Baldwin C1 problem...the one with the colorful push-buttons

[acorkos]

My cousin recently acquired a non-working Baldwin C1 Professional 2x12 amp...2 channels, channel 1 with vol/bass/treb only, channel 2 with vol/bass/treb/trem speed/intensity/reverb, and a switchable push-button tone modifying circuit....looks like an old car AM radio.

I found the schematic on page 181 of the 4th edition of my Jack Darr book, so i asked my cousin to bring the amp to me to see if I can sort it out for him.

All the control work, but the output is not right. channel 1 has low and very distorted output. channel 2 has clean and low output. Tone, trem and reverb controls are doing their job.

I measured the voltages against those on the schematic and they all check out...at least those on the channel 1 side, power supply and output circuit. There's a partition blocking access to the channel 2 circuitry. I haven't disassembled the amp yet to get to the channel 2/trem/rev circuitry, since I figure the problem may be common to both channels. Before I disassemble the amp to get to the channel 2 circuit, I am wondering if anyone has any advice on what to check next...? I put the diode tester on my DMM on the output transistors and they all behave similarly. Anyone with experience with this amp? BTW, what's a #1134 ballast lamp? it's on the schematic in series with the speaker +, and it's missing on this amp.

[52 Bill]

...I am wondering if anyone has any advice on what to check next...?

I worked on one a few years ago with similar symptoms, and had to replace a number of off value and open electrolytic coupling caps.

I believe that the #1134 is a 12v car tail light lamp. It was not in the one that I worked on either. I don't know if it was removed earlier by another tech, or if it never had one to begin with.

By the way, the schematic in the Darr book, and all the ones that I have seen elsewhere, are incomplete. The tone control networks on the switch circuits have not been drawn in detail.

[teemuk]

The ballast lamp was not initially part of that design; it was included later so not all amplifiers have it. There were also some other revisions – mainly to the preamplifier circuit - so schematic in Darr’s book may not be the correct one for every amplifier. The “Supersound” circuit (the coloured push-button tone control) also came in at least two versions. To best of my knowledge, circuits of both versions were depicted erroneously in the schematics. (I haven't had a chance to verify this, though).

[acorkos]

I worked on one a few years ago with similar symptoms, and had to replace a number of off value and open electrolytic coupling caps.

Thanks...I got some funny readings on the electrolytics. I will be replacing all of them tonight.

[acorkos]

cha-ching!

cap job completed....amp is working again. thanks for the tip.

[Enzo]

1134 lamp is a dual contact bayonette based lamp. That is the same base as the common 1157 dual gilament brake light lamp. But the 1134 has a 6.2v filament (3.91 amp). It is not shaped like the car lamps either, but who cares in a speaker?

[acorkos]

what is the lamp's purpose in the output circuit?

[Enzo]

If I had to guess, I'd say the same thing that large light bulb in series with your blown up amp on your bench - current limiting.

But I don't have your schematic.

[52 Bill]

Enzo: You're right about the bulb, I was working from my aging memory about the voltage and number. I was just too lazy to look it up.

Acorkos: Glad to hear the amp is working! I remember that model amp as having a nice full tone, with a great bottom end. But then again, I'm working from my memory here.