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ecc40 circuit adjusting posible fault
ecc40 circuit adjusting posible fault
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Old 9th April 2019, 12:45 PM   #11
Kay Pirinha is offline Kay Pirinha  Germany
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Quote:
Originally Posted by Pauld35 View Post
el41 pi and power tubes.
What does that mean? Is there a EL41 as phase inverter, followed by two EL41 finals? Or is it a self balancing final stage with just two EL41's? Or did you just omit another tube that is the PI?
Best regards!
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Old 9th April 2019, 09:35 PM   #12
Pauld35 is offline Pauld35  New Zealand
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hi, yes it is EL41 as phase inverter, followed by two EL41 finals,


first is ecc40 into ef86 into el41 Phase inverter from factory

ecc40 is first pre input stage for tape /p u, ef86 second stage
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Old 9th April 2019, 09:42 PM   #13
Pauld35 is offline Pauld35  New Zealand
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Quote:
Originally Posted by Kay Pirinha View Post
What does that mean? Is there a EL41 as phase inverter, followed by two EL41 finals? Or is it a self balancing final stage with just two EL41's? Or did you just omit another tube that is the PI?
Best regards!
hi, the empty chassis socket in photo is plug for speaker wiring no tube goes there, the output transformer is located in speaker cabinet enclosure from factory, so plug wiring for extra wires from socket is for speaker selector switch
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Old 10th April 2019, 09:05 AM   #14
Pauld35 is offline Pauld35  New Zealand
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Quote:
Originally Posted by Kay Pirinha View Post
What does that mean? Is there a EL41 as phase inverter, followed by two EL41 finals? Or is it a self balancing final stage with just two EL41's? Or did you just omit another tube that is the PI?
Best regards!
sorry of course you must be right a single el41 cant be a pi on its own i will have a better look at the output stage
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Old 12th April 2019, 09:55 AM   #15
Pauld35 is offline Pauld35  New Zealand
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Originally Posted by gingertube View Post
.

10K seems way too high for the cathode bias resistor on the first triode. The data sheet suggests it should be 2K2. Thats sets the first triode idle current and hence the anode voltage . That anode voltage is what is seen at the grid of the cathode follower so it effectively sets the idle current for the cathode follower too.

Hi, i havent made any bias adjustments yet because i thought best to take some readings, just worried about the 100k bias on pin 4 as well, wondering if i should change that to about 2k2 at the same time.



thinking cathode 137v pin 4 to the volume vr and ef86 is pretty high or maybe the by passed tone circuit is ment to drop the voltage more before the ef86


-readings for ecc40-


anode pin 5 .....132v
input grid pin 6 .....0v
cathode pin 7......... 43v


anode pin 2 ......... 182v
grid pin 3.........128v

cathode pin 4.......137v
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Old 12th April 2019, 09:22 PM   #16
Pauld35 is offline Pauld35  New Zealand
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hi, i'm wondering if the tone switches in the photos are not tarnished, or if they maybe burnt from 137v going through them over time, and if the volume pot is maybe half ruined too or if that kind of voltage is normal for those components?



I always thought signal levels were quite low voltages until you got near the output tubes but maybe tube amps are different.
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Old 13th April 2019, 01:21 AM   #17
PRR is offline PRR  United States
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> cathode pin 7......... 43v

We expect more like 9V, as seen G-K on the other half.

Bad reading? Bad cathode resistor? Bad joint?
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Old 13th April 2019, 04:28 AM   #18
Pauld35 is offline Pauld35  New Zealand
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Quote:
Originally Posted by PRR View Post
> cathode pin 7......... 43v

We expect more like 9V, as seen G-K on the other half.

Bad reading? Bad cathode resistor? Bad joint?
Hi, thank you. yes you were right, i read meter wrong. took the readings again wrote them on the schematic. Do you think this circuit as it is from factory can operate correctly or do think there is maybe a fault or in correct parts installed?


if it seems normal i will look back at tone circuit if it is there to create a v-drop to bring the pin 4 voltage down
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Old 13th April 2019, 08:12 AM   #19
Pauld35 is offline Pauld35  New Zealand
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i have reconnected the tone circuit and now have a reading of 2v at the volume pot instead of a crazy 130 something volts.
I will trace the tone circuit because i think there must just be a resistor to ground to adjust or a leaking cap letting to much signal ground that is causing the volume loss. the signal quality seems fine so i think maybe the ecc40 section is ok how they have built it

Last edited by Pauld35; 13th April 2019 at 08:15 AM. Reason: ad
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Old 15th April 2019, 10:10 PM   #20
Pauld35 is offline Pauld35  New Zealand
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have mapped out the tone circuit and what i mistaken for cross over distortion was too stronger signal being sent the gain next stage.
with the tone circuit reconnected the signal voltage was brought down too quiet again, which strangely was a similar symptom of too much signal to the next stage.


the tone circuit has been adjusted to let less signal to ground. the amp works fine so am not sure that the ecc40 stage was biased incorrectly.



will try and find an tube online calculator that work out what range it is operating in, then try some bias adjustment from there.


am thinking alot of guitar amps dont use Negative Feedback so am wondering about self bias output stages and if this type output design has the same effect on the signal trying to drive the output stage as the NF does?



switchable tone circuit gain increase
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