If you have freezer spray then definitely worth trying. Manipulate the can so you literally get one single drop at a time dangling on the end of the straw. Do it with the amp on and wait a few moments before moving onto the next suspect part.
If you blast a whole area then you never know what you actually cooled that fixed the fault.
A 100 watt bulb is fine because you only use it to initially check all is OK (no music, or at least not loud) and in that stae the amp draws very little current.
If you blast a whole area then you never know what you actually cooled that fixed the fault.
A 100 watt bulb is fine because you only use it to initially check all is OK (no music, or at least not loud) and in that stae the amp draws very little current.
So I ordered a couple of the 2N5551 transistors and noticed that they are TO-92 style, yet the originals for Q5 and Q6are appear to be TO-18 style with a heat sink since these get hot. Will this matter? I was able to find heat sinks for TO-92 style transistors, so I assume I should use them.
Clip on heatsinks are good idea if needed. I actually ran through a quick calculation this morning but didn't post it because it seemed OK as it was.
The 5551 has a max dissipation of 625mw but that is at 25C. In your amp the transistor sees around 45 volts across it under no signal conditions. The current is around 7.5ma. That gives a dissipation of around 400mW. The data sheet shows we must derate the 625mW by 5mW per degree C. Now I bet its running at around 60 to 70 C in the amp... hot in other words... and so we get a rough and ready value of 400mW allowable at that temperature. So add a clip on heatsink and it will be well into safe territory.
The 5551 has a max dissipation of 625mw but that is at 25C. In your amp the transistor sees around 45 volts across it under no signal conditions. The current is around 7.5ma. That gives a dissipation of around 400mW. The data sheet shows we must derate the 625mW by 5mW per degree C. Now I bet its running at around 60 to 70 C in the amp... hot in other words... and so we get a rough and ready value of 400mW allowable at that temperature. So add a clip on heatsink and it will be well into safe territory.
Hi Mooly. Playing amp this morning waiting for it to click off. I have a temp probe inside the amp and it has settled at 100 F / 37.7 C.
So with new lamp, I was seeing 40 vAC at the connections without it installed. Why would it be so dimly lit once installed? My amps light is much brighter but I haven't measured its current to compare.
So with new lamp, I was seeing 40 vAC at the connections without it installed. Why would it be so dimly lit once installed? My amps light is much brighter but I haven't measured its current to compare.
Hi,
If trying the freezing method do not make components to fail, you can try heating it with a hair blower. Use a cardboard to isolate the heat to a small area.
If trying the freezing method do not make components to fail, you can try heating it with a hair blower. Use a cardboard to isolate the heat to a small area.
You see 40 vac across the lamp holder because the bulb isn't fitted. There is a series resistor on the circuit that limits the total current available.
Imagine a 12 volt car battery where you can read 12 volts across the terminals. Now add a foot of wet string to the positive terminal. You would still read 12 volts at the end of the wet string but the resistance is now so high that virtually no current can flow.
Imagine a 12 volt car battery where you can read 12 volts across the terminals. Now add a foot of wet string to the positive terminal. You would still read 12 volts at the end of the wet string but the resistance is now so high that virtually no current can flow.
Hmmm. The bulb is wired with two leads. After removing original I saw 40. The replacement looks similar, 2 leads attached to bulb. Since I have left resistor in place and just swapped out bulb, I would expect it to glow as bright as mine unless either the bulb is wrong spec or the voltage is off. I'll have to get measurements on my amp to compare.
4 CDs later still no click off. Have to run some errands. I'll play it some more this afternoon.
4 CDs later still no click off. Have to run some errands. I'll play it some more this afternoon.
The bulb may have a different filament resistance and that is why its dimmer. You could always drop the series resistor a little to get a bit more voltage.
Ok. Just started playing again and it clicked off after 4th song. Put drops on Q5 & 6. No change. Drops on right channel Q2 & 4. No change. Drops on Q1 then 3 and music started briefly. Then, I thought a saw a wiff of smoke towards back of left side and possibly a flash under neath where relay is. Now when I turn it on, I get low static on left channel. Clear on right, turn up volume and get music out of both. The. Relay clicks off after a few seconds when I turn up volume. DC offset on left is 1-2 volts now until relay clicks off.
Which tranny did I just lose???
Which tranny did I just lose???
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Even numbers are the left channel ? and that is now the one with an audible problem... and yet freezing the evens didn't seem to have an effect.
Work with what we know and can measure. Carefully re-check the offset and confirm its still at 1-2 volts and if so lets look to fixing that first. I guess replacing the diff pair has to be high on the list.
(just a thought... freezing does produce moisture which is conductive of course. If the transistor was wet through then its possible the biasing could be affected until it dries)
Work with what we know and can measure. Carefully re-check the offset and confirm its still at 1-2 volts and if so lets look to fixing that first. I guess replacing the diff pair has to be high on the list.
(just a thought... freezing does produce moisture which is conductive of course. If the transistor was wet through then its possible the biasing could be affected until it dries)
While I thought we might have an issue with right channel, even numbers. Drops didnt change anything until I dropped on left channel, Q1 then Q3. That caused music to start again then stop and then I did give it a very small blast and things went south. It's the left channel with static and high DC offset now. I didn't check right side.
Relay clicks off very quickly. I'll let it cool a bit and start by checking both offsets.
Relay clicks off very quickly. I'll let it cool a bit and start by checking both offsets.
Ok. Went ahead and checked both offsets. Right is 0 to .5 mV. Left is .3v to 1.5v. Low static on left speaker still present.
Ok 30 minutes later, right offset still 0 to.5 mV. Left has dropped to minus .3v to -.8v. Sorry it was likely minus before as well. But. Static is no longer present. And music does not cutoff when I turn up volume. So looks like I'm back where I started. But as you say that left diff pair appears suspect.
Going to give it a rest rest of today and replace Q1 and Q3 in the morning and see how things go from there.
Going to give it a rest rest of today and replace Q1 and Q3 in the morning and see how things go from there.
Replaced Q1 & Q3 and was able to dial in 0v and 30mV on bias/idle. No fluctuation. And 0 v at .5 ohms. Right side is .007 mV steady.
Playing music now. No static anywhere. Clean music both channels.
Playing music now. No static anywhere. Clean music both channels.
then.So. While we wait and see, now, about that lamp. If I change resistance to effectively double the brightness of the bulb. What resistor should I go with? The current one is 750 3W metal oxide.
Finding the best value resistor would be a bit trial and error. Have you measured the voltage (AC remember) on the working bulb. Easiest just to measure from ground to the 750 ohm.
Bulbs tend to brighten quickly as the voltage creeps up. You could find 560 or 680 ohms would be OK. Whatever value suits, you would then need to calculate the wattage required although I would think 3 watt should cover all possibilities.
If you have a 2.2k half watt then just dab that across the 750 ohm and see what happens. It will give you an idea. Work up or down from that to get a value. A half watt will get hot very quickly (so mind fingers) but you will see if the bulb is bright enough or not.
Bulbs tend to brighten quickly as the voltage creeps up. You could find 560 or 680 ohms would be OK. Whatever value suits, you would then need to calculate the wattage required although I would think 3 watt should cover all possibilities.
If you have a 2.2k half watt then just dab that across the 750 ohm and see what happens. It will give you an idea. Work up or down from that to get a value. A half watt will get hot very quickly (so mind fingers) but you will see if the bulb is bright enough or not.
Ok. Thanks Mooly. And thanks too for help with the diff pair. Fingers still crossed. I'm into second CD.
Have to focus on Easter festivities. So I'll look at lamp some more tomorrow. Happy Easter everyone.
Have to focus on Easter festivities. So I'll look at lamp some more tomorrow. Happy Easter everyone.
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