Mod Transformer Elmac

[flintstone mop]

Hello Dear AMers
To my disappointment, I have discovered that the mod trnsfrmr in my AF-67 is dead, well kinda. Through mis-wiring errors in it's past, this poor AF-67 had the seocndary of the mod. transfrmr shorted. The secondary is now wired in series with the P.S. and the final and when I increase mod to about 80% all kinds of noises of arcing take place from inside the transfrmr.
I have a quote for a 'used-but-good' transfrmr from a fellow Ham who operates Land Air Comm somewhere in New York. $75

I wish I could have stripped some of those Rangers I was working on for Howard in 1995 of more than the power transfrmr. arrrgh
 
The question is..........would a Ranger mod transfrmr work in the Elmac? The load is the same for the final, I'm not sure about the modulator toobs. The Elmac uses 5881/6L6. I'm just thinking that there would be more Ranger transfrmrs than Elmac.
Would a Ranger transfrmr fit....electrically??? The space inside of the Elmac is pretty small.
Any and all thoughts is always appreciated.

Fred

[Carl WA1KPD]

Fred,
I thought I overheard the Tron at Hosstraders saying he was gong top replace the mod exfrmr n a AF-68 with a TCS 12 xfrmr. If that will work ai have several extra ones and we can work a deal

[flintstone mop]

OK
I'll check back. In the meantime I'll look in my Ranger junque box, maybe I did strip one out, I doubt it.

Fred

[flintstone mop]

Nope!!!!! Nothing in there but some toobs and a driver transformer and some knobs and odds and ends.
Fred

[flintstone mop]

Hello Guys and Ladies
I have received the replacement mod transfrmr for the AF-67. And after I installed it, keeping the wire colors exactly the same into the transmitter circuits, I discovered very little positive modulation. I thought, "GEESH the defective transfrmr had more pos peaks than this piece of s***!!!"

Out of desparation I reversed the secondary leads going to the final and wooosh, there were the beautiful positive peaks.

Anybody have any thoughts what happened here??

Now I have to get the audio driver tube circuit to have a nice flat response as the mic pre-amp circuit does.

I'll check back later..............thanks

Fred

[K3ZS]

Could there be a hard negative peak limiter added to the AF-67?  That would make the secondary polarity sensitive.

[K3ZS]

Or one of the modulator tubes is weaker than the other.

[KB2WIG]

.........            could it be SATAN?!?   .......

[flintstone mop]

The Af-67 saga continues...........
Satan might be in this Tx!!!
I was gettting really ugly audio and ugly waveforms on the scope, really severe distortion. I removed one of the mod toobs and lo and behold the audio was clean and there was 100% pos peaks. Looks like I bought a bum mod transformer. The guy that sold it to me operates a repair shop, and I don't think he'll take my word that he probably sold me a bad transformer. I'm gonna run it like it is with just one mod toob. If I get some extra money I might have Dahl rewind the dam thing.
Any other thoughts out there??
Thanks..............Fred.............MOP radio


FLASH
Oh yes my friends, who have these little monsters. I did an ER mod that eliminates the driver transformer and I now have a freq response of 80hz to 5khz on the 'scope. R390A receiver....'scope hooked up to the I.F. OUT. This setup has been used with many different transmitters, broadcast included, and seems pretty reliable.

The driver transfrmr in my AF-67 was replaced and who knows what quality was in that unit. It severly limited freq response of the modulator.
More de-bugging before this Tx hits the air.

G'day

[Jim, W5JO]

Mop:  Before you spring for a Dahl, consider Gary Brown, WZ1m who rewinds using your iron.  He is a bit cheaper and the quality is good.  I used him for a transformer and he did good, as we in the Southwest say.  gkbrown@gwi.net 
http://tubes_tubes_tubes.tripod.com/tubestubestubes/id33.html

Another source is Heyborer . 
http://www.heyboertransformers.com/overview.shtml

[flintstone mop]

Thanks I sent email to sniff for an estimate. He's kind of pricey.
But, I'll wait for an exchange of info and I'll look at the other fella rewinding.

I still want to investigate my Tx a little more before taking the plunge.

Fred

[flintstone mop]

I saw TimTron's turbo hookup for a mod transfrmr and the article using a power transfrmr. I have the time, I'll keep poking around here and I'll report to the forum what solution makes the Elmac almost Hi-Fi.

Fred

[flintstone mop]

OK Guys
Mr TimTron has done it again!!!
I got an old power transfrmr from a Knight kit 30w per channel tube amp. Using 4 ea EL37's in the outpoot and 2 ea 5AR4's for B+. This was a junker chassis. I have a working copy of the same amp. in the shack.  It is the KB-85 stereo amplifier from the 60's.

That power transformer is now outboarded to the AF-67 Tx. Both mod toobs are in their sockets and it makes A LOT OF MODULATION. That waveform looks sooo good!!
Freq response looks like 80 or so to 5khz.

I cudda saved $75 IF I would have slowed down a little and sparament........DAM
But it was fun.
Thanks for the suggestions and thank YOU TIM.

Mebbe this weekend the AF-67 station will take a maiden voyage with the Froggy 7700....hi Joe.

fred.................'MOP radio