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Ten Tec Centurion

Want to see those glowing tubes?
Nostalgia? Want warm and fuzzy?
Have OCTD? 
by Bob Hutchinson, N5CNN
                             Click any picture larger. >

have really enjoyed using the Centurion I modified and wrote about in previous articles: Ten Tec Centurion and Lighten Up. Removing the putt-putt plate transformer and arranging for outboard HVAC is a superb mod. In addition to making the "deck" a lot lighter, the availability of legal limit+ power is a fine benefit. Opening the side of the case and screening with 1/2 inch expanded stainless steel is a warm and fuzzy benefit for my well being.

But, I woke one morning and realized that my OCTD and well being needed another hit to maintain the euphoric state I have come to enjoy and appreciate. So I decided to fix another small design oversight, the top of the case. Ten Tec designed the area of the original case above the tubes with ventilation slots like on the side but wisely covered the opening on the underside with fine plastic screening to keep objects from entering or falling into the HV DC.

Well, very little cooling air flow actually exits the case here and the dark screen material doesn't really keep very small things like dust from falling into the amplifier and it restricts visualization of the warm glowing tubes through the narrow slots and, etc., etc. A desire to fix these problems is adequate rationalization for more whacking, huh? Yes, I believe it is.

Modify it, whack it.
A small band of Hams came by my shack/shop recently for a get together to pass truthful stories back and forth and to secretly talk about other Ham radio guys behind their backs. We also enjoyed a lunch catered by me. I picked up a Centurion whacking tool and started whacking the Centurion case.

Opening the side
I clamp the case upside down to the edge of the bench and use the sharp nipper hand tool to snip out the side opening and dress the edge. I then use the four holes at the bottom of the case to attach a 1 inch square wooden dowel  and clamp it to the bench to dress the other side of the opening. I drill holes for two #4 x 1/4 or 3/8 inch screws 1/4 inch from edge of opening at front and rear only for subsequent case fit clearance reasons. Washer are needed here to hold the expanded metal. Sometimes I drill six additional holes and glue screw heads to the holes to match the top opening. (See pictures.)

Opening up the top
I remove the ten #4 screws, save the little aluminum bars with pem nuts and remove the plastic screen, leaving the adhesive strip.

After snipping the slotted window completely out of the top of the case, I protect the case with cardboard and carefully clamp the left side of the case to the edge of the bench. I cut a 1" x 4" board at 45 degrees on the flat, screw it to the case through the center hole next to the edge of the opening. Other end is screwed to the bench. This sturdy fixturing supports the edge of the opening for dressing. The edge closest to side of the case is adequately supported when clamped to the bench. After all edges are dressed I blacken edges with a felt tip pen.

Tough stainless
The 1/2 inch expanded stainless steel is hard so I mark 5 1/4' by 8 3/8" with red pen and use an abrasive cut-off wheel on the Dremel tool to slice each segment of the metal.

Attaching the expanded metal in the top is easy. For the side, only holes 1/4 inch from edge in the front and rear of opening are utilized for holding because of clearance considerations when reattaching the case to amplifier. On one unit, for matching purposes, I drilled six more holes and glued screw heads in same pattern as top opening.

Not to tickle the B+
As much as I want unrestricted visual access through the top to see the tubes, I must give consideration to safety. I carefully cut a piece of 1/16 inch clear acrylic to fit in the top opening. All air flow exits the side. On the amplifier table, about one inch from the opening, I place a Radio Shack digital thermometer so I can monitor exhaust temperature. I adjust the fan speed for just the right amount of cooling for yammer, doing away with excessive noise. Wow! I love Ham radio.

Bob Hutchinson, N5CNN
President and Founder
Wireless Industry Association
713 467-0077

If you would like to publish an article here contact Bob Hutchinson, N5CNN.