Weber 5G15 Problem

[johno9]

I have a new build of the Weber stand alone reverb. With a pedal board feeding the input there is breakup/clipping when reverb is brought up with the Mix control. it seems to be accentuated with the Tone control in the treble region. I don't notice it with my Strat plugged straight in, but it does appear with a Les Paul & humbuckers plugged into it.

Voltages are all on the high side - PS point A-353VDC, point B-289VDC, heaters at 6.7VAC. They were higher with the PT wired to 120VAC, so I am using the 125VAC winding instead. No documentation on the point A expected voltage and the layout indicates that point B should be 250VDC.
The kit came with a JJ 6V6S tube, which I think can handle the point A voltage, but I think PS resistor R16 needs to be increased to lower the point B voltage to the 12AT7 and 12AX7 to 250VDC.

I don't see any forum posts elsewhere related to voltage problems with this kit. So I wonder...
Am I on the right track?


Weber 5G15 Schematic.pdf

[pdf64]

A voltage survey of all valves would be a good thing. Maybe mark up the schematic with anode, grid and cathode (& screen grid) VDC for every valve, controls at minimum.

[loudthud]

Does this breakup/clipping occur if you cut off the reverb with the footswitch ?

Does this breakup/clipping occur if plug your guitar straight into the 5G16 ?

It is unlikely that too high a Voltage at point B would cause the distortion you describe. What are the Voltages on pins 1,2,3,6,7,8 of the 12AX7 and 12AT7 ?

[Helmholtz]

Agree with the above.

Typically higher B+ increases clean headroom.
A 1k/2W resistor between the bridge and the choke would lower point A voltage by around 30V.

What is RT1?

The Fender '63 Reverb RI doc shows typical circuit voltages: https://schematicheaven.net/fenderam...erb_manual.pdf

[johno9]

Voltage survey
12AT7: 1-144, 3-2.0, 6-152,8-26
12AX7: 1-196, 3-1.5, 6-290, 7-132, 8-146
6V6: 3-344, 4-353, 8-27.3

[loudthud]

12AT7 pin 8 looks bad, check R4 resistance to ground at each end with power off.

[pdf64]

Yes, there’s something deeply amiss with the 12AT7 pins 6,7,8 section circuit.
1.4mA anode current, apparently 17mA cathode current.

[Helmholtz]

Maybe pin 8 voltage should read 2.6V?

[johno9]

My mistake with recording values on 12AT7. Pin 8 is 2.1

[Helmholtz]

My mistake with recording values on 12AT7. Pin 8 is 2.1

That makes the voltages looks ok.

Do you have a scope?

[Greg_L]

I have this same kit. Mine works beautifully. You asked for my voltages the other day in my thread about my own 5G15 build. Here's my voltages....

V1 12AX7
1) 193.5 VDC
2) 0
3) 1.5 VDC
6) 293 VDC
7) 133 VDC
8) 147.4 VDC

V2 12AT7
1) 135.7 VDC
2) 0
3) 2.16 VDC
6) 140.5 VDC
7) 4 mv
8) 2.3 VDC

This is where mine differs. I'm using a different OT and a NOS 6K6 output tube like the originals. IMO the 6K6 yields a much smoother and deeper sounding reverb effect than the 6V6 the kit calls for.

V3 6K6
3) 339 VDC
4) 340 VDC
5) 20mv
6) 348 VDC
8) 31.8 VDC

Hope this help.

[Chuck H]

I have a new build of the Weber stand alone reverb. With a pedal board feeding the input there is breakup/clipping when reverb is brought up with the Mix control.

Is it possible your pedal board includes a preamp type effect or device that may be increasing signal voltage? This wouldn't be likely to affect the dry signal, but it may overdrive the reverb signal through the unit. That might explain why the distortion is affected by the tone control. This theory is also supported by the problem being accentuated with higher output pickups. So, can you tell if the distortion is on the dry signal, reverb signal or both?

[Helmholtz]

V3 6K6
3) 339 VDC
4) 340 VDC
5) 20mv
6) 348 VDC
8) 31.8 VDC

As the 6K6 doesn't have a pin 6, what does the > 6) 348 VDC < value mean?

[Greg_L]

As the 6K6 doesn't have a pin 6, what does the > 6) 348 VDC < value mean?

That's just where the screen voltage lands, then it bridges to pin 4 through the screen resistor.

[Helmholtz]

That's just where the screen voltage lands, then it bridges to pin 4 through the screen resistor.

Thanks, but I don't see a screen resistor in the schematic of post #1.
Is your schematic different?