[Milsurplus] Powering the TBW-4

[Mark K3MSB]

 Ray and K4CHE --

I have not ignored comments and web sites;  you both have gone down paths I
was going to take that didn't lead anywhere, so I'm revising my design.

I started to use "PSU Designer" and I was able to simplify some of my
designs.  I plan to blatantly steal some of the good ideas you guys have!

More later!

73 Mark K3MSB







On Fri, Jun 14, 2024 at 9:32 AM Ray Fantini <RAFANTINI at salisbury.edu> wrote:

> L303 and 302 are important for the function of the oscillator, keep them
> in there. Also remember that the path to ground for the osculator is thru
> R213
>
> The cathode of V-301 is the return path for the osculator and you will
> need all that junk for it to work. I just used a regular 24-volt center
> taped transformer with the original circuit.
>
> I was able to build both transformers onto the bottom deck but only used
> the filament rheostat R201 for the 10 volt transformer for the 803, at
> first was worried about preserving the 803 but later learned that the 803
> is just about indestructible. In tune mode they keep the 500 volts applied
> to the screen of the 803 but remove the plate voltage, that would kill most
> power tubes but the 803 just sits there like its nothing! Brought this up
> years ago but have to say that I have never seen a failed 803 or know
> anyone who has.
>
> The second deck was used for the 500 volt supply all standard construction
> but I kept the original idea of keying the incoming AC to the HV and Plate
> supply and discovered that when they did this with 800 cycles the size of
> the filters were small but at 60 cycles the larger filters provided enough
> DC after you released the PTT or Key that you would hear the MO drift down
> the band. For that reason, I installed external bias at K301B that kills
> the oscillator and IA stage when the key is up. M301 is a good point to
> interduce bias, just remember that when K301B closes it will short the
> output of the bias supply to ground so you will need a current limiter on
> the bias line.
>
> R205 is in the negative side of the 500 volt supply to ground to develop a
> small negative DC voltage. In CW mode the suppressor is grounded and in AM
> its routed thru T204 and dumps a bunch of audio on the suppressor grid to
> produce modulation. Don’t think I got more the fifty watts or so in AM
>
> I did an external plate supply being it would be just about impossible to
> do the plate supply in that limited space.
>
>
>
> Thought Exercise:
>
>
>
> Is the TBW a repackaged TDE? Much of the TDE is similar to the TBW, was
> the TBW and attempt to build a light weight TDE for shore operations? What
> about the GO series that were in things like the PBY? What came first? TDE,
> TBW  or GO?
>
>
>
>
>
>
>
> Ray F/KA3EKH
>
>
>
> *From:* Mark K3MSB <mark.k3msb at gmail.com>
> *Sent:* Thursday, June 13, 2024 5:49 PM
> *To:* Ray Fantini <RAFANTINI at salisbury.edu>
> *Cc:* milsurplus at mailman.qth.net
> *Subject:* Powering the TBW-4
>
>
>
>
>
> Hi Ray
>
> My RMU had two of the three 800 Hz transformers missing.    Since I will
> be running my TBW off of 120 VAC I decided to get rid of all remaining 800
> Hz related parts and wiring.    This resulted in the bottom deck being
> completely devoid of parts and the middle deck almost free of parts.   The
> middle deck still has R-219 which is still needed but can easily be
> relocated.   I've attached two photos.
>
> I plan to mount all new transformers (except the 2 KV supply) onto the
> bottom two decks of the RMU.    This will be the 500V supply as well as the
> 2.5V, 10V, and 12.5V Filament transformers.
>
> At present, I plan to have all primaries go through the Filament Rheostat
> control.
>
> The two 837's require 12.6V for the filament but they are fed by an 18.6
> VCT secondary off of  the non-existant T-202.  I think this increased
> voltage was needed due to the voltage drop in L-302 and L-303 in the
> Oscillator filament circuit.    I think this then required dropping
> resistor R-213 in the filament circuit of the Intermediate Amplifier.   I
> plan on bypassing (shorting) L-302, L-303, and R-213 so that I can use a
> standard 12.6V transformer for the two 837's.
>
> The 2 KV supply will be external to the RMU and will be fed in via a new
> plug on the bottom of the RMU, then to S-208C.     The new 500V supply will
> feed S-208B.
>
> What I still haven't figured out yet is what voltage the 803 suppressor
> needs on Phone.   This voltage is developed from the non-existant T-203 HV
> secondary CT via the bias adjustment pot R-205.  There is nothing in the
> manual about adjusting R-205 (or maybe I'm not seeing it....).  Looking at
> the 803 data sheet,  for 2 KV plate voltage in Suppressor Modulated Class C
> phone operation, I'd need about -110V on the suppressor.     Still not sure
> of this area yet,  but I should have room for a bias supply in the RMU.
> The bias supply would feed into the ungrounded end of R-205 then to the 803
> via S-209A in Phone operation.
>
> The front panel AC ON/OFF and DC ON/OFF switches will be used as intended.
>    Both required a good bath in DeOxit for them to work  (Well, they are 85
> years old.....)
>
> I plan to repurpose some of the 4 front panel AC Compensation SPST
> switches.
>
> One will be for a  “TX/RX” switch for lack of a better term.   In TX,
> relay K-301 in the HF transmitter will close as it's supposed to do.
>  Except.....   I plan to ground the Oscillator with a new modern relay
> instead of K-301B.    That new relay will be controlled by the key or mic
> switch from the RMU.
>
> When receiving, the 2KV and 500V power supplies will still be providing
> voltages to the 803, but the oscillator will not be enabled.   I was
> discussing this with Howie and we feel this is OK as long as plate
> dissipation is not exceeded, and that concern may require me to run less
> than 2KV on the plates.
>
> I ran a TBW-5 for a few years with 1200V on the plate and that gave me
> more than 100W output on CW which is adequate for my needs.     Running
> phone with the TBW will be a new experience for me.
>
> Any and all comments welcomed.
>
> 73 Mark K3MSB
>
>
>
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