webster chicago transformer woes

[ALBATROS1234]

i purchased a webster chicago 81-1 wire recorder with the hopes or restoring it or at least converting jacks etc for use as a guitar amp as well. bringing it up on a variac the rectifier began replating at 70 to 80 volts applied to the ac line plug. i assumed shorted filter caps which i changed and got the same results. so i did a basic quick circuit rebuild. by this i mean i added a 3 prong cord replaced all of the rest of the capacitors which were paper/wax with a couple that were axial plastic molded tubes which i think are also paper with oil. i changed resistors that looked and tested bad. same result. i then striped down the circuit and rebuilt it as a simple single ended amplifier to eliminate the bias oscillator which is used for record functions plus anything not involved with signal amplification. same result. i was getting normal voltages on the rectifier plate pins and kathode pins until the variac was turned up to 70ish volts still rectifier red plated.i began to suspect the xfrmr. it was then i noticed a wire seemed to be missing. the center tap. so i extracted the xfrmr and it seems the center tap was soldered to a metal clip which was on the last leaf of the laminations. i have never seen or heard of this. testing with an ohm meter confirmed that the soldered on point was the center tap of both the high voltage as well as the 6.3v filament winding.with the transformer out of the circuit i am able to see proper voltages on both windings if hooked up to 120vac in reference to each other and the center tap.it seems that it is just one winding with a center tap and a 6.3v tap. i hooked it up to a basic 5y3 3 node power supply that i use to test circuits and transformer outputs and i get voltage out of the transformer on the plates but nothing coming out of the nodes. i didnt raise it all the way to 120v because it looked as if the 5y3 was also beginning to get hot.. i went to another transformer to test my 5y3 ps and it workd fine with other transformers so i know there is something amiss with the webster chicago xfrmr. has anyone seen this either with webster chicago or other circuits where the transformer center tap was grounded to the transformer laminations and should this be a separate winding from the filament winding( the wire recorder uses a 6x5 rectifier so the kathode is separate from filament) i have tryed all different tubes with the same result. i "think" that somehow a winding shorted so that the 6.3 volt is semi connected to the high voltage winding or laminations/frame. should i try to solder a wire on to the stubby leads which would allow a solid ground for the ct? i am grasping at straws at this point. i may have bit the big one and have a $100 paper weight.

[PRR]

> 6.3v tap. i hooked it up to a basic 5y3

Why the heck are you using a 5Y3 (needs *dedicated* 5V winding) with a transformer which *may* be intended for 6X5 (6V and can share a winding with your other tubes) ??

This is the 80-1, not the 81-1, but I would really wonder if you are trying to make high DC voltage on a grounded winding.

[John]

I'm just finishing up a build using a PT from an old Webster, and yes the case of the tranny itself IS the center tap. You should have just 2 HT leads, 2 fil leads and of course the 2 line leads. Mine has a copper leaf going between the 2 end bells which I assume serves to make sure they're all connected. When it's bolted to the chassis, then it's just like you connected the CT wire (that's not there)


It's possible someone before you used the wrong rect. tube. I am guessing it's supposed to use the 6X5 as mine does. Note the 6X5(GT) only is good for about 70 mA draw, so a single 6V6. My circuit is 12ax7, EF86, 6V6. I believe the voltage drop between unloaded and loaded is a good 60 or so.

[ALBATROS1234]

you misunderstood me prr, i only used a bench ps that uses a 5y3 to test the transformer after i extracted it from the recorder i used a separate heater xfrmr to heat the 5y3 and my goal was trying to see if i could make the xfrmr work with a known good ps.  i guess i worded it poorly.

it is definitely a 81-1 cuz it says so on the back. i can find no schematic that matches exactly as the schematic i found which claims to be for a 81-1 uses a 6j5 and mine uses a 6sn7 in the v2 position.

[ALBATROS1234]

thank you john thats what i was seeing too. mine has a 6SJ7,6SN7,6V6 and 6x5 i can find no schematic. it seems to me that i am either not getting a good ground to the chassis from that odd ground which is soldered to the clip like you say spanning between the bell ends and it seems just bolt and nut contacts the chassis as there is a rubberish pad btw the laminations and chassis.

the other thing i may be is that somehow the 2 windings are shorted together. did you check your xfrmr for continuity btw 6.3v and high voltage windings. i get continuity btween 6.3/hv and the grounded clip/ct.

