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Haze Caravelle (barn find!)

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vital spark View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote vital spark Quote  Post ReplyReply Direct Link To This Post Posted: 20 November 2018 at 10:39am
Originally posted by jbl_man jbl_man wrote:

If the amp on the right has been by-passed,is probably dead. Shouldn't be to hard to repair. The one on the left looks like a later up-graded module, (maybe the original died that side as well) with dual TO3 outputs per side,as opposed to the single ones on the right. Left hand amp also has larger caps. Will probably sound the same if you can fix the right hand one, as both use the same size transformers.
 
Transformers look the same, but they arent unfortunately. I'll do a proper diagram later, but the one on the right is as follows (as i remember it):
 
240v ac to the transformer input, Ov and 30v used on the secondary, through the bridge rectifier at 30v DC and on to the two caps. line voltage at the input fuse terminals 87v DC
 
Left: 240v ac transformer primary. Transformer secondary +30/-30v tappings. Centre tapped to caps/earth. AC voltage at bridge rectifier 60v, line voltage at the input fuse terminals 87v DC.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote vital spark Quote  Post ReplyReply Direct Link To This Post Posted: 27 November 2018 at 9:23am
Good Morning.

A bit of progress being made. All powered up, and the mixer seems to be mostly working fine. Only really the second mic input has a proper issue, and will investigate later.

Looking into the amps, and wired up the right hand amp again, and found its output weak and sounding pretty bad. Definately the amp itself.

Cant see any dry joints, fried components or broken tracks, but what i can see from voltage testing, is that one of the power transistors show 44v to its opposite DC line, where all the others (both amps) have 87v DC, so with my basic knowledge, i'm assuming i have a duff power transistor!?







Edited by vital spark - 27 November 2018 at 9:24am
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Post Options Post Options   Thanks (1) Thanks(1)   Quote concept-10 Quote  Post ReplyReply Direct Link To This Post Posted: 27 November 2018 at 9:56am
Loving this thread Smile
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Post Options Post Options   Thanks (0) Thanks(0)   Quote vital spark Quote  Post ReplyReply Direct Link To This Post Posted: 27 November 2018 at 2:45pm
Originally posted by jbl_man jbl_man wrote:

Besides checking the obvious 3773 outputs, i would check all the small signal transitors too,(probably BC184's or similar). One of them will be faulty.

Same with the power transistors, all the board mounted ones tested ok for resistance and direction. I'm not an expert by any stretch, and my fault finding is merely by comparison. If i voltage test again, would comparison be useful again (ie, all pretty much showing the same voltages each), or do you have any more tips for testing? For all the cost, i might just be as well replacing all of them though?

Thanks for the help, Al
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Post Options Post Options   Thanks (0) Thanks(0)   Quote APW Quote  Post ReplyReply Direct Link To This Post Posted: 27 November 2018 at 4:33pm
that amp appears to missing its driver transistors.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote odc04r Quote  Post ReplyReply Direct Link To This Post Posted: 27 November 2018 at 4:56pm
Yes they certainly are missing, you can see on the underside that there has been rework around where they should be. Getting originals might be difficult even if you knew what to go for. This is the kind of thing you might get some good help for on diyaudio.com

If you could spend some time tracing out and drawing the circuit people there would probably tell you exactly what to substitute in.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote jbl_man Quote  Post ReplyReply Direct Link To This Post Posted: 27 November 2018 at 6:15pm
Follow the circuit back,and see what is fitted on the other (working) amp PCB as drivers. Should be able to get a transistor number from the working one.
Be seeing you.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jbl_man Quote  Post ReplyReply Direct Link To This Post Posted: 27 November 2018 at 8:39pm
It will be the two that are mounted on the alluminium strip in the middle.



Be seeing you.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote vital spark Quote  Post ReplyReply Direct Link To This Post Posted: 28 November 2018 at 8:37am
interesting stuff  and thanks for your input. I did notice the potential missing transistors, but dismissed it, due to the fact there are other differences, such as the left amp has 4 power transistors, and other subtle differences, such as more resistors, and some other additional components connected to the heat sink.

Main thing is, both PCB's and enclosures are identical (Haze POWAMP MK3).

Question is, do i fit the two missing transistors and heatsink only, or change the right amp to match exactly the left (add 2 more power transistors), or a 3rd option which would help greatly with my OCD, which is to change the caps and tranny's also so they match. 

Third option might be deemed as sacralidge, since it would likely be torroidal transformers, and 21st century caps?

Whats your thoughts guys?

Job is growing slightly, but not outwith the realms of my capability, and i'm all for doing it right (and once only!)
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Post Options Post Options   Thanks (1) Thanks(1)   Quote jbl_man Quote  Post ReplyReply Direct Link To This Post Posted: 28 November 2018 at 9:28am
First thing would be to get the number off the existing driver transistors,and see if they (or an equivilant) are still available.
Be seeing you.
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Post Options Post Options   Thanks (1) Thanks(1)   Quote odc04r Quote  Post ReplyReply Direct Link To This Post Posted: 28 November 2018 at 12:31pm
Yep, follow the priorities. Also check to see if you can find spare power transistors for the missing slots. Beware of sales on eBay etc of harder to find devices, transistor fakes are rife if there is a profit to be made reprinting cheaper devices to pass off as older/rarer/more expensive. Power transistors are especially bad for this.

Personally I would draw out the circuits, figure them out and then substitute sensible modern components as required/necessary to bring them back to life. I'd definitely replace electrolytic caps, but I'd leave the small signal components alone if they tested well.

For me vintage kit is 99% the outside appearence physical functionality. I have no problem making sensible modern part swaps as necessary to amplifier modules and PSUs etc. Appreciate that other peoples opinion can differ.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote vital spark Quote  Post ReplyReply Direct Link To This Post Posted: 28 November 2018 at 12:52pm
Those transistors are  TIP41C's, and it looks like its readily available from a quick google.

Will definately draw out both circuit diagrams and take it from there.

Thanks for your input/opinions/advice so far. it's really appreciated.

My concern is that the differences between the two amps is to accommodate additional power transistors, possible a higher rated amp, so in my limited opinion, it makes sense to replicate the working amp with the same components, rather than take a stab in the dark as to how the non working one should be.

Al




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