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jamesdstark
06-03-2009, 09:47 PM
I scored what seemed to be a good deal on ebay for this amp. To my dismay when I hooked it up there was a loud distracting hum from the transformer, which isn't acceptable in my studio environment. I know it's the transformer because it happens when only the power is hooked up, and I can hear it emanating and vibrating from the large transformer. I tried tightening the screws, no help. I also tried some rubber washers on both ends, didn't seem to help much. I understand with old transformers this just happens, as is the nature of transformers to vibrate. Is it possible to replace the transformer with something stock/cheap? I might try setting the transformer loose on a vibration absorbing pad of some sort so it doesn't resonate through the chasis, but I have a feeling there is still going to be noticeable hum.

Sometimes I think I waste my money trying to get bargins and they end up needing more work than they are worth... and I should have just bought something new. Thanks for any ideas/advice...

JBL 4645
06-04-2009, 05:42 AM
I think its criminal to auction off items on eBay when the sealer knows for well the item is buggered up.:(

How much did you pay this person for the JBL Urei6230?

jamesdstark
06-04-2009, 11:26 AM
$145 with shipping, so it was cheap. I was originally looking for a crown d-75 or d-45, but I spotted this "deal". I do like the amp, it's very powerful for only listed rating of 75watt/8ohms.

hjames
06-04-2009, 11:30 AM
$145 with shipping, so it was cheap. I was originally looking for a crown d-75 or d-45, but I spotted this "deal". I do like the amp, it's very powerful for only listed rating of 75watt/8ohms.

Got one myself, like it a lot ... shipped price seems fair ...

Allanvh5150
06-04-2009, 11:57 AM
It could be just a loose lamination stack. The transformer can be disassembled and rebuilt. It is not all bad.

Allan.

JBL 4645
06-04-2009, 08:47 PM
Got one myself, like it a lot ... shipped price seems fair ...
Unlike that other one you brought was it the 6260 or 6290? That looked like dog was chewing on the binding posts.:D


It could be just a loose lamination stack. The transformer can be disassembled and rebuilt. It is not all bad.

Allan.

LOL I think eBay is only good for spare parts. LOL yeah lets make Frankenstein JBL Urei 6230 from spare parts shall we. Only you have to bid for silly over the top prices. LOL :D

tyler477
06-05-2009, 11:12 AM
yup, with repair work (bout 100 bucks with parts) you got a good price at 245. I've heard good things about using this unit bridged into a small bass cab.
Was the unit advertised as funtioning? if so give him negative!

hjames
06-05-2009, 11:29 AM
Unlike that other one you brought was it the 6260 or 6290? That looked like dog was chewing on the binding posts.:D



LOL I think eBay is only good for spare parts. LOL yeah lets make Frankenstein JBL Urei 6230 from spare parts shall we. Only you have to bid for silly over the top prices. LOL :D

Okay Ash - another misinformed opinion of yours, right!
FYI - I've done close to 300 deals on ebay - had maybe 3 or 4 bad ones, and I got reimbursed for all the baddies ... no money lost, just aggravation.

The badly packed vintage Yamaha receiver? Full refund.
That 6260 that was burned up? Credit card chargeback - I got fully refunded.
The scraped up Yamaha poweramp - refund less 1 way shipping ...

Stay away if you like, more deals for the rest of us who know how to take precautions!

jamesdstark
06-05-2009, 02:02 PM
I've been scouring the internet to find any solutions, it doesn't look very promising. I don't know any place that would repair this transformer, if I have to ship it to get it rewound it doesn't seem worth it, the transformer is huge and would be expensive to ship. From what I've learned transformers are very specific and I can't just buy a stock replacement, this one does 15v and 24v.

I emailed the seller my situation and said I'm going to have to open a dispute if he doesn't offer something, there were no indications in the auction listing of any problems with the amp. This amp would be OK for someone in a live situation, but in a studio/home it's not acceptable.

Does anyone know a place that does transformer repair, if I end up going that route?

JBL 4645
06-06-2009, 12:11 AM
Okay Ash - another misinformed opinion of yours, right!
FYI - I've done close to 300 deals on ebay - had maybe 3 or 4 bad ones, and I got reimbursed for all the baddies ... no money lost, just aggravation.

The badly packed vintage Yamaha receiver? Full refund.
That 6260 that was burned up? Credit card chargeback - I got fully refunded.
The scraped up Yamaha poweramp - refund less 1 way shipping ...

Stay away if you like, more deals for the rest of us who know how to take precautions!

Good on you.:)

Well I don’t give a toss about money I don’t have that much and I can do without the aggravation, don’t need it.

I’m sorry I even bothered getting an account on that site, even if I was loaded I doubt it will really interest me, well maybe.

Last month a few JBL 4675-A was going on the site and some JBL 4645 and 4645C thou I smelled something odd about the subs when I placed a bid there was someone sticking in bid that didn’t look right.

I told a friend and he thinks it’s a mate of the sealer might be bumping up the price forcing you to bid higher.

Besides the 4645 need a re-foam and the kits for that would have cost the same or more so it wasn’t really worth my effort at the last few seconds.

robertbartsch
06-08-2009, 01:26 PM
I could write a book on Fleabay sales. Apparently, most issues involve elctronics that have issues.

