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Author Topic: Fender Deluxe Reverb (1976) - Replacing Capacitors?  (Read 15177 times)

ajax11124

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Fender Deluxe Reverb (1976) - Replacing Capacitors?
« on: April 27, 2014, 08:00:05 PM »
To start off, I just joined this forum because I have been growing in interest in amplifiers. I went to college for computers, got interested in hobby electronics, started playing guitar and soon after wanted to get inside the amp and look around. That's my story, now to the question.

I just got a hold of a Fender Deluxe Reverb Silverface amplifier that I believe to be from 1976 after some research I did. It's been sitting unused for the past 30 years. I've read quite a bit online about how electrolytic capacitors go bad over 10-20 years, so by 30 years I believe they probably need to be replaced. I'm not an expert with electronics, but I believe I have enough knowledge to work safely inside an amp. I have quite a bit of experience working with soldering onto circuit boards and such, and although it's a little different on these older amps, I'd rather gather the knowledge and do the work myself, rather then pass it of to an unknown amp tech. I believe it should be fairly straight forward. Identify the electrolytic caps, read their values. Then buy equivalent caps, and solder them into the same place.

My main question to start out with, is does it matter what kind of caps I replace the old ones with? Do I have to replace them with electrolytic caps, or would another type of cap with the same values work as well? What are some good brands to go with? What's a good place to find them?

This is a link to all the pictures of inside my amp. Am I correct that all the large blue caps, as well as the white mallory caps all are electrolytic and should be replaced?
https://onedrive.live.com/redir?resid=7E33E45F4682CBE8%21105

I'd appreciate any feedback, and I would like to thank you ahead of time.

DrGonz78

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Re: Fender Deluxe Reverb (1976) - Replacing Capacitors?
« Reply #1 on: April 28, 2014, 02:06:05 AM »
The caps that you are referencing are not electrolytic filter capacitors. They are capacitors for tone sculpting and other such functions. What you are looking to find on this amp is underneath the chassis down where the tubes plug in to the amp. Reference the pic attached. You need to understand what you are working on and how dangerous that part of the amp can be too. Do a search on draining high voltage capacitors in guitar amps and safety.


« Last Edit: April 28, 2014, 02:07:34 AM by DrGonz78 »
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Roly

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If you say theory and practice don't agree you haven't applied enough theory.

g1

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Re: Fender Deluxe Reverb (1976) - Replacing Capacitors?
« Reply #3 on: April 28, 2014, 12:05:55 PM »
  The question is whether you want to replace just the electrolytic filter caps, or all electrolytics.
  As Doc mentioned, the main filters are on the other side of the chassis under the rectangular metal cover known as the "doghouse".
  The blue caps are non-electrolytic so are not prone to the same issues and are usually only replaced when they fail or go leaky.
  But the white mallory's with the + markings are also electrolytic.  The ones in the bias circuit should also be considered "filter caps" and replaced.  They may need to be replaced with higher voltage rated caps as they were sometimes under-rated and modern line voltages have increased.
  Other than that, there are some white mallories as cathode bypass  caps in the preamp, having gone this far you might as well replace them too.

Not quite sure which schematic/layout to post.  Does your amp have a "boost" pull switch on the volume control?

ajax11124

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Re: Fender Deluxe Reverb (1976) - Replacing Capacitors?
« Reply #4 on: April 28, 2014, 07:11:34 PM »
  The question is whether you want to replace just the electrolytic filter caps, or all electrolytics.
I did already know about the filter caps underneath, but I was under the impression that any cap in the amp that was electrolytic was worth replacing after such a long time period as this. I'd like to hear what you guys think about that though. My overall goal is to have an amp that still sounds good and can hopefully continue to last a long time. So if replacing more than just the filter caps would be beneficial than I'm fine with that.

The blue caps are non-electrolytic so are not prone to the same issues and are usually only replaced when they fail or go leaky.
What kind of cap is the blue ones? What causes them to go leaky?

Not quite sure which schematic/layout to post.  Does your amp have a "boost" pull switch on the volume control?
It doesn't have the boost switch. I believe that was added the year after mine.

I appreciate the information you all have provided. It's answered a lot of my questions.
I am aware the dangers exist and I don't plan on trying anything without research and precaution.
« Last Edit: April 28, 2014, 07:12:37 PM by ajax11124 »

DrGonz78

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Re: Fender Deluxe Reverb (1976) - Replacing Capacitors?
« Reply #5 on: April 28, 2014, 08:06:39 PM »
Sorry Ajax for not reading your question just right. I was thinking you were trying to reference the Main filter capacitors and I neglected to understand the question.

Those blue caps on the board are Film caps. Those caps could be mylar, polyester, polystyrene, and polypropylene film types. I think on the older amps those are polyester, but I might be wrong. There are more types of film caps than what I listed here too. Mylar film is a very common one that I see all the time these days on most amps that I am working on.   
“A person who never made a mistake never tried anything new.” -Albert Einstein

g1

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Re: Fender Deluxe Reverb (1976) - Replacing Capacitors?
« Reply #6 on: April 28, 2014, 08:15:10 PM »
  They didn't change much till the boost version so I'll attach the standard schematic and layout which should be close.
  The bias filter cap is the white mallory on the little board by the pilot light.  Replace it with something bigger with a higher voltage rating, like 100uf@100V.  All other caps should be replaced with same value, but can be higher voltage rating.
  After you have replaced the main filters, and the bias filters, there are only a few more electrolytics, so you might as well replace them too.
  The blue ones are non-electrolytic.  They are being used as coupling caps.  They block DC voltage from getting where it is not wanted, but they let the AC signal pass through.  They last much longer than electrolytics and generally don't go leaky for any particular reason.  Some brands/types are more failure prone than others, the blue ones used in the old Fender amps are usually not problematic.
« Last Edit: April 28, 2014, 08:18:46 PM by g1 »

ajax11124

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Re: Fender Deluxe Reverb (1976) - Replacing Capacitors?
« Reply #7 on: April 28, 2014, 09:03:07 PM »
That schematic is very helpful, and all the information you guys have given is much appreciated. I think I have enough understanding of how to do this now. So my last step is locating the parts to do it. Do I need to make sure the caps I buy are also electrolytic? Or are there other types of caps that would be fine as well? Anyone have a recommendation as far as brand/reliability?

