So It looks like the power amp and pre amp are fighting for current. The power supply puts out 75v the pre amp is taking 31 and the power amp is taking 50. So my guess is that the pre amp zener is has gone bad and that the excess load on the PS filter cap is what destroyed the last cap.
There is an x with 4 dots around it on the pc board. I know I have seen it some where but don't remember where. Can anyone help me with that one. I have not been able to find it online.
Next thing on the list is to put a 25v zener in.  If I knew what those x 's mean I would be more sure about moving ahead.

Ok, tested the BR with dc and it was good. So its back to the drawing board.
Thanks for the help!

Ok , so I put in the new cap. Fired it up and it sounded great.Till today... The main problem was that when it started up it would slowly fade in with white noise then be fine. Today rather than starting up like it should it faded up  but without white noise. I tested the bridge rectafier (on AC volts) by placing the Dmm probes on oppisite ends. I got a ( more or less) 53 on one set of corners and a 152 volts on the other set of corners.
I think that its off. My guess is one of the diodes is bad. Am I in the right neighborhood or should I look elsewhere?
Thanks

Thanks
I measured 54 V on the transformer under load. (54X1.41)-1=75.14 Does that sound right ?

I have a Yamaha Bass amp that needs a new PS filter cap. The cap has a 100 WV rating. My guess is that a 100 V cap can be subbed in but, I have never seen a WV rating on a cap so I am not sure. Why would they rate a cap like that?

I just realized I had some of these hanging around .

SK3450


Various :: Si PNP Lo-Pwr BJT   
Specsheet / Datasheet


V(BR)CEO (V)=80

V(BR)CBO (V)=80

I(C) Abs.(A) Collector Current=500m

Absolute Max. Power Diss. (W)=750m

h(FE) Min. Static Current Gain=160

@I(C) (A) (Test Condition)=150m

@V(CE) (V) (Test Condition)=10

f(T) Min. (Hz) Transition Freq=120M

Package=TO-92var

Military=N

Ok
I have a JC 77 with abnormal hiss. Abnormal even for JC 's. I used an audio proble to trouble shoot.
everythings cool till it hits these transisters on one of the amps. I done some reading on subing transisers but still find my self lost in the sea of numbers. Any help would be apreciated.
Thanks

Part Number = 2SA970GR
Manufacturer Name = Various
Description = Si PNP Lo-Pwr BJT
V(BR)CEO (V) = 120
V(BR)CBO (V) = 120
I(C) Abs.(A) Collector Current = 100m
Absolute Max. Power Diss. (W) = 300m
I(CBO) Max. (A) = 100n
@V(CBO) (V) (Test Condition) = 120
V(CE)sat Max.(V) = .3
@I(C) (A) (Test Condition) = 10m
@I(B) (A) (Test Condition) = 1.0m
h(FE) Min. Static Current Gain = 200
h(FE) Max. Current gain. = 400
@I(C) (A) (Test Condition) = 2.0m
@V(CE) (V) (Test Condition) = 6.0
f(T) Min. (Hz) Transition Freq = 100M
@I(C) (A) (Test Condition) = 1.0m
@V(CE) (V) (Test Condition) = 6.0
C(obo) (Max) (F) = 4.0p
@V(CB) (V) (Test Condition) = 10
@Freq. (Hz) (Test Condition) = 1.0M
Package = TO-92
Military = N

Well I formed the caps. They charge up at 215v the caps have a can take a surge of 400v so there  is a good chance they are fine. They are new caps not old or nos so maby they can handle that stuff better. So after all of that my amp still hums even when it is not connected to a speaker. The chanle leds flash from one chanle to the next for a split second when the amp is turned on. So I am going to test the diods next. The hum doesnt change when I adjust the volume and there is a hum when there is no speaker. So it must be in the power supply.
Thanks for the help!

I just put in new PS filter caps  ( 45uf 350v) in a ss tube hybred I dont have a variac So I  just fired it up. My amp seems to have 3 power supplies 1 for the power amp ,1 for the tube pre and 1 for the eq/reverb. What an odd amp. I just found and artical that said if you dont have a variac you can put some 100k 2w resisters on in line with the caps till they are charged.
Is that still option or do I need new caps? What did the surge current do to the caps ?

After looking at the schem that makes sense.
Thanks for the help!

Hello
I have a Legend 3OA amp with the problem most of these have which is humm. The last owner replaced the filter caps on the power supply and put them in with one cap - to ground and other + to ground. Which ever end is not hooked to ground is connected to the rectifier diodes. I though the last owner made a mistake and put them in like that but they took the time to draw arows indicating polarity. So I am scratching my head on this one.
Also does anyone know where I can get a schematic?