Homebrew transmitter progress updates

[W8ACR]

I will be posting updates here on the progress of my homebrew transmitter project.

Update#1. After looking at the picture of the control deck that I posted yesterday, I decided that it needed a bit of polishing. Today I removed all the lacing  , redid some wiring, and carefully relaced it, and it came out looking much better. Looks more organized and precise. New pics and a schematic are posted below.

Ron

[W7TFO]

Nice work.

I like the plug fuses and big pilots .

Chincy indicators (read LED's) just beg to be trash .

73DG

[W2VW]

FB layout. Looks relatively easy to troubleshoot.

Consider treating those MOVs across the mains as lit matches. They can flame out during a nasty surge event. If they are not physically contained bad things can happen.

I learned this from a ham who installed these thingies on all the electronics in his home. The place didn't burn to the ground but everything was smoke and water damaged.

[WD5JKO]

Nice control chassis! I like it.

Consider treating those MOVs across the mains as lit matches. They can flame out during a nasty surge event. If they are not physically contained bad things can happen.

  What MOV's? I see 110 volt indicators...

Jim
WD5JKO

[W8ACR]

This rig will be 1940's technology all the way. No MOV's or any semiconductor devices. What you see here are relays, fuses, switches, and 120VAC lamps. One more pic - front view.

Ron

[W2VW]

Looks like two light blue guys on the 3 terminal strip at the chassis rear. I've been wrong before.....

Read the schematic and they are called out as .01 caps

[KA0HCP]

Looks ship shape and spiffy!   The screw in fuses are a nice touch.

[K9PNP]

Good job.  Definitely my kind of construction.  Looks prettier than mine, though.

Yeh, disk ceramics now come in blue.

[K1JJ]

That is so commercial buzzardly it hurts!

Where did you get that old cloth wire and string tie?  Even added the number ID's.  Cool.

Easy to service. My kind of layout.

T

[W8ACR]

Hi Tom,

Some of the wire came from an old BC FM transmitter that was junked out of Minot ND a few years ago. I bought a spool of authentic 1940's cloth covered wire on Ebay a couple years ago (I won't do that again- $1.00 to $2.00 a foot!), and three old buzzard members of this website have graciously provided some from their junk boxes as well. I think I have enough to finish the project, but it'll be close. I have miles of newer wire, but I hope to use only real antique wire in this project. The waxed cord was obtained at the W0ZUS auction - three nice big spools of high quality waxed cord, strong stuff. The stick on numbers are a nice touch that I wouldn't have thought of, but I got a big stash of these also at the W0ZUS estate sale. They really do help in tracing wires around the deck.

So far, I'm pretty happy with how things are developing, and with the appearance and function of the first deck.

[W8ACR]

Update #2 - Rectifier deck is finished except for the plexiglas window and the leads for the plate caps. This deck will house the four 866's behind the window. Two will serve the RF final power supply which will be below, and two will serve the modulator power supply which will be above. Check out the ultra cool authentic vintage "radioactive" indicator lights.

Ron

[Ralph W3GL]

You might have a problem with the transformer on the left side,
looking from the front panel...   The filament output needs to
have better HV stand-off (lack of insulators).  The other one
looks okay.      (The key word here is "might", YMMV...)

Remember, you have the full HV to ground on the filament winding...

[W8ACR]

Hi Ralph,

That transformer is a Kenyon T-360. It is rated for 5000 VDC on the secondary. Also, you can't tell by the picture, but the wire leads are well away from the chassis ( 1/2 inch or so). That transformer will have about 1000 VDC on it. I think it will be OK. I do have some spare filament transformers, plate transformers, and 866's just in case. 

The other transformer will have 2000 VDC on it. Hence the beefier insulators and Packard 440 wire.

Ron

[W8ACR]

Update #3 - Tonight I mounted the components for the RF final HV power supply into position. The components are bolted directly to the floor of the 6 foot cabinet. The plate transformer is a Thordarson T15P19 which provides for 2500VDC@300mA. The chokes are a Stancor C1403/1413 pair. The HV capacitors are 4uf@3000V. The bleeder is 50K@225W. The picture shows the components in their mounted positions. Plate transformer to the left, chokes in center, caps to the right and bleeder in the rear. The large choke at bottom right is a Dahl 50H mod reactor rated for 275mA. The rectifier deck described earlier is in position above the power supply. The modulator power supply will be the next deck above the rectifier deck. The RF final plate transformer primary power will come via an 18Amp variac so I should be able to vary the final plate voltage from low to 2500VDC.

Ron

[W3RSW]

Very nice.  I'm envious.

