Recap Facts and Fiction

There seams to be some confusion on if or when to recap your older Boogie's. First off I am only talking about the power supply filter electrolytic caps. Lets start with my first MK3 I got it about 4 years ago, it had sum hum, so it was do for a check up. I have 3 or 4 ways of checking caps, first I have a curve tracer adapter on my Tektronix 468 & 465 so I can test in circuit components. If that shows a flaw I desolder one end of the cap and us a capacitance test. Results the 4 220uF 300v on the ps3c board were all bad the 3 B C D caps one was out of spec and not holding a charge for as long as a new one, thats another test method, out of circuit I charge and time how long it holds the charge. So I changed all 7 caps and amp was happy and without hum. So never changing caps is wrong! But changing every 10 years without reason is also wrong. Solution is to test them if your amp has to much HUM or if it's been idle for more than 2 years or more, yes Idleness is the cap killer also higher than nominal voltage.There is one more reason to change caps if you have to remove the main board on the Mark series especially, then you might as well replace the other hard to get at caps. PS.. I am an Electrical Engineer don't try this at home 450 volts can kill.

Your tests are a great way to tell if your caps are fading. I would also recommend testing ESR. Even if the capacitance and leakages are good, high ESR will make the caps underperform.

Unfortunately, most people, even techs, don't have the ability to test this stuff. For me, as long as the amp performs well (no hum or microphonics), I would change caps at about 15 year intervals. If I made a living with the equipment I might change every 5-10 years as basic maintenance. If I have a problem with an amp, I would change the caps if a tube change, new screen resistors and reheating the solder joints failed to do the trick.

I had a 1965 Deluxe Reverb that would hum periodically while playing, which would often stop or start if I slapped the top of the amp hard enough. Solved it with a cap change.

Hope you are using the one-hand rule...

Oh right forgot about ESR. I do have an old B&K esr meter but the curve tracer is similar in that it uses a 60Hz AC sine sweep and esr testers use high frequency around 100khz. As the curve trace gives you a quick pick of a section of a circuit or a single component. You can see resistance on a capp if its a nice circle on the scope that means low resistance. So if theres no resistor in parallel with the cap theres something wrong. Also on older amps things are failing or good.In a Quad Preamp 1989, I just found a .047 400vdc orange drop cap that was totally shorted. I think that only the second time iv seen that. Found that with my Fluke DMM ,Of topic there anyway I use ESR testers on brand new caps. The curve tracer like better for troubleshooting because it test everything caps res transistors diodes etc.. and I like seeing a component on a O scope instead of a number on ESR meter you then have to look up the number on the chart on the front of the meter to see what it means. As far as safety goes of course right hand only and, as little hot probing as possible, as a result Iv never ben shocked in over 15 years of amp repair, but with xmass lights got sapped a bunch of times.