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Post subject: Re: 5E3 Deluxe Build Questions
Posted: Tue Jun 25, 2013 4:29 pm
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Yep, Mr Aikens lays out the scenario that I prefer. Can't say I like the use of the term "star-grounding". When in reality, it was usually referred to as "down- stream" grounding of seperate circuits. But hey, I'm a Geezer! The grouping of individual circuits to a certain point and location in the amp is the ticket. His advice is solid stuff!!! Good Luck, Art

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Post subject: Re: 5E3 Deluxe Build Questions
Posted: Wed Jun 26, 2013 4:02 pm
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63supro wrote:
I'd check the wire routing too. Sometimes the way the wiring is run can cause parasitic oscillation.

Just read up on parasitic oscillation and have a basic idea of what it is now. Are you saying that I just need to move some wires around? Or is it more complicated than that?


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Post subject: Re: 5E3 Deluxe Build Questions
Posted: Wed Jun 26, 2013 4:04 pm
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aclempoppi wrote:
Yep, Mr Aikens lays out the scenario that I prefer. Can't say I like the use of the term "star-grounding". When in reality, it was usually referred to as "down- stream" grounding of seperate circuits. But hey, I'm a Geezer! The grouping of individual circuits to a certain point and location in the amp is the ticket. His advice is solid stuff!!! Good Luck, Art

Also, I didn't make use of star grounding in my build. Should I have? And could that be my problem?


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Post subject: Re: 5E3 Deluxe Build Questions
Posted: Wed Jun 26, 2013 5:28 pm
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Drew, I don't think the lack of star-grounding is causing the oscillation problem. Lack of good grounding scheme usually leads to excessive hum.

IMHO.... you need to rule-out coupling between stages, before proceding to hunting down the numerous causes to parasitic oscillations. I would simply replace the cap in the power supply (rail). I have a lot of spare caps laying about. :D

Make sure all the ground point in your power supply are good. Ground the power section caps to one point on the chassis. And ground only HV lines to this point. NO signal lines.

Try to keep the wires to-&-from the power rail physically separated from any other wiring. It's okay to have this wiring a bit longer, if that is what it takes to help keep the power rail (supply) lines away from other lines.

Be sure ALL solder points all good. No cold solder points --esp grounding points.

You can hunt down parasitic oscillation problems by pulling the signal tubes (9-pin 12AX7 and 12AT7) one-at-time, and seeing which tube when pulled, stops the problem.

Then, concentrate on that tube ---- wiring & parts connected to it.

Good luck. Keep us posted. :mrgreen:


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Post subject: Re: 5E3 Deluxe Build Questions
Posted: Wed Jun 26, 2013 5:37 pm
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DrewMeyer wrote:
63supro wrote:
I'd check the wire routing too. Sometimes the way the wiring is run can cause parasitic oscillation.

Just read up on parasitic oscillation and have a basic idea of what it is now. Are you saying that I just need to move some wires around? Or is it more complicated than that?


That's exactly what 63supro means. Let me give you an example.

I just finished building a high gain Trainwreck Express clone. Initially it had a very bad squeal when the controls were dimed. Most of the problems seemed to be around the tone stack.

In my original layout, the controls were wired from left to right: Treble, Middle, Bass, Volume. Note the length and position of the wires.

Image

After moving wires around with a wooden chopstick and consulting with other builders, I reconfigured the tone stack to: Bass, Middle, Treble, Volume. Notice the difference in the length and position of the wires now, compared to the original layout.

Image

I also installed the preamp grid stopper directly on the tube sockets and used shielded cable to connect the input jack to V1 and the volume control to V2. The squeal was now gone.

Like I said, this is an extreme example but should give you an idea what 63 supro is talking about. Good luck. It can be frustrating.

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Post subject: Re: 5E3 Deluxe Build Questions
Posted: Wed Jun 26, 2013 5:40 pm
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BMW2002Ti wrote:
Drew, I don't think the lack of star-grounding is causing the oscillation problem. Lack of good grounding scheme usually leads to excessive hum.

