Re: [drakelist] No TR-4 Am Transmit

[w1id]

The TR-4 and T-4 share the same "type" of AM, not the same circuitry. However the 13DE7 does supply screen voltage to the finals so a bad one could be the problem. Getting back to the TR-4 in need of troubleshooting: does it work on CW as well as SSB? The carrier shift of +1kHz is the same for AM and CW so if the relay is not operating properly, there won't be a carrier getting through the X SSB position at all in either modes. Is there a marked difference in pitch as the sideband selector is switched? One of the things the old TR-4's are known for is one of the filters crapping out leaving only one good one. The carrier oscillator crystal has also been known to drift out of adjustment range with the passage of time so no amount of trimmer adjustment will bring it back to tolerance. Also remember the key has to be shorted or pulled out of the jack for AM. Having said all this, in my opinion a stock TR-4 is not plug and play nor is it a desirable rig&! nbsp;fo r AM. Selectivity is much too narrow for pleasant AM reception. There is a well known modification whereby an AM filter is substituted in the CW filter position resulting in beautiful AM. I have done this to one of my TR-4's and I recommend it. The problem is you need a 3 position filter switch for this and they are not easy to come by. Plus you need to buy a filter. Modulation can be tricky to adjust without the aid of a scope or at least some kind of aural monitoring to ensure there is not too much audio distortion. However when properly adjusted and using a good high impedance mic, AM isn't too bad.

 

-------------- Original message --------------
From: "crawfish" <[EMAIL PROTECTED]>

>
> "crawfish" <[EMAIL PROTECTED]>made an utterance to the drakelist gang
> ----------------------------------------------------------------------
> The 13DE7 could be a culprit. The TR-4 uses controlled carrier modulation
> on AM(50 watts out). You can go to www.amwindow.org and go to Tech area and
> click on Mods.Then go to T-4. The text there that the TR-4 uses the same
> time of circuitry. The mod will change the modulator from controlled-carrier
> to screen. Lower power, but audio will sound better.
> Joe W4AAB
>
> ----- Original Message -----
> From: "Peter Hoon" <[EMAIL PROTECTED]>
> To:
> Sent: Tuesday, August 08, 2006 1:33 PM
> Subject: [drakelist! ] No TR -4 Am Transmit
>
>
> >
> > "Peter Hoon" <[EMAIL PROTECTED]>made an utterance to the drakelist gang
> > ----------------------------------------------------------------------
> > Need any and all diagnostic suggestions from list members who are familiar
> > with the TR4.
> >
> > A blind ham, Max N0HU, will be bringing his TR4 with AC4 pwr supply to
> our
> > QTH repair bench Aug 17th, with a complete set of spare tubes.
> >
> > Unfortunately, cannot get my hands on a readable schematic or block
> diagram
> > until Max arrives with his printed manual (and we can enlarge the
> pictorials
> > on a zerox machine).
> >
> > Max reports that he gets (what appears to him to be) normal output on SSB,
> > good SSB and AM receive, but no AM transmit.
> >
> > 1) Could it be that he misse! d the i nstruction from the manual that says:
> > "For AM operation, set function switch to X-AM position, and set sideband
> > switch to position X."?
> >
> > 2) Will test Max's AC4 power supply for ripple, correct bias and HV DC
> > under load. Though it seems unlikely, since SSB is working, could his AM
> > problem be due to AC4 not holding voltage under load (bad caps)? We have
> the
> > AC4R recap kit from Mike, ready to install if necessary.
> >
> > 3) Is another likely culprit a bad screen modulator tube, 13DE7? Other
> > possible tube culprits to check?
> >
> > 4) Could you still get some SSB operation, but no AM, if one or more final
> > 6JB6 tubes is bad?
> >
> > 5) Please send on other immediate (and less immediate) diagnostic hunches
> > to check out, so we can hit the ground running, for this lack of AM > transmit
> > problem.
> >
> > We will report progress notes to the list as we work on the TR4 next week.
> >
> > Ultimately, we hope to do a complete voltage check out and alignment
> check,
> > re-tube where necessary, since Max will be here for 3 days or so, testing
> > the rig, but it would be great if we could quickly solve the AM problem
> > straight off, which is our first concern.
> >
> > (We have a complete bench set up of test equipment: scope,
> transconductance
> > tube testors, VTM, counters, dummy loads, the alignment cap and resistor
> > suggested in the manual, watt meters, etc. All suggestions and ideas
> > appreciated.)
> >
> > 73s, Peter, VE1CHS, Nederland, Colorado
> >
> >
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