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Capacitors in Amps. Can they be upgraded? (2 Viewers)

Kevin. W

Oct 27, 1999
Sorry that should have read. "Capacitors in Amps, can they be changed." Therefore I was wondering if anyone has upgraded the storage capacity of their Amp by changing the capacitors. If it can be done how high can you go? What effect on performance would it have?



Senior HTF Member
Dec 9, 2001
I asked this about 3 weeks ago. I got a few guesses, but no real answers. I was referring to the 2 6800uF caps in my 250w plate amp.

Whatchoo got?


Second Unit
Sep 3, 2001
Maybe you could upgrade them to those multi-farad caps used for 200dB auto competitions.

But then there is another camp that believes in JBOSC (Just a Bunch of Small Caps.) They believe small caps sounds better than large caps. So they gang up a whole bunch of small unit ones. Note, small ones doesn't mean minirature sized ones, since film caps could be quite larege in size. So for each 6800uF electrolytic cap, make a add on board and fill it with 50-100 film caps in the 100uF range.

If you can't afford the room for that, just add 0.01uF teflon bypass caps to each electrolytic PS cap.

Roger Kint

Stunt Coordinator
Jan 2, 2002
Unless you have an engineering background or know exactly why they are they, it's probably not a good idea to mess around with them. It was engineers with years of schooling and design work who designed that into the product and they must have had their reasons for the design. BTW, what do you hope to improve with different capacitors?


Second Unit
Sep 3, 2001
Those engineers probably gave the thought 10 seconds to the capacitor size and count, especially if it is a mass market amp. They probably just plugged in a formula as to the ripple voltage as pct of DC voltage coming out of the transformer and got a number to on capacitance needed.

It is up to the fellow tweakers to improve upon that, listening to different caps in the power supply, whether it is electrolytic, slit foil, oil filled, gazillions of air or teflon cap, teflon bypass, multi-tier teflon bypass, centralized cap, distributed cap, centralize/distributed combination cap...


Senior HTF Member
Feb 15, 2001
I've heard that increasing capacitance beyond a certain point can stress some component to the point of failure. I don't remember if that was the diode bridge/rectifier, the transformer, a power transistor, or what. In general, you should be safe replacing any caps with better quality caps, making sure the ratings are the same. Changing values can lead to undesirable results, depending on the circuit design.

and they must have had their reasons for the design.
Those reasons very often include meeting a cost target, hence the desire to upgrade internal components to improve performance. This brings up a good point though, that the performance of a chain is only as good as its weakest link, so randomly upgrading parts won't necessarily improve things. For instance, upgrading power supply caps in a CD player might not be the best idea if the opamps used in the analog stage are cheap and noisy.

Roger Kint

Stunt Coordinator
Jan 2, 2002
So exactly what does the cap do? Saurav has a good point - how do we know what is a better value to use? What I'm saying/asking is what kind of improvement can we hope to get?

amps are simple pieces of equipment
I'd like to design one myself if they are so simple, but I'd probably start a fire or something.

Patrick Sun

Senior HTF Member
Jun 30, 1999
IF you wanted to beef up your caps, this is a big IF, you should seek to only beef up the voltage rating of the cap, but leave the cap value the same as the original.

Some sub amp blow up, and it's due to using caps that are under-rated voltage-wise. The fix (usually distributed as a service release to repair shops) is to replace the blown caps with a higher voltage rated cap of the same value.

Just increasing the cap's value isn't a good idea as it will effect the circuitry and cause unpredictable behavior in the amp's operation.

Roger Kint

Stunt Coordinator
Jan 2, 2002
From this thread, it sounds like we can either increase the voltage rating or change the number or type of caps.

But these don't answer my original question of what we hope to acheive? Or are we tweaking for tweakings sake?

Ken Situ

Stunt Coordinator
Aug 6, 2000
Most definitely you can upgrade the caps. There general two types of caps: signal and power. For signal caps, you can replace them with MIT, MultiCap, and many other "high-end" caps. You can general increase the capacitance in power supplies to a certain degree to have a more stable power source providing your transformer and other components can handle it.


