effects circuit. This was an extension to manually switch the effects loop switching on and off.

The complaint was that the effects loop switching frequently dropped out even when it was already working. That problem has been resolved, and the manual switching works perfectly.

As always, I immediately checked the amplifier further, and a few issues emerged that really need to be addressed for reliability.

The annoying thing is that before this amplifier arrived, someone with probably good intentions had missed or completely forgotten the first day of the “troubleshooting” course, the second day of “neat soldering,” and the rest of both courses. They
also never pickedup the lesson  “how to neatly clean up my mess” from their parents.

Problem 1

I’m probably cursing in church, but adjusting the bias of a tube amplifier with 1-ohm cathode resistors isn’t a bad idea, but it’s certainly not accurate.
The problem is that you’re not only measuring the anode current (and you really want to get that right), but you’re also measuring the grid plate current. So, a distorted picture.

As it was

But measuring something is better than nothing…. So, if you install cathode resistors for your measurement and you’re done, remove them. Fix what you’ve broken and don’t complain about having to install four more resistors next time.

In this case, one of the four had also been lost by the wannabe technician. That’s precisely why you shouldn’t want to leave it like that.

If my predecessor had attended the proper training day, it would have been perfectly clear how to properly adjust the bias with the correct measurement and the correct mathematical formula.

The next day, the course “How to Adjust the Bias with an Oscilloscope” and the course “How to Use the Bias Probe” were indeed two courses in one day.

Another “beautiful” piece of failed home craft is the following

Just removed connectors, did not insulate, and certainly don’t make them mechanically strong with wire that isn’t designed for soldering.
Half-baked solution… but because those connectors are really crap, so it’s a good thing they’re gone.

Then there’s the floating bias control… you can’t make me angrier… if there’s enough space but you’re too lazy to take the board apart… then you cut the resistors and put the control on poles… what a goofy….

Anyway… The amplifier works….ish, and we’re going to get everything neat and tidy.

Let’s begin fixing…

At the time, it wasn’t a huge problem and the owner had to play, but it had to be done.
Now, the time has come for this Peavey EVH 5150 amplifier to come and stay in my workshop, the wannabe problems are being resolved, and the effects loop’s signal path needs to be made reliable again.

Cathode ground restored.

I started by repairing and restoring the cathode bias method.
The printed circuit boards are scratched here and there, the “measurement resistors” are of questionable quality and even expired.
There’s only one good solution… Remove the mess and restore it to its original condition.

You can see a long, dark green “trace.” This is a silver-plated copper wire over the original printed circuit board trace. Soldered and neatly sealed.

I still need to fix the issues circled in red. Those are two burnt filament connector contacts that someone else bridged with wire that was too thin.

The intentions were good. The execution was far less so.

That connector immediately brings up another issue visible throughout the amplifier: malfunctioning connector problems that were poorly repaired in the distant past.

Although there’s little visible wrong with the Effectloop connector set, it’s the first one to be removed.
But first, let’s give the floating BIAS control a solid place on the main pcb.

The BIAS pot.

This is how I found the BIAS pot

The new BIAS situation neatly on the PCB

I think the photos and their captions say it all.

Effect Loop Connector

As mentioned before, the printed circuit board connectors used by Peavey have seen better days… let’s just say… and a few have already been removed by someone else.
We’re going to do it right this time: all the printed circuit board connectors will be removed and replaced with hard-soldered connections.

The old Peavey printed circuit board connector

has been replaced with hard-soldered connections

The original Peavey wire has been retained, and the overly long printed circuit board connector pins have been shortened.
For the rest of the project, I’ll be using pre-cut heat shrink tubing. This will produce a neater result.

I’ve also given the effects loop jack board on the back of the amplifier a PCB trace treatment. Again, my predecessor made a start on this, and it’s a great idea, but he didn’t fully follow through.

Lastly, I’ll replace the printed circuit board connector mounted there with hard-soldered connections.

Manual Effect Loop Switch

While tidying up the preamp board of this 5150, I’m also making a small change to the Effect Loop switch I made for the owner. This also brings it fully in line with the “connector-free” amplifier.

Time for the preamp tube board connectors.

The main board can be reinstalled in the chassis, and then it’s high time for the preamp tube board connectors. Some of it is already gone, but the way it’s been left… that ‘s just not acceptable.

Let’s solve it…

Bizarrely left behind by someone who’s worked on this amplifier before.

I have to say, Peavey was clever in putting the preamp tubes on a separate, small circuit board.

This way, mechanical vibrations are definitely much less transmitted to the tubes.

My solution is to completely remove the connectors on the tube side and make the necessary connections using new wiring.
On the main board, I left the connector pins in place and used them as solder points.
Of course, everything is insulated with heat shrink tubing (now neatly cut to size 🙂 )

My solution

Next up were the speaker jacks.
Another piece of DIY replaced with a solid solution.

The Old jack PCB

New Double tip jack entree’s

And wired up

And as last a “landscape” picture of all the changes

Look nice,  save and tidy again.