Fender Champ no sound

[mountaintop]

I have a '72 Fender Champ Silverface in good condition. I turned on the amp last week and nothing happened. The pilot light comes on be no sound. I replaced all the tubes with no effect. I noticed the tubes never get hot, even after 30 mins. Is it the power transformer? Help!

Ryan

[Albert Kreuzer]

Hi Ryan,

could be something simple like a broken heater wire or a bad solder joint.
So check all the connections first before suspecting the PT.

Cheers,
Albert

[Twist]

Can you see the filaments glowing inside the tubes?

[Amp Kat]

Check the cathode resistor and the capacitor also on the 6V6. If there is black around the ends it is likely toasted and will cause no sound. These output trannys are not very beefy and can blow quite easy in these, SE replacements are readily available and there should be a number on the top that you can use for a direct match-up if it is the problem. I've seen both and hopefully it's not the latter.

[6267]

#1 Try different speaker/make sure speaker is *well* connected

#2 Check speaker (with amp off and speaker disconnected) with ohm meter--it should not read infinity or zero, but somewhat close to its rated impedance (6-7 for an 8 ohm, etc)

#3 Depending on the age of your amp I would assume (and possibly be wrong) that the pilot light is a neon bulb/mini bulb lit by the heater winding. If the bulb is on the power transformer is *not* shot, but some of its windings might be. If the bulb is powered some other way, such as directly off the mains, this will not be the case (uncommon).

#4 In series heater amps (I don't think any fenders), one tube having an open heater will wipe out the entire preamp section. Try different preamp tubes.

#5 If there is no glow at the tops of the tubes, you are missing heater voltage. I would suspect a weird short before I replaced a transformer though. Check pins 4 & 5 of a *preamp* socket (i.e. 12ax7) or between 4 & 9. This should read either 12.6ish volts or 6.3ish volts (often 6.7 with 130v mains like I have)

#6 If you did not read voltage above, check with a DMM set for DC and then AC volts between the metal chassis and the ground pin of a socket (you could use a ground lift adaptor for an easier to access reference ground. If you are reading 6 or more AC or DC volts between chassis and the ground, you have a weird short. You might not measure anything here and still have a weird short.

#7 Some very strange amps power the preamps heaters with the negative DC bias supply from the power tubes. A failed power tube or other bias problem would also wipe out the heaters and preamp.

In conclusion, get a schematic, and also get some tube data sheets (http://www.nj7p.org/Tube.php or http://www.tubedata.org for tube info). This will tell you where to check for B+, Heater and cathode resistance to ground, among many other things. Also, you could carefully check between the heater windings coming off the transformer (if present) and see if there is AC there. Whenever dealing with high-voltage, keep one hand in your pocket! Sometimes this requires "balancing" one probe in place with the amp off (and physically stable!) but is much safer than using both hands.

Good luck, just some insights from my amp hacking experience.