Second Unit
Sep 3, 2001
Increased capacitance provides more energy reserve for your amplification stage. When great output demand is needed, the reserve will be tapped so as to drain out a steady stream of energy. If that great demand continues for a long time, that reserve in the capacitor eventually runs out and you will be pulling the voltage directly from the transformer, putting stress on the AC-line and loosing almost all filtering capability.

It also will provide a smoother DC voltage with less ripples (as indicated above.)

Increasing the voltage shouldn't effect it because the voltage limit is basically determined by the output tap from the transformer.

As far as film bypass, its purpose is to provide the power supply's ability to provide small minute amount of energy to the amplification stage quickly. Large caps are slow at charge and recharge, so if a high freq signal requires energy from the the power supply, a regular electrolytic cap cannot respond fast enough, that is where the bypass caps comes in.

That leads to the reason many companies utilize banks of small caps instead of soda can sized caps. Smaller caps reacts faster than big caps.

Then there is the notion of dedicated filter capacitors for each amplification stage so as to prevent one stage's energy requirement from detelerating the supply quality for

all the amp stage. Plus, every stage's power reserve is on tap for its own use.


Senior HTF Member
Feb 15, 2001
But these don't answer my original question of what we hope to acheive?
I have first-hand experience only with changing caps in the signal path, not in the power supply. In my case, it was in a DIY tube preamp, where I replaced cheap no-name caps (probably costing a few cents each) with better quality caps (costing about $3 each). The result was better sound - cleaner midrange and treble, and since I'd also changed the value of the cap, slightly deeper bass.

What the original poster seems to be trying to do is increase the power reserves, or dynamic power handling capacity, of his amplifier by putting in capacitors of larger value. I would suspect that this isn't as simple as just increasing capacitance. Though Nathan is right, amps are probably simpler than anything else.


Stunt Coordinator
Apr 1, 2002

I am not an amplifier designer, nor do a play one on TV. But, I've spent enough time around amplifier designers (including some fairly big names) to pick up a thing or two.

The point of power supply capacitors in an amplifier is to provide a backup "reserve" for transient peaks. At some point, in any amplifier, you can tax the power supply with a big bass transient -- running out of current and/or causing the rail voltages to sag. Basically, the storage caps stay charged during normal operation and are available to meet short term transient demands without allowing the rail voltages to drop. It's pretty much the same theory as using a car battery between a 12 Volt DC supply and a car stereo amp in a demo board.

Using large filter capacitors in the power supply is part and parcel of the "highly regulated power supply" theory of amplfier design where you attempt to hold the rail voltages constant with no sag, regardless of the current demands placed on the amplfier. The downside is that is expensive from a parts cost standpoint, so it's more commonly found in pricier high-end amplifiers.

One of the more extreme proponents of this highly-regulated power supply approach was Bill Johnson of Audio Research. My little baby Audio Research amplifier (2 x 50 watts into 8 ohms) was designed in 1979 and has two 60,000 uF capacitors. Of course, this was a very expensive little bugger. I think it retailed for over $1000 twenty years ago.

My 6 x 70 watt a/d/s/ amplifier has pretty big power supply capacitors as well -- 22,000 uF per channel for a total of 132,000 uF.

Among somewhat more affordable amps, the Rotel RMB-1075 (5 x 125 watts) has a total of 80,000 uF.

Compare this to the inexpensive subwoofer plate amps 1 x 250 watts) which have two 6800 uF capacitors. Or to the Pioneer "6 x 100 watt" receiver which appears to have two 4800 uF caps.

Would increasing the size of the power supply filter caps make a difference? Probably depends on the amplifier. If it has no current limiting, it probably would. However, most inexpensive Japanese brand amplifiers have mucho current limiting to prevent blowing up the outputs. As a result these amplifiers won't play a transient peak to begin with so I'm not sure that beefing up the power supply would make much difference. I dunno.

Kevin. W

Oct 27, 1999
Thanks for all that have responded. I have sent an e-mail to Rotel Tech support to ask for their input. Basically I have a Rotel RMB-1066 which has 6(6800uf) caps. I'm not sure of this is enough power reserve for intense transients in audio and really just want to know if larger ones can be installed(say 10000uf or 15000uf). I'm pretty sure the answer I'll get back is "No can't be done" or "Replacing internal parts will void your warranty". I understand that in lower end models they can't really be putting in the same componets as their upper end, but if it can be done why not do it?


Aslam Imran

Second Unit
Mar 1, 2002
Here is something I found that would help answer some of your questions, although it applies to radios.

Choosing New Capacitors to Replace:

Each capacitor has two values: a voltage rating and capacitance value. Both are important. The general rule for replacing capacitors is to use values that are either

equal to or higher than the originally-specified values.

Voltage rating tells how much voltage the capacitor can withstand. Tube radios use high voltage, so for safety reasons the voltage rating of the replacement must be

equal or higher than the original. It does no harm to exceed the original rating somewhat. For instance, it is fine to replace a 250-volt rated capacitor with a 450-volt

one. Almost all of the capacitors that I buy are rated for 450 volts. A very few (line bypass) capacitors may require a higher voltage rating, such as 500 or 600 volts.

Don't waste money buying capacitors with voltage ratings vastly higher than the originals. Your radio will not work any better with 1000-volt capacitors than with

450-volt units.

Capacitance value indicates how big an electrical charge the capacitor can store. This value should also be equal or higher than the original, as explained more fully

in the two following sections.

Choosing Values of Non-Electrolytic Capacitors

For small, non-electrolytic capacitors, the capacitance value of the new cap should be the same as the original, with a margin of error of roughly 20%. It is OK to

"round off" odd values. For instance, if the original is .047 it is fine to use .05 to replace it. The difference between .047 and .05 is only .003, less than 20% of the

original value. Likewise, you can replace a .022 capacitor with .02, and so on.

The 20% margin-of-error rule works because most old radio components were manufactured within a tolerance of about plus-or-minus 20%. That is, a capacitor

marked as .02 mfd could have an actual value as low as .016 (20% below the marked value) or as high as .024 (20% above the marked value). If you stay within

20%, you are well within the performance criteria for the radio's original design.

In practice, the operating tolerances of most radio designs allow for even more variation in small-capacitor values in certain circuits. An experienced repairman knows

these circuits by heart and knows when he can safely substitute a quite different value than the original. If you already know that much about radio repair, you don't

need to read this article, however! If you are still in the non-guru ranks, you will never go wrong by sticking within the 20% rule. And if you have the exact value, use


Choosing Values of Large Electrolytic Capacitors

For electrolytic capacitors, the same rules apply, except that you can safely use a capacitance value that is considerably higher. In general, you can go as much as

100% higher than the original capacitance value.

For example, when replacing a 10-mfd electrolytic capacitor in the radio's power supply, it is OK to use a 20-mfd or 22-mfd replacement. Likewise, you could

replace a 20 with a 33. The higher capacitance may do a slightly better job of removing 60-cycle AC line "hum" from the audio output of the radio. It is not unsafe to

go even higher, but you generally won't notice any improvement and the higher-value capacitors (33 mfd, 47 mfd, and so on) are significantly more expensive. Don't

waste money on a 100-mfd electrolytic if your radio sounds great with a 20-mfd unit!

Substituting for Unavailable Values

In a pinch, you can combine two capacitors to create one with the desired value. The rule to remember is that when two capacitors are wired in parallel, their values

are added.

For example, say that you need a .04-mfd capacitor, but all you have on hand are .02-mfd units. Wire two .02s in parallel, and—voila!—you now have a .04-mfd

capacitor. Likewise, wiring two 10-mfd capacitors in parallel creates a single capacitor of 20 mfd. Observe polarity when combining electrolytics (wire both positive

ends together and both negative ends together). Both capacitors should have a voltage rating equal or higher than the original.

What Type of Capacitor Should I Buy?

In the non-electrolytic category, there are several types of modern capacitors, such as polyester film, polypropylene film, metalized polyester, and so on. It makes no

difference which of these types you choose, as long as the capacitance and voltage ratings are appropriate. New capacitors—even the cheapest ones—vastly exceed

the originals in performance and reliability, so don't waste your money buying expensive, super-audiophile-quality replacements. The circuitry in your old radio is not

sophisticated enough to respond to such subtle differences.

The next photo shows an assortment of new non-electrolytic capacitors, ranging in value from .0015 to .01 mfd. The orange ones, known as "orange drops," are very

popular with restorers. The yellow cylindrical caps tend to be somewhat smaller than orange drops and are a great choice for cramped quarters.

In the electrolytic category, many old radios use multi-unit capacitors, as mentioned earlier. These are two or more capacitors inside a single can or tube. It is

sometimes possible to order replacement multi-unit capacitors that exactly match the original values. However, new multi-unit caps are quite expensive and it may be

hard to find the right value assortment in one container.

It is more economical to replace a multi-unit capacitor with individual capacitors of the desired values. For instance, if your original can contained capacitors of 20 mfd,

20 mfd, and 30 mfd, you can replace it with two new 22-mfd capacitors and one 33-mfd unit. Your radio will work exactly the same whether you use a multi-unit can

or individual caps. The next photo shows typical new electrolytics, ranging in size from 5 mfd to 100 mfd.

If you plan to fix more than one radio, you can save money by buying an assortment of capacitors of common values. Some merchants, such as Antique Electronic

Supply, offer a complete "kit" of popular values at a good discount. You can usually save money by ordering 10 or more of a given value, as well. The most common

values needed in old radio repair are .01, .02, .05, and .1 mfd for non-electrolytics, and 10, 20, 30, and 40 mfd for electrolytics.

You will use many more small non-electrolytic capacitors than large electrolytics. For a typical five-tube radio, you might replace a couple of electrolytics and half a

dozen of the smaller capacitors. Capacitors are not expensive. The electrolytics that you'll need will cost from one to four dollars each. Most non-electrolytics cost less

than one dollar each. It cost less than ten dollars to recap the Farnsworth radio shown at the beginning of this article.

Replacing Non-Electrolytic Capacitors

Now that you have the parts you need, let's install the new ones! Replacing small capacitors is the simplest operation, so we'll look at that first, then turn to the

electrolytics. Note, however, that in practice you will often want to replace the large electrolytics first. That will help eliminate any power-supply problems and simplify

testing the radio while later replacing the small caps.

Replacing a capacitor requires a wire cutter, small pliers, and a soldering iron. Another nice thing to have is a "solder sucker," a small rubber bulb with a heat-resistant

tube at one end.

I strongly recommend that you replace only one capacitor at a time and doublecheck the wiring of each replacement against the schematic. That way, if you make a

mistake, it will be easy to correct. If you replace several capacitors at a time, it could be much harder to figure out where you went wrong! Some restorers also take

notes, writing down each capacitor's value and factory part number, etc., when it is replaced.

Before replacing anything, of course you must unplug the radio from the wall and remove the chassis from the cabinet. (If you need help getting it out, see the following

page: Checking Out Your Radio.) Use a small plastic bag to hold the chassis mounting screws, knobs, and any other parts.

Turn the chassis on its side or back so that it will lie still while you work. Be careful not to damage delicate parts when you turn it over. Don't rest the radio upside

down on its tubes. If necessary, you can prop up one side of the chassis with a book, small block of wood, etc.

Some purists go so far as to hide new capacitors inside the shells of the small non-electrolytic paper capacitors. This preserves the original appearance, but it is rather

tedious. I have done this only in a few cases, for my most valuable radios. If you are interested in doing this, read the restoration articles for my Sparton Bluebird or

Colonial Globe.

Step 1. Remove the Old Capacitor

Using your wire cutters, snip the leads of the old capacitor about one-half inch from the terminals where they are connected. Leaving a little "tail" on the snipped wire

makes it easier to remove. Set the old capacitor aside.

Use your soldering iron to melt the solder on the terminal, then suck the excess solder from the terminal. Set your solder sucker aside. Using your thin pliers, remove

the snipped wire tail from the terminal. You will often need to unbend the tail a bit to work it free. If it is very firmly crimped onto the terminal, try snipping the bent

portion to free it in two pieces. Some times a thin implement such as a nut pick or the wire lead from a spare capacitor is useful to nudge the snipped tail out of its lair.

If the snipped tail is attached to a pin of a tube socket, avoid using too much force to pull it loose. You might yank the pin right out of the socket or even tear it in two.

The same goes for other components that are attached to the same terminal. Old carbon resistors are brittle and will break if handled too roughly.

Once in a while, a capacitor will be mounted in cramped quarters, so that you need to unsolder another lead or component to gain access. In such a case, make a note

or draw a picture so that you can reconnect everything correctly.

After you remove the snipped tail from the terminal, look carefully to make sure that you didn't leave any bits of wire or solder crumbs in the chassis. Small bits of

metal can cause problems later on if they lodge in between two connections and make a short circuit.

At this stage, the old capacitor has been removed and the terminals are clean.

Hint: if you do a great job of cleaning the old terminals, it may not be obvious to the eye where the new leads should go. If you are interrupted at this stage in the

process, loosely stick the leads of the new capacitor into the terminals so that you won't be scratching your head with puzzlement when you return. It's easy to forget

exactly where things went, after an hour or two.

Step 2. Install the New Capacitor

It is good practice to test every new capacitor before installing it in the radio. Modern capacitors are generally high quality, but every now and then a bad one slips

through. If you don't have a capacitor checker, you can at least test the capacitor's resistance using a multimeter. The ohmmeter should show infinite resistance on all

scales. Any continuity is a sign of leakage and a leaky capacitor must be replaced.

New capacitors usually have wire leads slightly longer than needed. Your first job is to trim these leads and bend them to fit the spot. Hold the new capacitor near the

place where it is to go, bend the leads to fit, then trim the excess wire from the end of each lead with the wire cutters. Leave enough length on the lead to allow for

crimping it around the terminal. Again, be sure to avoid leaving stray bits of wire inside the chassis.

Now slip the end of each lead into the terminal. If you did not clean all the old solder from the terminal, you may need to heat the terminal to soften the solder before

slipping in the lead. After the lead is through the terminal, carefully bend it around the terminal. Before soldering the new capacitor in place, you want to make sure that

it has a solid metal-to-metal connection with its terminal!

When both leads are securely crimped onto the terminals, heat each terminal with the soldering iron and apply new solder. Apply solder to the joint, not to your

soldering iron. If the solder doesn't melt when touching the joint, then the joint is not yet hot enough. Don't jiggle the connection while the solder is cooling. That can

create a "cold" joint that is not reliable.

Step 3. Check Your Work!

After replacing the capacitor, doublecheck your work against the schematic to make sure that you have connected the right component to the right places. If the radio

is in working order, I usually turn it on for a quick test after replacing each capacitor. Even professionals make absent-minded mistakes from time to time, and hearing

the radio play will reassure you that at least you haven't made things worse!

If your radio does not work at all, you will obviously need to do some other diagnosis and remedy the problem before turning it on. The "test after each replacement"

routine applies only to radios that are basically working in the first place.

Obviously, if you are testing the radio with the chassis exposed on your workbench, use extreme caution to avoid getting a shock. Temporarily put the knobs back on

their shafts before turning it on. Don't touch anything except the knobs while the radio is plugged in. Unplug the radio before resuming your recapping—an "AC/DC"

type radio can give you a fatal shock from its chassis when plugged in, even when its power switch is turned off.

That's all it takes! If you can replace one capacitor, you can replace 'em all, so go to it. Replace the remaining paper or molded paper capacitors one by one until you

reach the end of your list.

Replacing Electrolytic Capacitors

The mechanics of disconnecting the old capacitor and soldering in the new one are the same for electrolytic capacitors, so refer to the previous section for those


Electrolytics are special in a couple of ways, however. First, their large capacitance value means that they can store an electrical charge—enough to deliver a painful

shock—even when the radio is turned off and unplugged. Before touching the leads of an electrolytic capacitor, always discharge the cap by shorting its leads together.

Secondly, their large size introduces some complications in installing the replacements, which we discuss in the following sections.

To Hide Or Not To Hide?

When replacing large multi-unit electrolytics, you have two choices. One option, usually reserved for the most valuable or special radios, is to remove the old can, take

out its innards, hide new capacitors inside the can, and reinstall it. This is a lot of work for the sake of authenticity and I have done it only ocasionally. See Philco 60B

Cathedral, Hallicrafters SX-42, and Colonial Globe. Those articles cover the subject pretty thoroughly, so I won't repeat all the details here.

A second option, more practical in the majority of cases, is to disconnect the old can and leave it in place for appearance's sake, and wire the new capacitors out of

sight underneath the chassis. The radio still looks original from above, and you will save a lot of time and effort.

Installing New Electrolytics

The first thing to remember about installing electrolytics is that polarity matters! You must install them with the positive and negative leads in the right places. If you

reverse the leads, the capacitor may overheat and explode. Needless to say, your radio will not work, either.

New electrolytics are always marked to indicate which end is positive and which is negative. Most often, a band of arrows and minus signs is printed along the length

of the capacitor. The arrows point to the negative (-) end. In the following photo, the negative ends of the larger capacitors are all to the right.

If you are not hiding the new caps inside the original can, then you will need to decide how to mount them under the chassis. Many well-designed radios have enough

"elbow room" underneath to fit in a couple of additional components. Some battery portables, however, pack components tightly into a small chassis and may have

little if any spare room. The important factors are to mount the new capacitors securely and insulate all connections.

Multi-section cardboard capacitors are often mounted on the chassis with a metal clamp. In the next photo, the clamp has been removed from the top unit.

If the clamp is attached with a screw, you might be able to reuse it as a mounting point for your new capacitors. When the clamp is riveted on, I usually cut through the

band with a Dremel Moto-Tool and cutting wheel (don't forget the safety glasses!) and discard the whole business.

As mentioned earlier, some times the metal can itself comprises the ground connection for a vertically-mounted unit (see following photo). If you replace such a can

with a compatible metal-cased unit, you will need to make sure that the new can is well grounded to the chassis.

The can of a vertical-mount unit does not always provide the ground connection, however. In the following photograph, only the top unit is grounded in that way. For

the three units in the bottom row, the can (metal or cardboard) is electrically isolated from the chassis and the common ground connection is made through a terminal

or wire coming out of the can's bottom.

Note: The "ground" connection point in a radio is not always the chassis. In many radios with transformer-type power supplies, the chassis acts as the common ground

point. In others, however, including many transformerless AC/DC radios, ground is "floating," not connected to the chassis. When you replace electrolytic capacitors,

take care to connect the negative lead of each new capacitor to precisely the same location (or terminal) at which the negative lead from the old part was connected in

the chassis.

When you wire up the new capacitors, keep the leads as short as practical. Depending on the layout under the chassis, some times it will work better to remove the

old capacitor leads completely and solder the new leads directly to the appropriate terminals. In other cases, where the old leads were quite long but still in good

condition, it is acceptable to solder the new capacitor leads to the old leads.

If the underside of the chassis is cramped, you may need to mount the new capacitors somewhat distant from the original location. Look carefully at your schematic

and at how things are connected under the chassis. As long as your capacitor connects to the right points in the circuit, its physical location might not be too critical.

For example, if the common negative point is the chassis itself, there may be a closer ground connection available, making for a neater chassis layout when you are


Take another look at the "before" and "after" photos shown earlier in this article. You can see that two individual capacitors were used to replace the two-capacitor

cardboard can. One, colored light blue, was mounted inside the metal clamp that was left attached to the chassis. The other, colored darker blue, was mounted nearby

but pointing toward the top of the photo.

Try not to locate the new capacitor in a place that blocks access to other components. Some day in the future, you or someone else might need to make more repairs,

so don't make things more complicated than necessary. Avoid relocating components more than is necessary. Some circuits, such as the radio's RF section, are

sensitive to interference from other components.

Note: In both FM and other high-frequency radio and television receivers, pay strict attention to the location of each capacitor and do not relocate any capacitors. In

high-frequency receivers, capacitance is precisely calculated to provide proper RF tuning. Adding or deleting capacitance from a circuit will alter its performance

noticeably. Capacitance can be changed by adding or reducing the lengths of leads to the part. All leads must be kept as short as possible in high-frequency circuits. In

addition, power supply components must not be located adjacent to any RF tuning components or the receiver will suffer from increased radio frequency interference


In some cases, a plastic tie can be used to hold the new capacitor in place. For instance, you could tie the body of the capacitor around a nearby bundle of wires.

