Questions about the Harvey Wells Bandmaster

[n0tjl]

Hi Elmers,
I recently bought a Harvey Wells Bandmaster TBS-50C and I want to use a Heathkit HP-23 ps to power it. I am somewhat a newcomer to restorations so I need fairly detailed instructions. I have had some success at rebuilding tube receivers over the past few years but I have never tackled a transmitter. My goal is to set up s "50's" station using the Bandmaster and my R390a. Any help would be greatly appreciated.
Regards,
Tom N0TJL

[WQ9E]

Tom,

Are you willing to dedicate the HP-23 to the TBS-50 rather than using it to also power other rigs in its stock configuration?  If so I would rewire the HP-23 HV supply from a voltage doubler to a full wave bridge and use this section to power the TBS-50.  Set up as a normal full wave rectifier I would expect around 350-375 volts under load with reasonable size filter caps.

The LV supply of the HP-23 is a little marginal to power the TBS-50C, the LV transformer secondary and filter choke might stand up to the current OK but the TBS-50C is well over the normal rating for the HP-23 series LV supply and the voltage is going to sag considerably.

[n0tjl]

Thanks WQ9E,
I'm not sure exactly how to do this. Is there detailed info on this process somewhere that I can access.
Regards,
N0Tjl

[w4bfs]

this is what separates the men from the boyz .... get a schismatic of the hp23 and get one of the ham radio handbooks and get into the section on power supplies ... start comparing and list yer questions .... you can do this !

[n0tjl]

Hello W4BFS,
I have the HP-23 schematic and the Bandmaster ps schematic. Would this be a good place to start?
Thanks,
Tom, N0TJL

[w4bfs]

yes .... start comparing .... Rodger is spot-on about use of the hp23 .... what needs to be done first is to determine what voltages are used for receiving and then for transmitting .... a lot of rigs from that era switched on power amp stage b+ during transmit .... see what is going on in the HW ps .... this will jump start the process

the longest journey begins with a single step and ends with the same

[n0tjl]

Great, I'll get on with it.
Thanks,
N0TJL

[WQ9E]

Tom,

The ARRL handbooks from the mid-60s through mid-70s will have a theoretical explanation of various rectifier configurations (half wave, full wave, full wave bridge, etc).  along with practical circuits using them and the same is true of the Orr "west coast" handbooks of the same era.  I prefer Orr's writing/editing but either from the era are good.  Some of the earlier ARRL and Orr books are available as free PDF files on the web but I am not sure if any of the later ones are available.  A large library might have them available or you can find them on ebay or at hamfests.  A few of these are a very worthwhile addition to your technical library and you will use them frequently in the future.

If the HP-23 filter capacitors are original you will want to replace them during the modification.  With the HV winding reconfigured to a full wave bridge, 450V rated will work fine.

Since the TBS-50 was originally often used as a mobile rig, for an authentic station you could add one of the mobile receivers (Multi-Elmac PMR series, Heathkit MR-1, one of the Morrows, etc.).  You will find that for most of these receivers the low voltage supply of the HP-23 will be about right so you slightly modified HP-23 is the basis for a versatile setup for many pieces of vintage gear.

[RolandSWL]

http://www.heathkit.nu/heathkit_nu_HP-23B.html

It seems the HP-23 came in more than one flavor.

RSWL

[WQ9E]

The basic design was pretty stable over the years.  A switch was added so that the LV level could be chosen (and the supply could be turned off via that switch) so that rewiring wasn't needed to select voltage and the next version removed the variable bias feature from the supply since Heathkit provided the bias pot in the gear.  This made it easier to share the supply between multiple pieces of gear, having the bias pot in the supply instead was preferable when a single rig was switched back and forth from mobile to fixed station use.

The HP-23 series supplies are well designed and reliable as long as they are maintained (basically replacing filter caps as needed).  A version of this supply was built into the SB-400/401 transmitters.

Some of the most versatile external supplies were the Swan series and these are great supplies that can be used with a lot of rigs.  I also picked up 5 older Galaxy supplies at a hamfest several years ago and I have used these with several homebrew and commercial rigs.  I will be rebuilding something soon to go with a Trio TS-510 transceiver I acquired without its power supply.  The TS-510, also sold as the Allied A-2517, has a somewhat unusual external power supply which contains a fairly high current 150 volt regulator using a 6BM8 with a neon bulb reference source.

[n0tjl]

I do intend to recap the HP23 asap.
Regards,
N0TJL

[N2DTS]

Drake also made a nice supply, same basic setup as the Heathkit one.
I picked a nice homebrew copy of a Drake supply with a very nice large Hammond transformer in it for $15.00 on ebay.

[WQ9E]

Drake also made a nice supply, same basic setup as the Heathkit one.
I picked a nice homebrew copy of a Drake supply with a very nice large Hammond transformer in it for $15.00 on ebay.

