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  1. #41
    Les Paul Forum Member MapleFlame's Avatar
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    Re: HELP! Alamo Scematics

    Quote Originally Posted by j45 View Post
    Finally a gut shot:

    Very very clean inside. Tight quarters for sure. I see three filter caps, two on the right and one center. Typically the power tube electronic on top tend to drift or cause issues from the heat. Definitely excited to see this amp restored as its a wonderful example. Kerry clips will be cool too.
    Top carves are sexy

  2. #42
    Les Paul Forum Member Triburst's Avatar
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    Re: HELP! Alamo Scematics

    Wow - That reminds me of a cross between a Tweed Deluxe and an early Trainwreck. Did you get the guys over at Komet to have a look?

  3. #43
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    Re: HELP! Alamo Scematics

    j45, that's a nice looking amp. IT has had service before, obviously. Many of my original caps look nothing at all like those maroon caps there. I may think my amp is older than yours and the one pictured by valcotone. Both yours and htat '52 have molded toen and coupling caps whereas mine has paper-covered caps in almost all of those positions. My amp also has many more caps installed..original...in the area to the right of that 'tone board' above the 12AX7 that sits between the power tube and the rectifier.
    If you could do me the favor, what are the values for those fitler caps on the right end of the chassis? And...are they wired in series? From what I can see, they are...adn those are bleeding resistors with them. THat amp might come to life with new caps in that position. My amp has a replacement cap there....a very large, single 20mfd/600V cap. The terminal strips for those original caps are still there though.
    I would appreciate that bit of information, sir, if it isn't too much of a bother.
    LOoking at your amp and comparing it to mine, I see some differences. IT would be intersting to have them side by side...not suggesting that I should work on yours...just saying it would be interesting. It woudl be intersting to compare dates.. ???I wonder if the schematic was changed some?? What year is your amp in this pic? THe code on my OT is 220837....?Jensen OT? I have never seen that before. THe speaker is coded 220108. I believe mine to be an early '51. Valcotone says that the amp in those pictyures was considered a '52. I would think that that amp and your amp in this pic are from about the same time frame...but who knows. Thsoe purple caps are one clue. Maybe the am that Valcotone pictured is form '62??? I have one source that says the Birch 'A' cabs were built from '49-'62.
    At any rate, thanks for bringing this subject up. I have had my Alamo apart for far too long now. You have encouraged me to get this one back together.
    I thin I understand what is going on withthe first stage of filtering there, but the values woudl be of help if it isn't too much trouble.
    "As soon as man does not take his existence for granted, but beholds it as something unfathomably mysterious, thought begins." Albert Schweitzer

  4. #44
    Les Paul Forum Member j45's Avatar
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    Re: HELP! Alamo Scematics

    Quote Originally Posted by Wally View Post
    IT has had service before, obviously. Many of my original caps look nothing at all like those maroon caps there. .
    Did you look at the Model 6 on the previous page? Looks like the same caps to me. My other one which is much cleaner and appears virgin has those maroon caps too. Looks like this one. The P15N has a date code of 220247 which would be late '62 or late '52. Since is looks to have 12AX7's I would guess 1962?

  5. #45
    Les Paul Forum Member j45's Avatar
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    Re: HELP! Alamo Scematics

    Quote Originally Posted by Triburst View Post
    Wow - That reminds me of a cross between a Tweed Deluxe and an early Trainwreck. Did you get the guys over at Komet to have a look?
    Yes, they looked at it but not going to get far with them without a schematic.

  6. #46
    Les Paul Forum Member j45's Avatar
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    Re: HELP! Alamo Scematics

    Wow, my other Model 6 has its P15N with date code of 220247, too.

  7. #47
    Les Paul Forum Member MapleFlame's Avatar
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    Re: HELP! Alamo Scematics

    Quote Originally Posted by j45 View Post
    Wow, my other Model 6 has its P15N with date code of 220247, too.
    That's pretty rare to have both from the same date code. pretty darn cool.
    Top carves are sexy

  8. #48

    Re: HELP! Alamo Scematics

    Thanks for posting the gutshot of your amp, J45. Looks just like the one I posted earlier.... the wiring and components really look like a bastard cross between an early 50s Fender and a 50s Valco. I've repaired lots of my old Valco amps (check my username! hah), but this looks like an extra level of complexity with the pushbutton tone tone control. I'm guessing that it's an early 50s amp, just based on the components, even with the 12AX7.... but it still has a 6SL7 for the phase inverter which is another clue it's older than '62.

    Strange design choice to have the power cord exit the top of the chassis. Despite that, I love the design esthetic of these amps. With the tube lineup and speaker... I can *almost* imagine what it might sound like.

    The matching speaker date codes are interesting... I'm guessing that Alamo didn't build a lot of these bigger amps, and they probably bought a bulk supply of P15Ns from Jensen. I've run across the same thing in larger Valco amps.



    Quote Originally Posted by Wally View Post
    My amp also has many more caps installed..original...in the area to the right of that 'tone board' above the 12AX7 that sits between the power tube and the rectifier.