I have three that come to mind including a Denon pre-amp that buzzes, an Adcom power amp that unloaded DC into the speakers, and a Teac reel-to-reel that was missing transport parts.

In the future, I will NOT buy electronics or mechanical devices using this forum since my luck is poor.

jamesdstark
06-08-2009, 11:25 PM
I re-dipped the transformer in shellac and baked it. This gave some improvement, but not enough.

I finally resorted to letting to transformer rest free, sitting on acoustic foam. I also have the amp sitting on a bit of carpet. Now the sound is negligible, less that my computer which is pretty quiet.

So I finally got it hooked up to my 4311B's and it sounds great.

I probably would have been better off buying a new amp, but nostalgia always gets me, especially when it comes to JBL.

Allanvh5150
06-08-2009, 11:52 PM
[quote=jamesdstark;254863]I re-dipped the transformer in shellac and baked it. This gave some improvement, but not enough.

[quote]

Sometimes the lamination stack becomes loose in the core. It is very easy to pull it appart, clean the lams and reassemble it. A tad difficult now I guess.

Allan.

jamesdstark
06-13-2009, 05:44 PM
From the research I did rewinding is very difficult particularly if you haven't done it before. I did attempt to take it apart before dipping in shellac, and I wasn't able to get very far. I don't see how what you suggest would have ever been practical, at least for my particular transformer.

mech986
06-13-2009, 07:14 PM
Does it buzz in both stereo and mono modes? Are all grounds OK in the system?

Before you do anything else, consider other possible reasons why the tranny is buzzing. I'd suggest taking a close look at the rectifiers and power supply caps. These units are quite old now and handle all the voltage and current the tranny put out. Bad PS caps will not filter very well and lead to additional 60/120 Hz. on the amp rails. This "signal" gets right back into the PS via the floating ground.

As a matter of course, replacement of the big PS caps should be contemplated anyway as 25+ year old caps may be considered unreliable anyway. The 6800uf/80V caps can also be replaced with higher uf value caps - same volume caps probably push double the capacitance now. The rectifier bridge can also be replaced with newer Fast or Ultrafast Rectifiers (HexFreds seem to be popular) - may as well upgrade those too since its pretty inexpensive. Also, check the snubber cap across the bridge, should be replaced by the appropriate type too.

Even if it doesn't solve your problem, that part of the Power supply just got a whole lot younger and more reliable.

Schematic:
http://www.jblproservice.com/pdf/Vintage%20JBL-UREI%20Electronics/JBL-6230_%206260manual.pdf

Hope this helps.

Bart

Russellc
07-18-2009, 11:00 AM
I enjoy my 6230 a lot also. I also got it off ebay, about the same price shipped, ( under 150) and like yours, had some problems. It hummed like yours, and one channel would drop out, and come back it you jiggled it.

If you take the top off, you'll usually see where someone has added a wire, I inquired about it on mine here and was told it was anextra ground wire many added to reduce hum.

I had to basically reflow most solder joints.....These things have run fro hours on end and the transformer vibration slowly breaks them down over the years.
All the output devices, and so forth. If you search on this forum you will also found that there are three small value caps on the board associated with regulators I believe, and they stand right next to these toasty devices and get backed to death.

After all this, you want to see what kind of DC is coming out of the outputs. The power supply caps are remarkably durable, mine were still fine. Has worked fine ever since. This is basically a tank of an amp, its output devices are only being used at a fraction of their capacity. Once together, it should run fine another 25 years or so.

Russellc

KVThere
02-26-2010, 07:11 AM
I don't know if you solved the problem or not. I can suggest the following to aid in troubleshooting.

Disconnect the bridge rectifier from the secondary of the transformer (push on tabs). Turn on amp. If hum still there it is the primary windings that are loose and vibrating (not much to do about this). If hum gone, turn off amp and reconnect rectifier. Disconnect the positive and negative leads on the PS large caps that go to the boards. Turn on amp. If hum gone possible bad caps or big load on PS. Turn off amp. Reconnect PS Caps and disconnect + and - leads to boards. Turn on amp. Hum gone- problem is on boards causing big pull on PS loading transformer causing hum (normal). Hum still there bad caps (and or rectifier).

Hope this helps

Russellc
03-10-2010, 12:01 PM
I don't know if you solved the problem or not. I can suggest the following to aid in troubleshooting.

Disconnect the bridge rectifier from the secondary of the transformer (push on tabs). Turn on amp. If hum still there it is the primary windings that are loose and vibrating (not much to do about this). If hum gone, turn off amp and reconnect rectifier. Disconnect the positive and negative leads on the PS large caps that go to the boards. Turn on amp. If hum gone possible bad caps or big load on PS. Turn off amp. Reconnect PS Caps and disconnect + and - leads to boards. Turn on amp. Hum gone- problem is on boards causing big pull on PS loading transformer causing hum (normal). Hum still there bad caps (and or rectifier).

Hope this helps

This is the best advice, I doubt your problem is with the transformer, more likely something down steam has run a muck and is causing the transformer to load down. Chase it down like the above poster suggsts.

Russellc

caladois
12-15-2010, 12:05 PM
Can the home AC quality generate transfo hum ?