federicopol

Hello everyone, sorry for the necroposting: my sra 12s is misbehaving so time to grab the soldering iron. the plan was to get it repaired but... in the end i decided to do it myself. PLAN: Strip and Rebuild the AMPLI board completely Recap, and new diodes/resistances for the psu, recalculate the voltage divider for the normal bias from 200v to 230v Redo the pro bias circuit i added some years ago. Maybe strip and rebuild the IS amplifier stage (that i never turn on, so not useful per se but will do just because) I have a couple of questions: i remember seeing a service manual for this amp somewhere here but i can't find it anymore, someone has it? I see the toshiba to3 transistor is difficult to obtain nowadays, is this one suitable? https://www.mgelectronic.rs/tranzistor-2sc-1167# Do somone has a reliable sorce for 2SK30-O and 2SK30-GR? (or can point me to a substitute?) Thank you very much

Thank you very much. That way i will need one trafo only at expense of some more small parts. Will study, will copy, then probably ask again if doing it correctly. Thank you very much again

Hello everyone, here asking for some help wuth a build i am planning: I'd like to build a amplifier that has: pro bias and normal bias. Sounds reasonably good, Proven circuit. Simple to make and not to much expensive because i want to build up skills and confidence before a more serious build. So i choose the tubecad curcuit (stealing the schematics plus PS that @chinsettawong posted on his thread on the other forum) the only problem is that i also need normal bias. I plan to put a voltage divider on the BIAS PS and take 230v from that. Is my curcuit modification ok? Did i commit basic newbie errors that will kill me and burn my house? Or is the voltage divider a stupid idea per se? i plan to use an hammomd rrafo for valve amplifiers for HV and Heater and two small trafos with one wired backwards for the bias. Thank you very much

Hello, while i wait for some parts for restoring my sra12s i made some new earpads for my sigmas. I also made the internal dampening. Following the advice of Spritzer i used the most dense material i could find. By pure luck the material and quantities i used seems to be ok. The soundstage seems here, definitely the best of the headphones i own. The bass is present and clear so i am pretty happy of the final result. I decided to substitute the earpads because i don't feel comfortable using earpads that have been used by someone else for 30 years... I decided to not use a spare pair of lambda earpads because of the different shape of the lower back part. I made them in leather following the procedure Stax (or their supplier) probably used. I used an embroidery machine to sew the ear oval on the reverse side of fabrics, then i reversed the fabrics. With the fabrics now on the right side i added some low heigh memory foam cutted a couple of mm smaller than the finished earpad. Now i used the embroidery machine to close the earpads. Cutted the excess leather and here they are. They are a bit bigger than the original ones and are less stuffed, nothing dramatical but i will remade them the next time i have time to use the embroidery machine. The same method can be used to make them with a sewing machine for the oval and an overlock machine using 3 threads and a short lenght stitch.

Thank you very much, i'll remove them and try with something dense. By the way in my sra12s i have a +640V rail on the PS that feeds the amplifer board. Using that 640v point and a 2 resistors voltage divider to create the pro bias voltage is the normal way to do that? Ir therebis a better way? Thank you very much and sorry for the newbie requests...

Hello, i am new here and since the Mafia reside here... i'm gonna ask for a help to the Padrino or some of his associates.... I recently bought a sra-12s that needs some love (a recap, a pot cleaning and an adding of a pro bias out), i got a discount on the original asking price and i got gifted a pair of stax sigma Normal bias ("because i don't know what to do with them if i sell the amplifier"). The Sigma are really ok, the drivers are ok, they simply need a cleaning AND a new damping because the original glass wool dampening have been removed. My question is: What can i use for remake the dampening? (I llan to use quilt batting, is that ok?) What shape the dampening should have? (Should i cover all the planes except the driver one, am i right?) And there seems to be a pair of resistor attached to the cable connecting the driver, are they normal? Thank you very much.