Silver Jube Clone Oscillation?

[ViperDoc]

The Clean channel's distortion does not sound good. It has quite a "splat" to it.

I like my amps to have a smooth transition from clean to distorted. "Splat" sounds like this transition is rough. Is that what you're describing? I don't know what makes one amp awesome and one bad in this regard, but I suspect lead dress plays a part. Always looking for insight.

When engaging the Lead Channel, I have no complaints. Pure rock and roll. Engage the Clean: SPLAT. I'll try and get a sound byte. Entertaining family again at the moment.

BTW, your headphone trick strikes again with excellent results. I found that a 5-10 degree rotation on my OT made a huge difference when planning placement. I'll get you a pic.

[ViperDoc]

When this amp is cranked on the lead channel, it sounds like a high gain monster, but I think that may be hiding the "splat" I hear on the clean channel. Chop sticking has produced no results.

I pulled my power tubes and measured the following:

DMM resistance to chassis ground:
Primary: BRN = 8.5 M
WHT (CT) = 114.7 K
RED = 8.9 M
Secondary: 4R TAP = 0.5 R
8R TAP = 0.7 R
16R TAP = 1.0 R
I can play this amp good and loud now, but the distortion is garbage unless I'm cranking the lead channel. Do these readings suggest a secondary short to the OT core? Never been in these waters.

Here's a sound byte from my iPhone:

Viperdoc2550splat.m4a

LATEST VOLTAGES:
WALL AC = 121 VAC
HTS = 348 VAC
B+1 = 443

V1:
PIN1 = 240 VDC (These V1 plate voltages are about 30 volts higher than the Ceriatone reference chart. Will knock those down.)
PIN3 = 1.9
PIN6 = 214
PIN9 = 1.46

V2:
pin1 = 215 VDC
pin3 = 1.69
pin6 = 107
pin8 = 0.48

V3:
pin1 = 246 VDC
pin2 = 26
pin3 = 41.8
pin6 = 229
pin7 = 27.3
pin8 = 41.8

v4:
plate = 436
screen = 430
grid = -39.4
cathode = 37 mA

v5:
plate = 441
screen = 436
grid = -39.7
cathode = 35 mA

[martin manning]

I pulled my power tubes and measured the following:
DMM resistance to chassis ground:
Primary: BRN = 8.5 M
WHT (CT) = 114.7 K
RED = 8.9 M

Brown and red should be almost the same as the CT to ground since you're just adding the primary DC Resistance. Are you sure those readings are good?

Secondary: 4R TAP = 0.5 R
8R TAP = 0.7 R
16R TAP = 1.0 R
I can play this amp good and loud now, but the distortion is garbage unless I'm cranking the lead channel. Do these readings suggest a secondary short to the OT core? Never been in these waters.

If it sounds good on the lead channel the OT is probably fine.

Here's a sound byte from my iPhone: Viperdoc2550splat.m4a

LATEST VOLTAGES:
WALL AC = 121 VAC
HTS = 348 VAC
B+1 = 443

V1:
PIN1 = 240 VDC (These V1 plate voltages are about 30 volts higher than the Ceriatone reference chart. Will knock those down.)
PIN3 = 1.9
PIN6 = 214
PIN9 = 1.46

V2:
pin1 = 215 VDC
pin3 = 1.69
pin6 = 107
pin8 = 0.48

V2 pin 6 looks low, but if that is the one with 220k Ra and 470 Rk, it is probably ok.

V3:
pin1 = 246 VDC
pin2 = 26
pin3 = 41.8
pin6 = 229
pin7 = 27.3
pin8 = 41.8

v4:
plate = 436
screen = 430
grid = -39.4
cathode = 37 mA

v5:
plate = 441
screen = 436
grid = -39.7
cathode = 35 mA

V3, V4, and V5 look good. I would look for something amiss in the preamp boost switch wiring.

[ViperDoc]

Brown and red should be almost the same as the CT to ground since you're just adding the primary DC Resistance. Are you sure those readings are good?

If it sounds good on the lead channel the OT is probably fine.

V2 pin 6 looks low, but if that is the one with 220k Ra and 470 Rk, it is probably ok.

V3, V4, and V5 look good. I would look for something amiss in the preamp boost switch wiring.

Those are the readings if I keep the OT primary CT connected. Disconnecting the primary CT, I get a meandering 35-40M to chassis ground that eventually reads open.

V2 pin 6 has the 220K plate load resistor.

Thanks for the boost recommendation.

[bepone]

@viperdoc
i see several not ok things in layout but if you say that high gain is ok.. than ok what to complain
but you can/ for sure/ pull down to the chassis OT wires connected to the output tubes pins 3 (anode), to not to make "antenna" in the air (very sensitive circuit)

you can also try for the "clean", actually crunch circuit to break (unsolder) marked connection and see if you will like more the sound..

TEST.png

[ViperDoc]

@viperdoc
i see several not ok things in layout but if you say that high gain is ok.. than ok what to complain
but you can/ for sure/ pull down to the chassis OT wires connected to the output tubes pins 3 (anode), to not to make "antenna" in the air (very sensitive circuit)

you can also try for the "clean", actually crunch circuit to break (unsolder) marked connection and see if you will like more the sound..

TEST.png

If you see issues with the layout, I welcome all feedback.

The OT primary is tack-soldered just to confirm the proper orientation. Overall, there is buzz on both channels, but is much less notable on the lead channel.

I appreciate your circuit mod suggestion. One thing I don't understand is how many LNFB loops there are in the preamp. It's confusing to look at. You recommended disconnecting one of them. There is another that goes from the V2A grid to the distal end of the V2A plate coupling cap, and possibly one more.

[bepone]

i have owned shortly one orig. silver jubilee and one marshall donor to became jubilee.. i did it but actually i never liked this "plastic" sound from the diodes.. it is not natural and it is annoying with time..so maybe this nfb loop is choking the sound. you can try and see if it helps..also you have better quality components inside (marshall used regular Iskra MKT block caps in that time, a have thousans of them ) and your high gain tone is maybe more complex than the original

for wires, you can put down to the chassis OPT wires to the pins 3, this can make things better

[ViperDoc]

I was able to make some massive improvements in this amp this week after letting it rest for a bit (year).

My original plan involved deleting the stock FX loop and implementing Martin's presonance circuit, and my initial results were flawed. The clean was farty and the presonance wailed on half of the pot. My PI waveforms were also severely squashed, and so I deduced the problem was operator error, WHADDAYAKNOW. I removed the presonance and installed a presence circuit with a 5KL pot and .1 uF cap. That instantly sounded better. [edit: That’s no diss on the presonance mod, I just don’t think I did it correctly.)

But I still had that farty clean tone. I took a hard look at the schematic and decided to reinstall the components of the original loop that were deleted except for the jacks. Not having much room, I decided to use a .1 uF Solen fast cap I had in the drawer, along with the 100K/10K voltage divider.

The amp now sounds *glorious*. It has some very creamy rock tones on both channels with the right settings. It is characteristically dark like the stock amp, but sounds good with the gain turned up on the clean channel. The lead channel has excellent control with the additional lead gain knob (a la SDM 2550X), it sounds very controlled but lively with the lead gain down and the lead volume up.

I need to balance the PI plate voltages and work on the Metro Loop, but that should be a success.

The clipping diodes in this circuit are very harsh sounding (1N4007s). Any recommendations on how to smooth that out? I was thinking a clipper. See what I did there?

VIPERDOC 2550X 1.3 SCH.pdf