Another Kent amp to checkout

[AmberB]

Hello, all!
I have another Kent amp to check out for a friend.  This one is a model BA-170 head.  It uses two EL-84 power tubes, two 12AX7s, one for preamp, one for PI tube, and a 6AT6 for the tremolo, plus a 5Y3 rectifier tube.  This amp has some funky circuitry, and horrible heater wiring, and grounds everywhere in the preamp.  I suppose it's typical of cheap mid 1960s amps.  This one is cathode biased with a 5 watt 130 ohm resistor.
I have not been able to find a schematic for this model. 
When it was brought to me to check out, it had been given a new 3 wire power cord.  The weird thing is, instead of removing the "death" cap, they put another one in on the other side of the mains.  I took them both out.  Now to see if the thing works, or if it buzzes loudly...

[Stuff4bikes]

Got any pictures of the circuit?

[AmberB]

I haven't taken any pictures yet, but I will.

[AmberB]

I found a bad resistor in the power supply, the 10Kohm between the first and second filter was way high, above 200 Kohms.  I replaced that and now I have a decent voltage in the preamp.  Now I have to figure out why 1 of the EL-84s is red plating right away.  It may be the tube, I'm going to swap them and see if the problem follows the tube.

[AmberB]

The problem with the power tube red plating turned out to be leaky coupling capacitors between the PI tube and the grids of the power tubes.  Both of them were leaking voltage, but the one leaked a lot more than the other, causing the red plating.  There was about 15-16 volts on the grid of the EL-84 that was red plating, and about 4 volts on the other one.
Now I just have to figure out why I have to turn the amp all the way up to get any volume from the guitar.  Without an original schematic, I'm kind of shooting in the dark.  The amp had been worked on at some point and many of the caps are replacements.  I think most of the resistors are originals, but I can't be sure.
I'm attempting to draw up a schematic for the amp based on tracing the circuits that are in the amp now.
Another thing, this amp is running about 380 volts on the plates of the EL-84s...
Here's a couple of pictures of the amp.

[AmberB]

A couple more pictures.

[AmberB]

Well, lucky me, I finally got this amp working so that it amplifies the guitar signal decently to the speaker and, of course, it also amplifies hum.  It's quiet with the volume all the way down, the louder you turn the volume, the louder the hum gets.
I put all of the grounds I could find in the preamp to 1 point, and that's grounded to the chassis in the area of the preamp. 
The amp has a cap can that's grounded to the chassis.  The centertap of the PT secondary is grounded at the cap can.  The ground of the output side of the OP is also grounded at the cap can.
The amp output tubes are cathode biased, that ground is also at the cap can.  The cap can contains the bypass cap for the cathode resistor.
A couple of the tremolo grounds are grounded to the pots, but it amplifies the hum with the tremolo tube removed.
There's no center tap for the heater winding, and in true Kent fashion, one side is grounded to the power tube cathodes.  I probably should build an artificial center-tap  for the heaters...

[acheld]

Are the caps original?  I know nothing about Kent amps, but was struck by the all Japanese caps in the build.

[AmberB]

I really don't know if the caps are original or replacements.  This is the first one of this model of Kent amps I've had a look into.
I can tell you that at least 2 of the green caps were leaky.  I replaced all of them. 
I worked on a Kent DR-57 previously, all the caps in that preamp were ceramic disk caps.

[AmberB]

Well, another attempt to stop the hum on this amp.  I had all the preamp grounds wired to one spot, and I also put an artificial center tap on the heaters.  That didn't solve the problem.  So now I'm redoing the grounds to an isolated common ground that I'm going to wire to the ground of one of the input jacks and see what happens there.
I think this amp had less buzz with the grounds scattered all over the chassis...