Looking To Buy - 30-60 watt AM transmitter

[XEROX]

Hi All, Bart here.... anyone have an idea where we could find an am transmitter, with good audio for music, that puts out somewhere in the 30-60 watt range? If you can lead us in the right direction, email to XEROXduplicado@gmail.com.  Gracias.

[John Poet]

You might want to narrow that down:  do you mean an AM shortwave transmitter, or an AM Broadcast band transmitter?  

At any rate, eBay is probably your best chance at getting something.

For shortwave, the Heathkit DX-60 is one of the most numerous available, and meets your power requirements at around 40-50 watts out.  It is screen-grid modulated, so the audio isn't the best you could have, but adequate.  Depending on bidding, you ought to be able to pick one up at between $100-200; or less if you get lucky.

One trick to pump up the modulation of the screen-modulated rigs, is to run your grid drive at a somewhat lower level than the maximum, that the tuning instructions suggest.  It works.

[XEROX]

Yes, for shortwave... I see there are DX-60, DX-60A, DX-60B versions ..... is there a preferred model
for pirate use?  Thanks Poet!!

[John Poet]

Operationally, there should be no difference at all.

Here's a couple links about them:

Reviews by users-
http://www.eham.net/reviews/detail/3990

This shows one being overhauled by a new owner:
http://forums.qrz.com/showthread.php?259349-Heathkit-DX-60
(This says the power supply was improved in the DX-60B somehow)

Now if you get one, and it has anything like the big ugly yellow cardboard-tube electrolytic capacitors like the ones shown in the pictures, those need to be replaced; they are original equipment and degrade over time, and their eventual total failure have the potential to take other parts with them when they go, resulting in a bigger problem to fix.  If it has a cardboard tube, get rid of it.  If they are plastic or metallic cases, you are probably all right with them.  

Those electrolytics are polarized, + and -, so when changing them you must make sure to put the new ones in the right way.. or bad things can happen.

This updating ought to be done before you even run the rig to any extent.

You may also run across the older Heathkits, DX-20 to DX-40.  They have a little less output power than the DX-60s, and are older.  The DX-60 was being sold in the late 60s/early 70s as a kit.

I think I just read somewhere that "BoomBox Radio" is using one of these.

[John Poet]

Incidentally, this is a very good site to learn more about specific transmitters, or any other ham equipment-- with reviews by people who have used the stuff:

http://www.eham.net/reviews/

Transmitters:
http://www.eham.net/reviews/products/55

[Blakkzakk]

Just get an HF amateur transceiver with MARS modification.  Make sure it has AM mode (Most do).

[SW-J]

Just get an HF amateur transceiver with MARS modification.  Make sure it has AM mode (Most do).

The problem with that, Blakkzakk, is twofold:

1) The output power is only 25 to maybe 40W carrier (the ALC will be kicking in, limiting the AM peak envelope to 100W and even though the 'carrier' may measure 40W you're being fooled on actual 'talk' power vis-a-vis energy appearing in the sidebands once ALC begins to operate) with a nominally rated "100W SSB" radio. The PAs in these are rated for 100W peak (70.7 V RMS) into 50 Ohms so the power is 'allocated' one might say between carrier and sidebands in AM mode (it is 'allocated', but I want to avoid using vector math to describe and explain what is actually taking place at the moment for brevity's sake).

2) The audio passband *WILL* be limited without substantial modification, i.e. removal and replacement of components on several stages and on a last 10 years vintage radio this will be no small task!

Some of the older, tube-based xmitters were simple and mods are easily made ... making them easy choices for someone not put-off by tube-level voltages.

Even the venerable old Yaesu FT-101E (mostly discrete parts with leaded resistors and caps; no SMT!) has limited audio BW without making changes!

Yaesu FT-101E high-frequency Audio Frequency response test,
AM-mode High Frequency Transmit response at -3, -6, -10 dB points:

. . . http://www.youtube.com/watch?v=nQdc2ai6Fqk


The vid above shows the -3, -6 and -10 dB high frequency cutoff points in AM mode in transmit due to the audio response characteristics in a Yaesu FT-101E series transceiver's PB-1315 "AF UNIT" plug-in circuit board. The audio signal generator signal is input via the 'Patch' input in the rear, which is in parallel with the front panel mic input.

The modulation is adjusted for 100% then the HP Modulation monitor is put in the dB relative-mode .. this aids in finding the -3 dB (70.7 % modulation), -6 dB (50% modulation) and -10 dB (10% modulation) frequency response points as the audio signal generator is brought higher in frequency.


