Alamo Montclair w/ solid state preamp

[gui_tarzan]

Alamo schematics are like hen's teeth - difficult if not impossible to find for some models. So I thought I'd try to replicate it in a readable format but I have a couple of questions. No matter what variation of this schematic I look at I can't figure out what the symbol circled in orange is and I'm not exactly sure what some of the values are on a handful of components that are circled in blue.

I am interested in this version because my Alamo Paragon 2575 had a SS preamp but the board is long gone and no schematic exists for that.

[Jon Snell]

D5 protects the gate of the JFet from going positive more than the drain voltage. Otherwise if the gate rose too high it would strip the gate and damage the fet.
This type of Fet, (similar to a valve), requires a negative voltage with respect to the drain (cathode) of the gate (grid) to switch off.

[nevetslab]

My first Bass Amp was an Alamo....combo amp, 15" Jensen. Might have been a Paragon. I think I still have the schematic tucked away in one of my old notebooks in storage. Had a pair of 5881 power tubes, the rest as I recall were 12AX7's. Bought it with a Gibson EBO bass for $150 (if memory serves) from a small mom & pop music store in downtown Inglewood, CA. I didn't know squat about electronics then, just building cables, speaker cabinets, cobbling gear together for the band's PA system.

[gui_tarzan]

D5 protects the gate of the JFet from going positive more than the drain voltage. Otherwise if the gate rose too high it would strip the gate and damage the fet.
This type of Fet, (similar to a valve), requires a negative voltage with respect to the drain (cathode) of the gate (grid) to switch off.

So it's a diode? I can't tell from the pic.

[gui_tarzan]

My first Bass Amp was an Alamo....combo amp, 15" Jensen. Might have been a Paragon. I think I still have the schematic tucked away in one of my old notebooks in storage. Had a pair of 5881 power tubes, the rest as I recall were 12AX7's. Bought it with a Gibson EBO bass for $150 (if memory serves) from a small mom & pop music store in downtown Inglewood, CA. I didn't know squat about electronics then, just building cables, speaker cabinets, cobbling gear together for the band's PA system.

If you ever run across it I'd love to see it. I have a soft spot for Alamo amps.

[nevetslab]

All I have left is the schematic....no doubt had some mark-ups from whatever mods I might have made. The amp chassis left the combo case and into a cabinet made for just the head when I was using the wood shop in High School to build a proper speaker cabinet. Somewhere along the way, I sold the amp head, then having a Traynor YBA-1A replacing it, still sitting under my desk here in my shop, waiting for time to revise my restoration on it. When I get back to my lockers, I'll scan and post that schematic.

[gui_tarzan]

I have a YBA-1A too! Also in the process (sitting for a long time) of very mild refreshing. I don't know if I can still lift it or not, I have restrictions from aneurysm surgeries (and more to fix). I forget how much it weighs. Fifty pounds?

[Enzo]

The schematic notes spell out what the diode types are.

[gui_tarzan]

Thank you, I see that now. What I couldn't see in the schematic until I came back to it was that it is indeed a diode. D9. I still can't read some of the notes clearly enough to tell what they are. I have the start of cataracts and my vision is a little fuzzy at times. It still looks like a little star to me in this schematic.

This is part of the learning process for me. I am not very familiar with transistor circuits, but I'm trying and I'm getting there. In many ways they are laid out a lot like tubes but there just seems to be so many more parts to a transistor circuit. The way my brain works I sometimes get overwhelmed just looking at a busy circuit that has a lot to it and I have to put it down and come back to it. Sometimes several times.Forgive me for not spotting things as quickly as some of you can, you have a lot more experience than I do which is why I ask the questions. I do appreciate the help!

Doing this conversion from a fuzzy picture to a clear layout/schematic has two benefits - it helps me understand circuits better and it could help someone that is having trouble finding a readable schematic.

[35L6]

I don't see a 0V reference for Q3 or the PI cathode . Is that schem right ?

[gui_tarzan]

I didn't either and forgot to ask about that. I was going to look at other Alamo schematics to see what they had and I got distracted.

Edit - yeah, it's missing the ground. Thanks for pointing that out. I'm updating the schem. What's funny is it's missing on the original too.

[nevetslab]

I have a YBA-1A too! Also in the process (sitting for a long time) of very mild refreshing. I don't know if I can still lift it or not, I have restrictions from aneurysm surgeries (and more to fix). I forget how much it weighs. Fifty pounds?

Good guess. I just weighed mine, and a few ounces less than 48 lbs. I put a pair of spring-loaded handles on both ends of the top panel so it's easier to lift.