I agree about the Drake supply and that was a great deal on the homebrew copy!  Drake supplies usually sell at a premium price, probably because not as many Drake T-4 and TR-3,4 series are getting parted out as some of the other brands so there isn't a supply surplus.  I used a Drake supply for quite awhile to run my Gonset G-76, the only major change was the addition of a relay and snubber network for switching the HV output off for receive as is done with the real Gonset supply.  A few years ago I found the proper Gonset supply and the Drake supply was re-tasked to power a TR-6 with TC-2 setup.

[n0tjl]

Hi W4BFS,
HW requires 300 or 400V 275ma and 6V or 12V for the filaments.
HP23 delivers HV of 700V 250ma and LV of 300V 150ma and 6.3V or 12.6V for the filaments. The went on to say that on the LV high tap the duty cycle is continuous up to 175ma. What do you think?
Thanks,
N0TJL

[WQ9E]

Tom,

Keep in mind that if you reconfigure the HV doubler to a full wave circuit you can safely draw about double the current it is rated for in its current configuration.  That winding is much better suited to the demands of a TBS-50C running in AM mode.

The LV supply, even on the high tap, is going to be well under 300 volts under a 275 mil load which greatly exceeds its design parameters.  It would be OK for a TBS-50 running only CW but not for operation on AM.

Please keep in mind that the TBS-50 has exposed HV on the back so be careful and if your household has small children or pets it would be a good idea to at least use electrical tape over the exposed terminal strips.

[n0tjl]

Hi Roger,
This old HW can't have been operated for a long time. It took a bit of penetrating oil to free the bandswitch shafts. It might be a good idea to bring it back to life on CW first then move on to AM. To accomplish this, can I just wire an 8 conductor female connector on the xmtr end of the HP23 power cable and insulate off the unused conductors? I thought I would attach a plexiglas rectangle over the exposed contacts on the back panel of the HW.
Thanks,
Tom N0TJL

[WQ9E]

Tom,

For getting it going on CW that should be fine.  Set the switch on the back for 350 volt output and leave the bias and HV leads from the HP-23A disconnected.

Even with crystal control I wouldn't be surprised if there is some chirp when keying the TBS-50 on CW because the HP-23 as configured will have a significant change in output when keyed.  It may be OK on crystal and would be fine if driven by an external VFO with its own power supply.  Once the HP-23A supply is reconfigured to use a heavily filtered and lightly bled HV supply then the voltage regulation should not be an issue.

Good luck!

[n0tjl]

Rodger,
That sounds good. If I can't get it going on CW, it will never work on AM. I intend to use crystal control and am surprised that the proper crystals are so hard to find. I bought some crystals that were fairly close to frequency and ground them into the amateur bands. I used the signal generator - frequency counter - oscilloscope hookup to check grinding progress. This system works great. I am looking for an original HW VFO, I hear they are rare and expensive.
I appreciate the help.
Thanks,
Tom  N0TJL

[N3GTE]

Hey Tom
On the VFO the VF-1 is a good choice and not real expensive. Ive found that the H-W VFO drifts pretty badly. Have had three of them. Useable on 80mtrs 40 you have to retune about every 10 secs forget the higher bands.
P/s output need to be 475vdc or less. If you run more bad things will start to happen. Tank components will flash over and sometimes the modulator tube sockets will arc too.
GL Great and fun transmitters
Terry N3GTE
http://www.swedeart.com/harvey/html/n3gte.html

[MikeKE0ZUinkcmo]

Rodger,

Your TBS is a really nice looking, and I suspect earlier example, because of the much better looking name plate.  

Mine went under the "knife" at what appear to be several times in the past and was pretty messy inside.   Although its a "C" I got it with the mic preamp chassis, which hadn't been installed.

[WQ9E]

Mike,

That is a nice TBS-50 you have also!  There are a lot of ragged looking ones out there and I bet a lot of them were run in mobile service and have the battle scars to prove it

If they had continued making these transmitters with a simple power supply kit I bet they could have sold a few to the growing novice classes of the later 50s.  The basic style, particularly with the VFO base, with a new color scheme and knobs would have looked right at home in the late 50s and early 60s.

[n0tjl]

Thanks everyone for the help. I have another question, what is the connector on the top of the TBS-50 used for? I have seen these transmitters in use and have never seen anything connected there.
Regards,
Tom

[MikeKE0ZUinkcmo]

what is the connector on the top of the TBS-50 used for?

If you're talking about the RCA Phono plug mounted on the pair of 2" spacers just behind the short tuning capacitor, its the 2 meter antenna connector.

[n0tjl]

I overlooked the two meter section of the manual so I missed that part. Thanks for the info.
Regards,
Tom N0TJL

[WQ9E]

Harvey Wells was several decades ahead of the modern Yaesu and Kenwood "DC to daylight" rigs  

Although the power is very limited on 2 and efficiency is poor forcing the input to be strictly limited it was a pretty big accomplishment to sell a rig that cover 80 through 2 meters and could be modified to operate on 160.