Mike Stehr
Poverty Audio
This guitar amp has been sitting around for some time, and it's time to get to its rightful place or whatever.
I recapped the amp, everything except the four section multicapacitor being 20uF at 450v. It seemed to reform rather nicely for now...
It works except the tremolo, which has been the problem with the amp from the start.
There is a website with a handful of schematics of Alamo guitar amps.
None however cover the model 2571 being a 7591 PP circuit.
Okay, the Alamo Electra and Montclair and Galaxie are the same with regard to the circuitry using three 12AX7 and a 7199.
All the passive parts except for a couple resistor values, (220K,470K) and the layout are the same. Same with the tremolo circuit.
Even the heater circuit is the same. According to the schematics and me tracing through the 2571 circuit...
The Galaxie does have 1K grid stoppers at the grids of each 7591.
I thought this would be a pentode connected circuit. The Electra and Montclair circuits show a 220K resistor and 20uF cap section for the screens. "D".
The Galaxie has four primaries on the output transformer. The outer part of the primary winding has the plates of 7591 connected, the inner taps are connected to the screens of the 7591.
The B+ tap is in the center of the winding. The inner taps (screen) measure half in relation to DCR from the plate taps.
I think this an ultralinear connection, or is it some sort of humbucking...why the screen connection if for humbucking?
The Galaxie uses a 5U4 rectifier instead of 5Y3 used in the 6V6 PP amps. The first cap is a 20uF 450 section for B+, then 6.8K and 20uF for 7199.
I noticed on the Galaxie circuit the first cap is 20uF with a resistor of 47K then to B+.
From get go I should have paid more attention...I had thought there was an extra little output transformer for external speaker output. After tracing around it's a choke.
The external speaker output is tapped from the actual output transformer.
Thinking someone jeeped in a choke, I scrounged for other images online for Alamo Galaxie, and the images I found do have choke as well between the OPT and PS transformer.
The way the choke and first cap are connected to the rectifier is what I find odd.
It's wired that way in the diagram, and I'm pretty sure it's how the Alamo factory did it.
The 42mH value could be off from measuring in circuit...
I recapped the amp, everything except the four section multicapacitor being 20uF at 450v. It seemed to reform rather nicely for now...
It works except the tremolo, which has been the problem with the amp from the start.
There is a website with a handful of schematics of Alamo guitar amps.
None however cover the model 2571 being a 7591 PP circuit.
Okay, the Alamo Electra and Montclair and Galaxie are the same with regard to the circuitry using three 12AX7 and a 7199.
All the passive parts except for a couple resistor values, (220K,470K) and the layout are the same. Same with the tremolo circuit.
Even the heater circuit is the same. According to the schematics and me tracing through the 2571 circuit...
The Galaxie does have 1K grid stoppers at the grids of each 7591.
I thought this would be a pentode connected circuit. The Electra and Montclair circuits show a 220K resistor and 20uF cap section for the screens. "D".
The Galaxie has four primaries on the output transformer. The outer part of the primary winding has the plates of 7591 connected, the inner taps are connected to the screens of the 7591.
The B+ tap is in the center of the winding. The inner taps (screen) measure half in relation to DCR from the plate taps.
I think this an ultralinear connection, or is it some sort of humbucking...why the screen connection if for humbucking?
The Galaxie uses a 5U4 rectifier instead of 5Y3 used in the 6V6 PP amps. The first cap is a 20uF 450 section for B+, then 6.8K and 20uF for 7199.
I noticed on the Galaxie circuit the first cap is 20uF with a resistor of 47K then to B+.
From get go I should have paid more attention...I had thought there was an extra little output transformer for external speaker output. After tracing around it's a choke.
The external speaker output is tapped from the actual output transformer.
Thinking someone jeeped in a choke, I scrounged for other images online for Alamo Galaxie, and the images I found do have choke as well between the OPT and PS transformer.
The way the choke and first cap are connected to the rectifier is what I find odd.
It's wired that way in the diagram, and I'm pretty sure it's how the Alamo factory did it.
The 42mH value could be off from measuring in circuit...
