yes i already have a picture of it, that web site dont help at all, still need info on it, like what are the original tubes that it was made with and what are the safe substitutes and any other good advice for it.
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Tube Amp adjustment.
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Never had a diagram for that one. Had a beige-colored specimen here a while back, but with no name on it. Looked pretty similar.
Not sure what good a diagram will do for you, unless it's been trashed or badly modified. The circuit is pretty well cut down to the bare minimum.
My impression was that it's pretty unstable, prone to oscillate and behave erratically when you're tuning it up. Adding parasitic chokes to the plate caps of the four final tubes is a good place to start. Ed Dulaney knew he needed them on the 'baldy' driver tubes in all the D&A models he built with those tubes.
Parasitic chokes are a wild card. One set of tubes may work without them, and the next set of tubes will want to go nuts without them in the circuit. Never learned how to predict that in advance, so we usually add them if they are absent.
The shield of the coax that goes from the final Load control to the relay is not grounded. Adding a ground wire at the relay end, from the shield to a ground lug on the antenna socket helps, too.
Last, adding a faraday shield (piece of hardware cloth or "chicken wire) between the driver and final tubes serves to isolate the driver tubes from the finals and prevent it from oscillating that way.
Here's an example of this trick used in a Maco 300
And if yours behaves itself the way it is, all the better. Some of the old "glass-factory" amplifiers would behave well with tubes made in one factory, but not with tubes made by another.
Your mileage may vary.
73
Not sure what good a diagram will do for you, unless it's been trashed or badly modified. The circuit is pretty well cut down to the bare minimum.
My impression was that it's pretty unstable, prone to oscillate and behave erratically when you're tuning it up. Adding parasitic chokes to the plate caps of the four final tubes is a good place to start. Ed Dulaney knew he needed them on the 'baldy' driver tubes in all the D&A models he built with those tubes.
Parasitic chokes are a wild card. One set of tubes may work without them, and the next set of tubes will want to go nuts without them in the circuit. Never learned how to predict that in advance, so we usually add them if they are absent.
The shield of the coax that goes from the final Load control to the relay is not grounded. Adding a ground wire at the relay end, from the shield to a ground lug on the antenna socket helps, too.
Last, adding a faraday shield (piece of hardware cloth or "chicken wire) between the driver and final tubes serves to isolate the driver tubes from the finals and prevent it from oscillating that way.
Here's an example of this trick used in a Maco 300
And if yours behaves itself the way it is, all the better. Some of the old "glass-factory" amplifiers would behave well with tubes made in one factory, but not with tubes made by another.
Your mileage may vary.
73
Whups, just re-read the post #14,
Depending on the power-supply voltage, peak power of 120 to 150 Watts per tube is close to the red line for tubes that size. It will be safe to run at roughly half the power you want.
The drive power it's built to expect would be consistent with radios being used in the 1970s when it was designed. 20 Watt peaks will hammer it. A radio with 80 Watt peaks may make it lift the front wheels off the track, but don't expect too many quarter-mile runs between rebuilds running it this way.
Feel free to burn the rubber down to the rims if you wish, but this is NOT a "high-drive" amplifier. It's intended to take a wimpy 1974 23-channel base radio and make it large.
73
Depending on the power-supply voltage, peak power of 120 to 150 Watts per tube is close to the red line for tubes that size. It will be safe to run at roughly half the power you want.
The drive power it's built to expect would be consistent with radios being used in the 1970s when it was designed. 20 Watt peaks will hammer it. A radio with 80 Watt peaks may make it lift the front wheels off the track, but don't expect too many quarter-mile runs between rebuilds running it this way.
Feel free to burn the rubber down to the rims if you wish, but this is NOT a "high-drive" amplifier. It's intended to take a wimpy 1974 23-channel base radio and make it large.
73
Aren't these amps worth close to nothing if the tubes are no good? If they are good, it might be wise to treat them nice, since the replacements are almost non-existent or very expensive if available at all.
The way I have explained it to more than one customer is that if you got drunk and toasted your tubes Sunday night in 1975, you could earn enough to buy another set by lunch break the next work day.
Good luck with that these days.
