The AM Forum

Hi All,

New member here. Uh-Please keep ur seats. I'm waiting for delivery of a TR-3 I bought the other day over QTH.com. My question is:

How desirable is this rig for AM (ie. Rx-wise, mainly ???). I am hoping that the AM Rx is not simply SSB w/ a zero beat (fingers crossed...???). I understand that it uses exalted carrier for the purpose of Rx, but not really sure how that relates to standard, full sounding AM audio.

Also any remarks on the quality (or lack of) in the grid-mod arrangement on Tx.

Thanks in advance,

Rick

Hi Rick,

It's your lucky day. The TR-3 is a fun rig to play around with - and here's the info you need to make the transmitter section sound like a million bux on AM.  I did it for the Drake T4-X, but I understand the TR-3 transmitter stages are similar in design too.

http://www.amwindow.org/tech/htm/t4.htm

The exisiting screen modulated controlled carrier scheme needs work. These simple mods will make it a standard steady carrier hi-fi AM rig.


The receiver can be widened up to sound better too. Maybe someone here can make some specific suggestions.

Good luck with your new TR-3 and welcome to the AM BB, OM!


73,
Tom, K1JJ

The sweep tubes in that rig dont like to be pushed and replacements are very expensive. Place a muffin fan on top of the finals cage and orient it to exhaust the heat.

Ive had lots of Drake rigs in the past and the fans made a huge difference.

Carl
KM1H

Carl,

I'll go one farther on your statement...  I did the same thing Carl is saying, and found my Pout to start increasing, the longer I was on the key.

Fix was to put a pot on the DC lead of the fan.  This allowed me to slow it to the point of where Pout JUST started to drop....  If you find that your Pout isn't stable, after adding the fan, that MIGHT be the problem... As those tubes heat and cool, they change a bit...

Also, as they heat and cool that way, it puts a BEATING on the seals of the, as Carl pointed out, 'SPENSIVE sweep tubes.

--Shane

Thanks for the info, Guys. Tom, I checked the Tx mod you suggested and that sounds great. I haven't seen the schematic for the TR-3 yet, but the TR-3 sounds a lot like my DX-60's audio chain (waiting on a mod tube for that).

I also checked the prices on the final (12JB6 sweep) tubes. Seems the're available for 24.95 at RFParts, and a couple of other sites had them higher. The trick will be finding a matched trio.

I plan on putting it on the bench and checking it out, log all the readings for a baseline and just get generally familiar w/ it (put it on the air for a week or so)before I do any mods. Have a 12V muffin fan for the RF cage.

Thanks again, Fellas, for the great info.

73 and catch ya on 75,

Rick

That sounds like reasonable pricing on the sweep tubes.

If you want to do some work, you can convert it over to 6146's. I have done that to a couple of sweep tube rigs and beyond re-biasing and neutralization, no real issues. Of course the 12V will require fooling with the fils to get it balanced, because you have 3 finals. This conversion works best on two tube rigs like the NCX-3 and the SR-150, which used early sweep tubes.

The 12 equiv. of the 6146 is the 6883 and a super rugged mobile version is the 8298.

Yes a 6883A is an A and the B is a B, just like the 6146.

Sometimes you can find these cheap. One some rigs, switching will give you more output, on some less, depending on the dissipation and plate voltage.

Mike WU2D

Thanks for the tip, Mike. The 6883 sounds like the way to go (one less detail w/ fil. E in the conversion to deal with). I have an FT101EE (6SJSc sweeps) and I have not yet been able to get decent, reliable output w/ any finals I've put in it. The TR-3 having sweep tubes was a definite negative, but I'd also read a lot of good about the rig.

Like I said, I plan on running some tones through the TR-3, etc., and see what's up w/ it before I mod it.

Agn tnx, 73

Rick