I've found the volume pot, that was tricky since this radio has volume and tone on the same shaft. But by measuring the resistance I could see it change on the "back" pot when I turned the volume knob, without power of course.

I can see 5 taps off the volume pot, but I cannot get the guitar to play when I tap off of any of them. Here's what I have.

Tap 1 has 9v when the volume control is clicked on, 0v when off.  Tap 2 has 9v all the time.

On the bottom we have 3 more taps.

Taps A, B and C also have 0v when the volume is off, and 9v when the volume is on.

I pull the batteries and measure resistance (and yeah, I know, the pot is in the circuit so it isn't accurate but I'm just trying to find the "input" lead.

A always reads 4k Ohms, B varies from 2k to 4k, C is at 2k no matter what I do with the volume knob.

1 in always at 2k Ohms, 2 is 0 Ohms when off, 2k when on (which makes sense since it is connected directly to the battery)

So it seems to me that I should be hooking into tap B. So when I hook the rod-piezo to B and to ground I still hear the static of the radio and when I pluck the string, I do not hear the note out the speakers.

All the online tutorials make this look easy, but I'm baffled at this point.

Views: 272

Reply to This

Replies to This Discussion

I'm thinking that the 2-wire ribbon cable from the RF converter to the board is where you need to wire your guitar input. I would unhook the cable from the converter and check for voltage(radio should stop working) and if okay, hook up guitar.

Oh, I like that idea. I'm traveling now but will check it out when I get back home. Thanks!

I'm thinking that the last stage of the pot is actually a volume instead of tone. The cap could be a high pass filter.

The pot shown is a 3 stage pot. 1st stage for on/off, 2nd stage is obviously power distribution circuit. That would leave the 3rd stage for volume. Unless the 2nd stage is the volume that has shorted out to the power supply.

Do you have a schematic? What brand radio and model # is it?

More detailed pics could help.

https://www.radiomuseum.org/r/sears_roeb_silvertone_700_1217.html

looks like its a silvertone 700.  my first guess is that the input from the RF section will be to the base of T5, possibly biased via a resistor divider between gnd and bat + . also possibly also fed in through a DC decoupling capacitor... 

That link shows the pic posted by Paul Cezanne ..  its a super hetrodyne circuit but this only describes the RF side not how the amp section works so ??

On the schematic and pic, T5(labeled-Driver) looks like the output tranny to the speaker. If so, that's not the place to hook up to. He needs to find where the Radio's signal inputs to the preamp.

TR6 and TR7 are the audio output transistors. 

this is something similar to the circuit. i think i could be wrong( probably) but the amp output stage seems close..

RSS

The Essential Pages

New to Cigar Box Nation?How to Play Cigar Box GuitarsFree Plans & How to Build Cigar Box GuitarsCigar Box Guitar Building BasicsCigar Box Guitar Parts Store

Site Sponsor

Recommended Links & Resources

Forum

pickup

Started by Joe Williams in Performances, How to Play, Lessons, Concerts. Last reply by Joe Williams 2 hours ago. 10 Replies

Next CBG event in the UK?

Started by Wal Callaby in Fests and Concerts: Organizing and Promoting. Last reply by Blind Boy Fullers 9 hours ago. 2 Replies

Build This DIY Guitar Fuzz Pedal in 10 Minutes - VIDEO

Started by Shane Speal shanespeal.com in Feature Articles. Last reply by Paul Craig Jul 8. 19 Replies

Cigar Box Kalimba - Builder's Notes, Hacks & Blues Tuning Mod

Started by Shane Speal shanespeal.com in Feature Articles. Last reply by Shane Speal shanespeal.com Jul 7. 7 Replies

Latest Activity

Doug "Nomad" Farish posted a status
"Well build 3 is done and time to move onto the next."
8 minutes ago
Kenneth " Hammy " Hamblock liked Dave Lynas's photo
18 minutes ago
Kenneth " Hammy " Hamblock liked Dave Lynas's photo
18 minutes ago
JB liked Mineiro´s Blues's photo
19 minutes ago
Jason Taulbee posted a video

De Anza Jig Primus Cover on Slide Cheesebox and Tenor Ukulele

Here's a different one for ya... a request from my drummer for this funny gem. Rough take, so forgive the mix, but it has a cool groove going. Solo is pretty...
22 minutes ago
Uncle John commented on BeetleJuice!'s photo
Thumbnail

Upclose and personal - 1937 Aviator

"Well crap.  Turns out they have age limits and I am SOL. "
56 minutes ago
Uncle John commented on Dave Lynas's photo
58 minutes ago
Don Craig liked Mineiro´s Blues's photo
1 hour ago
Don Craig liked Mineiro´s Blues's photo
1 hour ago
Don Craig liked Mineiro´s Blues's photo
1 hour ago
Don Craig liked Mineiro´s Blues's photo
1 hour ago
Don Craig liked Mineiro´s Blues's photo
1 hour ago

Events

Music

Loading…

© 2018   Created by Ben "C. B. Gitty" Baker.   Powered by

Badges  |  Report an Issue  |  Terms of Service