Wood Welder TC
From: Jim Fosse [SMTP:jim.fosse-at-bjt-dot-net]
Sent: Sunday, April 05, 1998 8:43 PM
To: Tesla List
Cc: tlogsdon-at-conbio-dot-com; MALCOLM-at-directorate.wnp.ac.nz; rwstephens-at-headwaters-dot-com; 100624.504-at-compuserve-dot-com
Subject: Re: Wood Welder TC
>From: Thomas McGahee [SMTP:tom_mcgahee-at-sigmais-dot-com]
>Sent: Thursday, April 02, 1998 7:11 AM
>To: Tesla List
>Subject: Re: Wood Welder TC
>I have rehabilitated a few diathermy type machines that also were
>about 50 years old. I have found that some of the insulative
>materials had degraded to the point where they had to be
>replaced. Specifically, my units had some rubberized insulation
>that had become brittle from age and ozone. Replace such
>parts with newly fabricated parts. Yes, coax type wiring will
>usually require replacement with new coax.
>I also replaced all wooden parts with plastic/plexiglass, as I
>was concerned about moisture. These diathermy machines operate at
>high frequencies (as regards TC use), but you can make a very
>decent tube TC with them. I always enjoy working on the older
>machines, and it is a thrill when I get them operational again.
Thanks. I may even learn to subtract 1998-1958 = 40 years
old;( All of the plastics used in this unit appear to be in great
I open the unit up today and cleaned as much saw dust as I could get
out without actually washing it out.
I found that the last "shade tree mechanic" had installed the coax-ax
connector incorrectly. It was shorted! This connector is a _Wood
Welder_ manufactured item. A banana plug was soldered to the center
conductor of the coax and a brass tube was slipped over the dielectric
and under the braid. The last person to work on it had slid the brass
tube so that it covered the banana plug also.
I found that the 833As filament connectors had fatigued and 3 of the 4
had broken. I used "bailing" wire to firm up the contacts until I can
find a source for them. Does anyone have a source for filament
connectors for 833As? 833A sockets?
The rectifiers are 2 866s. One filament is visually much weaker than
the other. I'll need to replace it.
I powered it up. I can now adjust the plate current with the variable
cap in the head. I then tried to weld wood with it. No joy;) This
unit will heat wood up right quick but not "weld" it. I then placed a
bead of _Elmers Glue All_ (PVA based wood glue) between two pieces of
wood. It dried in 10 or 15 seconds flat. Amazing what a kilowatt of RF
When I opened the head up to disconnect the coax, I found that they
had placed a NE2 in the handle to give a visual indication of output
power -> correct tune. It does work. Any time I go above 450mA plate
current this NE2 lights. It only has 2 short wires near the head's
tank circuit for pickup.
I still don't know what this unit was meant to heat but, it will make
a grand tube TC. I paid $20 U.S. for it.
This morning I visited my nearest HAM swap meet and picked up a dual
250pF air variable cap. It has a 0.2" air gap between the plates. Any
thoughts what it's max rated voltage would be? In Shell dial-ax
transformer oil? It has had some minor arcing in it's past life;)
jim the wood welder - NOT