It is currently Mon Mar 16, 2020 8:26 pm

All times are UTC - 7 hours



Post new topic Reply to topic  [ 15 posts ] 
Author Message
Post subject: 1968 Dual Showman exploded filter cap
Posted: Fri Dec 02, 2011 10:27 am
Offline
Hobbyist
Hobbyist

Joined: Mon Sep 26, 2011 10:06 am
Posts: 17
This is a followup of an earlier post I submitted: 1968 Dual Showman filter cap replacement.
I figured I'd start a new thread relating to filter cap failure.

I replaced the filter caps in my 1968 Dual showman and experienced the dreaded aroma of an exploded cap.
I figure either the cap was faulty or probably the moron that put it in. Any comments are welcome.

Here are some pics...

The amp when I got it....
http://s1214.photobucket.com/albums/cc491/debeall/1968%20Dual%20Showman_when%20I%20got%20it/

New caps after meltdown...
http://s1214.photobucket.com/albums/cc491/debeall/1968%20Dual%20Showman_after%20cap%20job/



I just did a cap job on my 1965 Bassman that went well and will start a new topic on that to ask about possible mods that were done.


Top
Profile
Fender Play Winter Sale 2020
Post subject: Re: 1968 Dual Showman exploded filter cap
Posted: Fri Dec 02, 2011 12:57 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Wed Mar 31, 2010 12:48 am
Posts: 26417
Location: Tombstone Territory
Barring the catastrophic failure of a resistor in the power rail array, I'd say you got a bad Sprague right out of the box.

It happens (though thankfully rarely).

Arjay

_________________
"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


Top
Profile
Post subject: Re: 1968 Dual Showman exploded filter cap
Posted: Fri Dec 02, 2011 1:55 pm
Offline
Hobbyist
Hobbyist

Joined: Mon Sep 26, 2011 10:06 am
Posts: 17
Thanks Retroverbial.

Would you think that if it was a voltage problem, more than one resister would have blown?
I would think that the first one in line would have gone first.
Some people are telling me that the polarity should be reversed on the first resistor. I've seen picks of "Dual Showmans" with the first resistor reversed. I've seen picks The amp worked with the old resistors all in the same direction.

It's been over a month sense the meltdown and I swear I can still smell it in my work room. The smell went all over the house at the time.

I have couple of those resistors here, so I think I'll go ahead and replace it and then go outside or to the garage and turn it on.

Thanks again


Top
Profile
Post subject: Re: 1968 Dual Showman exploded filter cap
Posted: Fri Dec 02, 2011 2:05 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Wed Mar 31, 2010 12:48 am
Posts: 26417
Location: Tombstone Territory
Resistors are not "polarized". Filter caps are.

Yours appear to have been installed correctly as per the AB763 Showman/Dual Showman schematic......

http://web.archive.org/web/201001051830 ... _schem.pdf

The AB568 revision is identical.

HTH

Arjay

_________________
"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


Top
Profile
Post subject: Re: 1968 Dual Showman exploded filter cap
Posted: Fri Dec 02, 2011 2:45 pm
Offline
Rock Star
Rock Star
User avatar

Joined: Sat Jul 03, 2010 2:18 pm
Posts: 6544
Arjay, I believe those two 100 mfd/350 VDC caps were not aligned properly. If you look at the schematic, the two caps should be in series (+) to (-). Not (+) to (+). With top (+) to B+ and bottom (-) to ground. In essence the middle Sprague atom got shorted to ground. Check my SFSR schematic and the layout.


Dual Showman schemo:

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



SFSR (schemo):


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


PS caps layout:

Image


Top
Profile
Post subject: Re: 1968 Dual Showman exploded filter cap
Posted: Fri Dec 02, 2011 3:08 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Wed Mar 31, 2010 12:48 am
Posts: 26417
Location: Tombstone Territory
Whoops!

