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Old 27th August 2011, 09:03 PM   #1
emosms is offline emosms  Bulgaria
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Default ef86 - plate voltage

Hi,
trying to recreate the voxac15 pentode chanel.
Up til now, it sounds like any other valve, no highs, no chime, nothing special.
It breaks a little when cranked, but in low to mid range, dont like it.
Started to believe that they cheat in the demo and use some processor.
(vox ac15 heritage)
PT after rectifier, uder load - 294v
Voltage at plate, ef86 - 204v
Voltage at g2 - 34v
So, I suspect it is pretty low voltage, so the gain is not enough
(but the hum is already comming..)
What's the normal plate voltage for these? Pretty new, cant calculate it yet.
I followed this scheme>
View image: ef86 part

Last edited by emosms; 27th August 2011 at 09:05 PM.
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Old 28th August 2011, 04:36 AM   #2
korey is offline korey  United States
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http://www.mif.pg.gda.pl/homepages/f...010/e/EF86.pdf
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Old 28th August 2011, 11:10 AM   #3
emosms is offline emosms  Bulgaria
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Have no idea how the datasheet is related to the frequency spectrum.
You can run it with 100k or 220k anode resistors, getting different current through the valve, end..
How I can get more high range and some distortion?
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Old 28th August 2011, 11:17 AM   #4
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An actual measured plate voltage of over 200V is way too high. These things usually run with plates volts below 100V.

Cheers

Ian
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Old 28th August 2011, 11:52 AM   #5
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Hammond shows ninety v on the plate and ninety v on the second grid. 250 VAC plate source and a 220k plate resistor. See keyboard-partner.de H100 organ schematic, upper right. (input from the reverb).
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Old 28th August 2011, 10:12 PM   #6
emosms is offline emosms  Bulgaria
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After all
more distortion at lower current through the valve?
I noted, when I fire up the machine (no stand by switch), it sounds more distorted before heating is fully on.
The supply voltage is higher, but the current through the valve is lower
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Old 29th August 2011, 07:37 AM   #7
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Quote:
Originally Posted by emosms View Post
After all
more distortion at lower current through the valve?
I noted, when I fire up the machine (no stand by switch), it sounds more distorted before heating is fully on.
The supply voltage is higher, but the current through the valve is lower
I think the effect you are hearing is more due to lower emission than lower current.

Cheers

Ian
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Old 29th August 2011, 01:17 PM   #8
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Quote:
Originally Posted by emosms View Post
Hi,
trying to recreate the voxac15 pentode chanel.
Up til now, it sounds like any other valve, no highs, no chime, nothing special.
It breaks a little when cranked, but in low to mid range, dont like it.
Started to believe that they cheat in the demo and use some processor.
(vox ac15 heritage)
PT after rectifier, uder load - 294v
Voltage at plate, ef86 - 204v
Voltage at g2 - 34v
So, I suspect it is pretty low voltage, so the gain is not enough
(but the hum is already comming..)
What's the normal plate voltage for these? Pretty new, cant calculate it yet.
I followed this scheme>
View image: ef86 part
Mr ValveWizard
http://www.freewebs.com/valvewizard/pentode.html
has a few things to say why this is so, i9n his book. Basically, Vox runs the EF86 at a very high gain and high loading, which makes it sound "HiFi" and without character.
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