Luxman R-600 restoration

How many watts are dissipated across those resistors that make the heat sink necessary? Is that the design of the unit, making that much heat at that location?

Luxman did adopt bypass caps on their large PS caps as they are in a number of the units I have. None of them are cap coupled, though.

Nice work bringing this one back.
 
well i dont know exactly how many watts get burned off here. but taking down the voltage from 68 to 12 shure gonna dissipate some heat! if done the right way the transformer shoud have had a 12V winding also..for the tuner.

because the 2200uf´s are in the signal path i thought i´d try! and i guessd right! lytic caps dont belong in the signalpath of audio gear! be regular or tantal. they must be replaced with MKT film. well in this case its impossible

and thanks! these things (vintage amps) must be kept alive for the world to see and hear!
luckily i have a job doing something else, cause this aint bringing any money
 
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only worry i have is the 12V zeners for the tuner they get HOT! but on the other hand so did the old ones since the pcb is black. so i guess its ok and no point in messing with it more.

the design is so that if the zeners fail (go open)the tuner blows. atleast thats what i can tell from the scematic.
 
Hey F77, I tried your proposition to add bypass speaker coupling caps; on my jvc mca-v7e (quad integrated amp). The speakers are cap coupled with 1000uf electrolytics. First time thru I tried a pair of 1uf films on 2 of the channels which caused the electrolytics to vent. 1uf films measured fine- thinking that the film caps were sourcing too much current thru in reverse polarity once the audio power came in.

Replaced the electrolytics and tried again with the .47uf as bypass, powered up on the dim bulb all OK now. I staged it by doing 1 channel and comparing against another electrolytic only, didn't hear anything obviously different but went ahead with the other channels. The amp is doing sound for my wife's movie at the moment but I'll beat on it tomorrow. I put a scope on one of the bypass caps, a little bit of AC voltage on so its doing something. Given the reverse polarity current sourcing aspect of the bypass cap I don't think I'll run these as-is long-term, probably the fix is to switch over to a bipolar electrolytic and put the film across that. Or maybe 2 double-value axial electrolytics back-to-back, but set parallel to fit in the same footprint as the old cap.
 
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oh man! never seen that before! no idea what caused that to happen.

i dont think one can hear a differenence by A/Bing channels its not that big of a improvement.. i have a pair of HPM-50 as bench speakers, (not great but good enough for critical monitoring)
and i thought there was something off about the way the lux presented the highs. thats not so strange, if i were to put 2200uf electrolytics on the speakerwires it would be understandable why. thats basically what happens here. only its inside the amp.
the pro´s of doing this will be that it acts as a speaker protection if amp fails and goes DC.
the cons would be not so accurate sound,

best would be to mount a 2200uF MKT :)
 
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I'm also having trouble thinking up the scenario where the bypass cap blows the electrolytic, particularly because in the reverse bias case the lower driver transistor is pulling to ground- its not as if theres a negative rail behind it. I'm dubious about oscillation ideas too... perhaps resonance.. but I have no measurements to back up anything. In the failure case both electrolytics vented within a couple seconds of powering up- they did not burst- just oily smoke and a dark spot on the board.

I've never really liked the idea of a polarized electrolytic by itself in the output power path mostly from a symmetry perspective, but a film of that value sure isn't convenient in any respect lol. On the flip side, can't argue with the use of electrolytics in the speakers idea, so why not the amp as well. I'm not sure I'm into the idea of the electrolytics materially affecting the signal quality without some measurements to demonstrate. Series inductance perhaps OTOH these caps are pretty low in that respect. Not calling bunk at all, just wondering about how audible.

I did some looking around and the series reversed electrolytics would be OK but the doubled ESR is a downside and using 4 caps to divide that down is getting silly.
 
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Nice looking system F- very pretty! Now I appreciate more the dedicated 5vac winding on my Onkyo- the only thing it drove was the pilot lamp but also no need for a resistor to drop ~30v off B+ with all that heat...
 
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i will run it for a couple of hours after work today, and then pull the lid and check the CPU temp:)
lets hope i dont have to mount that fan!
wonder how hot i can let it run?

if i were to do this again, i would have mounted a 12V trafo in the back behind the main cap, and built a 7812 psu on a diy pcb, and mounted that where the heatsink is now.

not too late for that:idea: i think the dude will pick it up this weekend.
 
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ok! swinged by the shopping centre on my way home(hate those places). got a meter with temp probe so i can stop guessing:) will come in handy for coming projects too.

so i stuck the probe between 2 fins on the cpu cooler and put the lid on. played FM until the meter stopped increasing.

007.JPG 004.JPG
 
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That is pretty hot... the heatsink is fine I'm sure but such a waste- circuit design fail as noted in others comments. If you have the time, parts & inclination the 7812 and small xformer I think is better technically. A small perfboard panel with thru-hole mount xformer, small bridge, a few caps, and 7812 w/ screw-on heatsink along with thru-hole screw terminal strips would be fairly compact. Might be you could sneak your bridge inputs off one of the windings on the xformer, avoid having to add one of your own.
 
Forgot to mention, I did some research into the blowing-up electrolytic thing. It seems bypassing an electrolytic with a small film can be problematic wrt resonance/oscillation depending upon circumstances, can be quite sensitive to values of the film cap and clearly dependent on the surrounding circuit. As usual there is a lot of debate around the practice in general wrt audible effects, with the expected wrangling over theory- no need to bring that here. But I think its likely thats the culprit in my case above, funny thought that 1uf caps brought instant oscillation to both channels I mounted them, authoritatively frying both electrolytics (one measured 0 esr, one had 10* the esr of new) but .47uf was stable on all 4 channels with various content at various power levels (and I had a scope on- no oscillation seen).
 
i have parts for building the psu. snatching ac from lux trafo will endup with the 68vdc again and a new heat issue. so i think a 12-15v trafo is a must.
on the other hand 71c is hot but is it too hot? its a idiotic construction from the start and i might as well be the dude who puts it right....i´ll have a look what i can find trafo wise.

hmm interesting info there. you chose the wrong cap the first time. what are the odds?
 
Ahh, I was hoping there was a lower voltage winding available- 68v even off a centertap for half of it is still a big drop down to 12v- concur w/ need of a small aux transformer. 71C is hot, OTOH its just resistors there, running well under their rated capacity w/ a good heatsink I don't think theres a technical issue, its just kind of lame to be burning off so much power. 80's video game power supplies were like that; customer pays for the power so make 'em cheap and simple who cares. I think your lux is nicer than that.

Odds for selecting just the wrong film lol beats me. I now have about 8 values to choose from, selected 1uf off the top of my head because I thought the capacitors were a fun size and easy to work with. The Nichicon electrolytics are kind of pricey to be cooking off in a search to find out which films work best as bypass ;) perhaps more energy is available thru the larger films so smaller might be less prone to facilitate oscillation but who knows.

I have other issues in the set though- the rear channels synth circuit started acting weird on the bench. I did the caps and transistors when it was into it before but suspect some other part is causing it to occasionally go weird.
 
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ok. ill call this one finished now. dont think this will cause any more problems. i wonder how hot the original resistors were:) damn! all this heat but at 3 square centimeters. must have been 300c. but next R600 i will go for separate psu from the start. :)

what model is the JVC?
 
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