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Post subject: Re: Deluxe Reverb Vibrato PLate Voltage High
Posted: Tue Nov 24, 2015 1:46 pm
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Hi there! For the 414.4 versus 406.3VDC readings --- pull one leg of the 220k-ohm resistor and measure the static (no power) DC resistance across it. If it is shorted (or reads well below 150k-ohms) --- replace it.

If it measures to within 10% of 220k-ohm, you have a possible short across this resistor, somewhere. These are sometimes not that easy to find. It is a path of least resistance kinda thing. Pull V5 12AX7 & with one leg of the 220k-ohm resistor pulled, measure the resistance from the blue dot to the red one. Should be close to infinity.

Study all contacts from point B (just after the choke, in the main PSU). Anything going from B+ and bypassing the 220k-ohm resistor could be an issue.

EDIT: The vibrato is working? No distortion? Is V4 red-plating? Or does it seem to be working fine? If all is well, I wouldn't worry too much about the voltage readings. Since +100 VDC extra on the plates would definitely have a detrimental effect on the tone.


Last edited by BMW2002Ti on Tue Nov 24, 2015 2:09 pm, edited 2 times in total.

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Post subject: Re: Deluxe Reverb Vibrato PLate Voltage High
Posted: Tue Nov 24, 2015 1:48 pm
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The voltage fluctuations you've observed with the tremolo engaged are fairly typical for that circuit. I see no issue there.

As for replacement bias caps, these metal-cased Spragues are what I'm using......

Image

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: Deluxe Reverb Vibrato PLate Voltage High
Posted: Tue Nov 24, 2015 2:47 pm
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Quote:
Hi there! For the 414.4 versus 406.3VDC readings --- pull one leg of the 220k-ohm resistor and measure the static (no power) DC resistance across it. If it is shorted (or reads well below 150k-ohms) --- replace it.


Gotcha, just to be clear, when you say "no power" you mean amp off, Voltage drained? Or do I need to take the reading with the B+ flowing? (from a safe distance, observing all safety precautions...I use alligator clips, DC drained with amp power 'off' and standby switch 'on', 1000v rated pliers, and 1 hand only)

Quote:
If it measures to within 10% of 220k-ohm, you have a possible short across this resistor, somewhere. These are sometimes not that easy to find. It is a path of least resistance kinda thing. Pull V5 12AX7 & with one leg of the 220k-ohm resistor pulled, measure the resistance from the blue dot to the red one. Should be close to infinity.


K, clearly step 2. So i'll hold off until after I measure that 220K with the leg pulled.

Quote:
Study all contacts from point B (just after the choke, in the main PSU). Anything going from B+ and bypassing the 220k-ohm resistor could be an issue.


OK, ill have a look.

The vibrato is working? Yes! No distortion? No, sounds fineIs V4 red-plating No Or does it seem to be working fine? Seems fine

If all is well, I wouldn't worry too much about the voltage readings. Since +100 VDC extra on the plates would definitely have a detrimental effect on the tone. OK, can't say Im hearing anything weird. The truth is I wasn't in love with the tone (though to be honest, there isn't necc anything wrong with it), and wanted to check if everything was at spec. Plus situations like these are how I learn about amps :D Given all that, should I just leave it be? Like I said, I would love to hear the amp sound as its intended.

Arjay thanks for the photo, where do you order from? Canada has less...of everything. But the internet works!


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Post subject: Re: Deluxe Reverb Vibrato PLate Voltage High
Posted: Tue Nov 24, 2015 3:30 pm
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I usually find what I need on Ebay.

For contemporary parts, I use Tube Amp Doctor (aka "TAD"), Tubes And More, and -- periodically -- MCM.

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: Deluxe Reverb Vibrato PLate Voltage High
Posted: Tue Nov 24, 2015 5:57 pm
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OK, can't say Im hearing anything weird. The truth is I wasn't in love with the tone (though to be honest, there isn't necc anything wrong with it), and wanted to check if everything was at spec. Plus situations like these are how I learn about amps. Given all that, should I just leave it be? Like I said, I would love to hear the amp sound as its intended.

:D


Yes, I'd leave it alone. I am not sure why your voltage reading is so high compared to nominal values on the schematic. But, if that 12AX7 was truly "seeing" 400VDC on its plates --- you'd have a ton of distortion. Or red plating. Or both. Plus, that tube would only last a few playing sessions.

By the looks of the amp, the screen resistors were changed. As well as the global feedback resistor. Did the previous owner have any issues with instability or blown fuses? Just curious.

I've used this cap in the bias supply and bypass positions:

https://www.tubesandmore.com/products/C-ET33-160-FT


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Post subject: Re: Deluxe Reverb Vibrato PLate Voltage High
Posted: Tue Nov 24, 2015 10:38 pm
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BMW2002Ti wrote:
I've used this cap in the bias supply and bypass positions:

https://www.tubesandmore.com/products/C-ET33-160-FT


+1

Much closer to the bias circuit's original specs but with a modern voltage ceiling.

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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