Sunn Concert Bass

rehab of an old 1975 "classic" silver face Sunn Concert Bass amp,

in between revs, so things do no match up to documentation, half of this schematic mixed half of that,

Motorola 2N3055 transistors checked out ok, one had more gain than the rest so we used it for the driver to keep things somewhat matched on the 4 output devices,

made it into a "Dual Rectifier." 

there is one pwr bridge and two small ones, now we have two big and one small,

this in-between rev has a single supply out put stage of 50 volts running the show.

transformer wire color codes are different than triple supply schematic,

preamp board, 3 epoxy fets on input stages and two transistors, sockets for all,  distortion control is two ganged pot,

this is a transformer driven output stage, we replaced five resistors, old 2 watt carbon comps had drifted upward at various rates,

forced bias voltage divider,  resistor values vary over the years,  from 910 ohm 2 watters to 1.5 K  5 watters,

bottom resistors do not change, 22 ohms at 2 watts,  so V-eb  sets in at about 0.450 volts plus or minus a few mv,

replaced main filters, new caps are a lot smaller, two at 3300 uf at 63 V,

some schematics show two 6800 uf for dual rails, 

single supply models have 3400 uf for main rail,  1000  uf for preamp positive rail and 250 uf for preamp negative rail,

this model has neither of those values, it uses the 3300 for main rail, 3300 for preamp positive rail and 1000 uf for preamp negative rail.  had to trace out wires to figure out which amp we had,

took some output stage voltages, 100 K pot controls bias of first three transistors, the third transistor running at about 200 ma thru the xfmr primary,

no protection circuit, no output cap, but this design is pretty reliable with that transformer isolating things, however, there is a service doc on adding stability RC networks which fortunately this amp already has,

here is the dual supply version ,  concert lead and bass are mostly the same save reverb pan for git,

preamp board components with supply volts,

preamp schematic, will add voltages later,

another classic put back into service which will be scooped up quick as this town is crazy for Sunn amps for reasons unknown, especially the Beta series where you can blend clean and dirty.

pwr check says 100 watts all day with low heat generated.

I have a concert bass amp.  I need to check which version it is.  I fixed it a long time ago with replacing some caps but it’s been a solid performer for some time now.  Wouldn’t mine a schematic if the concert lead for comparison.

Years ago I saw the JEFF Beck Group with Carmine Appice and Tim Bogart  .  They played through Sunn concert and sunn coliseum SS amps .  Sounded great .  Beck used a colorsound distortion pedal.  It sounded great.  Very short lived but talented band.

that was my second show!

$4.50    no service charge, free parking.

Beck had a blue Univox,  twin cabs,  Carmine use to hammer those drums and scream like a mutha,

there are a ton of schematics online at various places,