Any idea what this thing is?

[Captn Dave]

The component in the center of the photo is a mystery to me.

[IMG][/IMG]

It's covered in a cotton braid and the ends are similar to that of a fuse.

This component is used in a DC filament circuit. The large 39 ohm resistor you see in the photograph is in series with a 12AX7 filament and the two of them stand across a dropping resistor that produces a 25 volt drop (The resistor value is equal to the DCR of the filament and the voltages are 350 and 325 VDC)

Now, this little jewel is connected at one end to the junction between the 39 ohm resistor and the tube filament. The other end is grounded. It would see about 315 VDC. The amp is a 1952 guitar amp.

It has no continuity in either direction.

Any ideas would be appreciated.

[tubelab.com]

I have seen wirewound resistors that look like that in old radios. I have taken several dead ones apart and measured the wire inside of them to get a guess as to the original resistance. Since then I have been told that they may contain asbestos, so if I had to dissect another one, I would do it outside.

If you fix old cars, the brakes and clutch are made of asbestos and it is already ground into a fine dust!

[boywonder]

Originally posted by tubelab.com


If you fix old cars, the brakes and clutch are made of asbestos and it is already ground into a fine dust!

That reminds me of auto shop class back in high school (in FL) Getting out the air hose and blasting off the drums and backing plates I'm sure that did wonders for the student's lungs. Good thing that problem is a thing of the past....

[Tweeker]

I know a ex Navy man who unknowingly blew off the BeO from many a burned power transistor. He uses someone elses lungs now.

[Captn Dave]

That would make sense. Thanks for help.

I had drawn the circuit wrong - mistaken pin number. The resistor and filament stand between the 6V6 cathode circuit at about 30 volts and ground. It takes another 100 ohm power resistor in series to bring down the voltage because the cathode buss goes up with the added resistance. In parallel it would be less because it would bring down the cathode buss.

I'll substitute a few power resistors and see what happens.

[nhuwar]

Wow never seen one of those before.

[Captn Dave]

Thanks George, you're my hero dejour.

A 100 ohm resistor did the trick. It brought the cathode voltage down to 25 which I figure it should be since the halving resistor is equal to the DCR of the tube filament. This seems to address the low volume issue which is the main problem with the amp.

BTW, I read the safety pages on your web site. Very well written. Good senseable advice without all the crazy scary stuff so often proffered. Good work.

[tubelab.com]

Wow never seen one of those before.

There were lots of funny looking things found in old (OK, really old) electronics. 1952 was the year that I was made. I took apart lots of old radios as a kid, but they were already old in the early 60's. Here is another one that causes confusion and blown tubes:

In the early days line operated radios used a power transformer. This was expensive, and there were still a few places, mainly rural farms that had DC power. Hence the AC-DC radio was born. These wired the filaments of all of the tubes in series and powered them directly off of the power line. Often a means of dropping the voltage was needed. There were tubes that contained only a heater, called ballast tubes, and of course big resistors. Big resistors make heat, which must be dissipated. Several creative methods of hiding the resistor were devised. Sometimes the resistor was part of the chassis, or sometimes there was a flanged, tapped, thingy mounted on the rear of the chassis. The real tricky place to hide the filament dropping resistor is IN THE POWER CORD! Yes, two prongs on the plug, three wires on the radio end. One wire is nichrome. Usually the cord is cloth covered, and full of (you guessed it) asbestos. As the cord wore out, users replaced it with a two wire cord, and poof blown tubes. Yes, the power cord gets warm in normal operation.

[DigitalJunkie]

Ohh...it seems the old radio-resto guys hate those blasted cords.. The cords have even earned a nickname, "Curtain burners".

[rcavictim]

Originally posted by tubelab.com


There were lots of funny looking things found in old (OK, really old) electronics. 1952 was the year that I was made. I took apart lots of old radios as a kid, but they were already old in the early 60's. Here is another one that causes confusion and blown tubes:

In the early days line operated radios used a power transformer. This was expensive, and there were still a few places, mainly rural farms that had DC power. Hence the AC-DC radio was born. These wired the filaments of all of the tubes in series and powered them directly off of the power line. Often a means of dropping the voltage was needed. There were tubes that contained only a heater, called ballast tubes, and of course big resistors. Big resistors make heat, which must be dissipated. Several creative methods of hiding the resistor were devised. Sometimes the resistor was part of the chassis, or sometimes there was a flanged, tapped, thingy mounted on the rear of the chassis. The real tricky place to hide the filament dropping resistor is IN THE POWER CORD! Yes, two prongs on the plug, three wires on the radio end. One wire is nichrome. Usually the cord is cloth covered, and full of (you guessed it) asbestos. As the cord wore out, users replaced it with a two wire cord, and poof blown tubes. Yes, the power cord gets warm in normal operation.

George,

I remember resistance power cords too. Ballast tubes and the shocks you could get from a hot chassis. I was made in '54. I was taking apart old radios and such well before I was 10.

I sent you an email.