The AM Forum

Looking for a mod transformer for the 5100B wonder if anyone knows where is the best place to find one.

Thanks
Steve

Can you give the dimensions the transformer would occupy?   Or are you looking for a direct replacement?

Al

Hey Steve,

   We moved one from a POS valiant into a 5100 10 or 15 years
ago. Worked fine, Still is. It hung over the mod deck a bit but
there was plenty of room for it. Rich FVJ has it now. I see em
on epay from time to time.

GL

/Dan

Steve those things are a bit difficult to find if you want an origianl.  If that is the case I suggest you have the one in it rewound.

Hi Al, the dems. are 3" wide x 3.5" deep and 3.5" high.  I am not particular just want to get the thing on the air.

Thanks
Steve

Get it rewound. I don't know if I can mention the guy I use on the site. If that's OK, I'll post it. Most of know the guys here know him and he does great work. But your not gonna find that transformer and if you do you'll pay as much for one that's used, and it may be questionable in quality. A rewind is as as good as new, for the same price.

Steve

Getting it rewound sounds like the best way to do things.  FYI, I just measured my Viking 1 mod iron and it is about the same size as you are looking for.  My UTC 100 watt mod iron is huge in comparison.  Even my Thordason 11m74 (40 watt) is bigger than that.  So, either rewinding it or if you can find a Viking 1, 2 that is a basket case but the mod iron is OK then that might work for you

GL es 73, Al VTP

Oh well,

Look here's the link to the guy I use to rewind transformers. If the mods want to delete it, by all means do.

http://members.tripod.com/tubes_tubes_tubes/transformerrewindingservice/index.html

He's very good and lists the mod iron you have as one of the ones he does.

John

That is a compact one! All the 100W size ones I have are much too large physically. The rest are 20-30W or less. Rewinding might eb the best route, with modern materials you will probably never have another issue.

Is the B&W one of those that barely gives 100% mod before its reached its limit?

If so, a suggestion - Rewind time would be the time to ask them to take a few turns off the primary, so you can easily hit 100 percent with some headroom. If I am not mistaken, 5-10% less primary turns (volts) would change it from 100% mod to 110% ?? - and the load on the modulator tubes would be a bit tougher current wise but still be acceptable unless you are doing heavy clipping or processing..

total primary to secondary, just some numbers with lots of assumptions..
B+ is 630VDC, modulator looks like an AB2 setup.

2:1 -straight transformer:
1260V peak: 1260V peak
8K CT pri.

1.8:1
1260V peak: 1400V peak
6480 CT pri.

Its worth considering because of the tube specs from RCA TT-4:
In CCS AB2, the 6146 at 600V loaded with 6800 CT delivers 90w @ 207mA with 200mW drive.
In ICAS AB2, the 6146 at 600V loaded with 5000 CT delivers 113w @ 270mA with 300mW drive.
In ICAS AB1 the 6146 at 600V loaded with 6000 CT load makes 95W @ 229mA. - you may not need to push any farther into AB2 with the better ratio than the set is designed to do.

100% modulation plus headroom and it ought to cost nothing extra.

Pat

The problem with doing custom winding is that the rewinder won't back things up.  I recommend going with OEM so the rewinder can stand behind his work.  It is interesting that these irons are minimalistic.  As I mentioned in a previous post, even my 40 watt Thordarson T11M74 is considerably larger than both the dimensions that Steve gave for the 5100 and the dimensions that I measured on my V1.  These mfgers were literally counting on the ninimal 300 - 3000 cycles that (what we now call) space shuttle audio calls for.

We live in an age where quality AM is the norm whereas I remember as a kid that you could count on one hand all the hifi Amers in New England.

Steve.  Did you try those tests I suggested on the air?  I think you really need to get the RF working in that rig first and then see if you still have a problem with the modulation.  However, if those tests I recommended suggest shorted turns then by all means, get one of the excellent rewinders have at your mod iron.

73 es good luck  Al VTP

Looks like I am going to bite the bullet and send it of to be rewound, based on all the advise given that seems the best route. Hi Al, I did all the checks you suggested and came to the conclusion that the xmfr was just ready to go, I haven't found anyother issues that would have caused it to get hot. Thanks to all who took the time to respond to my post.

73's
Steve

I would not recommend this on the 5100b. The mod tubes on this radio are running pretty hopped up as it is and adding current on those already stressed tubes could be problematic. Good thought though.

A pair of 6146s can easily make 120w of audio. That is good for 240w of CD inpoot to the final. It is all dependant on what the Ep is. (I dont remember what the HV in a 5100 is) If you have Gary rewind your transfoma, talk to him about it. He may allready have a "recipe" for that transfoma that takes care of the problem. A few turns added to the secondary can have the same effect as a few removed from the primary.