|shortcircuit||3/4/2018 9:06 AM|
|Epiphone Galaxie EA-33RVT adding grounded plug|
This looks pretty straight forward , does anyone see a problem with adding a grounded plug to this amp , by simply using the chassis for ground , or is C17 the dreaded deathcap. I apologize if my schematic didn't post
|Jazz P Bass||3/4/2018 9:37 AM|
|On the schematic it does appear that all 'grounds' are common to the chassis.|
So attaching the mains safety wire to the chassis will work.
And yes, remove C17.
|shortcircuit||3/4/2018 9:42 AM|
|davohilts||3/4/2018 10:28 AM|
|and be sure to run the hot to the fuse, then switch and tie the neutral directly to the other power transformer primary. Then install the ground to the chassis with the ground wire long enough that if the cord is pulled out it is the last wire to disconnect from the circuit.|
|shortcircuit||3/4/2018 2:23 PM|
|Enzo||3/4/2018 2:51 PM|
|The schematic shows one side of the mains going to the switch and the left side of the primary, and the remaining side of the mains going through the fuse to the right end of the primary.|
What he is telling you to do is run the left side of the primary directly to the neutral mains wire, and then move the switch to the other side of the primary between fuse holder and transformer.
So mains current comes in through hot wire, through the fuse, then through the switch, then through the transformer, and back out to the mains neutral.
|davohilts||3/4/2018 2:57 PM|
|shortcircuit||3/5/2018 9:21 AM|
|Jazz P Bass||3/5/2018 9:54 AM|
|The output circuit is 'cathode biased'.|
Measure across R26 (270 ohm cathode resistor).
Stated on the schematic: 17 Vdc across that resistor is the expected idle voltage.
You may want to lift the cathode bypass capacitor (C18) to see if that is affecting the bias voltage at all (it should not).
Or simply replace it.
|shortcircuit||3/6/2018 8:23 AM|
|shortcircuit||3/13/2018 1:44 PM|
|shortcircuit||3/13/2018 1:46 PM|
|davohilts||3/13/2018 2:07 PM|
|if you feel comfortable you might try the following to check the bias of the amp. |
1. Measure the voltage drop on the cathode resistor to ground. Write the value down.
2. Divide this voltage by the actual measured value of the cathode resistor. This gives you the amount of current being drawn by both power tubes in milliamps. Write this value down.
3. Measure the voltage on the plates of the power tubes to ground. Write this down.
4. Now, subtract the voltage from the cathode resistor in step 1 from the voltage measured on the plates. Write this value down. Take this value, and multiply it by the current (milliamps) from step 2. This will give you the dissipated power (in watts) of both power tubes. Write this figure down.
5. Take the figure from step 4 and divide by 2. Write this figure down. This is the power dissipation (in watts) of each tube. For 6AQ5s in Class AB, if it is over 9 watts, then you need to install a higher value cathode resistor. If it's 7.5 watts or less, you need to install a lower value cathode resistor.
6. After installing the new cathode resistor, do ALL of the steps again to see what you now have. You may have to repeat this process several times to get it dialed in, but it is worth it, and your ears will thank you.
|shortcircuit||3/13/2018 2:53 PM|
|davohilts||3/13/2018 5:49 PM|
|Looks pretty close, it would be interesting to check with a set of matched tubes. Good job.|
|shortcircuit||3/14/2018 9:54 AM|