Varmint XL-600

[88_bandit]

Yes I have two xl-600’s and was wanting to make a xl-1000 out of the two any Info would be helpful. I know they both use the same cabinet, the 1000 has one more driver tube and two more final tubes and one more transformer. I think I have all the parts needed just need some technical information

 

[nomadradio]

The XL1000 was built at least two ways I have seen. The first one used two transformers wired in parallel. Naturally, they have to be identical. Abe Brewer built his own power transformers, so this wasn't a problem. A later production used a single larger transformer.

The differences between the 600 and 1000 are kinda small. The filament circuit was powered from 12.6 Volts AC. Abe wired pairs of tubes in series. This holds up okay until you choose to use three driver tubes. Can't split 12 Volts 50-50 across an odd number of tubes. His solution was to use the 12.6-Volt version of the 6KV6 driver tube, the 12KV6. That number was a lot of effort to track down decades ago. Probably hasn't gotten easier since then. If it was me, I would probably just bolt a 6.3-Volt transformer to the outside back panel and use that to power three 6-Volt driver heaters in parallel.

One thing that changes going from four to six final tubes is the output coil for the finals. The more tubes you put in parallel, the smaller you have to make that coil.

Never mind why. Seems to me the XL1000 final tank coil was made from quarter-inch copper refrigeration tubing. I'll poke into our archives and see if we have any pics of that output circuit. You won't find much guidance from anything printed by Brewer Labs back in the day.

Might be a fun project. Bear in mind you're in the same spot as the guy who has unlimited access to a scrapyard and wants to build one good car from junked-out hulks.

He'll find that hoses, belts, seals and gaskets have a limited life span and old ones aren't reliable. The electrolytic capacitors in any gadget built in the 1970s all must be replaced. Reusing original capacitors will invite smoke problems. Brewer Labs shut down making linears between 1979 and 1980. If it says Varmint, it can't be newer than that.

Don't underestimate the possibility of old tubes going "SNAP" after you key it up the first dozen times. Odds are you'll need more tubes than just the number of empty sockets in the amplifier.

Have fun and be safe. The 1000 Volts DC in that model will leave a mark if you're not careful.

73

 

[nomadradio]

Found some pics. They're old enough to buy a drink. They're from a XL1000 we converted to high drive, removing the driver tubes.

The output coil is quarter-inch copper tubing. The Load control didn't have enough capacitance. There are two 68pf 2500-Volt disc caps in parallel with it. That brought the peak on that control nearer the center of the control's range.

73

 

[AudioShockwav]

removing the driver tubes.

The output coil is quarter-inch copper tubing. The Load control didn't have enough capacitance. There are two 68pf 2500-Volt disc caps in parallel with it. That brought the peak on that control nearer the center of the control's range.

73

That looks likely to last a minute with just 6 finals and no drivers.
Nice and simple.
Do you remember what the drive was on that set ?

73
Jeff

 

[nomadradio]

Do you remember what the drive was on that set ?

100 to 120 Watts peak, if memory serves. No telling how it was treated when it went back home.

73