peavey 5150 recap job

[seth-ep]

ok, im new on the forum, but ive been around in some others, i think i can handle the recap job, but i dont have a full idea on which ones i need to replace, need some advises, i live in mexico and theres no one i know or trust to do this job other than me here, so any help will be very appreciated. i have the schematics but any explanation or some kind of step by step procedure will be more than welcome. im very familiar with tube bias, soldering iron, and electronic's terminology, just never done this recap thing before...

[Steve Conner]

How do you know it even needs a recap? The 5150 isn't that old.

[Jazz P Bass]

And they are a PITA to work on!

[km6xz]

What are the symptoms that led you to diagnosis the problem to be caused by capacitors?
Don't believe everything you read on the internet. Most of the time, they are trying to sell you something that you do not need, or are clueless wannabes who are using buzz phrases to sound like they know something. Modern caps do not fail even 1/100th as often as claimed by amateur amp "experts". I think the fad was introduced by boutique cap retailers.
Sure, occasionally a part fails, when a cap fails it produces distinct symptoms and replacing the defective part is called for, not wholesale replacement with parts that might be better than the ones taken out. The odds of a part that has been performing for 10 years being more reliable than a new part are high, failures tend to occur when first put into service and than again at the end of its normal design life.

[seth-ep]

seriously??? this 5150 is a block letter, and from the first run, made in 1991 from what i researched, its 20 years old...
actually i hear some loud pops when ever i take the amp out of standby to the playing position. ive tried some other 6505's from friends and their sound is more articulate and with over all better bass response, ive replace the tubes (power and preamp tubes are new,yes the 9 of them), so what you guys think, is it worth trying?? while i open the amp i must replace some pots inside which are broken (ive been adjusting those pots with a screwdriver since i got the amp)

[km6xz]

20 years is not long for a decent amp to retain its specified performance.
You are going about this backwards. Instead of confusing the issue of sound characteristics being a refurbish project, treat it as a repair issue. If you have specific knowledge that it is not performing as it should, find out why. One reason is that there are many production changes over the years. The tubes are different. The conditions for playing(acoustic, speaker, source signal, tubes, etc) that are different between what your friend's amps produce so it is better to reduce variables to find differences, not increase ambiguity in replacing a bunch of parts and tubes. Put both on the work bench and measure gain, noise floor, frequency response, power output and distortion as a start. With a known signal, either a pure sinewave generator or a programmable arbitrary wave form generator if you want a complex wave form. Don't use a guitar because small changes in playing attack, pressure and tuning assuming the same guitar and cable, that makes pinpointing differences very difficult or impossible. Those measurements should give you an idea of what characteristics have changed and to what degree. Tone changes can be traced this way must easier than subjectively. Get the performance up to original then look for the factory production changes and add those if you like the results from newer amps.
Repair up to spec before any rebuilding or mods, it will save a lot of money and chasing phantoms.

[52 Bill]

And depending upon how and which pots are broken, they could be the cause of your loss of tone problems.

[tedmich]

Peavey parts will be able to sell you exact replacements, and then its just a matter of popping them off with a solder sucker and temp controlled solder iron, AFTER making sure they are discharged (typically a ~250k 2w across them for a few min)

It could probably benefit greatly with some higher cap values in similar sized cans; Mouser has pretty accurate dimensions listed and careful measurement could allow a 50-100% boost in filtering at the right sizes as cap tech has improved a ton in 20yrs.

Bad caps make NOIZE (60Hz/120Hz etc), bad tone is tubes 90% of the time IME

[seth-ep]

thanks alot guys, i think ive got enough useful info from you guys about the topic, im not replacing the caps yet... ill experiment with some different preamp tubes and try the bias a little colder... my is at 38ma and stock are about 15ma, i found some info that being colder gives tightness on bass, ill try a nice middle point of 32ma(never tried it before) and see how it goes...

[Steve Conner]

I could be wrong, but I think Peavey made a few tweaks to the 5150 circuit over its life. Maybe this is why the later ones sound better than the Mk1.

Different preamp tubes can make a big difference in a high-gain amp like this. And you may be right about the bias, I think Peavey designed it to sound best biased very cold. Cold bias will make the high-gain tone harder and more aggressive, but will make the clean channel sound bad. The 5150 never had any clean tones to start with, though.

[Billy R aka DynaFreak]

I work on a lot of these amps. Make sure the power section is up to snuff first. Check for blown screen resistors. Set the bias to 30ma. There are places on the pwr tube pcb where you sub a 1 ohm resistor for a wire link btwn cathode and ground, makes setting the bias easy. The 165 uf of filtering is plenty if the caps are ok.

If the pwr section is ok and the amp lacks something, look at the last preamp stage before the phase inverter. It has a very low value (.0047) bypass cap. Removing this cap and leaving the stage unbypassed can make the amp come to life. Of course you can also bypass it with a higher value cap. But be sure to try it unbypassed first.

Chinese 12AX7's are a good fit for these amps, IMO.