Tubes

[C2]

Hi All,

I was wondering about tubes and since I don't know anything about them, I thought I'd ask you all.

I just recently got an old Collins receiver (posted in the scanner forum), and it happens to work, but maybe it does not work very well? At least it does not seem very sensitive, even compared to cheap $10 AM radios...

So I was looking at the tubes and I notice that most of them looked burned black on the top, but they still light up, most of them. There are a couple that I can't tell if they light up because they look like they have a lot of black carbon deposited on the glass, and they are mostly covered by an metal casing to hold them down.

Anyway, I was wondering how much it might cost to retube this and if would be worth looking in to? Here is a list of the 18 tubes:

12AU7—AVC AMP AND IF OUTPUT

12AX7—DETECTOR AND AVC RECTIFIER
12AX7—NOISE LIMITER AND AF VOLTAGE AMP

5V4—POWER RECTIFIER

6AK5—CRYSTAL OSC
6AK5—RF AMP

6AQ5—AF POWER AMP

6BA6—1ST IF AMP
6BA6—2ND IF AMP
6BA6—3RD IF AMP
6BA6—BEAT FREQ OSC
6BA6—BUFFER AMP
6BA6—CAL OSC
6BA6—VARIABLE FREQ OSC

6BE6—1ST MIXER
6BE6—2ND MIXER
6BE6—IF MIXER

Is there a complete retube kit for these radios?

 

[nomadradio]

Pretty sure this fella used to sell Collins re-tube kits.

ESRC1 Corp.
6424 Pinecastle Blvd. Suite D
Orlando, FL 32809.
phone 407-826-5808, email: esrc1@aol.com

If you don't have a tube tester, this might be your only way to go.

Other things do go wrong in a 40 (or more) year-old radio. But without a full set of good tubes, there is no way to tell.

A tube tester is a big help with anything that has that many tubes.

73

 

[Beetle]

The appearance of the tubes as you describe them tells me you're looking at the residue from the "getter", which does look like a black, or more usually silver, deposit inside the tube.

When vacuum tubes are made, the manufacturer tries to pull as nearly perfect a vacuum on them as he can. However, nothing man-made is perfect, and there is still a small amount of air...containing oxygen...in the sealed glass tube at that point. However, the tube contains either a wire made of some reactive metal which can be heated to incandescence and burned up by applying voltage to the right points externally, OR a layer of powder with similar properties which can be "microwaved" into incandescence. These are called "getters", and they are used to "get" the last few molecules of oxygen remaining in the tube. They flash just briefly, and their residue is what you see as irregular blotches inside the envelope. Has nothing to do with whether a tube is "good" or not, other than if you DON'T see it, you might have cause to worry.

There's a lot of info on "getters" out there: Here's one.