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HELP! Alamo Scematics

j45

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I have a pair of pristine late 1950's Alamo Model 6 amps, the big ones in the beautiful wood "A" cabinets with P15N powered by two 6L6's.....somewhat similar to a tweed Pro. Both need some repair, have very complex tone circuits, and are true point to point without any turret boards. I desperately need schematics and have had no luck finding anything for the Alamo Model 6.

If anyone knows where I might find or can help me locate schematics I would be forever grateful. Either that or if somebody knows a tech very familiar with this particular circuit (it's a real nightmare if not) I would be happy to ship them. I've owned these for many years... one was just awesome before it went down and the other, although cosmetically pristine, needs work as well. I would be thrilled to have them working again....they've been sitting for way too long. Any help would be greatly appreciated.

oops *schematics" (title)
 

MapleFlame

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Kerry, shoot a pic of the innards and post it. Lotta these amps had the multi wire filter caps.
 

j45

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I'll get pics. The tone section is a series of push buttons that boost or cut selected frequencies, kind of a half a$$ varitone/parametric EQ and being true PTP it adds the equivalent of four or five bird's nest thrown in the mix. Hard to see anything but capacitor soldered to resistor upon capacitor soldered to resistor upon more and more of the same all swirled around in a big whirlwind of components. Never seen anything like it.
 

Diablo1

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I repaired an odd amp that was point to point wired with no schematic. It takes a little patience. You could draw up your own schematic by tracing wires and making measurements with a DVM. A good technician should be able to repair it, but finding a good technician may be a problem.
 

roadrunner

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I've got the same amp I've been wanting to work on for years... went looking for a schematic and... nada.

Hopefully, there's something out there.

What's wrong with your Kerry? Are they making sound?
 

j45

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It's been so long it's hard to remember what each is doing. I do know one was playing just fine...amazing, actually. I think I remember it just kinda a blew out and got softer and rough sounding...I believe. The other needed work, can't remember what but seems it made sound.

Do you think there are techs out there that could look at that circuit and figure it out? I'd be willing to send them off.
 

roadrunner

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It's been so long it's hard to remember what each is doing. I do know one was playing just fine...amazing, actually. I think I remember it just kinda a blew out and got softer and rough sounding...I believe. The other needed work, can't remember what but seems it made sound.

Do you think there are techs out there that could look at that circuit and figure it out? I'd be willing to send them off.


You've done the obvious thing, replaced the tubes, cleaned the tube sockets, checked the filter caps, checked for cold (or broken) solder joints?
If it's not the tubes, and all the electrolytics are ok, it might be an output transformer... hopefully not. That "getting softer" thing does happen when an output transformer starts to go south.

I've found, over the years, that tube amp problems are almost always tube related. I'd start there.

I got my amp up and running by retubing it, I had to replace the filters too, they were leaking badly. Ran great after that.

Make sure you run that old beauty on a variac, 115 volts or a little less... those old amps definitely don't like modern wall voltage, it's way too high for the design of those circuits and their components.
 

Diablo1

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Hey J45, where are you located?
If you are near Chicago, you could drop the amp off with me.
I'm not a pro, but I bet I can fix it.
 

j45

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Hey J45, where are you located?
If you are near Chicago, you could drop the amp off with me.
I'm not a pro, but I bet I can fix it.

I'm in Baton Rouge, La. Not close but I'd be willing to ship it if you'd like to give it a shot. If you will send an email to krhys at cox.net, I will send a note with details of what I know about the amp so far.
 

Diablo1

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Say J45, can you post up some gut shots of the amp?
I'd like to see some close ups of the caps and resistors.
I want to make sure I can read the values by eyeball since there is no schematic. I saw a pic of an old Alamo on the Music Electronics Forum and it was near impossible to read the values because of the deterioration. I don't want you to ship the amp unless I'm sure I can do you some good.
 

j45

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Will do...it may take a few days. The amps aren't here at home but I'll go get pics ASAP. Thanks.
 

Wally

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Feb 27, 2003
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I have one of those, too, j45. I am in the process of recapping it. My components' values are readable. Contact me if I can help with it.
I have worked thruogh a number of these older Alamos...and even a more 'modern' one from the mid-60's...without a schematic. I had a friend/customer who played harp and was into the smaller Alamo's that were the little brothers to this Model 6....same cab design just smaller.
 

Diablo1

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Hey J45, I'd send it to Wally, since he has a working amp to verify voltages and component values. That's a lot less sleuthing than I'd have to do.
 

cryptozoo

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Hey J45, I'd send it to Wally, since he has a working amp to verify voltages and component values. That's a lot less sleuthing than I'd have to do.

You really don't need a schematic to work on an amp. :rolleyes: This sounds like a puss-out. I enjoyed your bet of being able to fix it, and personally, I'd like to see what you can do.

Get an RCA handbook and compare voltages to what you find in the amp. Dump a seperate preamp signal into the power section to quickly see if the problem is with that satellite tone section. Prior to digging in, you need to trust most wax caps will be drifted while drop-style caps will probably be OK. Most of the resistors are probably OK. Cap values shouldn't be much of a mystery.
 

Wally

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j45, I was meaning to say that the cosmetic look of the cabs are the same...the stylized 'A' in plywood. Yes, the tone section/schematic is necessarily a bit more convoluted in the big Md. 6. Those push buttons remind me of the push button auto transmission in my first car...a 1960 Plymouth station wagon that would haul all of the equipment a young guitarist could need back in 1966.
 

Diablo1

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You really don't need a schematic to work on an amp. :rolleyes: This sounds like a puss-out. I enjoyed your bet of being able to fix it, and personally, I'd like to see what you can do.

Get an RCA handbook and compare voltages to what you find in the amp. Dump a seperate preamp signal into the power section to quickly see if the problem is with that satellite tone section. Prior to digging in, you need to trust most wax caps will be drifted while drop-style caps will probably be OK. Most of the resistors are probably OK. Cap values shouldn't be much of a mystery.

Puss-out? Maybe.
If it was my amp, I'd have a go at it for sure. I just think Wally is a safer bet because he has a working amp and knows the cap and resistor values by either measuring or reading the codes/labels. He also can measure the voltages at every socket pin on his working amp, so he can quickly tell where the problems are in the one that needs repair. What if it needs a new PT? Wally can figure out the requirements based on his working amp. How the heck could I possibly guess the right B+ voltage to spec? Sure I could get a transformer that would work, but I couldn't match an unknown B+. Here's one of mine that I fixed up without a schematic, the Capitol:

118j7kz.jpg

2rzti68.jpg
 

Diablo1

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Jan 20, 2008
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Ahh I know this company. They made amps for everyone. Lemme look to find the schematic.

Lectrolab was a name for them too.

Try this and match the tube chart.
http://lectrolab.wordpress.com/category/lectrolab-r600/

I do believe you are right about Lectrolab building my Capitol amp. However, it doesn't match any Lectrolab schematic or tube complement.
The Capitol has six 6EU7 tubes, four 7591 tubes and a GZ34 rectifier. It is a stereo amp with two output transformers. It is cathode biased, has a tube tremolo (cap and resistor network), grid leak bias for the input triodes, and a cathodyne phase inverter. The transformers are labeled "Tranco" and are dated to 1961. It has two Jensen C12R speakers that also date to 1961. My amp cabinet is also made of real wood, not press board like most other Lectrolabs.
 
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