Fender Red Kbob twin replacement capacitors and upgrades

[jalexquijano]

Just purchased a red knob twin on EBAY. I would like to do a total refresh and upgrade. Which capacitors are prone to wear and should be replaced? Should the potentiometers be treated with dexoit? Speaker Swap? Any advice and parts suppliers are greatly appreciated to get started.

[Enzo]

Should the potentiometers be treated with dexoit?

Are they noisy? If they ain't broke, don't fix them.

Speaker swap? How long have you had this amp? Have you given it time to decide what you think of the existing speakers? Speakers are completely a matter of taste, just because I like one and hate another doesn't mean you would feel the same about either one.

Capacitors don't wear out, but electrolytics can dry out. But again, I suggest you use the amp for a while before deciding to tear into it. Give it a chance to reveal any flaws it might have, and show any areas it seems to be falling short.

The film caps are most likely just fine, and replacing them is more likely to cause a problem than solving anything. AN individual cap might be bad for some reason, but wholesale replacing I recommend against.

I had a DieHard battery in my truck, it was a "five year" battery. 12 years later, that battery was still going strong, starting the truck reliably even in cold weather. I sure was not going to replace that battery just because it was past the five years.

My suppliers? For general electronic parts, I start with MOuser. For guitar amp specific parts, I start with tubesandmore.com. By specific, I mean the pots we use, the 500v electrolytic caps. There are of course other fine suppliers.

[Mick Bailey]

I've just done a repair on an well-gigged and battered early red-knob Twin. There are a few variants and your model may be different, but with this one all the electrolytic caps looked and tested good. When I get an amp in for repair I test every function and play through it (if it's working) then make a note of everything that's wrong. I only treat a pot if it's noisy - if it isn't I leave it alone. With the large Illinois electrolytic caps fitted to these amps a good telltale is to look where the + lead exits from the rubber seal. If there's a dry-looking yellow crusty substance around the lead, then the cap is on it's way out. The smaller caps are usually fine.

Over time things can slacken off remove the knobs and tighten all the pot nuts - these can come loose and in time crack the solder joints on the pot legs. Make sure the socket nuts are just about tight. Too much and they'll strip, too little and they can crack the joints.

The circuit boards in these amps have fragile tracks and pads. I see a lot where they've lifted due to owners carrying out unnecessary work.

[jalexquijano]

Thanks to both of you.

I got mine yesterday with a bent d shaft on the presence potentiometer and a broken bass pot on the overdrive channel. Luckily, i had a Brand new replacement pot for the bass 2 pot and managed to replace it. Tried to straighten the d shaft of the push pull presence pot but to a limit until it could turn. It seems to be working well. Anyway i read that it was recommended to change the stock carbón composite 470 ohm grid resistors and 1.5k resistors that come across each power tube. Should i replace them with Metal Oxide resistors to withstand the heat and quality?

[Randall]

If the grid and screen resistors measure in spec, they are most likely fine. But IMHO there is nothing wrong with being proactive and changing them for future reliability. The 470 ohm grids I would change if they were noisy as cc resistors are prone to be, or if they have drifted, since that would affect bias. One could also argue that Fender's choice of 470 ohms is not high enough, some say it should be no lower than 1K, but depends on what church you attend I suppose. No worries about heat and voltage here, but metal oxides would not be a bad idea.

The 1.5K screen resistors, if they are carbon, would benefit from flame proofs. Again, necessary? Maybe not. Prudent? COuldn't hurt.

[jalexquijano]

The amp is sounding fine. Just a little bit of rattle on the first few minutes of playing during warm up. I see it was built in 1990 and no cap job has been done. Should i purchase the same illinois brand caps of the same value or should in get F and T electrolytic caps?

[jalexquijano]

can you point out the correct technique for removing electrolytic caps and resistors that are soldered to PCB of this type of amps without lifting the tracks and pads? I want to preserve it as much as posible!

[jalexquijano]

Just got some 470 ohms 5watt resistors. Are these better