Luxman Power Amplifier Model L-480 Issues

[vortalexfan]

Hello everyone last year I told you about an old Bell Carillon tube stereo system from the 1960s that I was working on for someone and in turn I was going to get a Luxman Stereo Power Amplifier that I was going to fix up.

Well I got that Luxman Power Amplifier and I figured out that the issue it was having was with the a couple of transistors and resistors in the front end on the unit that got fried somehow.

the resistors which are R419a, R19b, R420a and R420b which are a matched quad of 100 Ohm 1/3 Watt Flameproof resistors were toasty looking and when measured with an ohmmeter, measured at over 1,100 0hms (1.1 kOHms).

Then transistors which were Q407a, Q407b, Q408a and Q408b had burn marks on the board below them like they may have gotten too hot or overheated, the transistors in question are a complementary set of transistors consisting of a set of 2SA949s and a set of 2SC2229s.

Which when I looked them up online the only transistors that cross referenced to them was the NTE 383 and the NTE399 respectively but not many places carry those transistors anymore that I feel comfortable with buying from, and then the resistors are also nearly impossible to find either because it seems that Mouser and Digikey neither of them carry any 100 Ohm 1/3 W flameproof resistors in their inventory without having to special order them which they say could take 13 weeks or more.

Any ideas as to how I could go about fixing this without having to special order parts or having to sink too much money into it, as I would like to fix this Luxman up and flip it for a nice tidy profit, as I was told I could turn around and sell this Luxman Amp for around $600 or more once it was fixed up.

Thanks for your help.

Picture of the unit in question posted below, picture was taken off the internet and isn't mine, as mine is in pieces right now, but its the same exact model as mine.

[Electronic M]

Resistors you can always replace with higher wattage rated parts...look at 1/2W those are probably easy to get.

[vortalexfan]

Originally Posted by Electronic M

Resistors you can always replace with higher wattage rated parts...look at 1/2W those are probably easy to get.

Even if the original resistors in the unit had a tolerance stripe?

I say that because the original resistors appeared to have a tolerance stripe but I couldn't make out the color because the color code stripes were too discolored from heat damage that I couldn't make out the colors they were originally.

Unfortunately the service manual for this unit doesn't list tolerances for the resistors just their resistances and wattages (even though I had seen several resistors in this unit that had 5% tolerance stripes on them.)

Also I do have a box of 150 Ohm 1/2 watt fireproof resistors, would that work in place of the original 100 Ohm 1/3 W resistors if what you say is correct for this situation?

How about the original transistors?

I need to source some replacements but I keep coming up empty handed, as they don't seem to have a modern replacement except through NTE which like I said the suppliers that their website lists that carries their replacements for these transistors are companies I have never heard of before and because of that I don't know if I want to deal with a supplier that I'm not familiar with unless someone here says otherwise.

Unfortunately these transistors don't crossreference to anything that Mouser or Digikey have in their inventory.

I did seem to find a matched set of NOS transistors like the ones I needed (they were the same number as the originals) on ebay for $5 plus $3 shipping, should I try those and see if those would work?

[vortalexfan]

OK so I have a question, why would an audio equipment manufacturer use a transistor that is normally used as a horizontal output transistor in b & w tvs in an amplifier's front end stage (the stage just before the output transistors)?

That doesn't seem to make any sense to me.

[Electronic M]

Originally Posted by vortalexfan

Even if the original resistors in the unit had a tolerance stripe?

I say that because the original resistors appeared to have a tolerance stripe but I couldn't make out the color because the color code stripes were too discolored from heat damage that I couldn't make out the colors they were originally.

Unfortunately the service manual for this unit doesn't list tolerances for the resistors just their resistances and wattages (even though I had seen several resistors in this unit that had 5% tolerance stripes on them.)

Also I do have a box of 150 Ohm 1/2 watt fireproof resistors, would that work in place of the original 100 Ohm 1/3 W resistors if what you say is correct for this situation?

How about the original transistors?

I need to source some replacements but I keep coming up empty handed, as they don't seem to have a modern replacement except through NTE which like I said the suppliers that their website lists that carries their replacements for these transistors are companies I have never heard of before and because of that I don't know if I want to deal with a supplier that I'm not familiar with unless someone here says otherwise.

Unfortunately these transistors don't crossreference to anything that Mouser or Digikey have in their inventory.

I did seem to find a matched set of NOS transistors like the ones I needed (they were the same number as the originals) on ebay for $5 plus $3 shipping, should I try those and see if those would work?

Tolerance applies ONLY to RESISTANCE and NOT to power rating.

If all the other resistors are 5% then the ones you need are probably 5% (especially if they are the same make and construction as the rest) go with something between 5% and 1% tolerance and you should be fine.

150 ohm resistors are not a valid sub for 100 ohm.

There was much less variety in power transistors in the 60's and 70's if it had enough power and was linear it could be used in an amp, linear devices can also be used for switching (horizontal output duty)....If it had the stones and the price point for the job it would get selected....the tube equivalent is that the 6L6 and 6BQ6 are the same tube only the BQ moved the plate connection to the top cap to avoid Corona and arcing issues with the plate pin on the L6....The L6 was common in audio amps and the BQ was common in horizontal circuits (though it also got used in audio occasionally).