    That could be the tremolo circuit (note that the trem controls are on the control panel right above that area). J45 - your amp is missing the 12AX7 for the trem... was that pulled for some reason?

  9. #49
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    Re: HELP! Alamo Scematics

    J45, my wording there leads to confusion, I think. "Many of my original caps look nothing at all like those maroon caps there." This statement was notmeant to imply that those maroon caps were non-orignal but that they were different from the orignal caps in my amp. These paper covered Illinois Condenser Co. caps in mine look to be an older style, adn I think that my amp is older than either of these amps that look so much alike...yours and the one in the earlier pics. Apologies for the confusion. My ap has quite a few balck Sprague caps from the center of the circuit on tot he right, and there are more of them there than are in your amp. Why? I don't know. Likeyou say, a schematic..or two....might be of interest. I have never seen one, though. I looked around some years back. Maybe they are buried somewhere downin San Antonio.....my birthplace by chance.
    I saw the grounded power cord and knew that your amp had been worked on. Those solder joints on the bleeder resistors don't look to be orignal, either, from where I see them. I could be wrong.
    IF you do have a chance and want to go to the trouble, the value of those two filter caps woudl be of interest to me....although I can probably take a guess as to what they are. The 5U4 gives us an idea of the max capacity at that point. IF those two caps are not in series but rather serve two different pints in the circuit, that is of interest to me, also....since I have only one cap serving that point.
    "As soon as man does not take his existence for granted, but beholds it as something unfathomably mysterious, thought begins." Albert Schweitzer

  10. #50
    Les Paul Forum Member j45's Avatar
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    Re: HELP! Alamo Scematics

    I'll get some values from both amps. Also want to check tranny date codes. I guess valcotone is probably right about the 1952 date. I think the 12ax7's are why these amps are so much more gainy and have great open top ends compared to the Fender tweeds from that same era which seem to have the metal preamp tubes..at least the ones I've had did. I find those earlier Fender tweeds to be too dark/dull sounding and not enough gain. That's why I was thinking this amp must be a '62. I didn't think Alamo would have been that far ahead of Fender in using the 12ax7's. These amps completely smoke a Fender tweed from the same era when it comes to overdrive and open top end. When did Fender start making the 12ax7's in the preamps standard?

  11. #51

    Re: HELP! Alamo Scematics

    Quote Originally Posted by j45 View Post
    When did Fender start making the 12ax7's in the preamps standard?

    1954 I think? I had a '53 5C5 Pro with octal 6SC7 pre-amp tubes.

  12. #52

    Re: HELP! Alamo Scematics

    Interesting detail on the two pictured amps... there are two extra leads going to the speaker or output transformer (in addition to black leads), looks to be red and yellow in colour. Sometimes this is an extra ground connection, but if they disappear up under the blue bell then it could be a F15N speaker (field-coil).

    Is the speaker model marked on the rim, P15N or F15N? I haven't seen that in any pics yet.

  13. #53
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    Re: HELP! Alamo Scematics

    I'll bet that bumblebee on the left of the board is leaky as hell. The brighter red caps on the board are probably good, the darker maroon ones in the center are more likely leaky than not. How leaky, and whether it actually affects things tonally, is a big question. These are just speculations based on my repair experiences. Those electrolytics with the bleeders to the far right are in series - you can see they are reversed end to end (black line marking negative on the wrappers) and they damn sure ought to be replaced. I can also see the terminals of at least one can cap near the center - that needs to be checked. Whoever ran the three-prong should have put the black lead to the side of the fuseholder for best practice - less likely to shock someone poking a fuse in there if they have a 'duh' moment and forget to unplug it. Why the trem tube (what I assume is the trem tube) is removed is anyone's guess but a lot of those "oddball" 50s trem circuits - Valcos especially - suffer from bleed through even when the trem is off. They tend to inject a pulsing hum into the background that gets annoying and they need a bit of "reorganizing" of the circuit to remove it. I also suspect it's using grid leak inputs. I would LOVE to draw out the schematic on this one! Looks very unique, kind of like a Valco on a fiberboard!!

  14. #54
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    Re: HELP! Alamo Scematics

    +1 with efk's observations on the wiring and those old e-caps. efk, you are correct about the grid-biased inputs. The input goes through .02mfd caps to the grids which are tied to the cathodes/ground via 4.7M resistors. I wish I were near you so you could draw the schematic off of this complete circuit I have here.
    "As soon as man does not take his existence for granted, but beholds it as something unfathomably mysterious, thought begins." Albert Schweitzer

  15. #55

    Re: HELP! Alamo Scematics

    Grid-biased.... another clue it's early 50s. I love my grid-biased amps.

    What a cool thread, thanks J45 and everyone for the input so far.

  16. #56
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    Re: HELP! Alamo Scematics

    Valco held on to grid leak biasing into the 1960s though, and I would not be surprised if Alamo did the same. It's a very effective input scheme, easy to implement, and it saved an electrolytic (cathode bypass) which were more expensive than cheap plastic caps. I still build most of my Supro-type amps this way on one channel, a real raw and old-timey sound/feel. It mates perfectly with those big honking 270K plate resistors. Which btw, it looks like this is using, based on the use of "smaller" .022 couplers.

