Old resistor codes

[bensysco]

Can anyone read the color codes on these resistors?

The orange one shows a sign of a red band but is is flaked off with age
Can you read these resistor values?
https://drive.google.com/open?id=0B4gy_ ... XJjNHhCYnM

Thanks
https://drive.google.com/open?id=0B4gy_ ... npUUU4yemc

This is a 1936-7 Gibson EH-100 or EH-??

[jthomas]

Can you post better pics with more light. The silver band is the tolerance (plus or minus 10 %). I only see two other bands, unless they are counting the brown base color of the resistor as a band.

Here is my best guess using the 3-band coding system: If there is no third band and the BRN is counted as one of the color bands, then BLK-BRN-YLO = 10K ohms and BLK-BRN-RED = 100 ohms. That said, I'd like to see the resistors under better light before accepting these values. There may be a third band that I cannot see or maybe there is some other, older coding system that I don't know.

Although this schematic does not show a 10K resistor. Hmm.

http://www.davidsonamp.com/sg/gschemeh100old.jpeg" onclick="window.open(this.href);return false;

Does it look anything like this if you pull back:

https://irationaudio.com/2015/03/26/126/" onclick="window.open(this.href);return false;
https://irationaudio.files.wordpress.co" onclick="window.open(this.href);return false; ... g_0794.jpg

[bensysco]

This is a 5 tube set, running 25L6 & 25Z5 tubes (2 each) and one 6C8G amp twin triode tube.



The POT and the RCA jack are someone's mod, that is a mess, I'll put that to rights if I do a refit



BTW, the orange resistor has the vestige of a red stripe, I'd read Orange-red-Silver, zoom in, the photos are high res.
Will This page return the correct values? http://www.camradio.net/resistors.html" onclick="window.open(this.href);return false;

[bensysco]

Thanks
I have never found a schematic for this rig.
There is no third band
The 2nd band on Orange was red but flaked off, I can see it with a loop.
If I had a schematic, Bob would be my uncle. I'm sketching out my own now.
All the color has gone from the wires.
Thanks for you help

[jthomas]

Ok... the 1930's resistors use a slightly different coding scheme but the color-to-number values apparently are the same. Here is what I found:

SEE PG 7 of this PDF for pictures.
http://www.philipstorr.id.au/radio/tech ... istors.pdf" onclick="window.open(this.href);return false;

<snip> Resistors made during the 1930's use a different colour marking system. The colours are read in the sequence
Body, Tip, Spot (also referred to as Body, Tip, Dot).

The colours themselves represent the same values as in the modern code in the table above. These resistors are
sometimes referred to as “Dog Bone” resistors. The resistance value of the resistor in figure 1 is read by the Body, Tip Spot method as 250,000 Ohms. The fourth band is the same colour as the body colour and so the tolerance is
unmarked and is 20 %. In figure 2, band B is Grey and band 10 is Silver making this an example of a 10% tolerance resistor of this type.

Most resistors encountered in vintage radios will be either 10% (silver fourth band) or 20% (no fourth band). So if a resistor has only three bands, it has a tolerance of 20%. This may seem quite a wide tolerance, but in practice it is not a problem because the circuits were designed to accommodate this sort of variation.

If you are checking the resistors in an old radio with a test meter, you should bear in mind the tolerance before assuming a component is faulty. A 10 K resistor with a 20% tolerance could actually be anything between 8 K and 12 K. In practice we can accept a 20% resistor if it is a bit outside this. I usually regard a 20% resistor as acceptable if it is within 25% of its nominal value. You may find it helpful to have a calculator with a percent function in the workshop. <snip>

The schematic that I posted may differ from your amp. Apparently there were numerous revisions of the basic amp under the EX100 model number. I might suggest that you post this info over on the "AMP/CABS TECH CORNER" subforum over at the Gear Page. There are several guys over there that would be of more help that I can be. The website that you posted will work for three-banded resistors and probably with the ones in your amp using the 1930's color scheme.

[jthomas]

Yours looks to be a first generation EH100

http://www.gibson-prewar.com/gibson-prewar-amplifiers/" onclick="window.open(this.href);return false;