Vintage Modern problem-Help!

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TM1
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Vintage Modern problem-Help!

Postby TM1 » 19 Sep 2017, 12:04

I have a 50 watt VM that looses signal at C13's output. Goes from a nice good looking waveform to zip.. All the valves test just fine on my Orange VT1000 valve tester.
Any clue why this has gone awry?
Cheers

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Re: Vintage Modern problem-Help!

Postby Anitoli » 19 Sep 2017, 18:14

If c13 was open you should still get a partial signal through the bottom of the stack. Is the signal passing the other points in the stack?

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Re: Vintage Modern problem-Help!

Postby TM1 » 20 Sep 2017, 13:37

There's signal all the way thru, it has the bottom clipped off and looks ugly. It starts at the Treble cap. I can plug right into the Effects Return and signal looks good there through the output. But the culprit is before starting with C13...

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Re: Vintage Modern problem-Help!

Postby Anitoli » 20 Sep 2017, 18:16

C13 could be bad. I have seen silver micas literally crack open before and cause irregularities in the signal. Same for resistors. Now when you say plug into the loop you mean you are injecting a signal at that point?

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Re: Vintage Modern problem-Help!

Postby SteveD » 21 Sep 2017, 00:51

What are the dc voltages either side of C13?
Still my guitar gently weeps

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Re: Vintage Modern problem-Help!

Postby TM1 » 22 Sep 2017, 17:02

On the 33k side there's 175v. On the other side there's no voltage( the side that goes to the pot).

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Re: Vintage Modern problem-Help!

Postby TM1 » 22 Sep 2017, 17:41

I swapped out the 500pf cause it was easy and That seems to be where it starts.. No difference. If I turn the Treble pot off/down the signal goes up, but still the bottom 1/2 is semi-lopped off. The OP tranny has a physical hum/vibration to it so wondering if there's an issue with it. When the amp is on Standby it's not there. Only there when it switched to "On" and the B+ voltage is present.
Thanks!

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Re: Vintage Modern problem-Help!

Postby Anitoli » 22 Sep 2017, 22:07

Can you post a pic of the waveform?

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Re: Vintage Modern problem-Help!

Postby SteveD » 25 Sep 2017, 02:07

Those dc voltages are ok

Does it make any difference to the waveform when you enable/disable the FX loop?

How about if you unplug CON2 altogether thereby totally isolating all following stages?
Still my guitar gently weeps

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Re: Vintage Modern problem-Help!

Postby TM1 » 06 Oct 2017, 12:40

Image
Image
Top shot is with the "Dynamic Range" button pushed in.t Loop is engaged

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Re: Vintage Modern problem-Help!

Postby TM1 » 06 Oct 2017, 12:54

SteveD wrote:Those dc voltages are ok

Does it make any difference to the waveform when you enable/disable the FX loop?

How about if you unplug CON2 altogether thereby totally isolating all following stages?
O.k... I feel pretty stupid here as with the loop off the amp looks just fine. When the loop is engaged is when the signal gets ugly.
I'm going to try a patch cable between the In & Out and see what happens when I activate the loop..
With a cable inserted and the loop activated it's the same(didn't think it would be any different.. ).

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Re: Vintage Modern problem-Help!

Postby TM1 » 06 Oct 2017, 12:57

With Con 2 disconnected there's barely any signal passing at all..
The owner of the amp uses the loop for his "Helix".. I would imagine that the Helix is what screwed the loop..

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