Working on my Packard Bell 771. I have 255vdc at pin 8 of my 6X5 rectifier static reading. When the audio transformer is connected the vdc drops to 0. The transformer that's in the radio is not the original. Is my transformer bad? If so, what kind of specs do I use to get another transformer? The resistance across the speaker coil is 3 ohms. Transformer primary resistance is 665 ohms and secondary is .8 ohms. All resistance readings taken with transformer isolated. Thanks for bailing me out again.

Make sure that none of the wires are shorted to the transformer frame, which would cause a short to the chassis if the speaker was in contact with the chassis, and would otherwise create a dangerous shock condition for anyone holding the speaker with one hand and the radio with the other.

Your resistances are otherwise normal. I am surprised that the 6X5 doesn't blow up when voltages drop to 0. New output transformers can be found at www.radiodaze.com or www.tubesandmore.com.

T.

Johnny:

Your reading sound normal. So perhaps when you are connecting the transformer you are simply completing the path to a short or heavy load.
For instance if your output amp tube has a tone capacitor (maybe .002uf) from the plate to ground... tht cap may be shorted or leaky. Even the final tube could be shorted inside.

So try isolating the elements that connect to the tube end of the transformer primary to locate this excess load.

Also here's a wonderful text link explaining the easy way to understand impedance and output transformers.
http://www.radioremembered.org/outimp.htm

also you can buy a used transformer from Gary at www.oldradioparts.com for just a few bucks.

:Hi Peter. I had the rectifier tube in to check the voltages on that tube only. All circuitry beyond that was isolated. All the conditions I explained are with all tubes removed. I'm having to do a complete rewire of this radio. Someone has really played around in here prior to me getting it. My concern right now is the aftermarket transformer that is in the radio because my 255vdc drops to 0vdc when I connect the primary lead of the transformer to pin 8 of the rectifier. Pin 8 being my 255vdc.
:
:Johnny:
:
:Your reading sound normal. So perhaps when you are connecting the transformer you are simply completing the path to a short or heavy load.
:For instance if your output amp tube has a tone capacitor (maybe .002uf) from the plate to ground... tht cap may be shorted or leaky. Even the final tube could be shorted inside.
:
:So try isolating the elements that connect to the tube end of the transformer primary to locate this excess load.
:
:Also here's a wonderful text link explaining the easy way to understand impedance and output transformers.
:http://www.radioremembered.org/outimp.htm
:
:also you can buy a used transformer from Gary at www.oldradioparts.com for just a few bucks.
:

:Thanks Peter! That's some good stuff on transformers. I printed it out to add to my collection of material useful for working on these radios. I sure appreciate everyones help with this stuff. I was able to determine that the transformer is good so I'm going to go ahead and use it. This radio looked as if someone was trying to repair it but knew even less then I did. Really bad solder joints, wires connected where they weren't supposed to be etc. They did however, put all new tubes in it. These things are in pristine condition and test very good. I'll let ya know how this thing turns out. I'm working on getting a new dial glass for it too. The art is there just a matter of Radio Daze making one. Looks pretty good. If not, I'll find one.
:
:Johnny:
:
:Your reading sound normal. So perhaps when you are connecting the transformer you are simply completing the path to a short or heavy load.
:For instance if your output amp tube has a tone capacitor (maybe .002uf) from the plate to ground... tht cap may be shorted or leaky. Even the final tube could be shorted inside.
:
:So try isolating the elements that connect to the tube end of the transformer primary to locate this excess load.
:
:Also here's a wonderful text link explaining the easy way to understand impedance and output transformers.
:http://www.radioremembered.org/outimp.htm
:
:also you can buy a used transformer from Gary at www.oldradioparts.com for just a few bucks.
:

Thanks Thomas. The conditions I explained are with the speaker disconnected and out of the radio. One secondary lead of the transformer and the speaker are connected to chassis ground. This is also what's shown on the schematic. No other transformer leads are shorted to ground. The .005mfd cap is in place across the primaries of the transformer and it is not shorted.
:
:Make sure that none of the wires are shorted to the transformer frame, which would cause a short to the chassis if the speaker was in contact with the chassis, and would otherwise create a dangerous shock condition for anyone holding the speaker with one hand and the radio with the other.
:
:Your resistances are otherwise normal. I am surprised that the 6X5 doesn't blow up when voltages drop to 0. New output transformers can be found at www.radiodaze.com or www.tubesandmore.com.
:
:T.

Well, as Peter said, check the output tube for shorts. ALso check the socket for shorts to the chassis. If there are any capacitors from the plate terminal of the output tube to any other terminal in the radio, check them for shorts. Check the output transformer thoroughly once more for shorts between the primary and the secondary, and the primary and the transformer's frame. Unless any of the above problems exist, there is no reason why the B voltage should drop to 0............although there could also be a very badly drifted resistor in the power circuit that loads down to near 0 volts anytime any load is placed upon it.

T.