:oops:

You're right, Steve. The first thing I did was consult an under-the-doghouse pic I've archived to visually check for the correct cap polarity. What I forgot was, that particular amp was a 6G14 Showman......the filter-cap configuration is different from the blackface/silverface amps.

DUH!

(smacks forehead with palm of hand)

Arjay

_________________
"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


Top
Profile
Post subject: Re: 1968 Dual Showman exploded filter cap
Posted: Fri Dec 02, 2011 5:22 pm
Offline
Hobbyist
Hobbyist

Joined: Mon Sep 26, 2011 10:06 am
Posts: 17
I really appreciate everyone's input on my problem here.

First of all, I need to point out that I'm Just a guitar player trying to learn how to work on my own gear. I'm limited on reading schematics. I can see where resistors are and their value. As far as tracking the voltage through the schematic....I haven't a clue. I'm learning more and more with the interaction on this forum though. Thank you.

...but I'm still confused.

The amp worked with all resisters in the same direction when I got it. (there are pics of the filter caps when I first got it in this thread)
Is there a different resistor layouts under the dog house for a Dual Showman with and without reverb? The pic that BMW2002Ti posted is a Dual Showman with reverb...I can see the reverb transformer. Dual Showman pics others have posted without reverbs have the filter caps all with the same polarity.

Dual Showman without reverb....caps in the same direction.
This pick is on the next thread..........sorry.

Don't get me wrong. I need to learn this stuff and I really appreciate the feedback. I'm just seeing 'Dual Showman" filter cap pics with different polarity on the first cap.


Please continue with more feedback...........

Thanks


Last edited by debeall on Fri Dec 02, 2011 5:39 pm, edited 1 time in total.

Top
Profile
Post subject: Re: 1968 Dual Showman exploded filter cap
Posted: Fri Dec 02, 2011 5:37 pm
Offline
Hobbyist
Hobbyist

Joined: Mon Sep 26, 2011 10:06 am
Posts: 17
I don't think the pic for the previous post came out....
here's a PB link...
http://s1214.photobucket.com/albums/cc491/debeall/Dual%20Showman%20non%20reverb%20filter%20caps/?action=view&current=63show13.jpg


Top
Profile
Post subject: Re: 1968 Dual Showman exploded filter cap
Posted: Fri Dec 02, 2011 5:48 pm
Offline
Rock Star
Rock Star
User avatar

Joined: Sat Jul 03, 2010 2:18 pm
Posts: 6544
Maybe what we need is a clarification of terms.

For electrolytic caps SERIES means that the (+) of one cap is connected to the (-) of the next cap. There is one free (+) end and one free (-) end.

PARALLEL connection means two (+) are connected and the two (-) ends are free. Or two (-) are connected and the two (+) are free.

Fender puts two 100 mfd/350 VDC electrolytic caps IN SERIES to effectively DOUBLE the voltage handling capacity (from rated 350 VDC to 700 VDC). But, in doing so the total filtering capacity id cut in half = 50 mfd.

The reason? In the 1950-60's 50mfd/700 VDC electrolytic caps were expensive and ENORMOUS beasts.

All you need to do is place two distributive resistors of appropriate value across the two caps, to better distribuate the voltage load.


Look at your Dual Showman (w/o reverb) schemo:

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

Those first two caps before the standby switch. Are they in parallel or series? And there's the answer. They are in series. And your photo showed them in parallel. It seemed.

Study your photo you just posted and, again, mine. See the difference?

http://i1191.photobucket.com/albums/z46 ... safter.jpg

HTH


Top
Profile
Post subject: Re: 1968 Dual Showman exploded filter cap
Posted: Fri Dec 02, 2011 8:10 pm
Offline
Hobbyist
Hobbyist

Joined: Mon Sep 26, 2011 10:06 am
Posts: 17
I think I need to start over again to make it easier on me.

