Ampeg V4 came in rough shape

[SoulFetish]

Here was an interesting case:
Customer came in to have an old V4 serviced with the instructions "make nice" and not a lot of history. I wasn't here to take it in, so I didn't even know if it worked for him. Right off the bat, it was missing 2 tubes - V1 and V3 with the wrong tube in the phase inverter. So at least I knew it wasn't making any sound in that condition.
If I don't know anything about an amp, I like to take it out and inspect it before I demo it just to make sure there was no catastrophic event and risking more damage. After looking this amp over, I could see that there was going to be a fair amount of work to do before even powering it up and bench testing. Someone had gone in and done some shoddy and unfinished work in the amp - Missing and disconnected components, poorly replaced filter caps, and a replacement output transformer looked like it was given up on half way through the install.

There was a replacement can cap that was not secured sitting in the chassis hanging on by the wires.

Unmounted can cap.jpg

So, I fixed the power supply repair and rebuilt the filter layout and wiring, installing axial caps mounted topside on the main board to take advantage of a better ground scheme.
I also replaced missing dropper resistors, and other components that needed it.

Once it was ready to test, I applied the mains power using my variac and monitoring the current just to make sure I didn't make any mistakes or miss something. Everything at idle looked normal, but when monitoring the output on my scope, the waveform was weak and squashed, but the amp was drawing current and I could hear the output transformer "sing" like it was driving a short.
After doing some testing on the OT, the OT looked okay, but the symptom persisted.
Was it the tubes, impedance switch? Something I hadn't thought of?
I temporarily clipped in a different OT using Wago lever nuts and ez mini hooks to try and see if the rest of the amp worked normally. With the sub output transformer, the amp operated looked fine, with normal output signal into the load.
It would be weird if the new OT the amp came in with was faulty, but it could be a bad switch, or some other phantom I wasn't even thinking of yet. So, I pulled the secondary connections from the switch and retested the amp using the V4 OT connecting the 8 ohm lead directly to the load. Now, the amp appeared to work just fine, and the OT worked just fine after all. We needed to order New 7027s, so we ordered a new impedance slide switch for the amp as well. His looked rough and had a one of the terminal lugs broken off, and figured the switch was most likely was the issue (the wiring to the 1/4" jacks was correct and appeared solid). We set aside the amp until the parts arrived.

The package from CE arrived at the beginning of the following week, so I put it back up on my bench and installed the new switch and rewired the secondary leads. I double checked it against the schematic and it was good to go. Installed the new 7027A's and powered it up to check the output on my scope just to make sure everything looked good, fully expecting the new quad to bring the amp back to life and send it out with a clean bill of health; pretty confident that we had isolated the problem and fixed the issue.
Powered on – monitored idle current – applied sine wave to the input..... Amp back in failure mode with the same condition. Collapsed output signal, with the amp acting like it was driving a short. I was like "what the hell is going on?"

Dude, here is the crazy part. I notice that the main speaker out jack was missing the fiber isolating washer, so I unscrewed the two speaker jacks from the rear panel to replace that while I thought about my life choices. While the jack remained suspended by the heavy solid core wiring inside the chassis, something caught my eye. By total luck I found the problem, the clear problem that would have remained completely hidden if I didn't lift those jacks from the back panel; and here it is:

IMG_8945.jpg

This solder had become wedged in there at some point and sorted the tip to the sleeve. I don't know how long it would have take me to find that otherwise, and I was thinking back over the whole timeline of this repair and the condition it came to us in. I think a previous tech got to a point with this amp that they had to give up one it, and it made me wonder if they ordered a replacement output transformer thinking that that would fix the problem. I wonder if somewhere out there, there is a perfectly good working V4 OT sitting is some scrap pile.
I replaced the pair of jacks and now the amp is working and sounding great.

Impedance Switch and Speaker Jacks.jpg

[Stevem]

Thanks for sharing.
These days if I take something in and see that some else has been in there I tell the customer that my labor rate is double now unless I find the root cause issue in the first hour of working on it.

Remember even though it’s a nice feeling to get a nice vintage amp back up and running, your doing what you do to make money, not perform a community service.

[SoulFetish]

Thanks for sharing.
These days if I take something in and see that some else has been in there I tell the customer that my labor rate is double now unless I find the root cause issue in the first hour of working on it.

Remember even though it’s a nice feeling to get a nice vintage amp back up and running, your doing what you do to make money, not perform a community service.

Couldn't agree more! I like the idea about your rate adjustment if someone else has been in there. I, admittedly, am an employee at the shop I work at so I don't set the ultimate prices. I have a lot of freedom and I like to interface with our customers, so I enjoy talking with them about their equipment and the service. I believe there is a lot of value in quality and reliability, and I find that musicians generally feel the same way and think it's worth paying for. Not all of them though .

A technician friend of mine shared some good advice that someone gave to him. He said "If you're not loosing customers, you're not charging enough money. The first ones to go are the worst anyway."

[Stevem]

I could not agree more with your tech friends assessment!

[Bobwith2Bs]

Do you remember what switch you ordered for the impedance selector replacement?

I need a couple for some V4 rebuilds i have going on. I think i just ordered some Switchcraft DP3T slider guys like this but haven't installed them yet:

https://www.cedist.com/products/slide-s ... 3-position

[Stevem]

Looks like the correct switch, but how many amps is that rated for?

The V4 can do more then 100 watts rms, so that’s over 5 amps and where not even talking about peak wattage!

I guess this is why the original ones fail over time.

[Stevem]

Looks like the correct switch, but how many amps is that rated for?

The V4 can do more then 100 watts rms, so that’s over 5 amps and where not even talking about peak wattage!

I guess this is why the original ones fail over time.