Dickerson amplifier part 1930's-40's

[MstrB]

I am working on a old Dickerson amp and found a piece I do not recognize. I would appreciate any help if you recognize it.

[Enzo]

That is the spark plug.


Where is it wired in the circuit? Looks like a very early point contact diode to me. I have seen them, but don;t recall specifically. My diode thought might be wrong.

[MstrB]

It is right off the input jack to the preamp triode grid. This is a very early amp with no power switch, tone or volume controls. Field coil speaker.

[Enzo]

Doesn't sound like a place for a diode then.

[JFC]

Have you tested it with a meter?

[MstrB]

I tested it and it appears open. That is why I neede to know what it was so I can replace it. I have never seen another Dickerson like this, nor have I found a schematic for it. 5Y3, 6V6, 6SQ7. The diodes in the 6SQ7 are not used.

[Jazz P Bass]

Input Capacitor?

[gmoon]

Check this page out; it describes the mystery part:

The component was a rare battery bias cell used to apply a negative bias to the 6SF5 preamp tube.

Here's a link to an image of the cell in his Dickerson:
http://www.charlestonarea.com/Dickerson/BiasCell.jpg

And another reference page...

[MstrB]

Thanks! that is the part and the very same amplifier model. I will have to check the tubes but this is a great lead.

[Steve Conner]

Well, I would honestly never have guessed. Maybe you could, shock horror, leave the battery out and just connect two diodes in the cathode circuit of the tube instead? It's 1.2V of bias either way.

Or I suppose a silver oxide button battery, the kind used in watches and old cameras would replace it.

Does yours have the mother-of-pearl finish? It's a beautiful looking cabinet.

[J M Fahey]

I *Loved* the

cathode bias, or bias derived from the voltage drop in the negative lead of the power supply system, has many disadvantages.

bit.
Salesmen will cook up *anything* to make the customer feel insecure about what he already has, which can be easily be solved by buying their product, whatever it is.
Things do not change that much, after all.

[Prairie Dawg]

Originally Posted by MstrB

I am working on a old Dickerson amp and found a piece I do not recognize. I would appreciate any help if you recognize it.

It is a bias cell. They were used in a lot of Knight PA amps. You can revive them by injecting a bit of distilled water into them and sealing up the hole with a little silicone sealer.

[Enzo]

COOL. I love learning new stuff, even if it is older than I am.


And I love the "mother-of-plastic" finish on the cab.

(No offense to the AMI fans)

[Prairie Dawg]

Originally Posted by Enzo

COOL. I love learning new stuff, even if it is older than I am.


And I love the "mother-of-plastic" finish on the cab.

(No offense to the AMI fans)

I was puzzled the first time I encountered one, but lucky me some nice person gave me the first thirty volumes of Photofacts bound. The cells did come back nicely after being treated with a little juice. I guess any way you can get a negative voltage is a good way.

[gmoon]

Originally Posted by MstrB

Thanks! that is the part and the very same amplifier model. I will have to check the tubes but this is a great lead.

Coitainly--and like Steve suggested, you could try replacing it with a button cell.

I also love the MOTS cabinet! Gotta wonder if there's a matching lap steel floating around somewhere...