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#1 2013-10-29 16:45:30

simondolanbass
Member
From: Montréal, Québec, Canada
Registered: 2011-11-28
Posts: 14
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V4-B Troubleshooting

Hi,
I'm working on this V4B for a while.

It's had EL34 installed and I put 7027 into. Also 6k11 circuit is bypassed.

I replaced the components using the schematic.

I can get out 10w of clean power and 50 W of distorted power. Something in the inverter is bad as I can see that only the lower half of the sine wave is distorted. I checked most of the resistors and they are good.

On tube V4 my plate voltage is bad. Nearly 100v higher that what is written on the schematic.

I replaced r52 and r53 in power supply with no changes. The 360V at C17 (square) is 415V and the 325V at C17 (triangle)is 394V! At R53 I've got 530V.

On the power tubes I've have those readings:
PIN 1 ----
PIN 2 HEATHER 6 VAC
PIN 3  531V
Pin 4  530.5 V
PIN 5 -57.5 V
PIN 6 -----
PIN 7 HEATHER 6VAV
PIN 8 0 V

I THINK THAT THE PLATE VOLTAGE AND GRID 2 VOLTAGE ARE too close.  Do I have to increase grid 2 resistor to decrease the voltage ? (R41,42,47,48)


Any help appreciated!

Thanks

Simon

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#2 2013-10-29 17:51:06

hangman
Banned
From: Seattle Washington
Registered: 2006-09-04
Posts: 1848

Re: V4-B Troubleshooting

Well,  your power supply voltage differences are easily explained if your 6k11 circuit is disabled. 
Less current draw from power supply point E means less current going through r51,r52,&53.  Which means less voltage drop across those resistors.   
You can't simply disable a portion of the circuit and not expect changes.

Your screen voltages are exactly what they should be.   You can up the resistors to 1k. But that won't really change the voltage there,  I advise doing  it just to make the power amp as stable as possible.   It prevents oscillations in the power amp.

If you feed a signal in the ext amp jack, does anything change?
If you feed a sine wave in to the input jack and then look at that signal at the ext amp jack,  what do you see there?

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