So I have been playing with some "old school amps" or so I thought. A older friend of mine tells me of a Fosgate amp he has stored and ends up bringing it to me. Holly crud! I don't know old school since it sure is not around the late 80-90 range, it's the mid to late 70's!
Anyway, I took covers off and took pics and measured power and ground leads and seem plausible. The speaker outputs all measure about 42ohm and that waved a flag to me. Sounds way too low. I studied up on how to power the amp up using a current draw on the red lead and it is cycling on/off about 2 cycles second. This is just like my friend told me it was doing when he tried it on a power supply years ago. He said it would play but only would stay going if kinda loud and would cycle if played at low volume, from what I recall from speaking to him. I was in shock after all. I did not hook up to a speaker or take any voltage measurements on the speaker leads yet as I am a little nervous with this rare amp. I thought it best to just go straight for some advise.
I tried powering with both a car battery and power supply combined and same result as just my 30amp power supply.
Anyway, I took covers off and took pics and measured power and ground leads and seem plausible. The speaker outputs all measure about 42ohm and that waved a flag to me. Sounds way too low. I studied up on how to power the amp up using a current draw on the red lead and it is cycling on/off about 2 cycles second. This is just like my friend told me it was doing when he tried it on a power supply years ago. He said it would play but only would stay going if kinda loud and would cycle if played at low volume, from what I recall from speaking to him. I was in shock after all. I did not hook up to a speaker or take any voltage measurements on the speaker leads yet as I am a little nervous with this rare amp. I thought it best to just go straight for some advise.
I tried powering with both a car battery and power supply combined and same result as just my 30amp power supply.
Just found this online and it sounds like a possible explanation?
"Your PR-250 IIR is virtually immune to blowouts from shorts or overloads because of Fosgate’s exclusive Short Stop begins operating with computer logic to monitor the power supply output voltage. If it fails to attain the proper level within one-quarter second, Short Stop shuts the entire system off. It then activates a timing circuit that restarts and stops The Punch at one-second intervals. When the short or overload has been eliminated, your PR-250 IIR resumes normal operation"
"Your PR-250 IIR is virtually immune to blowouts from shorts or overloads because of Fosgate’s exclusive Short Stop begins operating with computer logic to monitor the power supply output voltage. If it fails to attain the proper level within one-quarter second, Short Stop shuts the entire system off. It then activates a timing circuit that restarts and stops The Punch at one-second intervals. When the short or overload has been eliminated, your PR-250 IIR resumes normal operation"
I suppose so. It still cycles like protection mode with the one output transistor removed.
I am going to try connecting a cheap speaker to each half(dvc sub) and see if the amp wants to see a load on the speaker leads to power on.
The construction of this amp is very delicate so just pulling outputs out is a last resort.
I am going to try connecting a cheap speaker to each half(dvc sub) and see if the amp wants to see a load on the speaker leads to power on.
The construction of this amp is very delicate so just pulling outputs out is a last resort.
Yes, auto-switch is an output. I have tried first using a 6w 12v bulb from the red output wire to ground. That's when the amp starts cycling on/off or at least "sings" like it is trying to come on. I have not be able to see rail voltage on my meter when it cycles so maybe it is not coming on at all? I tried a 55w bulb briefly and it made no change; this was before the shorted output was found/removed. Maybe a retry with 55w bulb?
I have read in another forum, someone who used to have older Fosgates state a factory tech instructed him to use two 4 ohm 5w resistors in series on a switch to ground.
I don't think the preamp should have to be connected but I am a novice grabbing at straws.
I would think the 3-4amps the 55w bulb needs would easily simulate an old radio?
What about jumping around 5227/120k to power up the amp temporarily so rail voltage and such can be checked? Is this possible or just too risky even without speakers and such being hooked up? From B+ to what point if so?
I have read in another forum, someone who used to have older Fosgates state a factory tech instructed him to use two 4 ohm 5w resistors in series on a switch to ground.
I don't think the preamp should have to be connected but I am a novice grabbing at straws.
I would think the 3-4amps the 55w bulb needs would easily simulate an old radio?
What about jumping around 5227/120k to power up the amp temporarily so rail voltage and such can be checked? Is this possible or just too risky even without speakers and such being hooked up? From B+ to what point if so?
Yes, pretty steady. I could try putting a car battery along with the pyramid 30amp switching power supply but it seems pretty strong on its own. I had already tried to use the pyramid with a good car battery and the amp does the same. The fluctuation is at the same rate as the noise coming from around the power supply windings but the noise I do not think is from the winding; the vertical black thing that looks like a swollen tick. Its labeled 68k 15v; that's I think the source of the noise when it's cycling.
I received my DIN cables today and they did not make any change with preamp connected. I am happy about that actually.
I received my DIN cables today and they did not make any change with preamp connected. I am happy about that actually.