Harvey Wells TBS-50C

[iw5ci]

I falled in love with this lovely trasmitter when i saw it in a old book, so i got one on ebay last week and i am waiting for this little rig.
At first i have to build a suitable power supply, can someone give me a simple schematic of the supply and specs for the transformer? (i would like to use as much what i have in the garbage bag ).
My project is to put in a single box a power supply and a small DDS generator for vfo function.
Any help will be apprechiated.

[KX5JT]

http://bama.edebris.com/manuals/harvwels/tbs50bcd/


You'll need a djvu viewer, they are free.

[WQ9E]

After you follow John's link from the post above and download the transmitter manual then go to the parent directory for Harvey Wells and you will find the schematic for their APS-50 supply which was the official (and very simple) Harvey Wells supply for the TBS-50 series.

As you will see in the TBS-50 manual, it will run on a wide range of B+ voltage from 275 up to 425 volts but you have to wire the correct resistors/jumpers on the terminals on the back of the transmitter.  It is a very good idea to build a protective cover for this terminal strip since dangerous HV is otherwise exposed.  Since it was designed for mobile service the filaments can be run from either a 6 or 12 volt supply, AC is fine.

If your unit is a TBS-50C, it requires a carbon microphone.  The TBS-50D has a built in preamp for a dynamic mic and the TBS-50B was built without the modulator components.

It is an attractive little transmitter and very versatile.  It can work on 80 through 2 meters and there is a modification to put it on 160.  On 2 meters the output is minimal to put it mildly but I think it was the only transmitter of the time that would (intentionally anyway) provide output from 80 through 2 meters.   

[N0WEK]

After you follow John's link from the post above and download the transmitter manual then go to the parent directory for Harvey Wells and you will find the schematic for their APS-50 supply which was the official (and very simple) Harvey Wells supply for the TBS-50 series.

As you will see in the TBS-50 manual, it will run on a wide range of B+ voltage from 275 up to 425 volts but you have to wire the correct resistors/jumpers on the terminals on the back of the transmitter.  It is a very good idea to build a protective cover for this terminal strip since dangerous HV is otherwise exposed.  Since it was designed for mobile service the filaments can be run from either a 6 or 12 volt supply, AC is fine.

If your unit is a TBS-50C, it requires a carbon microphone.  The TBS-50D has a built in preamp for a dynamic mic and the TBS-50B was built without the modulator components.

It is an attractive little transmitter and very versatile.  It can work on 80 through 2 meters and there is a modification to put it on 160.  On 2 meters the output is minimal to put it mildly but I think it was the only transmitter of the time that would (intentionally anyway) provide output from 80 through 2 meters.   

On the carbon mic problem...all mics and headsets built for aviation emulate carbon mics. I've got David Clark headsets that have amplified dynamic and electret mics. I haven't measured the frequency response but they sound fine to me. All aviation hand mics emulate carbon mics as well.

[iw5ci]

Ok i got the ps schematics. I suppose i can substitute the rectifier tubes with diodes and put some modern condensers so i can go without the 5v secondary.
For the mic, i have some surplus mikes used with art-13 or maybe i can hook a d104 amplified mike.

[KX5JT]

Thanks Rodger, I was really busy when I read his post, but I figured I'd put the link out there to get it started.

[kg8lb]

 Many of the power supplies from that ERA work well. The Elmac M 1070 , Heath Utility etc are pretty easy to find or duplicate. In the event you cannot locate suitable transformers, you may drop me a PM or an email (Good on QRZ). I have plenty of suitable iron . I like to use Ranger transformers and chokes and have laid up quite a few of them . I also have all the major parts from an Elmac m1070 supply. Of course, the weight factor makes shipping an issue.

  There was an article in ER a few years ago where the guy used common filament transformers back to back with a doubler to make a power supply for the tranmitters of this size as I recall . Another possible is the 110-220 machine tool control transformers that show up.

[k7zmb]

Before applying power to your TBS-50, I would ditch the old paper cap first and replace it with a modern electrolytic. Those old caps can react violently when asked to perform after years of neglect. I would also check the resistors for drift, too.

I've been enjoying my foray into over-engineering an APS-50 replacement. In my enthusiasm for adding all sorts of meters, indicator lights and switches, however, I neglected to realize an important point: there was no safety ground back then. I won't go into details about all the magic smoke I let out of my new filament transformer, but I will suggest you rectify the filament voltage to DC if you're going to ground the case for safety. The radio was designed for mobile, and the filaments on all the tubes will be just fine with DC instead of AC.

For additional safety, put bleeder resistors across B+ in your power supply.

Do note, however, that before you take any of my advice, I still haven't finished the power supply and I just admitted that I already let the smoke out of a perfectly good transformer. Your mileage may vary. 

[iw5ci]

OK. The power supply is done! i had only to replace the strange 2x5K 2W series resistors with a new 10K 5W to revive the TBS-50C.
To test it, i used 2 old BC-221 (i suppose) xtals. One of 3500 khz and one of 7025 khz.
I managed to have about 15-18W output on all bands (80-10 meters).

As i want to use it in our AM italian net at 7190KHZ, i ordered a 3595 KHZ xtal and received some days ago.
I put the xtal in the circuit but it does not work!!! i have no oscillation in 80 meters and 40 meters, but it works fine at 3595x4 3595x6 and 3595x8 .

what's wrong with the crystal? the rig is OK because with the old 3500 khz xtal it works fine in 80 and 40 meters but no power at all (no oscillation) with the brand new 3595 khz.

Has anyone the schematic of the original TBS-50C vfo or can i adapt for example an heathkit VF-1 vfo?

http://www.youtube.com/watch?v=unESceyGETM

[Pete, WA2CWA]

Maybe the crystal was ground to be used as a 3rd overtone type crystal.

[KA0HCP]

Andrea,
The answer to the crystal is on the index card on the face of the radio.  More detailed information is on page 2 and page 3 of the radio manual.

80m Bandswitch:  frequency output is same as crystal frequency
40m Bandswitch:  frequency output is 2x crystal frequency
20m Bandwsitch:  and above  output is 3x crystal frequency.

I will give you a link to the VFO schematic and instructions.  It is a very simple circuit.

[KA0HCP]

http://bama.edebris.com/manuals/harvwels/vfo/

VFO instructions on BAMA Mirror.   If you have problems with the format, let me know and I can post them separately.  It is only 3 pages.

ciao, Bill

[iw5ci]

Thank you! I will work on the vfo circuit but i Also want to use a crystal.
When i asked for the custom xtal, i asked simply for a 3595 crystal as stated on the hw card. 3595x2=7190. And a could also use it on fondamental 3595 . Infortunately the xtal works only from third armonic. Which kind of crystal i have to ask for ?
May i also use a dds generator ( i have one with a display than maybe i can use instead of the xtal?!

[Pete, WA2CWA]

Which kind of crystal i have to ask for ?

Fundamental type crystals

May i also use a dds generator ( i have one with a display than maybe i can use instead of the xtal?!

I've used signal generators as a VFO. Capacitor coupled it to the crystal socket terminal(high side). You might need a 100 or so ohm resistor across the crystal socket terminals.