When the tubes were dirt cheap there was little incentive to treat them with any respect. If they wore out in a few months, no big deal.
Fast forward four decades and it pays to be nice to your tubes. If the amplifier's design doesn't make that possible, there are ways to reduce the operating stress on the tubes. The extra parts that allow this were typically left out to reduce the cost of building the thing. Adding grid bias, parasitic chokes and shields that were left out can do this.
But the economics are different now. If the tubes are in good shape, you can decide if the cost of rehabbing an amplifier is worth it to you. And if it will need a set of tubes to do this, it's just another part of the calculation.
After all, it's only money.
Speaking of which, a strong set of tubes may well be worth more than the amplifier that uses them, with the tubes installed and working.
More people looking to buy tubes than looking to buy amplifiers.
More than once I have advised a customer to sell the "good" set of tubes from his amplifier and use the money to buy a solid-state amplifier.
73
Good luck with that these days.
When the tubes were dirt cheap there was little incentive to treat them with any respect. If they wore out in a few months, no big deal.
Fast forward four decades and it pays to be nice to your tubes. If the amplifier's design doesn't make that possible, there are ways to reduce the operating stress on the tubes. The extra parts that allow this were typically left out to reduce the cost of building the thing. Adding grid bias, parasitic chokes and shields that were left out can do this.
But the economics are different now. If the tubes are in good shape, you can decide if the cost of rehabbing an amplifier is worth it to you. And if it will need a set of tubes to do this, it's just another part of the calculation.
After all, it's only money.
Speaking of which, a strong set of tubes may well be worth more than the amplifier that uses them, with the tubes installed and working.
More people looking to buy tubes than looking to buy amplifiers.
More than once I have advised a customer to sell the "good" set of tubes from his amplifier and use the money to buy a solid-state amplifier.
73
Just noticed you also asked what kind of tubes it uses.
The final tubes should be 6LQ6 or the much more-expenisve 6MJ6.
Driver tubes could be 6KV6, 6JG6 or 6JT6.
The 6KV6 is the stoutest of the bunch, and tends to be more expensive.
Do you have any way to test the tubes that are in it?
Sure would have a large impact on the cost of putting it on the air.
The age of the filter caps is a big deal. If this thing is a "barn find" with no actual mileage on it, all the caps might still be good. Sure does look clean on the inside for its age.
73
The final tubes should be 6LQ6 or the much more-expenisve 6MJ6.
Driver tubes could be 6KV6, 6JG6 or 6JT6.
The 6KV6 is the stoutest of the bunch, and tends to be more expensive.
Do you have any way to test the tubes that are in it?
Sure would have a large impact on the cost of putting it on the air.
The age of the filter caps is a big deal. If this thing is a "barn find" with no actual mileage on it, all the caps might still be good. Sure does look clean on the inside for its age.
73
i just got it and hooked it up and when i key it up the green light dims and it humms loud and puts no power out and i can smell something hot, i know i put the tubes in it ok and none look broke on shipping, the whole thing looks ok dont see anything lose underneath i am so disappointed ,
Umm, okay.
You found a 1974 car that was kept under a tarp in a barn. Everything looks okay, but it won't start. Tries to catch, but won't start or idle. Just dies when you let your foot off the accelerator. And there's a burnt smell coming from under the hood.
It would not be a complete miracle to see an amplifier this old come to life and work like it should. But it would be out of the ordinary to find that it had no problems as old as it is.
When one of these comes in for service, we check for shorted filter capacitors, and make sure the tubes are not broken down BEFORE any power is applied to it. This minimizes collateral damage that can be caused by simply hooking it up, flipping the power switch and seeing what happens.
Hams call this the "smoke test" method of trying out an old piece of equipment.
Sounds as if yours has some predictable troubles in the power supply. Shorted filter capacitors are very likely. The rectifier diodes are usually damaged by the overload when the filter caps short. If so, they'll have to be replaced along with the filter caps. We *ALWAYS* replace the bleeder resistors. If the old ones have changed their resistance value with age, it can damage a new filter cap if you replace JUST the cap and leave the old bleeder resistor in place. New bleeder resistors are just cheap insurance. The fuse in this sort of amplifier is frequently large enough that it won't protect the internal parts when there is a breakdown. Mostly the fuse serves to prevent it from setting your house on fire.
