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VE3LYX
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« Reply #25 on: January 10, 2013, 11:18:38 PM »

Thought I had problems with a shorted cap or something. I had reworked my bench supply to run both the BC 454 recvr and this ARC tx for testing etc. I kept finding it keyed when I hadnt keyed it so before Christmas I set it aside till winter really hit. Today because of that thread Tim VE6PG had on the old Bellradiophone I was tempted and succumbed to the urge to pull my single tube 45  TNT transmitter out, fire it up and put it on air. I used the same supply. Strange, it was live even though the key was up. Same trouble I had when I last worked on the ARC 5. After some voltage checking and finding my new glasses I discovered a solder sliver from the cathode or B- pin of the PS octal socket down to the #7 pin just below it .( I use octal beam power tube wiring for all my power plugs. 2 and 7 for heaters , 3 for B + and 8 for B- . That way any radio can be plugged into any shack power supply without fear.) Anyway when I rewired this one for a separate plug for the ARC 5 stuff I had a solder drip making the connection between cathode B_ and pin 7 of the heaters. So the heater was grounded and it just happened to be the right one by chance. The PA cathodes were grounding through the heater as well, bypassing the CW key and jack completely Probably nothing wrong with the radio. Just all caused my this accidental goof on my part when I went from twist together test set up to properly connected and soldered. I had set the radio aside for a better time as I didnt want to risk ruining it. Good thing I did. I will dig it out again next week and get it going. First with Cathode modulation (after a bit of CW of course! ) and then perhaps build a Heising type modulation set up.  Why my resistance to plate modulation? Good question . I know it is the best  but I just cant bring myself to use two radios(one Rf and one audio with similar tube counts and probably even the same tubes) to run one. There is another way to do it as well I had heard of but never tried. It does not use a transformer. I may try it on the TNT first to see if it works at all. If it does I will say so. If not no one will ever know.
Don VE3LYX
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« Reply #26 on: January 13, 2013, 12:53:02 PM »

You can also plate modulate which gives very good results. A 12AX7 and a pair of 6L6's work fine. A 12SL7 and a pair of 807's or 1625's work fine with a preamplified microphone or add a 12SG7 or 12SK7 speech amp on a low level microphone. You can use a transformer interstage coupling for phase inversion or an old HiFi phase splitter like this.

I have had the best luck with 2:1 or 3:1 modulation transformers like 6000 CT to 3000 Ohms running higher voltage on the modulators than on the ARC-5.

Mike WU2D

Mike,

Is there supposed to be a blocking/coupling cap between the plate of V1a and the grid of V1b?

Just checking, I like the circuit!

Greg
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CW is just a narrower version of AM


« Reply #27 on: January 14, 2013, 10:04:28 PM »


[/quote]
Mike,

Is there supposed to be a blocking/coupling cap between the plate of V1a and the grid of V1b?

Just checking, I like the circuit!

Greg
[/quote]

Nope Greg,

You can direct couple low level audio stages with tubes or transistors as long as you bias them correctly and you have enough voltage compliance for linear operation.

Mike
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« Reply #28 on: January 15, 2013, 08:19:41 PM »

I'm running Navy (black wrinkle finish) ARC-5 transmitters at one of my stations on 160, 75 and 40. They are powered by a power supply/modulator
I built  with 807's for the modulator. Running 650 volts to the rig and 807's I get 60-75 watts out 100% modulated. I have 250 volts regulated on the VFO and the PA screen comes from a 47K dropping resistor off the modualed B+. watch that plate blocking cap in the PA tank if you plate modulate, best to replace with new before you get to agressive with the B+ voltage. other than that I have no failures in 3 years and the little rigs work great with only minor mods- improved RF bypassing of VFO plate, PA screen and cathode, per an old CQ magazine ARC-5 conversion manual. I chose to leave mine set up for 28 volts, and run 28VDC on the fils and relays. much less invasive conversion that way. 
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« Reply #29 on: January 15, 2013, 09:50:04 PM »

I am running my SCR-274/ARC-5/ATA components mash up using a T-19 or T-22 ARC-5 transmitter, and the SCR-274 BC-456 screen modulator/dyno unit.  I recall that the screen dropping resistor value for the finals is different between the 274 and ARC -5 units, but they are otherwise very similar.  I changed the screen dropping resistor in the ARC-5s to the value used in the SCR-274Ns.  
 

