old varmint XL-250, please advise!!

Here is a link for tuning and drive information and a schematic.

Varmint

Almost every one of these I've seen that still has the gold colored electrolytic caps has them go bad shortly after starting to use them again after a long storage period. Most of them look pretty nasty if they are original. Bulges and leakage usually. Might want to look them over before running it too long.

I have one of the Varmint XL250s. Got it off the floor of a CB shop for $20, retubed it, cleaned the keying relay, and whala - been using it for 2 years trouble free. It was really clean when I got it though. Mine is 1 6kv6a driving 2 6lr6. That is what the schematic calls for that jp1116 posted on cbtricks as well. The tuning info is also there - but it works better if you tune it for max pep, not max deadkey.

I get a little over 400 watts swing. It dead keys 250 watts at 4 watts drive, but I turn down the drive on the radio's variable till the deadkey is at 100 watts and swing it to 400.

click the thumbnail below for big pic:

so did you end up getting it?

Lazybones1222 said:

I have one of the Varmint XL250s. Got it off the floor of a CB shop for $20, retubed it, cleaned the keying relay, and whala - been using it for 2 years trouble free. It was really clean when I got it though. Mine is 1 6kv6a driving 2 6lr6.

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That thing is clean…. It’s been a long time since I have seen one of them. That was one of the very first amps I saw in use back in 72-73 when I was just starting out. Brings back some memories.

Those amps are almost obsolete today, so it’s not worth spending a lot to fix them. But if they are in reasonably clean shape and the transformer is not cooked, then why not.

I have experience repairing the entire Varmint line, up to the heavy sided XL-1000 base. In fact, a lot of my knowledge of sweep tube designs spawned from fixing those amps back in the ‘70’s. Buy the time I was 15 I had made my first copy of the Varmint XL-1000, and later drove the final with a Johnson Viking transmitter.

If anybody has any problems getting those or any other sweep tube amps going don’t hesitate to ask.

Wolf

Wolfradio fixes Varmints. I'll remember that. Thanks for the reply.

WolfRadio.com said:

That thing is clean…. It’s been a long time since I have seen one of them. That was one of the very first amps I saw in use back in 72-73 when I was just starting out. Brings back some memories.

Those amps are almost obsolete today, so it’s not worth spending a lot to fix them. But if they are in reasonably clean shape and the transformer is not cooked, then why not.

I have experience repairing the entire Varmint line, up to the heavy sided XL-1000 base. In fact, a lot of my knowledge of sweep tube designs spawned from fixing those amps back in the ‘70’s. Buy the time I was 15 I had made my first copy of the Varmint XL-1000, and later drove the final with a Johnson Viking transmitter.

If anybody has any problems getting those or any other sweep tube amps going don’t hesitate to ask.

Wolf

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I just picked up a rare varmint xl 50. I know it has one tube. I powered it up but the tube looks dim. I barely see an orange glow. I've read all the dangers abour reaching in there. How do I know if the tube is good or not. ?

You need a tube tester.

Grunt142 said:

I just picked up a rare varmint xl 50. I know it has one tube. I powered it up but the tube looks dim. I barely see an orange glow. I've read all the dangers abour reaching in there. How do I know if the tube is good or not. ?

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You need access to a tube tester to find out.

I powered it up but the tube looks dim. I barely see an orange glow.

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The dim orange glow from the very center of the tube's structure is probably about right. This is the tube's filament/heater and should not be all that bright to begin with.

The large gray metal structure just inside the glass should NOT get hot enough to show any color. If it does, the life of the tube is being sucked down the toilet fast.

Hardest part of using this box is to find a radio small enough to match it. A single tube really can't take more than about 15 Watts peak. A 3-Watt carrier is on the edge of too much. This box was designed 45 years ago. Radios have gotten a lot bigger since then. The amplifier has stayed the same size.

The radio's carrier should be set to hold the carrier coming out of this box down to 30 Watts or less. Yes, it says "50" on the front. And the 1968 Ford Galaxie 500 was not supposed to go 500 miles per hour, either.

A bone-stock Cobra 2000GTL with the carrier set for safe output level from the box is about right. But most radios made since the early 1970s have more peak swing than that.

Just like any hot rod. If you want to burn rubber you should stock up on tires.

A single-tube amplifier like this one might show 100 Watt peaks on a proper peak-reading meter, but that's the "shot out of a gun, downhill with a tailwind" power you would see with a fresh, hot tube. A weak tube might show only half that, and a decent tube only 60 to 80 Watt peaks.