Dern shame you didn't beat the odds and find them in working shape.
But if they did work like they should, this WOULD beat the odds. It happens, but not all that often.
Do you have any of the tools needed to test for shorted parts? Any way to test the tubes?
Sounds as if that's what's next for that one.
73
You found a 1974 car that was kept under a tarp in a barn. Everything looks okay, but it won't start. Tries to catch, but won't start or idle. Just dies when you let your foot off the accelerator. And there's a burnt smell coming from under the hood.
It would not be a complete miracle to see an amplifier this old come to life and work like it should. But it would be out of the ordinary to find that it had no problems as old as it is.
When one of these comes in for service, we check for shorted filter capacitors, and make sure the tubes are not broken down BEFORE any power is applied to it. This minimizes collateral damage that can be caused by simply hooking it up, flipping the power switch and seeing what happens.
Hams call this the "smoke test" method of trying out an old piece of equipment.
Sounds as if yours has some predictable troubles in the power supply. Shorted filter capacitors are very likely. The rectifier diodes are usually damaged by the overload when the filter caps short. If so, they'll have to be replaced along with the filter caps. We *ALWAYS* replace the bleeder resistors. If the old ones have changed their resistance value with age, it can damage a new filter cap if you replace JUST the cap and leave the old bleeder resistor in place. New bleeder resistors are just cheap insurance. The fuse in this sort of amplifier is frequently large enough that it won't protect the internal parts when there is a breakdown. Mostly the fuse serves to prevent it from setting your house on fire.
Dern shame you didn't beat the odds and find them in working shape.
But if they did work like they should, this WOULD beat the odds. It happens, but not all that often.
Do you have any of the tools needed to test for shorted parts? Any way to test the tubes?
Sounds as if that's what's next for that one.
73
Whoa, sure enough. The filter caps do look new. And so do the bleeder resistors. So long as they were all installed correctly, they should not be causing trouble.
The video sounds as if there is an arc inside somewhere. Could the plates on one of the air-variable tuning capacitors have been bumped, knocked together and shorted?
The calibrated eyeball is your friend. Is there any kind of blue flash from inside any of the tubes when you key the radio? A shorted tuning control could do that, and a bum tube can too.
For that matter, turning it over and watching for an arc on the underside when it's keyed could narrow down where the fault is located. If something gets knocked loose in shipping, this could cause a short-circuit fault.
Another thing to check is to remove all the tubes and try keying it that way. If you still get the hum and dimming lights, THAT fault is not in a tube.
If the problem goes away, you may have a failed tube.
Never underestimate how many things can be damaged in shipping.
73
The video sounds as if there is an arc inside somewhere. Could the plates on one of the air-variable tuning capacitors have been bumped, knocked together and shorted?
The calibrated eyeball is your friend. Is there any kind of blue flash from inside any of the tubes when you key the radio? A shorted tuning control could do that, and a bum tube can too.
For that matter, turning it over and watching for an arc on the underside when it's keyed could narrow down where the fault is located. If something gets knocked loose in shipping, this could cause a short-circuit fault.
Another thing to check is to remove all the tubes and try keying it that way. If you still get the hum and dimming lights, THAT fault is not in a tube.
If the problem goes away, you may have a failed tube.
Never underestimate how many things can be damaged in shipping.
73
Rock on!
The calibrated eyeball strikes again!
I would replace all eight rectifier diodes with type 1N5408. It's a 3-Amp 1000-Volt part. Eight of them are only slight overkill. The "170" number should mean that the original diodes were rated for 2.5 Amps.
They're cheap enough I wouldn't consider replacing "just two", or using one smaller than the 1N5408. It's a more-rugged part than the originals.
Good catch!
73
The calibrated eyeball strikes again!
I would replace all eight rectifier diodes with type 1N5408. It's a 3-Amp 1000-Volt part. Eight of them are only slight overkill. The "170" number should mean that the original diodes were rated for 2.5 Amps.
They're cheap enough I wouldn't consider replacing "just two", or using one smaller than the 1N5408. It's a more-rugged part than the originals.
Good catch!
73
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