General tech questions

Help with amp maintenance

1

Hello all,

Can you guys help me out a bit? Here's a BF VibroChamp. It's staticky and probably needs maintenance. It'll be my fist time working inside a tube amp. I don't want to take it into someone, i wan to learn how to do this myself.

I've included 2 pictures of the guts. My questions is how do I figure out what needs changing? I have a multimeter and a soldering iron... and a strong desire to learn :)

It looks like some parts have already been changed out. Anyway where do i start? Also, I'm guessing i should change that 2 prong to a 3 prong power chord?

Where do i start?

Thank you in advance for any pointers and tips!

3

You don't want to hack a vintage amp from mistakes -- light noise, etc. can be just cleaning the tube sockets, etc. If it were me, I'd get a pro to fix this and learn on some PTP amp where you can make mistakes, learn, etc without too much heartache. Be sure you know how to work around voltage! A wrong move could be very serious.

And yes to any two prong cord going to grounded.

4

Check out some Youtube videos, theres plenty out there that will explain the basics.

Funny you Posted this as I just picked up an Amp book at the Local Library yesterday to read up on Tube Amp basics since Im also a rookie.

6

Hoffmans amplifier forum, mentors/help available there. Remember that tube amps run at 350VDC plus, can KILL YOU and can retain a charge even after turned off and unplugged from the wall Only use one hand inside the amp if you can help it to keep high voltage from running through your heart..and KILLLING you Did I say KILL yet?

You need a schematic of your amplifier and the ability to read one. A physical layout helps as it can help you learn the schematic these are available online. You need to discharge all the filter capacitors before proceeding An easy way to do this is to hook an alligator clip(you should have some of those too) from pin on of V1 to ground. After a short while all your electrolytic caps(including the filter caps) should be discharged. With any tube amps or ANYTHING, do the easy stuff first Test your tubes. replace any that are microphonic, noisy or test bad Staticky would make me think tube clean your tube sockets with de-oxit (dip tube pins in puddle of de-oxit insert in socket a few times)

Then it's good insurance to replace your filter caps with modern equivilents. Only replace what you have to

Did I say amps can KILL you

that said it is possible to learn by yourself i did and have built myself several nice amps since

7

I'm also looking to build a Tweed kit.. a Champ or Princeton. Maybe I should tackle that first... i dunno. I really have a strong design to do this. I'm part way through Dave Hunter's amp book, and I can pretty much find my way around the schematic and layout chart... mostly.

I guess i can start with new tube and cleaning the sockets. I know it needs tubes. It's got the old RCA's in there, but they are pretty shot.

I'm still reluctant to take into someone to do the work. I'll never learn if i do that. A mentor to help me along would be awesome. I guess a can post an ad on craigslist and see what comes from it.

I know i shouldn't hack an old "classic" BF Fender. But I'm not planning on hacking it. I'm taking my time and i have respect for the technical details involved.

Thanks for the link on safety, I'm going to check that out. I've already read how deadly this can be.

8

Static could be coming from dirt/corrosion. Find a can of DeOxIt contact cleaner. Ethyl alcohol (NOT rubbing alcohol) and stiff bristle type pipe cleaners can clean jacks and tube sockets as well. Get a mentor, as Twangmeisternyc suggested, is your best move. Building a kit will help as well. Have fun with it all, and don't let the smoke out.

9

What do you mean the amp sounds "staticky"? I've heard guitars with static coming from hands rubbing on the scratchplate but I'm not sure what a staticky amp sounds like. Not being clever, just curious. Crackly sounds can be from tubes getting old - and IME 99% of issues with tube amps are from tubes.

There are many sources for intermittent noises in amps which can be caused by cold joints, old CC resistors, loose screws, loose sockets, dirt in sockets and contacts, old pots, blah blah blah... The main things which need changing in old amps are the electrolytic caps. Unless something is failing it usually doesn't need replacing.

But more detail in the noise you are experiencing will help us diagnose it. Does it happen only when you are playing? Does it happen when you're not playing?

10

ya it's a crackling, staticky sound. not only when playing. just there. more so when turning any knobs.

i'm not panning on changing every part. i figured the electrolytic caps and tubes needed changing. the cap can looks like it is not original (not pictured here)

i'm going to start by getting tubes and cleaning the sockets and contacts.

Thanks for the advice so far!! it's helpful.

11

If it happens when adjusting controls, the pots need cleaning. DeOxIt will do the job. Tubes might be OK. Clean the contacts first before spending bucks on new tubes. I got a stereo amp working once by blowing the dust out with high pressure air. Good luck!

12

Beside the crackles, if the amp sounds good the tubes are probably fine. Turn the lights off and watch the tubes in the dark. If the crackles are caused by tube arcing, you'll see it.

Bleed off the filter cap bank before sticking your fingers (or a solder iron) in there. The carbon resistors LOOK okay. Use an exacto knife to scrape off the flux around each socket pin. Then use electronics cleaner and q-tip swabs to clean up the sockets. I've often traced micro-arcing to these spots.

Like others suggested, clean the pots with DeOxit.

13

ya it's a crackling, staticky sound. not only when playing. just there. more so when turning any knobs.

i'm not panning on changing every part. i figured the electrolytic caps and tubes needed changing. the cap can looks like it is not original (not pictured here)

i'm going to start by getting tubes and cleaning the sockets and contacts.

Thanks for the advice so far!! it's helpful.

– Chris-O-Matic

The caps on the board have already been changed.

14

Has the amp been stored in a humid environment?

15

not specifically... in my closet.

don't the electrolytics need to be changed out every 10 years?

16

Beside the crackles, if the amp sounds good the tubes are probably fine. Turn the lights off and watch the tubes in the dark. If the crackles are caused by tube arcing, you'll see it.

Bleed off the filter cap bank before sticking your fingers (or a solder iron) in there. The carbon resistors LOOK okay. Use an exacto knife to scrape off the flux around each socket pin. Then use electronics cleaner and q-tip swabs to clean up the sockets. I've often traced micro-arcing to these spots.

Like others suggested, clean the pots with DeOxit.

– Powdog

looking at the tubes in the dark... what am i looking for exactly?

17

Flickering, flashing, lightning. Same with dirty sockets causing arcing. You'll see the sparks.

18

ok! thank you... i got some DeOxit on the way :)

19

Crackling can be dirty jacks and resistors.

Resistors make a frying pan sound, especially the one attached to the input jack.

Does it crackle when no guitar is plugged in?

"more so when turning any knobs."

I wouldn't bother with knob noises.

20

Be careful with DeOxit! It dries very slowly and can arc and CATCH FIRE if it hasn't fully evaporated! Ask me how I know...


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