Best practices for SS amp recaps and general maintenance - Yamaha JX50-related

[ancient_places]

Good afternoon all.

I've recently gotten the bug to pickup an older solid state amp with good clean headroom and great reverb and, after doing some looking around, decided to go with a Yamaha JX50. It seems Yamaha's G series of SS amps is a little more beloved, but those don't seem to pop up a lot around here in the EU as opposed to the JX50's that do seem to be around. The samples I've heard on YouTube sound perfect for my personal taste though, so I decided to go for it. It'll be used in a studio environment as either a high-headroom clean amp or a pedal platform.

In a different time in my life I worked under an amazing tech and did tube amp recaps and maintenance. I continue to suck at reading schematics, but I was a solid solder monkey and was capable of good work, so I'm aware of that looks like and consists of.
Sadly, I no longer own a soldering station setup (or have space to keep one setup), so I may get a 3rd party to give the JX50 some TLC once it arrives.

I'm hoping to learn from people more knowledgable than myself what "best practices" tend to be for SS amps of this era. I would assume the power section electrolytics are all far beyond their best days, but may still be functioning for now. I'm personally in the philosophical camp of always replacing old power caps before they become a problem, so I'll definitely want to explore getting that done.

Outside of a good DeOxit session, are there other electrolytics, resistors and the like that tend to float dramatically out of spec on these amps and become problematic?

On Fender tube amps it was very predictable what we'd do for a standard recap and I'm hoping to just come up with an idea of what to update to get it in the best shape possible for both performance and reliability.

I've been able to find the JX50 service manual pdf, so that's a great start.

Thanks so much!

Lee
 

[ancient_places]

I've just discovered something that might be helpful to someone in the future. It looks like Yamaha released the VX55 after the JX50 and used the exact same board layout and schematic. The existing schematic/manual for the JX50 is quite poorly scanned, so having access to the very nicely scanned VX55 service manual is a nice alternative.

I've just recieved the amp in the mail and got a little time to play through it. It's in good shape and works, but there's a constant underlying hum that makes me feel like a recap is the wise way to go forward. 

[Jazz P Bass]

Thanks for that info!

[phatt]

I've just recieved the amp in the mail and got a little time to play through it. It's in good shape and works, but there's a constant underlying hum that makes me feel like a recap is the wise way to go forward. 

Replacing caps in blind faith assuming that will fix it is mugs game,, Far more likely you have grounding issues.
Ground plane isssues can be hard to track down.
Schematics don't tend to show where they all connect, you just get a whole lot of Arrows pointing to some elusive Ground/Common path.
Finding that path in the actual Chassis can be confusing.
Some sockets use the metal outer ring to ground to the chassis but over time corrosion can cause the grounding path to fail causing hum.

Every Amp builder uses a different layout so you have to work out where each ground node interconnects back to Chassis common.


If it has a reverb tank that can be a hum issue
Phil.

[g1]

As a general rule, if it's a cap issue the hum should be 120Hz.  60Hz hum would be more likely ground issues, as outlined by phatt above.

[ancient_places]

I hadn't come back to look at this for a while. I appreciate all of the constructive feedback very much. I've just let the amp be and played it as is for the time being.

I did open it up and take a boatload of good photos since there's really not clean pictures of it out there that I've found. I've put everything up onto Imgur and I'll link here in case they can be of help to others:

Yamaha JX50 - Detailed amp interior pictures

I think the earlier comment about the reverb being the cause of the noise floor might be correct. It goes up significantly as the reverb level is raised. The tank is also mounted onto the bottom of the chassis, so I don't know if the proximity to transformers, caps, etc. could also be problematic. It might be interesting to try getting some longer cables and putting it further away from the chassis.

I don't see any deformation of the electolytics at the moment, so I don't feel an urgent need to recap. There is an occasional, single, low-frequency "wump" when I power the amp on or off. The other night there was also about 2 minutes of a strange parasitic, high frequency crackle, but it went away after the episode and I haven't heard it again since.

I took some time to really play with the EQ on the amp and it's unlike anything I've used before, sonically speaking. With all of the EQ rolled counter clock-wise there's no sound at all. The amp has a lot of low end, so I ended up keeping the bass knob at around 2. The treble and bass could be adjusted to taste from there. The control set doesn't feel like typical fender eq at all, but the amp was able to take pedals fairly well and there's a good range of sound depending on how you setup the master vol. vs the normal volume control.

Not knowing what the amp sounded like new, it's a little hard to say if the voicing has more to do with speaker choice (or a dead-ish speaker) or perhaps is just the way the amp itself is voiced. I'd like to understand the EQ better, but I can't find a use manual, just the service documents. Those are a little above my pay-grade, so I haven't seen anything that clearly explains in them what to expect from the EQ in terms of where the controls are fixed, frequency-wise.

If anyone has speaker upgrades ideas, I'm very open to hearing them. It's not my heaviest amp, but if there was a neo speaker that might sound nice in it, I'd be open to swapping one in.

Thanks again for the feedback.