[sluckey]

the other thing i may be is that somehow the 2 windings are shorted together. did you check your xfrmr for continuity btw 6.3v and high voltage windings. i get continuity btween 6.3/hv and the grounded clip/ct.

Of course they are 'shorted' together. Just like a gazillion other tube amps.

[ALBATROS1234]

so i guess now that i know this is intended to be a ct grounded to the transformer EI laminations and i dont have a broken of ct wire missing, what i need to know is for a circuit which contains the 6SJ7,6SN7,6V6 and 6x5 is it ok if the filament winding as well as the high voltage winding have continuity and share a ct as if the 6.3v is but a tap off of the 1 main winding? or are the 2 secondaries shorted/connected together is a fault most likely caused by overheating or some other short caused too musch current to be drawn?

[ALBATROS1234]

thanks sluckey, in my limited experience i have not seen a transformer in which the filament winding(s) are have continuity between itself and the high voltage winding.

[ALBATROS1234]

because if its ok to have the 6.3 as a tap off of the main secondary than i have another problem because its not working now and i have tryed multiple fixes and i am left scratching my head. i have only been messing with tubes less than 2 years so i am for sure a newbie and i know transformers like both i drew above exists but i have not yet seen one where both windings are combined in a tube amp schematic. so i wonder is it busted or am i missing something in the circuit?

[sluckey]

The filament winding is a totally separate winding of big, high current wire. IT IS NOT A TAP ON THE HIGH VOLTAGE WINDING. The only thing those two separate windings have in common is the fact that their center taps are both connected to chassis ground. That does not mean that the high current of the filaments flows through the high voltage winding or vise versa.

[ALBATROS1234]

i see what you are saying they can both ct can be grounded to the same point and show continuity. i guess i have some more troubleshooting to do then.

[sluckey]

There were some really "innovative" PT designs, especially in consumer electronics. You're seeing one of them. One of my favorites was the tv PT with a 5U4 socket built into one of the end bells. What an idea. Can't believe that didn't catch on!

http://audiokarma.org/forums/index.php?threads/need-help-identifying-a-transformer-with-built-in-octal-socket.811277/

[ALBATROS1234]

now thats interesting. must be 1940s with that 5u4 in the bell. i am sure there is much more to see as i acquire more old gear.

[1blueheron]

i purchased a webster chicago 81-1 wire recorder with the hopes or restoring it or at least converting jacks etc for use as a guitar amp as well. bringing it up on a variac the rectifier began replating at 70 to 80 volts applied to the ac line plug. i assumed shorted filter caps which i changed and got the same results. so i did a basic quick circuit rebuild. by this i mean i added a 3 prong cord replaced all of the rest of the capacitors which were paper/wax with a couple that were axial plastic molded tubes which i think are also paper with oil. i changed resistors that looked and tested bad. same result. i then striped down the circuit and rebuilt it as a simple single ended amplifier to eliminate the bias oscillator which is used for record functions plus anything not involved with signal amplification. same result. i was getting normal voltages on the rectifier plate pins and kathode pins until the variac was turned up to 70ish volts still rectifier red plated.i began to suspect the xfrmr. it was then i noticed a wire seemed to be missing. the center tap. so i extracted the xfrmr and it seems the center tap was soldered to a metal clip which was on the last leaf of the laminations. i have never seen or heard of this. testing with an ohm meter confirmed that the soldered on point was the center tap of both the high voltage as well as the 6.3v filament winding.with the transformer out of the circuit i am able to see proper voltages on both windings if hooked up to 120vac in reference to each other and the center tap.it seems that it is just one winding with a center tap and a 6.3v tap. i hooked it up to a basic 5y3 3 node power supply that i use to test circuits and transformer outputs and i get voltage out of the transformer on the plates but nothing coming out of the nodes. i didnt raise it all the way to 120v because it looked as if the 5y3 was also beginning to get hot.. i went to another transformer to test my 5y3 ps and it workd fine with other transformers so i know there is something amiss with the webster chicago xfrmr. has anyone seen this either with webster chicago or other circuits where the transformer center tap was grounded to the transformer laminations and should this be a separate winding from the filament winding( the wire recorder uses a 6x5 rectifier so the kathode is separate from filament) i have tryed all different tubes with the same result. i "think" that somehow a winding shorted so that the 6.3 volt is semi connected to the high voltage winding or laminations/frame. should i try to solder a wire on to the stubby leads which would allow a solid ground for the ct? i am grasping at straws at this point. I may have bit the big one and have a $100 paper weight.

