Ok so I still work on vacuum tube gear. Mainly pro audio gear: big, heavy, dumb power amps. Musicians and audiophiles love them, and I do too. Not micro tiny, not super digital sand based DSD/DSP, built to last. The ancient opposite of this rockford fosgate on the table.
Red plating happens when mainly two things happen. The first is end of life: the anode plating wears thin after lengthy bombardment by electrons. The electrons all run through the thin spot, heating up the area. The second is excessive bias current. Operator or tech sets the bias current too high such that the power tube runs out of its SOA envelope. Usually doesn't happen on push pull stages without signal; tech sets bias, amp goes home, operator cranks it up and plays in the danger zone until roasted. Usually does with single ended class A; tech sets bias and then smells burning transformer.
Gut shots enclosed as well as a far out shot of the operating table. I had to get Christmas crap out to get to the scope meter. Klipsch satellites swapped out with some power hungry JVC.
Red plating happens when mainly two things happen. The first is end of life: the anode plating wears thin after lengthy bombardment by electrons. The electrons all run through the thin spot, heating up the area. The second is excessive bias current. Operator or tech sets the bias current too high such that the power tube runs out of its SOA envelope. Usually doesn't happen on push pull stages without signal; tech sets bias, amp goes home, operator cranks it up and plays in the danger zone until roasted. Usually does with single ended class A; tech sets bias and then smells burning transformer.
Gut shots enclosed as well as a far out shot of the operating table. I had to get Christmas crap out to get to the scope meter. Klipsch satellites swapped out with some power hungry JVC.
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I see that ir got bought by vishay. I trust the usual parts houses, but will the new ones look like what's obviously not original in this amp, or will I get nos parts? Is nos any better or worse than current production? Knockoff factor on next day prime? I'll be ordering a half dozen or so outputs and already have source resistors. Fwiw, I tacked on a 0.22 sand block to the 0.2 that tech before me put in after initial inspection. Took it out after q111 shorted.
This amp is making me crave a hot air station already. Not a fan of micro pencils or hot tweezers.
This amp is making me crave a hot air station already. Not a fan of micro pencils or hot tweezers.
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What was the location where you installed the 0.22 ohm resistor?
The hot air stations are virtually useless for replacing parts. They can be used to replace the parts on the MEHSA strips but I prefer a culinary torch (small butane torch).
What do you mean by:
"but will the new ones look like what's obviously not original in this amp"
Are you concerned about appearance?
NOS can be OK but new is typically better unless something has changed in the manufacture of the part that makes it incompatible.
The hot air stations are virtually useless for replacing parts. They can be used to replace the parts on the MEHSA strips but I prefer a culinary torch (small butane torch).
What do you mean by:
"but will the new ones look like what's obviously not original in this amp"
Are you concerned about appearance?
NOS can be OK but new is typically better unless something has changed in the manufacture of the part that makes it incompatible.
I'm asking two things. First, what kind of markings do new production vishay ( or whoever authorized substitute) have? Do they look like what's in the amp? Or did previous tech sub turds? Looking up in mouser, I get 17 results. Obviously this is a common transistor. Yes, some of them have different pins and packages, but that leaves me with 6 or so flavors. 89 cents to 2 dollars each.
Second, being that it's a common part, there are lots of listings on Amazon. Packs of 5 or 10, going between 60 cents and a dollar each, free prime shipping, be here in two days cuz it's after next day deadline. Lots of stock photos (digikey and mouser have a blank or an unmarked to220 pic) to see. Whether or not I should trust other transistors in the amp that may or may not be genuine is the issue here. As a rule I learned long ago, I don't trust gear until I see it work. I trust the rear two channels of this amp. The front has been tampered with, so I suspect the other channel that currently works along with the one we're hunting down now.
Second, being that it's a common part, there are lots of listings on Amazon. Packs of 5 or 10, going between 60 cents and a dollar each, free prime shipping, be here in two days cuz it's after next day deadline. Lots of stock photos (digikey and mouser have a blank or an unmarked to220 pic) to see. Whether or not I should trust other transistors in the amp that may or may not be genuine is the issue here. As a rule I learned long ago, I don't trust gear until I see it work. I trust the rear two channels of this amp. The front has been tampered with, so I suspect the other channel that currently works along with the one we're hunting down now.
Unless you want to risk getting counterfeit or second rate parts, do not buy from ebay or amazon. Buy from reputable parts distributors like Mouser or Digi-Key.
Post working links to the parts you are thinking about buying.
Post working links to the parts you are thinking about buying.
Why through amazon when Mouser and Digikey are so easy to deal with directly?
Farnell has typically been a European distributor.
Farnell has typically been a European distributor.
I’ve read through your posts on here .
