Old Alamo amp tube help needed

[jwj4856]

I have an old Alamo model 120525 amp head that is supposed to work, previous owner took tubes out and put in another amp and does not remember what tubes were in it. Does anyone know what tubes it takes in this amp, it takes six tubes, 3 are smaller tubes and 3 look to be larger tubes by the sizes of the sockets.

[sumgai]

jwj,

This is gonna get tricky....

(EDIT: I missed a reference, so I've edited my original post.)
I saw lots of other Alamo amps aboot the innerwebs, but for your given model number, I only found photos.

I'm no expert on these, but most, if not all, of the postings/web sites I've encountered so far showed a tube chart stapled to the bottom (inside) of the cabinet..... is yours intact, or completely gone?

HTH



sumgai

[cynical1]

sumgai pretty much laid it all out. The only reference I found to that part number was "Alamo 2 Channel Head #120525" from a list of amps that Sonic Circus is selling off as a package.

You might want to send them a quick message, or call them at 1-888-SC4-GEAR (724-4327) or 1-802-365-9190. If they still have the amp maybe they can tell you what tubes are in there.

Hope this helps.

Happy Trails

Cynical One

[D2o]

Failing any of that, you could look at reviews of Alamo amps on Harmony Central.

Some of the reviewers list the required tubes, and you may get lucky and find some other model/name/serial number that matches your head.

If you do think you've found it, report back here to sumgai before doing anything - just to be safe.

D2o

[sumgai]

CynicalOne hits it pretty close, but I "sort of" missed that one reference from Sonic Circus. You might look at these photos, and see if your amp looks like this:
Alamo Head - Front.
Alamo Head - Back

I didn't read every review at Harmony Central, but those I did read referred to only one tube at a time - what's up with that? I did find a forum (AmpTalk) that dealt with a tubeless 6A, you might give that a gander.

Otherwise, we'll have to go inside and look at some of the components, then we can make some sort-of educated guesses about the tube complement. Let's hope we don't have to go that far!

HTH



sumgai

[jwj4856]

I think I have found out what they are, maaybe some of you can tell me if this sounds right,
3 - 12AX7
2 - 6V6
1 - 5y3 or 5U4GB

and I looked at the pics you referenced to sumgai and that is the amp I have, it may be old and ugly but the price was right (free) and it is supposed to work with new tubes put in. I guess I will see.

[sumgai]

Just be aware that Alamo was all over the map, tube-wise, using whatever seemed to be "the flavor of the day". Your guess is fairly common, but it's founded in Fender's history.... Not every manufacturer copied Fender slavishly (like a certain British company), many of them took pains to make sure they were not a Fender wannabe.

I'd still look at the circuitry inside the chassis before I stuck anything in those sockets. At the very least, I'd look to see what the filament voltage is, and how the power tubes are biased. Lots of other things too, to make sure I'm getting the right idea about which tube to use, but that's probably not what you're looking for, here and now.

In fact, let's do this: Plug in only the rectifier tube. Essentially, they're all pin-compatible, they just have different operating characteristics. (Yes, there are internal differences, but for our purposes.....) Turn the unit on, and wait 10 seconds or so - does the rectifier light up?

If no - STOP! Check the fuse. If it's blown, replace it with the correct value (the chassis should be marked), and try again. If the fuse is good, but there's no filament light (perhaps a pilot lamp on the front panel is lit up?), then you have a major problem - STOP RIGHT NOW! Unless you are an electronics technician with experience in tube circuitry, then get you fingers out of the furshlugginer chassis, and disconnect the power cord. Put it all back together, and take it to a trusted amplifier repair dude.

If yes (the rectifier lights up), then you may continue to march. Power down for a moment, and insert the first two pre-amp tubes. Power up, and check for glow (the pre-amp tubes, Sparky - not the glow plug of your Fox Spitfire 049!). If they're good, then repeat with the remaining 9-pin tube, powering down first, then back up after the insertion.

Still good? Repeat with the power tubes, but first make sure all the controls are turned down to Minimum! Make sure a speaker is connected, then power up. While you're listening for hiss, static, or whatever, keep a sharp eye on those power tubes. Also, keep your nose peeled. If there's a bad capacitor in the power supply, now's the time for it to start mis-behaving. Either it'll stink, or it'll pop (loudly!), be prepared.

If at any stage something doesn't light up, and you're sure the tubes are good, then I strongly suggest you invest in a qualified amp repair person. If you're on a budget, look to see what comparable amps (Alamo or otherwise) are going for on both eBay and craigslist in your area - that's about how much you should be willing to spend on a repair job. Any more, and you're upside-down, anything much less, and you've got good reason to smile.

Oh, and if you possibly can, perform these initial tests with used (but known good) tubes - no sense in risking frying a brand new one, eh?

HTh



sumgai

[jwj4856]

amp did not have any type of name or anything on it but I did find out that it uses
3 - 12 AX7
2 - 6V6
1 - 5Y3 or 5U4GB

Got them in and it works just like it is supposed to. Pretty good sounding amp with a single 15" Jensen Speaker cabinet.