[ARC5] TBW-5 Update

Fri Mar 26 18:50:33 EDT 2021

 Anybody looking for another one of these?I know where might be a transmitter only , but in very good condx.

    On Saturday, March 13, 2021, 4:26:38 PM EST, Christopher Bowne <aj1g at sbcglobal.net> wrote:  

 Great to hear about the TBW and even
more about Bob.  He used to be one of the regulars on the Sunday night 2100 Eastern Old Military Radio CW Net, but we haven’t heard him on there in quite a few years.  Can’t recall what rig he ran there but it’s likely at some point it was your TBW.  We’d love to have you fire it up and join us. Of late we have been running the net on 3567 kHz instead of our long standing 3570 kHz frequency due to the digital invasion of that part of the band.

73 de Chris AJ1G
Stonington CT

Sent from my iPhone

> On Mar 13, 2021, at 12:26, Mark K3MSB <mark.k3msb at gmail.com> wrote:
> 
> 
> 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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