A Peavey Bass Top Mark III from 1978 was on my bench.
It produced a loud annoying buzz - mhm -
generally this is no good sign as probably this indicates burned power transistors.
So I checked these with a DVM without finding any suspects.
This amp is a quasi-complementary BJT class ab-amp
fitted with motorola transistors with custom markings,
so there is very little chance to find replacements nowadays.
Next I powered it up using the bulb tester, which did not show a full short circuit.
But looking at the supplies the neg rail sagged extremely,
so I had a look at the bulk capacitor 5000uF/55V.
The tester read 93,55nF!
Although the pos cap looked fine, I replaced both -
and - success!
Btw I found it remarkable to learn that this baby already had a built-in limiter.
It produced a loud annoying buzz - mhm -
generally this is no good sign as probably this indicates burned power transistors.
So I checked these with a DVM without finding any suspects.
This amp is a quasi-complementary BJT class ab-amp
fitted with motorola transistors with custom markings,
so there is very little chance to find replacements nowadays.
Next I powered it up using the bulb tester, which did not show a full short circuit.
But looking at the supplies the neg rail sagged extremely,
so I had a look at the bulk capacitor 5000uF/55V.
The tester read 93,55nF!
Although the pos cap looked fine, I replaced both -
and - success!
Btw I found it remarkable to learn that this baby already had a built-in limiter.
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One can generally just put in ON MJ15024’s in place of Je ne sais quoi NPN outputs for amplifiers of that vintage, as long as doping out the circuit doesn’t reveal that they are darlingtons (which would be unusual for Peavey). So there would have been recourse. But if the caps are bad, the caps are bad. Back then stuff was designed to be fixed, and not to cascade fail and take half the circuit board out in a flameball.
It’s not really a built in limiter, is what the power supply does when there isn’t enough capacitance. Whats remarkable is that the amp was still well behaved with only one supply dropping. That can often result in latch up and send the opposite DC to the speaker.
It’s not really a built in limiter, is what the power supply does when there isn’t enough capacitance. Whats remarkable is that the amp was still well behaved with only one supply dropping. That can often result in latch up and send the opposite DC to the speaker.
Long update to the Mora clock project
Having cleaned up the exterior of the Swedish Mora Clock I bought my wife and given it to her (she loves it by the way).
I could then do a full clean of movement and re-oil with the right stuff.
Cleaning was done with switch/contact cleaning fluid on cotton buds to remove old gunk in the bearings.
Then filling the bearing pots with the right grade oil, that just sits there, even when the movement is vertical.
I had to raise and fix down the mechanism and set the face to the right height.
The movement is the same (pretty crude, but effective) one I've seen on many Mora clocks of this age.
Right down to the wooden weight pulleys and crude mounting board.
The face however looks suitably rustic but the holes would never quite line up with the movement's winders.
Probably come from somewhere/thing else?
I made some brass ferrules to sort that out. Aged the brass with a blow torch.
The clock runs fine.
The two chime bells were sitting ontop of each other so the strikers only made one dull sound.
Should be a distinct 2 pling chime, not a bim-bam.
I'm currently playing with different weights as the over that came with it (cast iron) seem excessively heavy!
6kgs for the chimes and 6.8 for the time movement.
Heavy heavy fuel
The chimes run too fast on 6 kgs.
I'm testing at 4kgs.
2kgs was too light to always activate the mech and when it did, too slow🙂
4 seems about right and runs reliably.
The time movement seems fine on the 6kgs weight.
It would stop on 3, 3.5, 4 and 5kgs!
Not sure they are supposed to be this heavy?
Plenty of different weights at all manner of kgs on the internet.
I also made a winder from one my dad had kept but with the right size square, machined in
Quite a fun hobby clock tinkering.
Having cleaned up the exterior of the Swedish Mora Clock I bought my wife and given it to her (she loves it by the way).
I could then do a full clean of movement and re-oil with the right stuff.
Cleaning was done with switch/contact cleaning fluid on cotton buds to remove old gunk in the bearings.
Then filling the bearing pots with the right grade oil, that just sits there, even when the movement is vertical.
I had to raise and fix down the mechanism and set the face to the right height.
The movement is the same (pretty crude, but effective) one I've seen on many Mora clocks of this age.
Right down to the wooden weight pulleys and crude mounting board.
The face however looks suitably rustic but the holes would never quite line up with the movement's winders.
Probably come from somewhere/thing else?
I made some brass ferrules to sort that out. Aged the brass with a blow torch.
The clock runs fine.
The two chime bells were sitting ontop of each other so the strikers only made one dull sound.
Should be a distinct 2 pling chime, not a bim-bam.
I'm currently playing with different weights as the over that came with it (cast iron) seem excessively heavy!
6kgs for the chimes and 6.8 for the time movement.
Heavy heavy fuel
The chimes run too fast on 6 kgs.
I'm testing at 4kgs.
2kgs was too light to always activate the mech and when it did, too slow🙂
4 seems about right and runs reliably.
The time movement seems fine on the 6kgs weight.
It would stop on 3, 3.5, 4 and 5kgs!
Not sure they are supposed to be this heavy?
Plenty of different weights at all manner of kgs on the internet.
I also made a winder from one my dad had kept but with the right size square, machined in
Quite a fun hobby clock tinkering.
"New" McIntosh MC245 power amp reservoir cap repair : better here or in
https://www.diyaudio.com/community/threads/mcintosh-rubycon.413119/ ?
https://www.diyaudio.com/community/threads/mcintosh-rubycon.413119/ ?
My homebuilt tube buffer ( fm1 ) sometimes dropped sound in one channel. It could be cured by tapping
or disconnecting/connecting some of the RCA connectors.
Eventually i decided to fix this. Using coolspray gave nothing. I had problem reproducing the problem but later it
happened that i lifted a corener of the chassies on the workbench i could ( sometimes) provoke the problem.
Looking at solder gave nothing. Then i decided to replace old carbon-comp resistors, they can "break". No cure,
problem remained. Then i started substitute capacitors ( they also can loose internal contact). THEN i notised
the problem, one cap was unsatifactory soldered by me 15 years ago. Anyway i replaced it and reassebled the
unit.
I considered myself a competent solderer. How wrong i was !
or disconnecting/connecting some of the RCA connectors.
Eventually i decided to fix this. Using coolspray gave nothing. I had problem reproducing the problem but later it
happened that i lifted a corener of the chassies on the workbench i could ( sometimes) provoke the problem.
Looking at solder gave nothing. Then i decided to replace old carbon-comp resistors, they can "break". No cure,
problem remained. Then i started substitute capacitors ( they also can loose internal contact). THEN i notised
the problem, one cap was unsatifactory soldered by me 15 years ago. Anyway i replaced it and reassebled the
unit.
I considered myself a competent solderer. How wrong i was !