silvertone 1448

[bosobrne7]

my girlfriend has a 1448 and channel one isn't producing any sound at all. channel two sounds great, the effects work fine, but there's no sound in channel two. could it be a bad tube; possibly a 6L6GC or a 6CG7/6FQ7?

[Zee]

my girlfriend has a 1448 and channel one isn't producing any sound at all. channel two sounds great, the effects work fine, but there's no sound in channel two. could it be a bad tube; possibly a 6L6GC or a 6CG7/6FQ7?

Double check that model number. The 1448 schematic I looked up says that's the amp in case model, which has no effects, only one channel, and none of the tubes are 6L6 or 6CG7.

[bosobrne7]

it's a 1484.. my mistake.

[Zee]

Ok, that makes more sense. First, keep in mind that most others who post here are far more experienced that I with tube amp repair. I chose to reply because I had a similar issue with my old Danelectro amp.

My amp failed a couple times, both times due to plate resistors opening up. I ended up replacing 3 or 4 other resistors because they had drifted way out of tolerence. Everything else in the amp except for the piezo crystals in the reverb is still original.

Looking at the schematic, there's a 220 K ohm resistor on pin 6 of the first 12AX7. After the tone and volume controls channel 1 goes to the second 12AX7. That plate resistor is a 68 K ohm on pin 1. Either one of those being bad would kill channel 1, while leaving channel 2, reverb and vibrato functioning normally. That's an easy place to start since you can make a quick check with an ohm meter with no power applied to the amp.

Of course, if that's not it, it will require a bit more effort. It depends what your skill level is with electronics. Remember, amps can be dangerous, even when unplugged.

[Zee]

One more thing I should have been clear about. Based on the way my schematic is labelled, the first 12AX7 is the third tube from the right when looking at the back of the amp. There is a 12AX7 on the left and the right of that tube.

The second stage 12AX7 is immediately to the LEFT of the first 12AX7 when looking at the back of the amp.

[Bruce / Mission Amps]

And check to be sure it actually is a 12AX7 in the socket.... a good one.

[bosobrne7]

i'm thinking it might be a bad 12AX7... there's just no power to the channel. everything on the other channel works fine.

[Zee]

i'm thinking it might be a bad 12AX7... there's just no power to the channel. everything on the other channel works fine.

When looking at the back of the amp, the second tube from the right is also a 12AX7. It's for the reverb. Try that tube in the other two 12AX7 positions and see if channel 1 starts working and the reverb stops working.