Any chance you could post a picture of your $100 paper weight that shows what wires/colors you have and tell us what voltages you actually were getting on which color wires at a specific input voltage?   I don;t think I have seen an actual voltage posted yet and "normal" can mean many things.  I think I am normal but my wife would tell you different...

[ALBATROS1234]

ill post some picks although its all in pieces atm. the first is just a pick which shows it before i disemboweled it. the transformer is completely out of the chassis for testing but ,i set it in the hole for you to see its location, another gut shot last but much is detached at this point as i disconnected everything that wouldnt be just an audio circuit even the input is floating so i could clip on a 1/4 phono cord which has 2 alligator clip ends so i can inject a guitar signal at different points in the circuits i mess with. i was just trying to figure out why it kept red plating with known good tubes and replaced components etc.in the bottom pic behind the speaker is a choke which was the first issue i found when i wasnt getting any plate voltages. i traced the wires and got big sparks cuz the wires connected to the choke were rodent eaten or rotted through and broke off when i lightly pulled the wires. oh er and yea dont forget a clean desk is a sign of a dirty mind lol.

[sluckey]

   Danger Will Robinson! Danger!

[1blueheron]

ill post some picks although its all in pieces atm. the first is just a pick which shows it before i disemboweled it. the transformer is completely out of the chassis for testing but ,i set it in the hole for you to see its location, another gut shot last but much is detached at this point as i disconnected everything that wouldnt be just an audio circuit even the input is floating so i could clip on a 1/4 phono cord which has 2 alligator clip ends so i can inject a guitar signal at different points in the circuits i mess with. i was just trying to figure out why it kept red plating with known good tubes and replaced components etc.in the bottom pic behind the speaker is a choke which was the first issue i found when i wasnt getting any plate voltages. i traced the wires and got big sparks cuz the wires connected to the choke were rodent eaten or rotted through and broke off when i lightly pulled the wires. oh er and yea dont forget a clean desk is a sign of a dirty mind lol.

Thanks for the pics, I am speechless at this point.  Are you sure the rat is not still in there that ate the wires? 

[ALBATROS1234]

blue heron wanted to see it so i stuck the pt in its hole and snapped. lol

[Papa Jim]

At first glance in that bottom (last) pic I thought the tube sockets were mounted in a piece of wood. 

[ALBATROS1234]

its copper, or copper clad. i have seen pictures and videos of other webster chicago stuff from this era and they all have the copper chassis. the whole framing which holds the upper and lover sections together and copper clad. i assume copper clad because copper is so maliable and this is pretty sturdy so probably mild steel and i would imagine some sort of copper electroplating.

[PRR]

I believe (I was not there) that after WWII there was an overstock of rust-resisting copper-plated sheet steel. Some of the hot-spots in that war were incredibly damp. Stories of troops losing contact with their forces because radio coils and even chassis rotted in months. I have seen a lot of late-1940s (into 1953) tape/wire/phono chassis built in that stuff. It also eases soldering, but not so a consumer company would pay for that much copper. I think it was war "surplus". Not as in Jeeps or Allisons packed in Cosmoline, but as new-made sheets partly paid-off when the war ended before the Gov took delivery, the leftovers offered to general market.

[sluckey]

Copper clad steel chassis were very common in tv sets during the 60s. Easy to solder to with a big Weller 250 watt gun.

[shooter]

At my scrappers place he had 10 copper bars, 18'X3.5"X3/8" from a substation that took a direct lighting hit, annealed the S :cussing:T outta them !
so I bought a chunk n made this, the Copperhead (GA-8T PSE)