[vortalexfan]

Originally Posted by Electronic M

Tolerance applies ONLY to RESISTANCE and NOT to power rating.

If all the other resistors are 5% then the ones you need are probably 5% (especially if they are the same make and construction as the rest) go with something between 5% and 1% tolerance and you should be fine.

150 ohm resistors are not a valid sub for 100 ohm.

There was much less variety in power transistors in the 60's and 70's if it had enough power and was linear it could be used in an amp, linear devices can also be used for switching (horizontal output duty)....If it had the stones and the price point for the job it would get selected....the tube equivalent is that the 6L6 and 6BQ6 are the same tube only the BQ moved the plate connection to the top cap to avoid Corona and arcing issues with the plate pin on the L6....The L6 was common in audio amps and the BQ was common in horizontal circuits (though it also got used in audio occasionally).

Ok, thanks, that makes sense now. I'll keep an eye out for 100 ohm 1/2 W resistors that are flameproof.

As for the transistors, I'll just buy those NOS matched set for sale on ebay.

[vortalexfan]

well I have an update on this amplifier, I replaced the damaged parts with the new ones I bought and went to test out my work and the dumb thing smoked my brand new parts!
Which means there's still something wrong with this amplifier that's causing those transistors and resistors to get smoked, and the weird part is that it smoked those parts not even 2 seconds after I turned on the power switch, so any ideas as to what could be wrong with this amplifier?

Is there anything in particular that these old Luxman amplifiers were notorious for as far as failing parts goes that I should look for?

Any help would be appreciated.

Also as a side note, the power supply in this amplifier does have a protection relay in it but for some reason or another that part of it isn't working (which is why these parts are getting smoked right away) its acting almost as if someone had bypassed that part of the amplifer's power supply circuit, which may be why this amplifier got smoked in the first place.

[KentTeffeteller]

Originally Posted by vortalexfan

Hello everyone last year I told you about an old Bell Carillon tube stereo system from the 1960s that I was working on for someone and in turn I was going to get a Luxman Stereo Power Amplifier that I was going to fix up.

Well I got that Luxman Power Amplifier and I figured out that the issue it was having was with the a couple of transistors and resistors in the front end on the unit that got fried somehow.

the resistors which are R419a, R19b, R420a and R420b which are a matched quad of 100 Ohm 1/3 Watt Flameproof resistors were toasty looking and when measured with an ohmmeter, measured at over 1,100 0hms (1.1 kOHms).

Then transistors which were Q407a, Q407b, Q408a and Q408b had burn marks on the board below them like they may have gotten too hot or overheated, the transistors in question are a complementary set of transistors consisting of a set of 2SA949s and a set of 2SC2229s.



Which when I looked them up online the only transistors that cross referenced to them was the NTE 383 and the NTE399 respectively but not many places carry those transistors anymore that I feel comfortable with buying from, and then the resistors are also nearly impossible to find either because it seems that Mouser and Digikey neither of them carry any 100 Ohm 1/3 W flameproof resistors in their inventory without having to special order them which they say could take 13 weeks or more.

Any ideas as to how I could go about fixing this without having to special order parts or having to sink too much money into it, as I would like to fix this Luxman up and flip it for a nice tidy profit, as I was told I could turn around and sell this Luxman Amp for around $600 or more once it was fixed up.

Thanks for your help.

Picture of the unit in question posted below, picture was taken off the internet and isn't mine, as mine is in pieces right now, but its the same exact model as mine.

Don't install NTE semiconductors in a Luxman or use improper parts in one. This is a very respected amplifier. Please don't take shortcuts. TV shop Grade semiconductors don't belong here, unless there is no other option, they won't perform correctly. And these transistors need to be suitable for this circuit. Most HiFi circuitry has specific transistor characteristics which must be adhered to for it to be stable and perform as intended.

[vortalexfan]

Originally Posted by KentTeffeteller

Don't install NTE semiconductors in a Luxman or use improper parts in one. This is a very respected amplifier. Please don't take shortcuts. TV shop Grade semiconductors don't belong here, unless there is no other option, they won't perform correctly. And these transistors need to be suitable for this circuit. Most HiFi circuitry has specific transistor characteristics which must be adhered to for it to be stable and perform as intended.

Well unfortunately I gave up on this amplifier because I wasn't able to find the correct parts for it and I also wasn't able to track down the issue on this unit, like I thought I did. It turned out there was more wrong with this thing than those aforementioned transistors and resistors because I was able to track down some non-NTE transistors and some proper resistors for this thing but they ended up being NOS transistors I found on ebay and the resistors I ended up finding at Digi-Key, but as soon as I installed them and powered the unit up it smoked them again and I figured out it was more than likely the output transistors which were some oddball transistors that I wasn't able to track down any new replacements for without having to pay way more than I wanted to sink into the unit, or than I could afford to sink into the unit so I donated it to a local computer shop where one of the co-owners's dad was an electrical engineer for Sony for many years and enjoys repairing electronics as a hobby could work on it.