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PostPosted: Tue Dec 01, 2020 1:46 pm 
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Location: Shawnee, OK
Looking good. "I love it when a plan comes together".

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PostPosted: Sun Jan 03, 2021 7:19 pm 
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Finished the build. Here's some pictures. Testing is next.


Attachments:
File comment: Mosfet leads wired up
MosfetLeads.jpg
MosfetLeads.jpg [ 3.09 MiB | Viewed 1918 times ]
File comment: Board installed in chassis
BoardInstalledInChassis.jpg
BoardInstalledInChassis.jpg [ 2.34 MiB | Viewed 1918 times ]
File comment: Power Level knob soldered
PowerLevelSoldered.jpg
PowerLevelSoldered.jpg [ 1.98 MiB | Viewed 1918 times ]
File comment: Mosfet soldered to board
MosfetInstalled.jpg
MosfetInstalled.jpg [ 2.24 MiB | Viewed 1918 times ]
File comment: Bias switch soldered
BiasSwitchSoldered.jpg
BiasSwitchSoldered.jpg [ 1.52 MiB | Viewed 1918 times ]
File comment: Preamp Socket soldered
FinishedPreampSocket.jpg
FinishedPreampSocket.jpg [ 1.81 MiB | Viewed 1918 times ]
File comment: A view showing the input jack and volume knob
FinishedInstall2.jpg
FinishedInstall2.jpg [ 2.22 MiB | Viewed 1918 times ]
File comment: All finished!
FinishedInstall.jpg
FinishedInstall.jpg [ 2.55 MiB | Viewed 1918 times ]
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PostPosted: Sun Jan 03, 2021 7:25 pm 
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So before I begin testing, here are a few questions I have:

1) Why do I have four 68k resistors left in my kit? I don't see ANY 68k resistors in the diagram?!?
2) DRAIN. It mentions installing a 220k 2W resistor on the B+ line, but I see a couple in the schematics... is this already done? If not, how do I figure out which is the plate pins?
3) I understand how to measure the AC voltage and the B+ 400 VDC voltage. But I don't understand where the rectifier pins are, or the filament voltages. Maybe at IDLE all the pins should be 3.15 V? Is that AC or DC? And how do I measure 6.3 V?? across the heater wires?

Thanks! I'm excited to try it out.


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PostPosted: Mon Jan 04, 2021 2:12 pm 
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rschultz wrote:
So before I begin testing, here are a few questions I have:
1) Why do I have four 68k resistors left in my kit? I don't see ANY 68k resistors in the diagram?!?
2) DRAIN. It mentions installing a 220k 2W resistor on the B+ line, but I see a couple in the schematics... is this already done? If not, how do I figure out which is the plate pins?
3) I understand how to measure the AC voltage and the B+ 400 VDC voltage. But I don't understand where the rectifier pins are, or the filament voltages. Maybe at IDLE all the pins should be 3.15 V? Is that AC or DC? And how do I measure 6.3 V?? across the heater wires?


OK, I think I figured some of this out. The rectifier pins are the 2 diodes at the end of the PT red secondary leads. That should be 630VAC, although the PT chart in the manual still says 275x2 or 550 VAC. The PT was updated in 2018 to higher voltages.

Also, the filament voltages are just the voltages on the tube pins according to the chart in the back of the manual.

Still curious about the DRAIN method and the 68k resistors.


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PostPosted: Mon Jan 04, 2021 10:33 pm 
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I fired it up tonight.
Rectifier pins: 650 VDC
B+ 440 VDC
Heater voltages all good.
2nd cap increased as VRM increased.
2nd cap @ 400, all tube pins are correct EXCEPT V1 Pin 1 was 195 instead of 203. ?!?

Plugged in my guitar. Sounds like a guitar amp. Only initial observation is that the bass knob does nothing, treble knob is a little noticeable. The FAT switch is very noticeable. But I had a small 4ohm speaker hooked up, so maybe a good 10" will give more of a bass change.


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PostPosted: Sun Jan 24, 2021 5:23 pm 
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Today I added the OT switch for EL34s, and modified it to use KT66's.

The KT66 mod suggested is to replace the 560 ohm resistor with a 1kohm. So I did that onto the board. But then I wired a 1k5 ohm in parallel with it to a switch so that when the switch is OFF, it is 600 ohms (close to the original 560). But when the switch is ON, it does nothing and only the 1k is active for the KT66.


Attachments:
File comment: OT switch for EL34's
OT-Switch.jpg
OT-Switch.jpg [ 2 MiB | Viewed 1849 times ]
File comment: 1k5 over the top of 1k ohm for KT66
CathodeResistors.jpg
CathodeResistors.jpg [ 2.14 MiB | Viewed 1849 times ]
File comment: ON - just 1k for KT66.
OFF - 1k in parallel with 1k5 = 600 ohms

KT66-Switch.jpg
KT66-Switch.jpg [ 1.55 MiB | Viewed 1849 times ]
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