In the last two weeks, I have connected up  a clean audio feed consisting of my old 1968 vintage WB2ZPS Shure Sphere-O-Dyne dynamic mic, octave band EQ, and a small mono utility amp with a 25 volt line output into a military RM-12 remote control unit, which was used to connect remote land line  field phones into things like the BC-191 carbon mic input.  This is sent directly into the all original BC-456 screen mod/T-19 setup.  The result is extremely clean, wide band  near 100%  modulated audio at about 15 watts carrier output.  "Test audio" testing into a dummy load sounds pretty good, better than some of the local FM stations around here (especially WMOS 102.3, where they constantly crank in too much bass and distort the heck out of their audio).. I swept this setup with my HP-201 and it was clean from about 100 Hz to way above 10K at close to 100% peak modulation.  Nice symmetrical envelope, no flat topping, near full 100% positive peaks just prior to hitting the negative peak clipping point .  Another thing that I think helps keep the waveform clean is the use of a impedance matching RF  network that presents a very low impedance antenna feed to the transmitter output , which was what it was designed to work into in the aircraft installations. The network consists of a parallel tuned LC circuit, with the transmitter fed into the coil about 3 turns above the cold end via a 200 pf series cap. Antenna tap is at 6 turns above the cold end. This circuit was presented by Walt,KJ4KV back around 1990 in one of his ER in Uniform columns about the Command sets.  Using this network, I can get about 55 watts in CW out of the otherwise stock dynamotor powered system.
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VE3LYX
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« Reply #30 on: January 16, 2013, 06:50:29 AM »

I am reading this with great interest. So the screen resistor change I assume (rightly or wrongly) cuts it approx 50% which is then added back in at full modulation. I could do that easy enuf if so. I am no whiz on the ARC5 , just learning but it seems to me screen supply is external and I had thought I could cut whats coming in and add it back in audio or have I missed something there.
Don Ve3LYX
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« Reply #31 on: January 16, 2013, 07:19:47 AM »



   I read these posts with interest since I have an original ARC-5 which covers 80m. I do wonder though about the MO-PA configuration, which might have a tendency for the oscillator to 'pull' with PA loading changes, and also some PM or FM when the PA is plate modulated?

   With the advent of SDR receivers, it turns out that some of the vintage AM transmitters DO INDEED have one sideband reduced in amplitude due to oscillator 'pulling' during modulation. My Gonset G-76 does this on 15m with the internal VFO with a MO-Buffer-PA configuration. Using a different VFO or a crystal, and the folks using SDR receivers say the sidebands are equal. I confirmed this issue using my selective Icom R8500 receiver; my LSB was about 30 DB below the USB. So regarding the ARC-5 Xmitter in MO-PA configuration, there has to be an effect here. Has anyone looked at this? For sure the antenna swinging in the breeze will 'wiggle' the VFO.

Jim
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« Reply #32 on: January 16, 2013, 07:41:19 PM »

The ARC-5s MOPAs do wobbulate a little when you modulate, but nothing serious to be concerned about.  With a BFO off, you don't notice it.  Even the BC-191s and BC-375s SBE effect can be tamed by careful neutralization.
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Chris, AJ1G
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« Reply #33 on: January 21, 2013, 02:00:13 AM »

Set up a simple audio monitor circuit today to listen to test audio through the BC-456 screen modulated T-19 using a small signal diode tapped off the O scope and  counter pick up link on the coax between the watt meter, and in this case, dummy load.  Fed the diode output right into the aux input of the duty bench Fisher Studio Standard amp and speakers.  All I can say re the results is whoa!!!.  I thought this little transmitter sounded good through the R-392, but being able to hear the full spectrum without any bandwidth limitations or distortion in the receiver feeding the amp really gave me an appreciation on how good these things can sound. I guess when the entire modulator consists of two transformers and a single ended Class A 1625, there's not too much you can do to screw up what you feed into it!

After an hour of so of pumping 15 watts carrier plus continuous test audio to the Bird dummy load, the transmitter and modulator themselves were not too warm, but the DM-33 dyno was pretty hot, about 165 degrees on the case as read with a infrared surface temp scanner.  What's the typical rated temp rise limit for a continuous duty dyno?
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MikeKE0ZUinkcmo
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« Reply #34 on: February 01, 2013, 12:52:54 AM »

Interesting thread.  

I'm in the later stages of putting together three sets of Tx/Rx units for 160/80/40.   For a modulator I'm using an old SS stereo amp and a 220VAC Filament transformer with a 10V 10Amp C.T. secondary.   Feeding it backwards I get plenty of audio for hi level modulation.  I use a National NCX-5 power supply as a source, and  designed SS regulators to provide all the required operating voltages.   The transmitters put out about 45 watts which is good enough.

