[Guest]

Hello,
This model 70 early chassis is driving me crazy! I have replaced the capacitors and corrected the hum, now I have no volume or static coming thru the speaker. If I switch the tone control I can hear static in the speaker from the switch, so the speaker is working. Is there a common item I should look for, or can someone direct me to specific areas I should check?
Thank you[/b]

[Ron Ramirez]

Hi John

Have you checked voltage readings? Are the coils OK? The primaries of the coils are known to go bad frequently.

How about that large multi-tapped resistor? Sections of these resistors can go bad.

Make sure your resistors are within 20% tolerance, change as needed. Also check the RF choke at the plate of the Type 24 2nd detector tube for continuity. Make sure none of the mica capacitors have shorted.

[Guest]

Thanks Ron,
With the testing I have done Im thinking the tapped resistor. Should I replace with another tapped style and if so where may I find such a beast.

[Ron Ramirez]

John

A new multi-tapped resistor such as that used in the original is, unfortunately, unobtainium these days. Replacement with individual resistors is your only option.

I have done this in the past by removing ALL of the resistance wire from the multi-tapped unit and using the terminals as tie points for not only the original wires that connected to the several terminals, but also for new resistors to replace the individual sections.

[Terry Judkins]

Here is a neat solution.
http://www.edrington.com/files/candohm.pdf

[Guest]

Yeah Terry, I downloaded that PDF from you off the ARF. That is EXCELLENT work!! Thanks, Friend
And Ron's method of retaining the Candohm, but replacing the resistances..using the Candohm as the original tiepoints for wiring..is a GOOD idea!! More original that way.

[Ron Ramirez]

Guys, don't forget that the resistor in question, in the Model 70, is NOT a Candohm, but instead a large ceramic tubular resistor with multiple taps. A Candohm has a metal housing and is mounted flat against the chassis. The ceramic resistors as used in Model 70 require standoffs for mounting.

This is why I didn't mention the Candohm replacement which I also saw on that quaint little alternative forum . But the idea presented there of a Candohm replacement is, indeed, an excellent one. Many thanks to Terry for posting the link.

Edit: You do NOT want to use the terminals on an old Candohm as tie points for new resistors; if you do, you could be in for all sorts of problems. This is why a bad Candohm needs to be eliminated. The "popfog" method is a great Candohm substitute.

[Guest]

Good point,Ron..what you're referring to is a voltage-dividing resistor, but not a Candohm. Thanks for straightening that out. See I LEARNED something today...saved myself from a potential house fire!!

[Chuck Schwark]

Philco called these ceramic form, wire-wound units 'BC' resistors. I'd guess because they divide the B+ and bias (C-) voltages in the sets they were used in.