Alamo amplifier, anyone know where to find schematics?

[Mr Johnny Birchwood]

Hey guys, just had an Alamo Fiesta model 2573 show up on the bench. SN#125-T65. I've heard of these things but never seen one until now. Seems pretty simple, this one works minus the tremolo. Quick google search turned up some incomplete historical background but no schematics or tech info at all. Anybody wanna point me in the right direction? Worth restoring or should I just hack it up and mod the crap out if it?

[Enzo]

Schematic Heaven has this Fiesta version:
http://www.webphix.com/schematic%20h...iesta_1962.pdf

Under bargain bin amps, there are a few others. Also, sometimes you find an Alamo with a different brand and model name on the outside.

Schematic Heaven. Where All Good Amp & Effect Designs Await Resurrection...

[olddawg]

If you have the amp with Enzo's schematic it is a series filament with a 50L6 but has an isolated primary. The trem problem is probably bad caps. I would say this is not a good amp platform for mods. If it is in decent shape I would fix it (keep the old parts), sell it, and look for something you really want. There are people out there that collect Alamos and such.

[Mr Johnny Birchwood]

If you have the amp with Enzo's schematic it is a series filament with a 50L6 but has an isolated primary. The trem problem is probably bad caps. I would say this is not a good amp platform for mods. If it is in decent shape I would fix it (keep the old parts), sell it, and look for something you really want. There are people out there that collect Alamos and such.

this one is series filaments with a 12av6 12au6 30c5 output tube and 30w4 rectifier. Got an isolating power tranny that appears to be low voltage, filter caps are 150v. Haven't powered it up yet to take readings bu I'm guessing 120 plate volts on the 30c5 pushin about 2 watts through the cts 8 incher. My buddy got this for free out of a junk pile, and he's not sure what he wants to do with it yet. Need to work up an estimate. If the tremolo worked it might make a fun little bedroom amp. If I was gonna mod it I would basically just use the chassis and output transformer.

Thanx enzo for the schematic link, I was striking out pretty bad randomly searching google. There is a facebook group dedicated to these things and they have some cool novelty value to em I guess. Neat little thing.

Edit: 35c5 35w4 --- the 35c5 does not look original, the tube designations are hand-written on the chassis, and the portion of the factory sticker with the tube layout has been ripped out. Gonna have to add another load in series, 35+35+12+12=84 and 122-123 vac will cook those fils pretty quick I bet..

[Enzo]

Many products from that era have tubes that do not "add up." The remaining voltage drop would be across a power resistor inside the chassis.

[Mr Johnny Birchwood]

Many products from that era have tubes that do not "add up." The remaining voltage drop would be across a power resistor inside the chassis.

correction. 35+35+12+12=94 not 84 derp! OH, and I checked the schematic, the fils are wired series and powered from a tap off of the secondary of the mains tfx, with one leg grounded and half wave rectifier for the b+.The fils tap looks like a ctr tap in the drawing but the tap could be any voltage I guess. If the tubes are ok then it probably just needs re-capped. My buddy wants it to be a bit more 'lively' so I may re-work the front end of the circuit a bit to coax some more gain out of it. I may just add a solid-state rectifier and maybe swap the 12au6 for a 12av6 and swap the grid-leak for cathode bias...

[Enzo]

SOlid state rectifier, eh? Then you will have to make up for the 35v drop that 35w4 represents.


The 12AU6 is a pentode and has a hell of a lot more gain than the 12AV6 triode.

Before you go modifying it, do recap it. That might be all the more liveliness it needs.


Remember, the schematic I linked to uses a 50L6 octal tube, so yours may be VERY similar, but there will be differences too, so always doublecheck your amp matches the parts of the swchematic you are working on.

[Mr Johnny Birchwood]

yeah a 200-250 ohm resistor in place of the 35w4 fil should drop the vac enough. Rewiring the front end tube would require a modification to the tone control as well. That pentode should produce plenty of gain, you are right. It's definitely a wise move to recap the thing before considering any mods. I'm curious enough about this thing that I'm just gonna take the time to tab out my own schematic before proceeding. The CTS pots and speaker date to the end of 1965 so this amp isn't any older than that. They probably changed the design between 1962 and 1965. This model also has a tremolo intensity control.

I may just offer to trade him for something that will suit his needs better if I'm gonna put that much time into it. My friends know by now that if they bring me something really interesting they typically get a bunch of work done for free..