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September 15, 2019, 10:58:08 AM

Author Topic: high voltages with E80CC Mod  (Read 166 times)

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Offline mudvin

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high voltages with E80CC Mod
« on: May 18, 2019, 03:17:23 AM »
Hello,

I recently built my latest crack with a few mods, aiming of running E80CC tubes as the input tube. Other than some cosmetic mods, I installed 470 Ohm resistors in the appropriate position and changed the transistors on the small speedball board from MJE350 to MJE5731 (why not).

The amp sounds great!, no noise at all. Unfortunately the voltages on the Big board are slightly high with the E80CC tube. I will mention that I am in Australia with a true 240 volt supply (so in practice it varies from 240 to 245 or so), and I think this may be related.

I have tried 4 different E80CC tubes from different sellers and date codes however the voltage only varies a little (10 volts up or down on the key measurements)

I have built a SEX plus another crack with no issues before, and I did try swapping in the speedball boards with the same result.

So given the figures below and wish to continue running e80CC , I'm just wondering if I should change the biasing resistors or if there is something else I need to look at.

Thanks,
Rob

Small Board (E80CC +470 Ohm resistor)

OA - 94
IA  - 178.2
B - 0
IB - 178.1
OB - 92.7

Small Board (12AU7 +237 Ohm resistor)

OA - 71.3
IA  - 184
B - 0
IB - 183.3
OB - 70.2

Large Board (E80CC +470 Ohm resistor)


OA - 121.5
OB - 120.3
G - 0
B+ - 190.3

Large Board (12AU7 +237 Ohm resistor)

OA - 103.8
OB - 105.6
G - 0
B+ - 182.3

Base Crack (12AU7 + 6080)

1 - 81
2 - 180
3 - 0
4 - 179.9
5 - 80

6 - 0
7 - 108.4
8 - 0
9 - 107.2
10 -0
« Last Edit: May 18, 2019, 03:23:12 AM by mudvin »

Online Paul Birkeland

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Re: high voltages with E80CC Mod
« Reply #1 on: May 18, 2019, 06:58:31 AM »
You could try a 510 ohm resistor to nudge the plate voltage down a little more.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline mudvin

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Re: high voltages with E80CC Mod
« Reply #2 on: May 18, 2019, 03:29:09 PM »
Thanks for your help Paul.

I swapped in 511 Ohm resistors that I had on hand. Im thinking it looks pretty good now, although the large board voltages are still high (due to wall voltage ?)

Regards, Rob

Voltages (E80CC  +511 Ohm  Resistor)

Small Board
OA - 84.6
IA - 193
B - 0
IB - 193
OB - 83.2

Big Board
OA - 115
OB - 116.9
G - 0
B+ -  192.5

Online Paul Birkeland

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Re: high voltages with E80CC Mod
« Reply #3 on: May 18, 2019, 03:44:14 PM »
That looks good.  The output voltages on the large board will follow those of the small board a bit.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline mudvin

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Re: high voltages with E80CC Mod
« Reply #4 on: May 19, 2019, 03:22:34 PM »
Thanks for your help!

Rob