Alamo Fury Schematic?

[CJ]

check the usual suspects, but can not find schemo,

7868 pwr tubes with a solid state preamp,

ultra linear bass amp,

like the matching pc board! art deco


works but lots of transistor noise, i guess i could trace it out,

thanks for any help!

 

[Gus]

Looks like a fun little bass amp.
The solid state section does not look to bad to trace. It looks like two transistors

 

[Gus]

CJ found the following

https://www.mouser.com/datasheet/2/149/2N5210-193106.pdf
https://www.mouser.com/datasheet/2/68/2n5088_2520series-1130989.pdf
https://www.mouser.com/datasheet/2/149/fairchild semiconductor_mpsa18-325943.pdf

Depending on what the preamp power supply voltages is MPSA18 or 2n5089 might work if the transistors are noisy.

I would check the tropical fish cap and the other caps I have measured a few that had leakage issues with age
I would check and change the preamp electros.
The carbon film resistor are most likely good

When I work on something like this with an unknown story I will often test and replace if necessary every suspect part, it is often faster than trouble shooting and thinking you fixed it changing one part and hours or days later something else fails.

https://www.premierguitar.com/gear/ask-amp-man-reviving-an-alamo-fury.

 

[CJ]

thanks Gus! traced it out, couple of H parameter 5210's with a a bax/james in between,

vol pot on J1 appears to be a mod,

rev 1 schemo,\>

 

[CJ]

pain and suffering sheet 1

 

[fazer]

Conjunctive filter. Interesting

 

[Gus]

It has a low input impedance a buffer might help a opamp(or what you like) buffer with 220k to 1meg input resistance might

I like split emitter resistors one for gain setting(less than 47k in parallel what is after it/1K gain each stage) and the other for biasing(two resistors added together for DC biasing and one being cap bypassed.

If the power supply voltage is not too high it looks like you could try high beta low noise transistors and they should work.

 

[CJ]

replaced q1 and q2 with ksc1845 low noise transistors,

improves voltage rating from 50 v to 120 v, hfe about the same,

measured hfe of originals as q1 394 and q2 at 315 (4v, 15 ma)

sounds good, quiet, customer had me put a JBL D120 15" in there,

new schemo with test voltages and opt info>