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Celestion Ditton 662 Fuse Blowing

T

TanMecEng

New Member
Hi,

I recently acquired a set of Celestion Ditton 662 speakers, since the reviews on them were quite good and so was their condition. I have them paired with a mostly overhauled Sansui AU-9500, and first impressions are good, but not as great as expected. Especially considering that the cheap set of Cerwin Vegas that were previously paired with the amp sounded just as good. After playing them at relatively high volumes for some time it seemed as though I lost much of my treble. At first I thought it could be my amp, but after further inspection found that both 0.5 amp fuses on each speaker were blown (I believe these are for my tweeters?). Replaced the fuses, and played them for another 10 minutes and one fuse blew again, and the other while still having continuity, did look stressed. Just wondering where I should look first, my amplifier or my speakers? The speakers are rated for 160W, so it shouldn't be an issue of too much power. Could it be the speaker crossovers?

Any help would be greatly appreciated, as my excitement over this setup is quickly deflating.

Cheers
 
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500 Milliamps fuse.... that's not heavy stuff.... Does the receptacle of the fuse mention 500ma fuse ?
Maybe that's where the problem is.....
If speaker ( tweeter ) fuses blow, then your are maybe sending too much juice to them... ?
Your Sansui is a very good amp, it should not be the problem.
Then again, I think it is not the right fuse.

Or am I wrong ?
 
Are you sure those are the original woofers and tweeters? Google up some photos of that model and verify.

Are your tone controls flat and loudness off, or _?_.

Are you hearing any distortion anywhere in the spectrum, besides just having the treble drop out?

Depending on the answers to those questions, it might be time to open them up and have a look at the crossovers.
 
sax6 said:
If the crossovers were, let's say, short or almost were, it is your Sui that would go into protect.

Scratching my head here.....
Click to expand...

Hmm...maybe so.

What if there were shorted turns in the tweeter voice coils, but the tweeter cap was still intact. Relatively low power into the tweeter normally, so the amp can supply it, but the impedance has dropped considerably, drawing too much current. Kinda farfetched but it might explain how a tweeter fuse could blow w/o the amp overloading.

Tan, do you have a multimeter? You could also check DC resistance on the tweeters. This is an 8 ohm speaker so they should be somewhere around 5-6 typically.
 
Sorry for the delayed reply.

I can't see any amperage rating on the fuse holder, I had just replaced the fuses with what was in there. I tried looking online but can't seem to find much technical information on these.

Yes, the tweeters, mids and woofers all appear to be original. I would definitely say that is a good description of my tone controls, flat, as in they don't seem to do much when I adjust them (most notably the mids and highs). There does also seem to be distortion, particularly at high volumes, but again, this is kind of subjective, since I don't know how they are "meant" to sound. However, I do feel they should sound better. If I do open them up and look at the crossovers is there visual signs I can look for (e.g. shrunken caps)?

Also, yes, I just took my multimeter and checked both tweeters (disconnected from crossover) and they measured around 6.7 ohms each.

Is the evidence starting to point towards my crossover? I guess it's possible both could be old and deteriorated? I could try hooking up another receiver I have, and see if it sounds the same?

I also must note, which may or may not be relevant, but prior to getting the new speakers I had cleaned some switches in my amp. The volume control was dirty, so I went in and cleaned that, as well as some others (which I probably shouldn't have), including the high and low filters.
 
"Flat" means treble and bass are not boosted or cut but set in the middle for zero effect. It sounds like you are not cranking the tone controls or using loudness, any of which can strain the amp into distortion at high volumes, and/or stress the speakers. So that's probably out as a cause.

Aside from technical info, any chance of finding just an owner's manual? That would give you the fuse rating. I was able to find a spec sheet with a schematic but no values for any of the components including the fuse.

You might search AK and see if there are any owners you could ask to check their fuse or manual.
 
Tweeters sound OK at 6.7 ohms.

If your meter can do capacitance, you might check the tweeter caps at least and see how they read. They are likely to be small values but I notice from the schematic there are about 4 caps in the tweeter circuit and a bunch in the mid circuit. I'd check anything under 10 uf. And look for bulging, leaking, melting, etc. At this age (80s?) they probably do need a recap.

It's gotta be that or the wrong fuse. Half an amp should be enough for a tweeter but with a higher order crossover it is going to waste some power. The sensitivity looks a little under 90 db (rated 90 db at 2.9W, strange way to do it, usually it's at 1W) so moderately inefficient speakers. I'd make absolutely sure before going to a higher fuse value.
 
This sounds more like your amp needs a service...

Edit, you say mostly overhauled, what exactly was done to it? I've never ever come across a pair of speakers with crossovers causing this issue, it's always been the amp being faulty or clipping. Ive also had a pair of 442's, lovely series of speakers.
 
I played the speakers for more than two hours yesterday and the fuses remained intact. This leads me to believe that maybe it is or was an amplifier issue. By mostly over-hauled I mean that everything was basically replaced, besides the main capacitors which tested good.

One thing that did become apparent, was initially it seemed like I had no tone control, I could crank bass, mid and treble back and forth and it didn't seem to do anything. However, after the amp "warmed up" the controls worked, could the amp be going into the fore mentioned safe-mode? Can someone elaborate on this more? Or could this be a result of my control cleaning, seams a little coincidental.
 
Safe mode would cut out output to the speakers !


Did the tone controls made some '' static '' while beeing oprerated ?
Maybe some transients made the fuse to go overloaded...
While I'm not shure about this belief ( mine ), anything is possible in electronics.
Issues that go from, well, issues, and then quiet themselves out are the most notorious to find out about
And the most frustrating too.

Keep informed of the rest.......
 
I apologize again for the delayed reply.

I had a chance to play the setup some more, and still sounds like my tone controls are intermittent. I hooked the speakers up to my Marantz receiver and there is a very notable sound change when operating the tonal controls from one extreme to the next. However this not the case with my Sansui (not all the time anyway), just wondering if you have any input on what could be causing this? e.g. speakers, my control cleaning, amplifier.

Like always, your response is much appreciated.

Regards,
Tanner
 
This amp has a fairly complex set of tone controls. Three controls, each with a separate knob to select the turnover frequency of the control, or turn it off (DEFEAT).

I am not sure how all this works internally, but clearly there is more circuitry involved than with the typical bass+treble controls. So there could be something going on inside.

BUT...It may be that the switches on the lower set of knobs are just dirty and not making contact, and/or the pots in the top row. I don't remember if this has been discussed yet but if they have not been cleaned, that would be a place to start. I have a Sansui AU-517 and it is notorious for losing contact in various switches. DeOxit fixes it, for awhile anyway.

If that does not help, I would suggest you ask this question in the Solid State or Sansui forums, and make the subject line include the make/model of the amp and 'tone control problems'. Include a link to this thread in the text and describe what's happening and that it started with blown tweeters which led to finding issues with the amp. The reason I suggest this is that experts on the 9500 are likely to see that thread, whereas they would be much less likely to see THIS one which has a subject line about Celestions and is in the Speakers forum. But the first thing they will ask you is whether the switches and pots have been cleaned recently.
 
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