Webster 80 to 5C1 Champ Success!

[jonathan_kea]

Finally got the 5c1 conversion working! I do have a question, though. I understand that these amps are not typically very loud, but this incarnation seems quieter than what I would expect.

The original Webster circuit had a 1k voice coil (speaker) resistor built into the circuit (see images below). If I were to remove the resistor from the circuit, would it make the amplifier louder? The voltages below were taken after the amp had warmed up for ~20 mins with the resistor in place:

6X5
PIN 2:   3.2 VAC (Heater)
PIN 3: 335.2 VAC (Plate)
PIN 5: 335.2 VAC (Plate)
PIN 7:   3.2 VAC (Heater)
PIN 8: 340.2 VDC (Cathode)

6V6S (JJ)
PIN 2:   3.2 VAC (Heater)
PIN 3: 277.6 VDC (Plate)
PIN 4: 301.4 VDC (Grid 2)
PIN 5:   0   VDC (Grid 1)
PIN 7:   3.2 VAC (Heater)
PIN 8:  18.93 VDC (Cathode)

6SJ7
PIN 2:   3.2 VAC (Heater)
PIN 4: -1.384 VDC (Control Grid)
PIN 6: 20.89 VDC (Screen Grid)
PIN 7:   3.2 VAC (Heater)
PIN 8: 149.9 VDC (Plate)

1st Filter Cap (16uf): 301.7 VDC
2nd Filter Cap (8uf):  299.6 VDC
3rd Filter Cap (8uf):  283.0 VDC

[sluckey]

The original Webster circuit had a 1k voice coil (speaker) resistor built into the circuit

Put a jumper wire across that 1K resistor. B+ voltages should increase. Any better?

[Latole]

B+ voltage will increase a bit give more power... in theory ( a little bit ).
 IMO you won't ear it.

[jonathan_kea]

Thanks! I will try it this evening and let you know how it goes...

[PRR]

Do you have the "square" 25uFd cap shown on the Webster plan?? Without that, voltage is about 2/3rd and power is about 1/3rd.

[jonathan_kea]

No, just the 16, 8, 8 filters prescribed by the Weber 5C1 layout.... Not to be confused with Webster...

The original Webster 80 had a 6J5 between the 6SJ7 and the 6V6. Considering adding it back, but not sure if that will kill the bluesy 6SJ7 tone...

[jonathan_kea]

Latole - you were correct! It got a smidge louder but not noticeably. It did seem to increase the headroom some. Off to work on some chassis mods and a cabinet. Thanks all!

[terminalgs]

after removing the 1K (or jumpering across it)  what are your voltages for the B+ (@ 16uf cap), and 6V6 plate,screen/cathode?


 If you are using an original webcor OT, you might want to figure out the winding ratio.  A lot of those webcor OTs came with really high primaries (possibly 2X higher than what usually goes in a champ),  The original could be a 20K:4 or 15K:4 OT.

[jonathan_kea]

terminalgs - I took some readings right before I buttoned it up, and they didn't seem to go up dramatically. I will say that I was initially using a little 4ohm, 6" speaker to test with. When I hooked it up to a 12" 8ohm speaker, it was absolutely perfect - not loud enough to gig, but perfect for the house. The OT calls for a 4ohm speaker, so I am going to shop around for a 8-12" speaker for it.  I am working on bending the original chassis and housing into a more head-like shape (currently somewhat trapezoidal), and will post the B+ and other voltages just out of curiosity. I am itching to start a new project, so might be a minute before I open it back up.

PS - I am game to tackle the winding ratio question, too. Need to watch some instructional videos, etc, on how to do that. I have a 12v transformer on hand, which if memory serves might help to apply voltage in a safe manner. I think I saw Uncle Doug do it on YouTube, but don't quote me on that.

[sluckey]

Look here...

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