    Edit: I should edit this by stating that while it may at first appear to be a "rat's nest" or nightmare as J45 put it, I don't see it that way. I build most of my amps on terminal strips or with direct soldered flying leads, and once you work in this manner and get away from turret boards a bit (not that there's anything wrong with that, just different), it becomes much more natural-feeling. I prefer it, now, to a typical Marshall turret board arrangement for example.
    Last edited by efk; 03-22-13 at 05:12 AM.

  17. #57
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    Re: HELP! Alamo Scematics

    Also looks like the heaters have no center tap but run one side to ground, aka like some very old tweed Fenders as well as the Supro single ended amps. That might be adding some noise if so Looks like the two maroon caps mounted right on the output tubes are the couplers from the phase inverter (.022 as well? can't read) they've been subject to a good deal of heat over their lifetime. Definitely want to check those carefully for leakage as the amp will do funky things when they start leaking.

  18. #58
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    Re: HELP! Alamo Scematics

    efk, those caps above the power tubes are .002mfd/1000V on mine. I take them to be original because they are the oldest looking caps in my amp. (AS I noted, none of these coupling or tone caps in my amp are the maroon caps that we see in these pics in this thread.) These .002mfd's look to have seen a lot of heat as you say, and they have accumulated more dirt than any other cap in my amp. Teh values are readable after lightly rubbing soem of that oily dirt away. These .002's contact to pin 3 plate on the
    6L6's. They then are contacted on pin 6 with 3 wires that lead on to the right of the circuit as we look at these pics. When I have more time, I will try to delve farther into that area. You probably have an idea as to where they lead.....trem function?? IT gets 'interesting' in there. All of the caps...Illinois Cond. Co and black Spragues... that occupy the other places where we see these maroon caps in these pics are .02mfds as far as I have been able to ascertain.
    "As soon as man does not take his existence for granted, but beholds it as something unfathomably mysterious, thought begins." Albert Schweitzer

  19. #59
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    Re: HELP! Alamo Scematics

    Wow! Pin 6 is a tie point (no tube connection), so they could be going anywhere, and being as "small" as .0022, they might even be going to ground off the plate as tonal shaping (much darker) as well as anti-oscillation aka the Silverface amps with the .0033 off the plates. Valcos certainly used a lot of 500 pf and 1000 pf caps to ground to kill oscillation due to "hasty" layout. If these have anything to do with trem function, that just might be the wierdest thing I've seen yet.

    One of you guys send me your chassis! I'm dying to map one out.

  20. #60

    Re: HELP! Alamo Scematics

    efk, thanks for your comments... it's a pleasure learning from another Valco enthusiast like yourself. I dig what you're doing with your amp builds as well.

    Hopefully, an end result of this thread might be a schematic and sound clips, if those involved are willing and able to move things in that direction!

  21. #61
    Les Paul Forum Member
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    Re: HELP! Alamo Scematics

    efk, I realized that htat pin 6 is a blank....great p iont fro connectiong to parts unknown. Maybe Sudnay I'll get this on the bench and do some more investigation.
    I have tried a time or two to draw schematics...with accurate but amateurish results according to those more knowledgable and experienced in mapping things out. I have no problem finding the path of the physical circuit...it is simply understanding how best to convey that via the schematic that ismy challenge....that and time.
    "As soon as man does not take his existence for granted, but beholds it as something unfathomably mysterious, thought begins." Albert Schweitzer

  22. #62
    Les Paul Forum Member j45's Avatar
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    Re: HELP! Alamo Scematics

    Quote Originally Posted by efk View Post
    I would LOVE to draw out the schematic on this one! Looks very unique, kind of like a Valco on a fiberboard!!
    Hey efk, if you would, please your email address to krhys@cox.net . Thanks

  23. #63
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    Re: HELP! Alamo Scematics

    Bringing back a dead thread I am.
    JT45, what ever went on with your Alamo? I have mine back online albeit in less than 100% function.
    The tone section does not work, and the trem speed is not adjustable. I have to find the time and the inclination to dive off into that circuit to cure those problems. Otherwise it sounds great.
    To draw the schematic for tis amp would entail tearing major portions of the circuit down, and that is probably what will have to be done to get that tone section working. As your picture there shows, that section is an electronic enigma wrapped in a messy puzzle, right?

    I was wondering if you got it worked on and if so how it came out..and who did it for you?

    I recently rebuilt a 1966 Alamo Fury for which there is no known schematic. Getting the amp working without the schematic was no problem as it is a simpler circuit without such clutter. The Sonics of the amp were so interesting that I had to draw the schematic...interesting tone section. The Bass control acts differently than a ‘normal’ bass cut circuit. Very interesting amp to play, imho.
    "As soon as man does not take his existence for granted, but beholds it as something unfathomably mysterious, thought begins." Albert Schweitzer

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