Varmint XL-600

[nomadradio]

I do hope the original AC power plug is still intact.

It's a product called the "Eagle" plug. Has two fuses inside it. It saved Abe the cost of putting a fuseholder inside the amplifier.

But nothing lasts forever, and that plug was made from some fairly-brittle brown bakelite plastic. Any time the AC cord or plug gets replaced you MUST add fuse protection inside the amplifier. Running one of these with no fuse is risky.

73

 

[88_bandit_88]

Yeah I hooked the wire where you said and it just blows fuses. I checked for continuity (blue arrow in picture) and in fact had it at these points don’t know why but the amp does work with the wire unhooked I’m just confused about the three capacitors !!!!

 

[88_bandit_88]

Here is the pic

 

[Dmans]

I’m just confused about the three capacitors !!!!

88_bandit_88,
See Nomadradios explanation of the 6 capacitors below.

The three caps mounted on tie strips under the transformer are in parallel with the set on the power supply board.

A possible explanation for the blown fuse.

But nothing lasts forever, and that plug was made from some fairly-brittle brown bakelite plastic.

Bear in mind that these filter caps are over 40 years old.

Don't expect them to last long.

 

[nomadradio]

Here's what I think happened.

The string of three filter caps shorted. The previous owner discovers that taking the hot wire loose from them stops the fuse from blowing.

He leaves the wire loose, so it will work well enough to demonstrate and sell.

The new owner gets to discover this 'unadvertised feature' the hard way.

73

 

[88_bandit_88]

but why does the three capacitors have continutiy between the positive and negative leads? How do i fix the problem because its just too nice of a box to just be running half throttle! I want to give Thanks to everyone's input on this thread.

73's

 

[nomadradio]

They show continuity because they have failed and become a dead short.

This is a common way for an electrolytic cap that's over 40 years old to fail from age alone. This kind of component is not meant to last more than 10 or 15 years, let alone 40.

We sell a board on Ebay with three 220uf 450-Volt electrolytic caps in series. It's used to repair Maco amplifiers, typically.

http://www.ebay.com/itm/113168677499?ssPageName=STRK:MESELX:IT&_trksid=p3984.m1555.l2649

Even if you replace the set of three capacitors, the power-supply circuit board behind the blower has a half-dozen or more capacitors of this type. They are the same age as the set of three that has failed. If you put the amplifier back into regular use they will fail fairly soon. Just can't predict which one will be the first.

Taking that wire loose was a quick-and-dirty way to make it power up again. Replacing only those three caps is the same sort of lick-and-a-promise patch.

Then again, you could take the three 100uf caps hiding under the power-supply board completely loose, and use our board hooked up where the three caps in the picture are connected. It would take the place of two sets of 100uf caps just fine by itself.

Still leaves the other handful of smaller electrolytics there to quit, one by one.

Unless you replace them all. By far the best strategy.

73

 

[88_bandit_88]

ok i got all the capcitors out and am fixing to order them i have a question, do the 100mf 350v caps have to be exactly the same values?

 

[nomadradio]

When you wire electrolytic capacitors in series, they should match as closely as possible.

If they don't, one capacitor can "hog" more than the one-third share of the voltage. Using caps rated for 450 Volts gives you some safety margin that the 350-Volt parts would not provide.

General rule is that the closer they match, the longer they last. If you take three "leftover" parts removed from junk equipment, they might balance okay, might not.

The three bleeder resistors are wired one each in parallel with each capacitor. They serve two purposes. Naturally, to bleed off the stored charge when you turn it off, but also to equalize the 1000 Volts equally three ways across the capacitors. Once the shorted capacitors are out of the circuit, check the resistance of each of the three bleeder resistors. If they are all within 10 percent of the same reading, it's okay to reuse them.

If they show readings that are more than 10 percent apart, this calls for a new set of three bleeder resistors. The resistance value is not critical. Any value from 220k to 470k will work. Just so all three of them are the same. Should have a 2-Watt rating.

73

 

[88_bandit_88]

Got all the new caps in powers up fine but relay won’t click when I key the mike, if I manually push down on the relay it while having the radio keyed it transmits rf on the watt meter what could be causing this? I also replaced the doides and the two transistors on the hv power supply board.

 

[nomadradio]

Sure does sound as if some part of the keying circuit is not exactly right.

Since you removed parts from the keying circuit and replaced them, this is where I would look for an error like a transistor turned the wrong way or a diode that's backwards.

The keying circuit worked before you replaced parts in it, so the logical cause would be with the parts you changed.

That part of the amplifier was working. Why did you try to "fix" that part of the board?

73

 

[88_bandit_88]

I was just wanting to replace all the parts with new ones whole o had the board removed there was two transistors a

 

[88_bandit_88]

And one diode I replaced

 

[nomadradio]

A circuit that worked until it got disturbed and won't work now pretty well has to have a fault with the new parts.

Or, more likely, with the way they were installed.

A new part that's bad is really rare. The assignment of the three legs on the keying transistor as Base Emitter and Collector are not always the same, even for transistors that look alike. Older american-type small transistors had the base lead in the center of the three. Japanese types tended to (not always) have the collector on the center lead.

What kind of substitute did you use for the keying transistors?

My best guess is that one or both of them is turned around wrong.

73

 

[88_bandit_88]

2n3416 and 2n3417 got them from mouser