smackoj

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Re: Fender Deluxe Reverb (1976) - Replacing Capacitors?
« Reply #8 on: April 28, 2014, 09:26:17 PM »
Ajax; I wouldn't replace the blue coupling caps until after I had the amp up and running. Then you can see if you like the tone. Changing those caps to other varieties will mildly change the tone and one of the reasons for wanting a silver faced fender amp is that sought after tone. I would definitely do the startup of this amp using a current limiter. It's not a bad idea to then bring the amp up slowly on a variac to allow the older caps to get used to having current through them again.

Yes, you need polarized electrolyic caps to replace the main filter caps and the bias cap. Be careful to ensure you replace them with correct polarity observed.

I like Sprague Atom electolytic caps and I also like F&T which are made in Germany. Spragues are more expensive than the F&T. 

smacko  jack

Roly

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Re: Fender Deluxe Reverb (1976) - Replacing Capacitors?
« Reply #9 on: April 29, 2014, 11:01:43 AM »
Or see "limiting lamp" thread.
http://www.ssguitar.com/index.php?topic=2093.0

If you are going to recap, the first phase should be the power supply network electrolytics.

Once that is done you can look for current-leaky coupling caps (the blue ones) and off-value, but these generally don't give trouble.  Some types like waxed-paper do, but not those fitted in your amp.

Clean/replace pots and connectors would be my next step, then look at signal caps if I have odd voltages or funny sound.  Don't fix what ain't busted.
If you say theory and practice don't agree you haven't applied enough theory.

g1

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Re: Fender Deluxe Reverb (1976) - Replacing Capacitors?
« Reply #10 on: April 29, 2014, 10:18:28 PM »

Yes, you need polarized electrolyic caps to replace the main filter caps and the bias cap. Be careful to ensure you replace them with correct polarity observed.
And a reminder:  The bias cap has it's positive end going to ground.  This is opposite of all the other electrolytics and is normal and correct.

ajax11124

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Re: Fender Deluxe Reverb (1976) - Replacing Capacitors?
« Reply #11 on: April 30, 2014, 07:03:27 PM »
Before I start ripping this thing apart I was just wondering If anyone could explain what I'm looking at underneath. I took a picture and labeled the parts im curious about with numbers. Number 1 I believe is where I need to go to get the the filter caps. I'm just curious, What the other parts are. I can tell you guys have a lot more knowledge than I do, and I'm working on growing mine. So I thank you for your patients and assistance. I admit fully understanding this amp is a little over my head, but I'm trying to learn as much as I can and get a good understanding of this amp before I start taking things apart.

UPDATE: I took off the cover and found the filter caps, tested them with a multimeter all of them are showing 15V. Is this normal after discharge?
« Last Edit: April 30, 2014, 07:23:39 PM by ajax11124 »

phatt

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Re: Fender Deluxe Reverb (1976) - Replacing Capacitors?
« Reply #12 on: April 30, 2014, 07:40:01 PM »
Hi Ajax,
             Small resiual voltage after discharge is normal. Don't worry about it. :tu:

Having just looked at the pic of this it's obviously in immaculate condition with no sign of being on the road for years on end,,,, So I'd would check if any leaky main filter caps and if it runs normal sounds good then don't fix what ain't broke. 8)
Phil.

bobhill

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Re: Fender Deluxe Reverb (1976) - Replacing Capacitors?
« Reply #13 on: May 01, 2014, 10:37:37 PM »
You identified your number 1, the rest are the various transformers that make these old amps wiegh a ton.

In order as you have them numbered,

2: Reverb transformer for coupeling to reverb unit.
3: Output transformer - on one side couples plate voltage to the 6v6 plates, the other side talks to the speaker.
4: Power supply filter choke. More ripple and transient cleanup for the DC side of things.
5: Power transformer - takes that nasty real world AC voltage and turns it loose inside your amp.

And to repeat what others have said, definitely change the power supply and bias caps. The cathode bypass electros (the white 25v 25uf polarized parts) will probably need it, one of the signs of a bad bypass cap is motorboating, but when their value changes, so will the frequency response of that stage, so that some frequencies will be amplified more than others. This changed sound may be desirable, or otherwise. Your ears will have to decide on that one, but any motorboating, just change them all. They are not expensive and the amp will thank you for it. The other caps will hardly ever go bad, although I did have a ceramic disc break a leg on one of my Bandmasters trem circuit.

All told, you could recap it, doing it yourself, for $40. And learn a bit about the design while doing so. Have fun, and respect those DC voltages. You will have somewhere north of the 420vDC the circuit originally called for depending on how much your house current varies from the old 110/220 vAC standard. Measure carefully, and use the old tech standby, keep your left hand in your hip pocket.

Roly

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Re: Fender Deluxe Reverb (1976) - Replacing Capacitors?
« Reply #14 on: May 02, 2014, 02:20:16 AM »
Another odd fault that old Fenders can exhibit when the electros are going down is that the volume goes down to zero at about 1 or 2 on the knob, then comes back up again from there to zero.
If you say theory and practice don't agree you haven't applied enough theory.