I’ve ordered parts from mouser and digikey and have had 0 issues with the parts
The are both authorized distributors .ive blah day an amp come in for repair where they guy bought parts off of amazon and the amp had nothing but issues after I replaced the parts I got from mouser electronics the amp worked perfectly it’s been going for 2 years now with no issues .
Not sure why you don’t trust mouser or digikey . Never had an issue with them .
And from your photos it appears you have mismatched outputs in the amp 2 resistors are the wrong package size and it appears you have some out of tolorance resistors in the 100 series channel along with defective diodes atleast that’s what it looks like in your photos .
I’ve ordered parts from mouser and digikey and have had 0 issues with the parts
The are both authorized distributors .ive blah day an amp come in for repair where they guy bought parts off of amazon and the amp had nothing but issues after I replaced the parts I got from mouser electronics the amp worked perfectly it’s been going for 2 years now with no issues .
Not sure why you don’t trust mouser or digikey . Never had an issue with them .
And from your photos it appears you have mismatched outputs in the amp 2 resistors are the wrong package size and it appears you have some out of tolorance resistors in the 100 series channel along with defective diodes atleast that’s what it looks like in your photos .
Ok so it's not all for me. I will most likely be buying through Newark, because they're in Louisville KY, about 40 miles from me, right next to the UPS World Hub, right next to about 3 Amazon warehouses. My example with farnell was a motor control chip for a whirlpool duet washer. The usual suspects: nla. It popped up on Amazon one day through farnell, so I ordered two. Yee haw, 26 bucks for 2! Do you have any idea how much Whirlpool duet washers sell for? Hmmmm... 600 bucks is what I sold the set for (matching dryer= 100 off FB market). Still going strong.
Farnell is under the avnet umbrella now, along with Newark element 14 and others. The Amazon guy is the internet sales guy. So my amazon order got filled by the same guy as someone who bought from the newark/farnell/element 14 websites. Yes, just like eBay, you gotta be diligent who you buy from. These transistors are small beans for big bangs; spending 20 bucks for a handful isn't uneconomical. But everybody and their brother sells on eBay or Amazon or both (hence my Newark farnell example). It's a big market. With big companies. Not just ching chong chung import limited.
As for the amp, I haven't touched its guts except for tacking a .22 ohm sandblock onto the source resistor (obviously fried previously with the smd resistors in parallel with it) of the complementary transistor to the one that just ran away short. The diodes you may be speaking of were lifted to rule out the associated circuitry during this thread. I'll be taking the board and mehsa assemblies loose and having my first look at the bottom of the board shortly, when I change the source resistors in this channel. As of now, I'm up in the air about whether to change all of the transistors on the mehsa for known good parts while I'm in here or not. Cuz the other stuff works, but I don't completely trust it.
Farnell is under the avnet umbrella now, along with Newark element 14 and others. The Amazon guy is the internet sales guy. So my amazon order got filled by the same guy as someone who bought from the newark/farnell/element 14 websites. Yes, just like eBay, you gotta be diligent who you buy from. These transistors are small beans for big bangs; spending 20 bucks for a handful isn't uneconomical. But everybody and their brother sells on eBay or Amazon or both (hence my Newark farnell example). It's a big market. With big companies. Not just ching chong chung import limited.
As for the amp, I haven't touched its guts except for tacking a .22 ohm sandblock onto the source resistor (obviously fried previously with the smd resistors in parallel with it) of the complementary transistor to the one that just ran away short. The diodes you may be speaking of were lifted to rule out the associated circuitry during this thread. I'll be taking the board and mehsa assemblies loose and having my first look at the bottom of the board shortly, when I change the source resistors in this channel. As of now, I'm up in the air about whether to change all of the transistors on the mehsa for known good parts while I'm in here or not. Cuz the other stuff works, but I don't completely trust it.
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Yayyyy Newark electronic package arrived . For the curious, and the opposed, me and mine ordered and received all this "stuff" from the automaton in the same time period. Plus a pizza cutter and a couple of sets of guitar strings.
Over the waiting period, the 12 volt supply I was testing with got swiped to fix another computer. So... Nudder trip to the electronic dump and we will be set to go back in and see what happens with the rockford fosgate power amp. I'd fix the old atx supply, but you absolutely cannot beat free. Free donor parts, free hulk disposal, only thing to pay is my truck and it's drinking problem.
Over the waiting period, the 12 volt supply I was testing with got swiped to fix another computer. So... Nudder trip to the electronic dump and we will be set to go back in and see what happens with the rockford fosgate power amp. I'd fix the old atx supply, but you absolutely cannot beat free. Free donor parts, free hulk disposal, only thing to pay is my truck and it's drinking problem.
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Ok so I have time to get something done to the amp tonight. Got the board loose from the heatsink and got a look at the underside. It's obvious that what got changed last time due to the solder joints. Looking from above, I thought the 300/400 side mehsa hadn't been touched. I was wrong someone has changed q5 and q7. Everything else looks original. From the transistor fitment and lead bends, this looks like a very previous repair compared to the problem area I'm focusing on.
The 100/200 mehsa is a different story. It looks like d8 was the only thing not changed. The other 7 transistors are all transplants. I'm feeling better about the components used in the repair though.
Which brings me to the next point: what I got from Newark for 1.50+ per transistor, plus ample shipping, plus waiting an extra week looks like the ching chong chung import crap on Amazon for 37 cents. Not like the ir stuff in the original mehsa, it has a siliconix logo and the accompanying unrefined appearance. I'm not salty, but it feels like I got peer pressured into waiting a week and paying 222 percent. Oh well, at least it wasn't a Chinese reissue mullard power tube.
The 100/200 mehsa is a different story. It looks like d8 was the only thing not changed. The other 7 transistors are all transplants. I'm feeling better about the components used in the repair though.
Which brings me to the next point: what I got from Newark for 1.50+ per transistor, plus ample shipping, plus waiting an extra week looks like the ching chong chung import crap on Amazon for 37 cents. Not like the ir stuff in the original mehsa, it has a siliconix logo and the accompanying unrefined appearance. I'm not salty, but it feels like I got peer pressured into waiting a week and paying 222 percent. Oh well, at least it wasn't a Chinese reissue mullard power tube.
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Follow up on this amp: I swapped out the power transistors in the 100 section, left everything else alone, and let her rip. The left channel exhibited the same odd symptom: looking fine at first, upon warming up, sounds great up to about half power. Ran into a wall about 30 watts or so. Top of signal folded like a vertical output in a crt.
Eventually, one of the irfz40s in the power supply section gave out. Some more mehsa fun and a new pair of irfz40s later, and it's showtime again.
Eventually, one of the irfz40s in the power supply section gave out. Some more mehsa fun and a new pair of irfz40s later, and it's showtime again.
Strange those devices were never used from the factory in the power supply. The factory devices were IRF3205. I'm not saying they wont work, but I'd recommend using the IRF3205.
Well, I thought I was done with this amp, but no.
During the Christmas holiday, I installed it in my gas saver. 2002 Saturn sc2. It's been doing well up until this week. Front channels are still doing well, driving a 6½ component set at 3 ohms. One rear channel is sounding a lot like the previous repair. They've been driving a 4 ohm pair of MB quart speakers on a 6db high pass and a 4 ohm 10 bridged. Left rear channel is gutless and distorted.
During the Christmas holiday, I installed it in my gas saver. 2002 Saturn sc2. It's been doing well up until this week. Front channels are still doing well, driving a 6½ component set at 3 ohms. One rear channel is sounding a lot like the previous repair. They've been driving a 4 ohm pair of MB quart speakers on a 6db high pass and a 4 ohm 10 bridged. Left rear channel is gutless and distorted.
Ok, I will post up some gut shots and pics of signals after I get a few rough measurements.
Follow up to Seankane: I was quoting the schematic about the switch mode fets. I replaced the shorted ones with the same numbers. The schematic said irfz, but in reality, the board had 3205.
Follow up to Seankane: I was quoting the schematic about the switch mode fets. I replaced the shorted ones with the same numbers. The schematic said irfz, but in reality, the board had 3205.
Ok so I got a power supply for Christmas, right about when I wrapped up this amp last time. So this time, no Xbox brick. Yayyy! It's an Eventek kps305d.
Initial powerup and poke around reveals a power supply issue. Idle current is ok, at 1.6 amps. HV rails are -26.5V and WAS around +13V. Low voltage was -13V and only around +4V. Went to go find equipment and now the positive rail is normal. Hmmm
Initial powerup and poke around reveals a power supply issue. Idle current is ok, at 1.6 amps. HV rails are -26.5V and WAS around +13V. Low voltage was -13V and only around +4V. Went to go find equipment and now the positive rail is normal. Hmmm
Bad positive rectifier, bad solder connection, bad via...
Push on/flex the board to see if the problem is repeatable.
Push on/flex the board to see if the problem is repeatable.
Gut shots while I try to replicate the symptom. Right side is the one I repaired and the negative rail side. Left side hasn't been modified by me, except maybe some solder touch up last time. All I really see is some corrosion on q5, center pin. Shot of the now dry q-tip after a light wipe. The green chunk fell off, right into the liberal thermal grease. I'll toothpick it out and do some more solder and flux touchup while I'm in here.
I tap tested it with the bic stick and poke flexed the board, then loosened the four main board mounting screws a turn or two, then tried again. Starting cold, warmed up, it won't break for me! I know if I put it back to work, it'll go on strike again! Grrrr...
I tap tested it with the bic stick and poke flexed the board, then loosened the four main board mounting screws a turn or two, then tried again. Starting cold, warmed up, it won't break for me! I know if I put it back to work, it'll go on strike again! Grrrr...
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