I've had the 80 Meter setup on the local morning net with good reports, but need to insert an attenuator in line so I can run it through the NC-2000 linear.  So far, its been a fun project.

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« Reply #35 on: February 01, 2013, 05:59:51 PM »


I've had the 80 Meter setup on the local morning net with good reports, but need to insert an attenuator in line so I can run it through the NC-2000 linear.  So far, its been a fun project.



Mike, have you tried just lowering the output using the antenna coupling control?  OTOH, not sure how that will throw off your loading and linearity of final amplifier.  I assume since you are making 45 watts of carrier that you are plate modulating.  I have a few more 3-4 MC transmitters around, and a few tube mono hifi amps, notably a Newcombe 75 watter running 7027As that i should try plate modding with.   Also going to get the SB200 going again to hang on to the end of the screen modded T19/ARC-5.  That little thing sounds really sweet, but needs a boost from the 10-15 watts carrier it can put into the antenna.
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VE3LYX
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« Reply #36 on: February 02, 2013, 08:21:07 AM »

It was the cap at the top of the coil which isolates the B+ tothe plates from ground. I subbed in a 2kv .01. Hope that value will work. Also during y hunt for the probpelm i discovered one of my1625s is no good. Top where cap is is broken from the glass although one couldnt see that by just looking.
As to modulation I i understand how they were modulated in the past . As for plate modulation , as much as everyone is in love with it, I refuse to build a radio to modulate a radio. And that is about what one s doing. Huge power supplies, Same tubes as finals driver tubes , transformers etc etc. No thanks.
I built a cathode modulator for it as per 1956 ARRL handbook. Some cant say cathode modulator so it is a simple grid modulator which goes beteeen b- and the cathode in any cathode keyed rig. Call it what you will. I heard from many who have used that method with success.  Ben from G call land also gave me a high voltage transistorized version. For a carbon mic whch ilike.
Don VE3LYX
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« Reply #37 on: February 03, 2013, 09:24:49 AM »

Almost sounds like you had a bad experience with a plate modulator or something Don Grin with the refusing stuff and all Roll Eyes

Your choice of course. Have fun.

Al VE3AJM
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« Reply #38 on: February 03, 2013, 09:46:28 AM »

Don said,

Quote
I refuse to build a radio to modulate a radio.

I agree!! Hi-Quality, High Level "Goldburg" Modulation is extremely difficult to achieve.   I think I have about half an hour and 2 bucks in this setup, since both the transformer and amp were given to me.   Roll Eyes

I'll have to get a '56 handbook and look at the cathode modulator.   A fellow on the morning AM net uses one for several different HB and Mil rigs.  



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Mike KE0ZU

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« Reply #39 on: February 03, 2013, 04:39:22 PM »

I suppose it would be extremely difficult if you only had a half hour and twenty bucks...I've built many a HB plate modulator with very good quality and fidelity noted. Smiley 

Al VE3AJM
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« Reply #40 on: February 03, 2013, 05:11:01 PM »

But Al that is you. I am interested in low level modulation of all types.  To me it seems two power supplies, two sets of finals , two drivers  add infinitum is not something I want to do right now. Doesnt float my boat . It does yours and I have no problem with that if it brings you pleasure. Same BTW goes for me with PP circuits. A waste of one tube to my Schwaben brain.
Now I know it is not that simple and that both those have advantages and very good advantages but currently my interest lys elsewhere.
I got the cathode modulator working on my TNT even.  (See cathode modulation thread.) So it should be no problem for the ARC 5.  I also have a single, modulated double triode working on 10M. Still working on it to see how far it will go. Got new tube comong for the ARC 5 and I believe I have sorted out the snag.
Don Ve3LYX
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« Reply #41 on: February 03, 2013, 05:24:22 PM »

Almost sounds like you had a bad experience with a plate modulator or something Don Grin with the refusing stuff and all Roll Eyes

Your choice of course. Have fun.

Al VE3AJM

Of course Don. Thats what makes ham radio and AM fun. We enjoy different things more and less. Pulling your leg. BTW St. Kitts hamfest was very good.

Al VE3AJM
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VE3LYX
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« Reply #42 on: February 03, 2013, 05:32:49 PM »

Buy any ARC5s there?
Don
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« Reply #43 on: February 03, 2013, 05:41:53 PM »

Close..there was a HB pair of 807s tx for $75..I got the Lysco 500/600 VFO/tx..its a cool old rig.

Al VE3 AJM
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MikeKE0ZUinkcmo
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« Reply #44 on: February 04, 2013, 01:01:45 AM »

I've used two different PS/Modulator combinations with the 80m setup.  One using a more or less stock Gonset power supply for the old Twins, and the second using the NCX PS and stereo amp.