Here is a link to the actual picks of my amp, "caps before and after".
The "Caps when I got the amp" pic are the caps that worked when I got the amp.
The "After cap job" pic is the reason for this post.
The amp actually sounded OK but you couldn't put the lid on the dog house because of the "Marshall" type caps in there. I decided to replace the caps with proper ones that would allow me to put the dog house lid on. All I did was replace them the same way they were before. Then BAM!!!.....smell from hell.

As you can see, all the caps in the "Caps when I got the amp" pic are all in the same direction, polarity wise.
The amp worked before I put the Spragues in.

.........before and after pics........
http://s1214.photobucket.com/albums/cc491/debeall/Dual%20Showman%20caps%20before%20and%20after/


Top
Profile
Post subject: Re: 1968 Dual Showman exploded filter cap
Posted: Fri Dec 02, 2011 8:33 pm
Offline
Rock Star
Rock Star
User avatar

Joined: Sat Jul 03, 2010 2:18 pm
Posts: 6544
Those "Marshall" style are radial lead type. The others are axial. Do you remember the value of those radial lead caps? And how they were tied together?


We'll get to the bottom of all this. BTW... unless someone rewired the B+ and ground leads to that doghouse... the "exploded" view of the Sprague Atom is not connected correctly. As far as I know, all Fenders with standby switches have the first two big caps inverted (polarity wise)---at least in most of the BF and SF era. Which run two caps in series before said standby.


Top
Profile
Post subject: Re: 1968 Dual Showman exploded filter cap
Posted: Fri Dec 02, 2011 9:25 pm
Offline
Hobbyist
Hobbyist

Joined: Mon Sep 26, 2011 10:06 am
Posts: 17
The radial caps were 47uf at 500v each and they were wired in series. + of one to - of the other.
I didn't change any wiring. I put the new caps back in the same direction the old ones were in. Like I said, it worked when I got it.


Top
Profile
Post subject: Re: 1968 Dual Showman exploded filter cap
Posted: Fri Dec 02, 2011 9:46 pm
Offline
Rock Star
Rock Star
User avatar

Joined: Sat Jul 03, 2010 2:18 pm
Posts: 6544
Well, prolly best to pull all caps and check continuity of the B+ path and ground. And be sure to solder up the new caps as the schemo shows--- mindful of those 70 or 100mfd/350 VDC caps and how they should be oriented.

That much damage may have tweaked the set down resistors in the power supply. Worth a check.


Good luck!


Top
Profile
Post subject: Re: 1968 Dual Showman exploded filter cap
Posted: Sat Dec 03, 2011 9:22 am
Offline
Hobbyist
Hobbyist

Joined: Mon Sep 26, 2011 10:06 am
Posts: 17
debeall wrote:
Thanks Retroverbial.

Would you think that if it was a voltage problem, more than one resister would have blown?
I would think that the first one in line would have gone first.
Some people are telling me that the polarity should be reversed on the first resistor. I've seen picks of "Dual Showmans" with the first resistor reversed. I've seen picks The amp worked with the old resistors all in the same direction.

It's been over a month sense the meltdown and I swear I can still smell it in my work room. The smell went all over the house at the time.

I have couple of those resistors here, so I think I'll go ahead and replace it and then go outside or to the garage and turn it on.

Thanks again


I just noticed I got that one all wrong. That whole thread was about the filter caps, not resistors. SORRY!!!


Top
Profile
Post subject: Re: 1968 Dual Showman exploded filter cap
Posted: Sat Dec 03, 2011 11:47 am
Offline
Rock Star
Rock Star
User avatar

Joined: Sat Jul 03, 2010 2:18 pm
Posts: 6544
Debeall,

May want to check the dropping resistors on the B+ rail and the distributive ones (220k-ohm, 1 watt) on the 100mfd/350 VDC electrolytic caps, too. That much damage to the cap may have also wiped out a resistor or two.


Good luck with the amp!


Top
Profile
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 15 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: