Is this a sign of worn out filter caps?

[EasilyAmused]

I just bought a 1976 Traynor YBA-4. These are a very similar circuit to the fender bassman/mashall JM45. The amp is completely original other than having had a new 3 prong cord put on it.

It sounds fantastic, but shortly after I bought the amp it has started producing low level distortion. The clean sound is still there, but there is a low level, distorted sound at the same time.

I tried replacing the pre-amp tubes with ones I had lying around, no difference. I don't have an extra pair of EL34s to try out yet...

Knowing the age of the amp, I'm thinking the filter caps likely need to be replaced regardless... I'm just curious if this is a sign of bad caps or not?

I've built a couple of amps before, so I should be able to change those before, I just don't have a lot of experience with older amps or the problems they can develop.

Thanks!

[Wally]

WIth experience, one can hear the effect of e\weakening filters. There are outof-tune subharmonics in the lows....the A on the 5th fret, 6th string is a good place to listen.
Low freqs get 'farty'. HIghs lose the sparkle. The amp will have no 'dimension' because the harmonics are not correct and the notes don't develop as they would with healthy filters.
I don't play vintage amps much at all until they have been recapped. OThers have varying opinons. In addition to good sonics that healthy electrolytics yield, I also do not experience the loss of thransformers due to failing electrolytics.

[Ricky D.]

Be safe and don't let it blow up on you! Change out the caps, you know they need to be done. IMO, of course, don't let me be too focused here.

[jefrs]

One sign of failing filter caps is their inability to do their job, result increased 50Hz hum, and resonant frequencies of this (it's G1=49Hz), so reinforced bottom G-notes.

Now mains hum may have other causes i.e. ground loops and wiring loom layout. I'd expect a '76 UK spec Traynor to have had a 13A earthed mains lead from new, no probs there.

With dead caps, the amp will get noisily loud (un-smoothed DC off the rectifier) wet raspberries, but the transformers will survive although if you leave it on like that it may wreck the valves.

Having said that, if it ain't bust, don't fix it.
Despite oft recomendations to change electrolytics every 5 minutes, I do have an old WEM with 30yo caps that are still at their full value and it plays as clean as can be: it's my quietest amp hum-wise. So -

Electrolytic caps can last 30 years or more, especially if they have been kept charged by use and a visual reveals no leaking. They can be tested and although their value may have dropped by 10% they still work fine. Changing the caps may alter the fantastic sound of the amp by altering the volts on the HT. They die a slow death but yours are reaching their life expectancy :-(

Try re-seating the EL34, then replace them, check all the 'moving' parts (jacks, scratchy pots etc), finally replace the caps.

[celeste]

Originally Posted by jefrs

Electrolytic caps can last 30 years or more, especially if they have been kept charged by use and a visual reveals no leaking. They can be tested and although their value may have dropped by 10% they still work fine. Changing the caps may alter the fantastic sound of the amp by altering the volts on the HT. They die a slow death but yours are reaching their life expectancy :-(

Try re-seating the EL34, then replace them, check all the 'moving' parts (jacks, scratchy pots etc), finally replace the caps.

The usual failure mode of an electrolytic is not a change in capictance, but an increase in ESR. The exploding cap is caused by the heat generated across that now increased ESR. Just because the capictance is in specs, does mean it is a good cap. The most useful piece of test equipment when working of SMPS is an ESR meter.

[celeste]

Originally Posted by jefrs

Electrolytic caps can last 30 years or more, especially if they have been kept charged by use and a visual reveals no leaking. They can be tested and although their value may have dropped by 10% they still work fine. Changing the caps may alter the fantastic sound of the amp by altering the volts on the HT. They die a slow death but yours are reaching their life expectancy :-(

Try re-seating the EL34, then replace them, check all the 'moving' parts (jacks, scratchy pots etc), finally replace the caps.

The usual failure mode of an electrolytic is not a change in capictance, but an increase in ESR. The exploding cap is caused by the heat generated across that now increased ESR. Just because the capictance is in specs, does mean it is a good cap. The most useful piece of test equipment when working of SMPS is an ESR meter.

[DH82c]

if yours has the big brown 40/40 450V dual caps I might be able to make a suggestion next week.
I just bought a 73 YGM-4. tubesandmore have a 35/35 cap that I hope fits a little better than the more common 40/40 cap cans. Ordered last week. Hope they are here before the weekend.

Enjoy :)

[EasilyAmused]

I just opened the amp up and was suprised by the filter caps.. they aren't the old brown caps, and they look newer than the rest of the amp, but I've never see caps that look like these, so I'm not sure how old they might be.

They are big neon orange things and the replacements are 80uF instead of 40uF.

I'm going to order some new filter caps regardless - worse comes to worse, I'll use them in another amp project.

Just from a visual inspection, the amp looks great. No obvious leaks from caps or anything like that. It may well be be the 33 year old EL34s in the amp.

[DH82c]

EasilyAmused.. you have fallen into my trap. You know it is rude to open an amp without taking tons of pictures and posting them online??? :D

We are patiently waiting lol

[EasilyAmused]

You are right! My wife is out with our camera right now, but I'll try to post something a little later today.

Patrick

[Groovey Records]

Running an amp that has sat idle for years opens up the Caps that may have dryed up

Sounds by your description that certain frequencies that were previously filtered ae getting through.

But what do I know, you need specific test equipment to fault isolate your problem.

Just swapping out the caps may do more harm then good.

Fist swap your tubes and if that doesn't fix it have the amp brought back to spec by a good amp technician.

You don't want to replace vintage tone shapers with any old cap of the same or different value. different caps interact with different results.

