[Milsurplus] TBW-5 Update

[Mark K3MSB]

Hi All

I received a few questions about my TBW so here's my attempt to answer
them.

The TBW-5 is running nicely on 80,40,30,20, and 17M with 200W output
(slightly less on 17M).

My wife and I drove down to GA in October 2019 to pick up the transmitter
from Bob Lackey W4QBE.  Bob had purchased the TBW from Steve Finelli N3NNG
(Easton PA) in September 2000.   Easton PA is about 3 hours NE of where I
live, so it took 20 years for the TBW to make the round trip from PA to GA
and back to PA.     I don't know if Steve is still around, but I plan on
contacting him for the history of this TBW before 2000.   BTW, Bob and his
wife were very gracious hosts;  it was nice visiting them.

The TBW has a distinctive chirp which is probably due to the fact that the
HB regulator installed on the grids of the OSC tube isn't working.   The
chirp gets a lot of nice comments though.  My ARC-5 transmitters also chip
a bit, and I've found there is a sizable subset of the ham population that
doesn't know the difference between a chirp and a T6 tone.

When I picked up the transmitter, Bob gave me at least 6 completely hand
drawn schematics that represented what his HB circuits (PS, Keying, spot
etc) were like at various stages of the transmitter's life.   He fully
admitted that he wasn't sure which was correct,  so that's been one of the
challenges working on this radio.   Also, he nicely gave me his thick
binder of documentation for the radio for the 20 years he had it.

Bob demoed the radio and it put out 200 watts on 40M.    When I put the
radio on the air (which was about a year later.... 2020 had it's challenges
as we all know),  it was indeed putting out power, I just couldn't figure
out where!   I searched and searched with my SDR but was never able to find
out where.  Also, the keying was a bit intermittent. Knowing what I know
now about tuning the TBW, I think the signal not being where I expected it
to be was cockpit error on my part.  The keying was intermittent, and the
transmitter would not follow the keying if I went above about 7 WPM.

Bob had added some circuits to keep the OSC running all the time as well as
a SPOT switch – implemented differently at various times as per the various
schematics  He said there were a few switches on the PS that were not
connected....  but they actually were.....   So, I made the decision to
remove all the non-stock additions and key the transmitter as close to the
original way as I could.      That involved grounding R-213 which
originally was attached to the CT of T-202 in the Modulator/Power Supply
unit (which I don't have).    In the keying circuit that was in the radio
was a notation of R-213,  but R-213 was missing.   So, my junkbox had the
correct reisstor and I added it to the PS front panel and I am keying the
transmitter by grounding it.  Keying is now solid, and I have no trouble at
my normal sending speed of between 15 and 20 WPM.

There are several power supplies in the PS “Cart”.  The HV is controlled by
a variac on the bottom left of the PS cart which feeds a transformer (2260V
270 mA secondary) that powers the HV supply.   I need about 1200V DC to get
200+ watts output.   I normally run around 100W and that requires between
600 and 700V.   A second variac on the mid-left of the power cart controls
the HV supply (500V).   There is a bias supply as well as the filament
transformers.   Bob did a wonderful job on that power cart.    The only
drawback is that the power cord is not grounded due to ground loops.
There is the AC ground,  HV ground and chassis ground.   The ground issue
makes me uncomfortable.   That, and the fact that I would like to have the
TBW on one of my operating benches, has led me to decide that I will
rebuild the power supplies and address the ground issue.   But first....

The original 803 was replaced with an 813.   I plan on restoring the 803.
I have an 803, but no socket... more on that later.....  I want to get the
803 working before I rebuild the power supply so that needed power supply
changes can be addressed only once.

There are some other issues, such as R-312 is missing as well as it's
supports on the back frame.  This isn't a big issue, but the point is I
want to restore the TBW to as stock as I can,   verify it runs,  then
rebuild the PS.

I have a pair of RBM-5 receivers with power supplies awaiting restoration
and they will be paired with the TBW (although using my Drake 2B/2BQ with
the TBW is one fun station to run!!!).

Bob gave me his HB AM Modulator.  I'm not sure if he ever used it or not,
and it may be a prototype for a friend who may or may not have used it (I
can't remember what Bob told me).  It's based on ART-13 components and is
in rough shape --- but it's all there (sans tubes).

It would be nice to have the TBW and at least one RBM on the air at Gilbert
PA (if it occurs this year).

Many thanks to Howie WB2AWQ, who uses a GO-9, for being a sounding board
and providing technical help.   We've had a few GO-9 to TBW-5 CW QSOs
already on 40 and 80.


73 Mark K3MSB
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