Yaesu FT-101E, low-frequency Audio Frequency response test,
AM-mode Low Frequency Transmit response -3 and -6 dB points

. . . . http://www.youtube.com/watch?v=rgy8bJzqCgI

Tabulated Results:

. . . . . . . . . . . Spice . . . . . Actual
. . . . . . . . . . . Modeled. . . .Measured
 Point . . . . . . . Hz . . . . . . .Hz
--------- . . . ----------     -----------
Peak . . . . . . .  881 . . . . . . . 1000

-3 dB . . . . . . 279 . . . . . . . 363 Hz
-3 dB . . . . .  2730 . .  . . . . 2637 Hz

-6 dB . . . . . . .192 . . . . . . . 261
-6 dB . . . . . . 3950 . . .  . . . 3781

-10 dB . . . . . . 136 . . . not measured
-10 dB . . . . . 5710 . . . . . . . 5538


As one can see from the results, the measured upper and lower 3 dB points are 363 and 2637 Hz respectively.

Nominal voice BW is usually spec'd to be 300 - 3000 Hz, and this particular FT-101E doesn't even meet that! Not very wide and certainly not 'music' quality ...

[Blakkzakk]

Yeah,slipped my mind about the narrower audio on a ham transmitter.  As far as power goes,  a small amp will probably do the trick.

Maybe Allan Weiner of WBCQ and former famous pirate station operator could help.  He claims to be supportive of pirate stations.

http://www.wbcq.com/?page_id=2

[XEROX]

Thanks for everyone's input, I'm learning a lot from these postings!  Speaking of Allan Weiner... there's someone who goes by the name of "Tim Tron"? who works with Weiner that I guess had modified tube rigs in the past. Does anyone know if he might be able to help or is he out of the hobby now?

[Blakkzakk]

Thanks for everyone's input, I'm learning a lot from these postings!  Speaking of Allan Weiner... there's someone who goes by the name of "Tim Tron"? who works with Weiner that I guess had modified tube rigs in the past. Does anyone know if he might be able to help or is he out of the hobby now?

Timtron still has a show on WBCQ, according to the net: http://schedule.wbcq.com/main.php?fn=show_program&id=42

He's still hammin' (WA1HLR) and has his own page: http://webpages.charter.net/wa1sov/meet_the_amers/wa1hlr.html

He <3s them tubes!
I love his 'fridge tuner!!!! http://webpages.charter.net/wa1sov/meet_the_amers/refrigintuner.html

[XEROX]

Wow!  Tim Tron has an old bus in the Maine woods as his DX shack, you gotta love it!  Looks like he's got alot of old tube transmitters as well. I'll try to get in touch with him and see if he can help.
Thanks again to all for your postings!  Bart.

[redhat]

In all fairness, most of the older ARRL handbooks have tons of info on tube theory and other necessary common sense to work on these older rigs.  I HIGHLY recommend you brush up on some theory before embarking on such a project.  OTOH, if you don't mind electrical shock and occasional acrid smoke, then by all means, dig in.  There is a lot to be gained by hands on experience.  We all had to start somewhere.

FWIW, The EF Johnson Viking and Ranger models are pretty popular among pirates, regarded for their great audio, and ease of modification.  Don't forget too, these guys are plate modulated, if memory serves, and do sound pretty fantastic when rebuilt.  There was a nice write up in Zeke's book about modifying these for MW service.

To echo the comments of others, I would change out all the power supply caps at least before you even plug it in.  Test the tubes, and you should be good to go.

Good luck, and for god sakes', be careful!

+-RH

[ff]

Hi Bart - I echo redhat, the Johnsons are great performers and EZ 2 modify - I started out years ago with a Valiant.  However, with the resurgence in popularity of AM amongst hams, you'll need to remortgage your house to buy a (complete) unit.  The DX60s are decent, but not Cadillac.  I rebuilt a "B" long ago and I had good luck with it.  As Poet said, underdrive a little bit and you'll have more headroom left over for modulation.  The DX40 is easily modified and the voltages are a bit less lethal (a good starter rig).  However the power output is also less.  I believe the last year for tube info in the ARRL handbook was 1988.    You need to be looking for '88 or before.  60s and 70s handbooks are the best way to go.  You can usually find these older copies at hamfests.  Often sans covers.  RF Parts carries many RF tubes and parts.  Fair Radio Sales is a good source for surplus tuber parts stuff.  If you need transformers and chokes rewound, Peter W. Dahl is expensive but does excellent work.  One more thing - start collecting high voltage caps.  You'll be needing lots of them.  Have fun and be careful...

[XEROX]

Thanks Redhat and FF. Lots of great information there!