Does Brinsley Swartz still repair amps in London?

I'd try to find him

[EasilyAmused]

Just to clarify to a few comments from people who have been looking at my location - I'm in London, Ontario, Canada - not London, England.

I've ordered some new tubes, so I'm obviously going to check that out first. The less I change, the better, IMO. The tubes are original 1976 Seimen EL34s, so there is a good chance that they may be the problem at this point.

Having said that, I am somewhat supsicious of the caps, as it does seem to be a power filtering thing, as I've played with it more. The high notes come out clear, but the low notes are distorting...

[Wally]

Re: visual inspection of electrolytic caps.....
I have seen many amps that looked wonderful...and yet sounded less than stellar. The same can be said of electrolytic caps. THey don't have to bulge, leak, or blow up before they exhibit weakness. Those 3 conditions assuredly indicate 'weakness', but there are sonic considerations that override what one sees. These sonic realities hit the ear long before the visual indicators hit the eye, ime. AS always, looks can deceive.
EASily amused, you mention that the 40 mfds have been replaced by 80 mfd caps.
Were all of the 40 mfd's repalced with 80mfd's? If so, you might consider changing the
last two stages or even 3 stages back to 40...or even 20. USing that 80mfd in the preamp stages will allow the preamp to develop very flubby bass freqs. Bumping the capacitance in the first stage will firm up low end, but too much capacitance in the preamp sections can muddy things up greatly.

[DH82c]

You probably need new power tubes anyway but I agree it sounds like the filter caps. Replace the electrolytics. You will have to do it some year anyway. I have never heard of an amp sounding worse because it got new caps. While you are at it clean the contacts and pots. YMMV.

Sooo.. at that point you have done what should be done with any 30yo amp when you buy it so no harm, no foul. If, after that, you still have the problem then try more troubleshooting:

Speaker rub?
Bad preamp tube (I think you tried that)
Check the voltages (if you know what you are doing, how to discharge caps safely etc etc).

[EasilyAmused]

Originally Posted by Wally

Were all of the 40 mfd's repalced with 80mfd's? If so, you might consider changing the
last two stages or even 3 stages back to 40...or even 20. USing that 80mfd in the preamp stages will allow the preamp to develop very flubby bass freqs. Bumping the capacitance in the first stage will firm up low end, but too much capacitance in the preamp sections can muddy things up greatly.

Yep, they've all been changed to 80mfds.

That's really good to know, actually. I was thinking of putting them back to stock values anyways, except for the first stage where I'd put it at 80 mfds for better low end response.

Patrick

[EasilyAmused]

Here is my a quick guts photo for those that are interested. Not that detailed, but I can add more if wanted.

Not the big orange caps... looking at them, they are labelled Sprague Atom capacitors, but I've never seen bright orange Spragues like that... Any idea how I might find out how old they are?

[DH82c]

Ok. So we probably safely assume the original caps were replaced.
If they replaced one 40mF cap with two 80mFs in series that would explain something as well. I dont know if Spragues have date codes. My originals are Mallorys and they do. Sorry I cant tell you the age.

Are you keeping the polarity switch in?

[DH82c]

Sorry. just checked the schematic. Should be 4 40mF caps so that would rule out someone using 80s in series. Getting them back to spec would be a good start if it were my amp.

[EasilyAmused]

Problem solved!

I learned a few things today. First off - sprague does date their filter caps - and despite looking all shiney, those bright orange filter caps were from 1974!

So I tossed in some 47mfd 500V caps in their place... the amp makes a little less AC hum, but still didn't fix the problem.

So I spent some time listening more and more and realized that perhaps it wasn't a electric thing at all... I figure if everything is original, that speaker must be as well.

I hooked the amp up to another speaker cab I had and viola - no more distortion on the low notes!

So clearly there is a problem with the speaker... so, just on a whim, I wondered if perhaps merely the weight of the speaker had, over the years, stretch the speaker to create voice coil rub (I'd never heard voice coil rub before, so that's my best guess, anyway).

So as an experiment, I merely rotated the speaker upside down and again - ta da - no more distortion. The amp sings!

What an remarkably easy fix. I imagine I should replace the speaker in the near future, but for the time being I'm loving the way it sounds. I think I'm going to try it out on a gig this weekend (with a backup amp, of course).

[DH82c]

Very cool. You learn something new yada yada. I had mentioned speaker rub before but would NEVER have thought of just rotating the speaker.
So how does it sound ??? The schematic looks a lot like a Marshall 1987 (and everyone compares it to a Marshall anyway) but how do YOU find it sounds?

[giginthesky]

man, i love this place. guess the relic thing for amps will be speaker rub though.

[EasilyAmused]

I've never plugged into a JTM45 or 1987 marshall, so I can't compare it to them, but it is pretty similar to the fender bassman's I've played. I haven't had a chance to crank it up yet to see what it is like when it really comes to life, but right now it is super warm and creamy.

I would say it is significantly warmer and more complex than the 59 bassman RI that I played for years. The absolutely HUGE transformers that traynor used to use probably have something to do with that. It's got a smokey flavour that will sit well in jazz settings, and despite the similarities to a marshall, I feel like the amp sounds a little more like American amps of the 50s-60s than the british ones I've tried.

Overall, I think these are a killer deal in the vintage world.

[DH82c]

I am seeing tons of them pop up suddenly in the montreal area for around 500$. I dont need one.. dont want one.
When the ygm-4 popped up at 500$ I also hesitated but finally bit.

[Wally]

Easily amused, thanks for following up and revealing that speaker thing....good job.