Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: dude on January 12, 2012, 12:58:31 pm
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Hi all, my wife gave me this Alamo amp for Xmas. Nice gift. It was made around 1974 when Alamo went to solid state preamps and tube output, a pair of nice gray plates GE 6V6s and one RCA 12Ax7 for the driver, the rest, well a board with turquoise crayon-like caps and cc resistors.
Doesn't sound bad after I replaced the speaker surrounds but full of crunch and more crunch. The has two channels as you can see. Simple tone and volume channel one and tremolo other.
I'd like to change the preamp to a couple of 12ax7s and get rid of the solid state, pretty simple task. I can't find a schematic for this amp but that's not a problem for me. What I'd like get is a copy of a schematic that I can use to follow for the change. The PT looks rather small and with two more tubes, I'd like to get another, any suggestions? I'd like to stay with cathode bias and kind of the old brown tone and keep the diode rectifier but I guess if I need another PT I might as well use a 5Y3 or 5AR4 or the like...?
Just a simple tone/volume and tone/volume - intensity/speed I want to keep the face plate exactly the same.
Can anyone direct me to a schematic that fits this bill? I've been searching Schematic Heaven but thought it might be a little faster to ask here.
Thanks in advance,
al
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I found a nice 18 watt Marshall model 1974 that looks like it will fit well.
On the OT in this amp, see pic's.
There are two secondaries for the speakers, (white and blue wires). The one that is hooked up plays around 8 ohms (two 14 ohm speakers in parallel) the other goes to an extension speaker jack but what ohms?
How can I tell what the ohms is on the blue sec. wire?
al