It is currently Mon Mar 16, 2020 9:07 pm

All times are UTC - 7 hours



Post new topic Reply to topic  [ 5 posts ] 
Author Message
Post subject: Discharging the caps safely from the top side ?
Posted: Mon Mar 19, 2012 4:33 am
Offline
Professional Musician
Professional Musician
User avatar

Joined: Tue Jul 17, 2007 3:08 pm
Posts: 2889
You guys got me through the filter cap job with no harm.

I built my cap discharger and followed the rules, now i need to check some topside resistors and solder joints hum and a little snap & crackle in there,

How do I use my new tool to safely discharge the caps from the top of the chassis, without removing the filter cap pan again ?

Thanks

Image

_________________
Keepn' the Blues Alive

2004 50th Ann. Limited edition AMSE Stratocaster
2017 50's Baja Telecaster BSB

1968 Bandmaster with 2X12 cab C-rex speakers
VHT Special 6 Ultra combo

Visual Sound Route 66
Cmatmods Signa Drive


Top
Profile
Fender Play Winter Sale 2020
Post subject: Re: Discharging the caps safely from the top side ?
Posted: Mon Mar 19, 2012 6:04 am
Offline
Professional Musician
Professional Musician
User avatar

Joined: Tue Jul 17, 2007 3:08 pm
Posts: 2889
I went from pin #1 to chassis using my discharge tool.

Look what I found on the bias board, no freak'n solder at all in one connection and very little in the other.

My 470 ohm resistors across the power tubes were more like 570

Image

Using my bias probe one tube was 32ma the other 57 ma the hum balance pot evened them out a bit and i lost a bunch of hum.

getting the soldering iron hot as I write this.

_________________
Keepn' the Blues Alive

2004 50th Ann. Limited edition AMSE Stratocaster
2017 50's Baja Telecaster BSB

1968 Bandmaster with 2X12 cab C-rex speakers
VHT Special 6 Ultra combo

Visual Sound Route 66
Cmatmods Signa Drive


Top
Profile
Post subject: Re: Discharging the caps safely from the top side ?
Posted: Mon Mar 19, 2012 6:20 am
Offline
Rock Star
Rock Star
User avatar

Joined: Wed Feb 17, 2010 11:38 am
Posts: 4333
Location: Tennessee
I turn the amp off with the standby on....and attach a jumper to pin 1 of the preamp tube like you did....I measure the voltage to be sure.


Top
Profile
Post subject: Re: Discharging the caps safely from the top side ?
Posted: Mon Mar 19, 2012 11:53 am
Offline
Rock Star
Rock Star
User avatar

Joined: Sat Jul 03, 2010 2:18 pm
Posts: 6544
I usually clip one end of draining tool setup to the STANDBY switch contact. Amp off & unplugged, of course. Then, the other end of the drain tool right onto a clean bolt, nuts, screw, etc of the chassis. Standby switches are usually fairly easy to find. Turn this switch on-&-off a couple of times while drain wire is attached. Just to clear any residual charges.

Once you think that you've drained the caps, measure the VDC across (+) to (-) of any of the big filter caps. Just to be sure, you don't have a little surprise "wake-up" call!

Schemo is of AA165 Bassman, just for visual aid. Layout is toward the bottom of the page.

http://www.webphix.com/schematic%20heav ... _schem.pdf


Top
Profile
Post subject: Re: Discharging the caps safely from the top side ?
Posted: Mon Mar 19, 2012 12:55 pm
Offline
Professional Musician
Professional Musician
User avatar

Joined: Tue Jul 17, 2007 3:08 pm
Posts: 2889
Excellent idea ! I'll try that next time Beemer.

90% of the hum is gone, still a little white noise, so...... somewhere there is an iffy solder joint, other than the two i pointed out earlier, those i fixed.

I love vintage stuff, follow safelty guidelines and even a knuckle Head like myself can make em sound right.

_________________
Keepn' the Blues Alive

2004 50th Ann. Limited edition AMSE Stratocaster
2017 50's Baja Telecaster BSB

1968 Bandmaster with 2X12 cab C-rex speakers
VHT Special 6 Ultra combo

Visual Sound Route 66
Cmatmods Signa Drive


Top
Profile
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 5 posts ] 

All times are UTC - 7 hours

Fender Play Winter Sale 2020

Who is online

Users browsing this forum: No registered users and 2 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum

Search for:
Jump to: