Boomer deluxe 35 amp no power

[dozerman]

Just bought a Boomer power supply and amp at a yard sale. I know, nothing is for sure in a yard sale. Get it home, slide the top cover out to see what transistors are in the amp. Power ed it up and smoke rolled from one of the big caps in the back. Shut it off, ordered caps to replace them. Put those in and the transformer won't make more than 8.11 volts. When I push the reset to turn it on, voltage drops to 4.09v. Any suggestions?

 

[2315 Robert]

Check all the transistors attached to the heat sink in the back. The boomer is a regulated power supply correct?

 

[2315 Robert]

I also had to replace the a bridge rectifier in my 20 amp Janson regulated power supply.

 

[dozerman]

Check all the transistors attached to the heat sink in the back. The boomer is a regulated power supply correct?

Yeah that's right. I've pulled them out and so far all of them test good albeit lowish gain. They are TIP 35's. haven't looked them up to see what the HFE is on them. I'm assuming low, it's high 90's on most all of them.

 

[dozerman]

Yeah that's right. I've pulled them out and so far all of them test good albeit lowish gain. They are TIP 35's. haven't looked them up to see what the HFE is on them. I'm assuming low, it's high 90's on most all of them.

Just looked and the data sheet says an HFE of 40 is usual. And I'm measuring 4 volts more on the collector at idle than the data sheet says. Ugh

 

[2315 Robert]

Copy. I had one transistor that was shorted and a bridge rectifier(can't remember if it was showing short or open). I thought they may have the T0-3(metal can type trasistor_ like my Janson.

 

[dozerman]

Copy. I had one transistor that was shorted and a bridge rectifier(can't remember if it was showing short or open). I thought they may have the T0-3(metal can type trasistor_ like my Janson.

Well after replacing the 3 caps in the power supply, a relay, tip31 transistor and power switch, I have power from the supply side again. Now, apparently something is shorted on the amp side. With a radio keying 2 watts, the amplifier has a dead key of 300 watts and swing to 400. As soon as I key, the transformer really grunts and can manage a 3 second key and it pops the fuse. Are these things junk or am I missing something?

 

[Robb]

Well after replacing the 3 caps in the power supply, a relay, tip31 transistor and power switch, I have power from the supply side again. Now, apparently something is shorted on the amp side. With a radio keying 2 watts, the amplifier has a dead key of 300 watts and swing to 400. As soon as I key, the transformer really grunts and can manage a 3 second key and it pops the fuse. Are these things junk or am I missing something?

Sounds like the amp is drawing more current than the power supply can deliver.

 

[nomadradio]

If you only replaced one bridge rectifier, this probably explains it.

Not sure how you checked the one that wasn't shorted. I think the "good" one has a problem.

We have been replacing both bridges when one of them fails for a long time now. Consider that your two replacements should match as well as possible. The factory bought thousands at a time. Parts from the same batch typically match reasonably well. But if you have two bridge rectifiers from different suppliers, one of them could end up taking more than half of the load, then overheat and fail prematurely. And if both of them have the same markings, and came from the same supplier at the same time, they will probably match well enough. Two parts with different markings will only balance by accident, even if they are both rated the same.

A transformer that grunts under load probably has some DC current in the transformer's secondary winding. A full-wave rectifier like a bridge is DC-balanced. That is, the transformer's current in one direction is always equal to the other direction,

But a rectifier with a bad section allows more current to flow one way in the winding, than when it flows the other way during the other half of the cycle.

Called a "DC offset". This reduces the inductance of the winding, raises the temperature of the whole thing. That "grunt" is a warning to back off until the rectifier circuit is working properly.

73

 

[dozerman]

If you only replaced one bridge rectifier, this probably explains it.

Not sure how you checked the one that wasn't shorted. I think the "good" one has a problem.

We have been replacing both bridges when one of them fails for a long time now. Consider that your two replacements should match as well as possible. The factory bought thousands at a time. Parts from the same batch typically match reasonably well. But if you have two bridge rectifiers from different suppliers, one of them could end up taking more than half of the load, then overheat and fail prematurely. And if both of them have the same markings, and came from the same supplier at the same time, they will probably match well enough. Two parts with different markings will only balance by accident, even if they are both rated the same.

A transformer that grunts under load probably has some DC current in the transformer's secondary winding. A full-wave rectifier like a bridge is DC-balanced. That is, the transformer's current in one direction is always equal to the other direction,

But a rectifier with a bad section allows more current to flow one way in the winding, than when it flows the other way during the other half of the cycle.

Called a "DC offset". This reduces the inductance of the winding, raises the temperature of the whole thing. That "grunt" is a warning to back off until the rectifier circuit is working properly.

73

I replaced both rectifiers. Two 25 amp rectifiers that have a printed circuit board that slips over their posts and solders to them. Both have the same markings and came from the same manufacturer. Now they were purchased from eBay so the could be junk. But would that explain the extremely high dead key?? I've got the correct voltage coming from the supply to the amp side and it doesn't fluctuate when keyed up. It's not like it has run away voltage causing it. I will take the rectifiers back out and do it again. I probably hooked it up wrong

 

[dozerman]

Sounds like the amp is drawing more current than the power supply can deliver.

As @nomadradio was saying, it's probably the rectifiers. I just went out and looked at them and one of them is pretty black looking thru the circuit board. Don't know why I didn't see this last night. Like I said, I probably had the transformer hooked up wrong to the bridge. Yet another learning experience.

 

[nomadradio]

Have a look at the DC output voltage on the front-panel jacks. If the voltage regulator has failed, you could be running the amplifier at a voltage high enough to be a hazard.

73

 

[dozerman]

Have a look at the DC output voltage on the front-panel jacks. If the voltage regulator has failed, you could be running the amplifier at a voltage high enough to be a hazard.

73

They are at 13.9-14.1 volts. But that can be adjusted from 9 volts to 16 volts. I've got 13.8 ish there, the hot going to the amp board and 13.8ish on the base of the final transistors. I've tried hooking the transformer up differently to the bridge, but can't get power in any other configuration, which would make sense if I've hooked it up wrong to begin with and ruined one of the rectifiers

 

[nomadradio]

Seeing the right DC output voltage does confirm that the voltage regulator is working. Just didn't want you to try keying it if the regulator had run away and was putting 23 Volts on the linear side. It wouldn't last long that way.

But the reading of 13.8 on the base terminal of the RF transistors is a really, really bad sign.

Any time we see a solid-state base amplifier with power supply trouble, we take the DC output loose, and hook the amplifier side to our power supply. I don't want to spend money on the customer's power supply if the amplifier side is also damaged. And if the linear side works on our power supply, it should work from the internal supply when it's repaired.

But the base terminal of the RF transistors should NOT show that voltage. If it does, this strongly suggests that those transistors are shorted internally, and you won't see any power from it until they are replaced.

73

 

[Onelasttime]

I would start at one end of the power supply and work my way through each section following the circuit. It always takes more time jumping around than it does to just go through the entire thing one end to the other taking voltages and such as you go.

Same thing applies to radio's often if you have a problem in a radio acting as if you are giving it an alignment is faster than trying to out think the problem. Just test everything in a methodical manner and see what you get. Write everything down. Often when we draw out a problem or put numbers on paper and look at it things that would allude us jump right off the paper and smack us in the face.

You would not believe how often diagramming a problem makes the elusive seem insanely simple!

I agree with Nomad though. Often times replacing things in pair's is the answer. Even with capacitors and resistors sometimes matching them solves a problem.