Using the Gonset supply/Modulator, It supplies all the correct voltages for the Tx/Rx pair as is, and I only needed to add a fet, source follower after the OA2, to boost the current to handle the receiver and Tx Osc/Buffer.  I also have to pull one 1625s  so the power supply doesn't over load.   This gives me about 20 Watts out.


The NCX setup with the various regulators, gives me 40+ Watts with the Amp/transformer modulator.


The Gonset powered arrangement, with an attenuator, is what I'll use to drive the linear.
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« Reply #45 on: February 04, 2013, 08:02:42 AM »

That is quite a set up Mike,  WOW.
Al I just bought 10 1625s NOS. I needed one for the ARC5 (cap broke (glass also) Now I have a lifetime supply probably. I am thinking a fresh pair in the ARC5 and a quad 4 Linear.
Actually some of these not restorable ARC txs would make an excellant HF PA. Everything is there.  Tuned input (use osc tank) and tank with a pair of 1625s which at 750 volts can give good results. And an antenna tuner included in the package. Wish I had a spare as I would give it a whirl. This one is a functional unit in good condition so I am not going to butcher it although if my triode modulator like I built for the TNT performs  I will remove the calibration Crystal octal plug in and install the whole deal right in the same socket using a 6 volt tube and resistor so I can steal the carbon mic voltage accross the resistor with a diode and 470uf x 35v cap. If I use a metal triode no one would know the difference. Would be a nice compact selfcontained AM /CW rig.
Don VE3LYX
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« Reply #46 on: February 04, 2013, 08:27:27 AM »

Yeah, thats is quite a Rube Goldberg setup that actually works well in those pics apparently...lol....hopefully the 220v/secondary winding thats being used as his mod transformer, and that carries audio and HV B+ has good insulation properties for the obvious reasons.

Sounds like a good score for you Don. So it was the 1625 tubes and more ARC5s?

Al VE3AJM
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« Reply #47 on: February 04, 2013, 11:51:48 AM »

HMMmmmm  Test equiptment porn.......

That is really a nice set up. The 'cubbies fer the stuff, and the table looks like its on wheels.

klc
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« Reply #48 on: February 04, 2013, 12:49:51 PM »

I dont know about more ARC5s. I have been working on my ARC5 project today already though. 6SQ7 tube I think will do the trick. Although I could use a 12SQ7 and just use 12 volts on the carbon mic too. Probably wouldnt hurt it and I could just pop some R in there to cut it back a bit.
Just seemed to me 1625 which are as you know just 12v 807 have a lot of potential. Ancient perhaps but good power at moderate voltage. If one has ten  Well seemed like a good idea anyway. I needed one for sure and it would be smart to pop in a pair keeping the oldy for a spare. We will see. Really I love homebrew and its challenges. I got into the command set stuff as you remember at Durham Hamfest when that fellow gave me a badly battered BC454. It was quite easy to convert to 12 volt heaters and I had it running in a couple of hours. I made a tuning knob and PS connector and I was hooked.  I bought the T18 for $17.50 and had it shipped to my older brother in NY state. He sent to me here. It was not real hard to get it into 80m quite aways although not all the way in . About 3700 I think with no parts mod, just a tune. Soldering a couple of wires, OSC coil turn and PA tank coil turn would get it at least to 3725 I think. Conversion to cathode keying had already been started so I completed it. Now if I can modulate it with either the 56 ARRL modulator or ideally with the homebrew version I got to work on my 45 tubed TNT I will have a decent power AM rig for probably under $100. Parallel 1625s at 700 volts  with everything else as is should have a decent poke.
I try not to get carried away. I already have far too many radios both tx and rxs not to mention three HB transceivers. If I had my druthers I would like to find another No 11 tank set. I had a complete one as a teenager and when cars and girls got my attention I left it behind in a move. Any more ARC5s? Probably not.  I might someday try for a ART 13  but at the moment I am a busy lad with what I have. 
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« Reply #49 on: February 04, 2013, 07:39:04 PM »

Al said,

Quote
...hopefully the 220v/secondary winding thats being used as his mod transformer, and that carries audio and HV B+ has good insulation properties for the obvious reasons.

Look back up the thread to the pic of the transformer, and you'll see it has Hi-pot rating of 2KV.


Kevin said,

Quote
...and the table looks like its on wheels

Yes it is.  That makes moving gear around a fairly easy task.   The shelves are fixed, but the vertical dividers can be moved around to accommodate the various widths of gear.

I'm making a second bench so I can separate the T.E. and the radios.




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