Thursday, January 7, 2016

The Little Amp That Couldn't: The Egnater Vengeance

An Egnater Vengeance 60/100 head arrived here in the middle of a raft of other rocket science, dark matter, higgs boson amp projects last month so it took a little while to get to it.

The story given was that the owner while playing a gig and watching his power monitor saw a huge power surge at a particular local venue that will not be named. His Egnater died, laid down on the job, quit, gave up the ghost and generally took a dump right then and there. There are dark rumors and mutterings that this was not the first time this happened in this particular place although I haven't seen the proof of it.

If there's anything to take away here, when you've got an amp with no output, measure the voltages fer chrissakes. Often it will tell the story. On the average eight pin octal based tube such as everyone's favorites the 6L6GC, the 6V6, the EL34, and the 6550 you can measure pins 3-plate voltage, 4-screen voltage, and 5-negative bias voltage.

Missing voltages and no output has been the story around here the last couple of months. First there was the Sunn 100S with a defunct choke, then there was the Music Man 2100-65 with an open choke, an open filter capacitor and an open capacitor on the board I sussed out with my tone sniffer. Then there was the Vox AC15 HW with no output, a Marshall MA50 with no output, and a few others with various and sundry ailments. On the other hand it has given me an opportunity to put my scope to good use and take baby steps along the long learning curve to scope competency.

In this particular Egnater, there was no screen voltage present. A little work with the schematic located the correct voltage on the standby switch, and it dived into the power supply circuit board bit didn't come back out. A little more work revealed that one of the 100uf/500v radial snap in capacitors had shorted out, and two of the three 10w ceramic resistors were open.

Then the fun started. Getting the power supply board out to gain access to the back side required: removing the voltage selector switch, the power switch, the standby switch and the foot pedal board, unbolting the power transformer to get enough slack in the leads to push them far enough away so as to pull the circuit board up, clear the nearest 10w resistor to the chassis, and then remove the offending components to replace them. I would say it took a good solid hour and a half to accomplish this task.

While inspecting my nifty silver solder joints I managed to burn a hole through an unopened 12 ounce bottle of Coke and made a mess all over everything.

Here you can see the offending bulged shorted capacitor; some of the mass of wire on top of the PS board; ; more wire spaghetti ; yet more wire spaghetti; the PS board emerging; more wire spaghetti; and the new Ohmite 10w resistors.

In addition I was trying to do a clean install of XP on my library computer because one of its critical files had disappeared overnight.

This morning I expect to finish the XP reinstall and start the burdensome and onerous task of installing a bajillion updates and service packs.

Then, and only then, I may try the registry hack that will convince Microsoft that this old workstation is really a "point of sale" device and get more updates.

Of course the wireless business would not cooperate so things came to a screeching halt on the computer front. 

Somehow the usual abbreviation "P.O.S." seems appropriate.

UPDATE: I think that the long road of XP has come to the end. I knuckled under and bought a copy of Windows 7 and a new wireless adapter. These ought to arrive fairly soon and I can then see how well the box operates with a modern-ish operating system.

UPDATE: I got the Egnater running this morning and on the scope it was putting out a good 90w clean, so I proceeded to put the head in the cabinet and to give it a last road test before it went home. The volume had dropped down to nothing, about 2 or 3 w. What now?

I took it back to the shop and opened it up again and this is what I found. I think I'm pulling the captive nut and spring clip and losing them somewhere. The screw had jammed right into the footswitch board. I'm guessing that the hole in the chassis and the mating hole in the cabinet were mislocated.


  1. Hi Robert,

    I own a Harmony H-322 bass amp like the one you restored and featured in this blog entry. I would like to replace the selenium rectifier in it as you did in yours.

    If you get the chance and remember the details of what diode, resistor you used along with the 10k bias pot and any other materials you used please let me know. Looking at the photo you posted it looks like there is a black capacitor used on the fiberboard too, but I can't tell where the connecting wires go.

    Many thanks,