Don't use a plastic tie to go around uninsulated leads or any component that gets hot. If the leads of the new capacitor are short enough, they alone may hold the

capacitor in place. I have also used metal clamps or even a dab of epoxy glue to secure new capacitors. Don't use hot glue for this purpose. The heat of the radio may

soften the glue and allow the capacitor to fall loose.

No matter how you install the new capacitors, you should always use spaghetti tubing or other insulation as needed to make sure there is no chance of short circuits.

The hot ends of these capacitors carry the highest voltage in the entire chassis. You will be very sorry if one of them slips loose and fries your newly restored radio!

While you are replacing capacitors, it is also an excellent time to replace the power and cord and install a fuse on the power line if your radio does not have one. A

fuse is a very important safety feature which most radios lack. A 1-amp fast-blow fuse works fine for most radios. Install it on the "leg" of the power cord which is

switched by the on/off switch.

If you replace the electrolytic capacitors in the power supply circuits and your radio still emits a loud hum that is not affected by the volume control, carefully check

your wiring against the schematic diagram. It is a common beginner's mistake to wire an electrolytic backwards (with positive and negative reversed).

It's Easier Than It Sounds!

Recapping is easier than this article makes it sound. I have included a lot of details to explain the process clearly, but with a little practice you will find that you can

recap the average radio in an evening. Even if the radio "works" before you start, replacing the capacitors often improves its performance. And you will certainly

improve its reliability. The new capacitors that you installed could easily last your lifetime!

Hank Frankenberg

Senior HTF Member
Oct 13, 1998
Suarev was onto the answer. If you increase the capacitance of your power supply storage caps (the big electrolytic ones), it will indeed help reduce the ripple voltage and will provide a larger stored "reserve" for sudden dynamic spl demands, BUT if you increase the total storage capacitance beyond a certain point, then yes, you will stress other components: The power transformer, the diode bridge rectifier and maybe even the wiring and/or circuit board traces. The reason is that when you first power up an amp, the power supply storage caps will want to suck up lots of power to charge up to their rating. This instantaneous inrush of current is taken into consideration by the original curcuit designer in specifying the wiring, transformer, bridge rectifier diodes, etc. Those components all have amp ratings and you can exceed those ratings with too much power supply capacitance. First to blow would likely be the bridge rectifier diodes. Oh yes, include the power switch as a possible casualty. If you don't know circuit design, please be very careful.


Stunt Coordinator
Apr 1, 2002
Basically I have a Rotel RMB-1066 which has 6(6800uf) caps. I'm not sure of this is enough power reserve for intense transients in audio and really just want to know if larger ones can be installed(say 10000uf or 15000uf). I'm pretty sure the answer I'll get back is "No can't be done" or "Replacing internal parts will void your warranty".
I'm sure that it could be done -- although it would require a lot of disassembly and you may not have the real estate on the circuit board for larger caps. Also, keep in mind that Rotel generally uses British slit-foil caps, so finding replacements of similar quality may be tough. Perhaps you could go to the 8,000 uF caps from another Rotel amp, but that change would be almost certainly insignificant and a waste of time and money.

I'm equally sure that Rotel (or any other manufacturer) would void your warranty for that kind of modification. It would only be reasonable. Why should they be responsible for you altering their design?

Will it make any sonic difference? I really doubt it. You should be using the RMB-1066 to drive all of your speakers set to SMALL. The amp will not be delivering low bass notes in that configuration and it's the bass notes that are most likely to benefit from the reserve power of larger filter caps because its the bass notes that really hammer the power supply and cause the rail voltages to sag.

Given that the Rotel already has well above average capacitor (and overall power supply) sizes for a 6 x 60 watt amplifier and given that you already get some additional headroom from the fact that all five channels seldom hammer the power supply at the same time, I really doubt that you would hear any difference whatsoever.


Feb 11, 2001
This instantaneous inrush of current is taken into consideration by the original curcuit designer in specifying the wiring, transformer, bridge rectifier diodes, etc. Those components all have amp ratings and you can exceed those ratings with too much power supply capacitance. First to blow would likely be the bridge rectifier diodes.
Or, if it is a proper design, a fuse.


Hank Frankenberg

Senior HTF Member
Oct 13, 1998
Doug, the danger there is that some people would just replace the fuse with a higher amp one and then the circuit components would be exposed to the excessive current.

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