Slight aside:  IF you are going to run AM exclusively with this rig, no CW, why do you need a stiff 50k bleeder in the plate circuit drawing 125 watts?  The class C final will be drawing pretty stiff current. Oscillators, buffers, etc. in Class A will be drawing constant current too.  I'd use just enough bleeder to safely draw down the supply caps after "turn off" in a decent time interval.  Of course, you definitely need some bleed for a supply that is severed from the load.

A good bleeder or regulated supply is desired in a screen circuit supply.

[ke7trp]

I think its a better option to put a thick wooden floor into the bottom of the rack. Then use short course screws to mount the iron.  This way, they are insulated from each other and the chassis. Mine uses 1 inch thick MDF wood used in counter tops. Maybe thicker.. Cant remember. It was scrap.

C

[ka4koe]

Do you have the entire design worked out? I"d be VERY interested to see what your doing. OR, is this a one piece at at time deal?

Philip

[W8ACR]

Hi Philip,
  
I have the design figured out in my head, and I have most of the schematic drawn out. This will be a 160/75/40 meter transmitter.  I'll give you a brief overview here.

1. 1st six foot cabinet will have the following decks - 2500VDC PS for RF final, rectifier deck, 1000VDC PS for modulators, modulator deck, speech amp deck, 300VDC commercial regulated PS (Lambda 0-324).

2. 2nd six foot cabinet will have the following decks - Variac deck (housing a 22A and an 18A variac), control deck as shown above, Meter panel, RF final bias/filament deck, RF final deck.

Tube lineup is as follows:

Rectifiers: 866A's
Speech amp: 6SJ7, 6J5, PP6A3's
Modulators: zero bias 811A's
RF exciter: Johnson Viking 2/VFO
RF final: 254W @ 400W input, pi network tank circuit with grid neutralization

Transformers: Driver: UTC S-9 (or an LS 47 if I can find one)
                      Modulation: UTC S-22
                      Mod reactor: Dahl 50H@275mA
                      Audio capacitor to use with mod reactor 2uf@6kv

Ron

[W8ACR]

Update #4 - 3/21/13 - Got the rectifier deck finished, and most of the RF HV power supply wired up. Need to wire the primary side of the plate transformer yet. Pictures show the ps/rectifier deck from both the front and rear. The front panel has been removed to show things from the front.

Ron

[W8ACR]

I also have two preliminary pictures of the second cabinet. Form bottom to top. Variac deck, control deck, meter panel, bias/filament transformer deck, RF deck, window space. The RF and bias decks were built about a year ago. I am going to make some minor changes, but they should be relatively easy to finish.

Ron

[W9GT]

Looks great Ron!  Assembling those old parts is like stepping back in time and I'm sure you will enjoy the rig when you get it on the air.  Your pictures and descriptions are good info for all of us who are, or may be in the future, building home brew rigs.  I'm chipping away at a pair of 6C21s modulated by a pair of 304TLs.  Lots of drilling and blasting work to do, but I am going to get some assistance from a fellow amateur who has a machine shop and has volunteered to help me cut some nice neat panel holes.  I'm planning to have plenty of viewing windows for the tubes and especially the mercury vapor rectifiers.  They will provide quite a light show........then when I'm interested in saving energy  , I can insert the diode strings.  I will try to post some pictures when my project progresses a little farther.

Good luck with your transmitter and we hope to hear it on the air soon!

73,  Jack, W9GT

[W3GMS]

Great job Ron!  Unfortunately, I can't help you with the LS 47 driver xmfr your looking for, but let me know if you need any parts as you complete the project.

Joe, W3GMS

[Opcom]

Won't the UV from the 866's cloud or haze the plexiglass window? How about a real glass window (not quartz because it will pass the UV if you worry about such things). It could be held in place with little clips or something. The TX is so beautifully made, why not use a nice 1/8" to 1/4" thick piece of glass. Why spoil it with plexiglass!

[W8ACR]

Update#5 - 3/22/13 - I wasn't completely happy with the 2500V power supply wiring, so I redid it as shown in the photos. Laced it all up when I finished it. I also moved the bleeder to the back of the cabinet. Rick, I found an 82K/200W resistor to use as a bleeder, so I adopted your suggestion of increasing the bleeder resistance. There was no particular reason that I used a 50K at first. Patrick, good suggestion about using real glass. I think I'll do that.

I also added a 0-4000V DC voltmeter to the bottom front panel. That is quite a chore cutting a hole in a steel panel with a hole saw and a hand drill. There is now a 4meg dropping resistor for the meter on the floor where the bleeder used to be.

Ron

[W8ACR]

Two pictures of the front showing the voltmeter.