But any radio with more than 15 or 16 Watt modulated PEP will assassinate it fairly soon. Maybe before the 40 year-old filter caps explode, or the relay starts to cut out.

Just remember to peak the Tune and Load controls for best modulated power. If you peak with only the carrier driving it you'll sacrifice audio quality.

73

Hi I'm trying to do some shooting on my varmint XL350 the tubes light's up but when bleeding from the chassis to the tube it has no acre and before I could hear the relay key with the mic now the relay unkeys when I speak into the mic any help or advice will be appreciated thanks

Most likely faults are with the electrolytic capacitors.

Note I said "faults", not "fault".

The three large filter caps for the high voltage should hold a charge for a while after you power it down. Since you don't see the discharge from the tubes' plate caps, this means they no longer hold a charge.

No big surprise. They weren't meant to last more than ten or fifteen years. It's not unusual to see them last 25 or 30.

But your Varmint is over 40, since 1979 is when the FCC went after Abe Brewer and shut him down for good.

Likewise, the smaller filter cap for the 12 Volt DC relay is probably the cause of the relay issue.

Probably.

You'll be lucky if filter caps are your only problem. But until you replace them all, there won't be any way to troubleshoot any of the other problems that may remain in the rest of the amplifier.

The relay itself won't be the cause of the "unkey" problem when you modulate the radio. The contact surfaces tend to go bad after this many decades, so the relay can still cause trouble once you get it to stay closed while you modulate the radio. Cleaning the contacts should be done by passing a paper strip soaked in solvent through them while pressing the contacts against the paper. When the paper no longer shows a dark streak when passed through, that side of the relay is done.

Kinda like getting a 40 year-old car to start. Has a bad fuel pump and caruburetor. You won't hear the collapsed lifters until you first put that stuff on and get it to start.

Here's hoping the tubes are still good.

73

WolfRadio.com said:

That thing is clean…. It’s been a long time since I have seen one of them. That was one of the very first amps I saw in use back in 72-73 when I was just starting out. Brings back some memories.

Those amps are almost obsolete today, so it’s not worth spending a lot to fix them. But if they are in reasonably clean shape and the transformer is not cooked, then why not.

I have experience repairing the entire Varmint line, up to the heavy sided XL-1000 base. In fact, a lot of my knowledge of sweep tube designs spawned from fixing those amps back in the ‘70’s. Buy the time I was 15 I had made my first copy of the Varmint XL-1000, and later drove the final with a Johnson Viking transmitter.
Wttf
If anybody has any problems getting those or any other sweep tube amps going don’t hesitate to ask.

Wolf

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Hey wolf I'm a newby, I just got a varmint back from a friend and it was abused.. ordered 2- 6lr6 and the driver is a 6jt6a,in the meantime I worked and tune and adjusted and new fan I'm touching 400 on the swing with a 100 watt dead key.. my question is is that y the same driver that the 250 xl had or several different? Thanks ridgerunner ,505; paint rock Tennessee in the woods

Pretty much any amp that has a single drive tube is bad news if you run a modern radio.

There is a common misconception that you can use a radio as big as you like on a linear, just so long as the carrier is turned down.

Not really.

When that amplifier was designed, a typical base radio would struggle to push more than a 3 or 3-1/2 Watt carrier, and would bust a gut to show more than 12 or 13 Watt peaks, more or less.

Fast forward 45 years, and a typical legal 40-channel radio can deliver twice that much modulated power or more.

Twice.

A "10-meter" (snicker) radio with two finals can push four times that much modulated drive into that poor, little single driver tube.

Just turning down the radio's carrier knob won't reduce this hazard.

Overdriving a tube by a factor of two-to-one or four-to-one won't end well. Bypassing the driver tube isn't a trivial thing to do, but for someone with a "black" base radio that puts 35 or 40-Watt peaks into the amplifier it's the only viable long-term strategy.

Driving the radio's 35 Watts directly into the two final tubes will reduce the power a little, but not enough for anyone to tell. Nobody but the wattmeter watcher.

Mostly we get asked to bypass the driver after the customer's DX2517 assassinates the single driver tube.

A better move than installing a new driver and lather, rinse, repeat.

We have installed attenuator resistors to knock down 3/4 of the radio's drive power. That works too.

People just like to see big wattmeter numbers. Until they find out what that means to the life of the tubes.

73