IMHO.... you need to rule-out coupling between stages, before proceding to hunting down the numerous causes to parasitic oscillations. I would simply replace the cap in the power supply (rail). I have a lot of spare caps laying about. :D

Make sure all the ground point in your power supply are good. Ground the power section caps to one point on the chassis. And ground only HV lines to this point. NO signal lines.

Try to keep the wires to-&-from the power rail physically separated from any other wiring. It's okay to have this wiring a bit longer, if that is what it takes to help keep the power rail (supply) lines away from other lines.

Be sure ALL solder points all good. No cold solder points --esp grounding points.

You can hunt down parasitic oscillation problems by pulling the signal tubes (9-pin 12AX7 and 12AT7) one-at-time, and seeing which tube when pulled, stops the problem.

Then, concentrate on that tube ---- wiring & parts connected to it.

Good luck. Keep us posted. :mrgreen:


To add to what BMW said, anytime you have two wires crossing, be they two signal wires, power and signal, etc., try to have them cross as close to 90 degrees as possible to minimize coupling. If wires have to run parallel to each other, play with the spacing between them. You will find a point were coupling occurs and goes away just by the change in sound.

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Post subject: Re: 5E3 Deluxe Build Questions
Posted: Wed Jun 26, 2013 5:47 pm
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Oh boy, looks like I've got a lot I can look at. By the way, just remembered this. When the amp is doing this oscillating sound, the power tubes are pulsing a blue glow back and forth in time with the oscillation. Does this mean anything important?


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Post subject: Re: 5E3 Deluxe Build Questions
Posted: Wed Jun 26, 2013 6:25 pm
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Possible bias-supply issue?

Arjay

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Post subject: Re: 5E3 Deluxe Build Questions
Posted: Wed Jun 26, 2013 9:41 pm
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Retroverbial wrote:
Possible bias-supply issue?

Arjay


5E3 is cathode biased.

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Post subject: Re: 5E3 Deluxe Build Questions
Posted: Wed Jun 26, 2013 10:00 pm
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DOH!

:oops:

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Post subject: Re: 5E3 Deluxe Build Questions
Posted: Thu Jun 27, 2013 1:01 am
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" When the amp is doing this oscillating sound, the power tubes are pulsing a blue glow back and forth in time with the oscillation. Does this mean anything important? "

This is a typical symptom of a circuit oscillation issue. There are two usual suspects to rule-out first. Positive feedback or coupling in the power supply, due to insufficient isolation of sections. And poor global feedback control (GNFB) from the secondary side of the output tranny to the PI or other gain stage.

Does your amp have this circuit?

http://www.webphix.com/schematic%20heav ... _schem.pdf

There is no GNFB. The input and phase inverter stages cannot have too much gain. If you are running 12AX7 in both the input and PI, you might want to try a 12AY7 in the input. And see if that tames the oscillations.

You can try 20mfd/500 VDC caps in the power supply rail. A good 5Y3GT can easily handle the extra capacitance & you may get better isolation between each stage.

Good luck! Keep us posted!

:D


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Post subject: Re: 5E3 Deluxe Build Questions
Posted: Thu Jun 27, 2013 2:24 pm
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BMW2002Ti wrote:
" When the amp is doing this oscillating sound, the power tubes are pulsing a blue glow back and forth in time with the oscillation. Does this mean anything important? "

This is a typical symptom of a circuit oscillation issue. There are two usual suspects to rule-out first. Positive feedback or coupling in the power supply, due to insufficient isolation of sections. And poor global feedback control (GNFB) from the secondary side of the output tranny to the PI or other gain stage.

Does your amp have this circuit?

http://www.webphix.com/schematic%20heav ... _schem.pdf

There is no GNFB. The input and phase inverter stages cannot have too much gain. If you are running 12AX7 in both the input and PI, you might want to try a 12AY7 in the input. And see if that tames the oscillations.

You can try 20mfd/500 VDC caps in the power supply rail. A good 5Y3GT can easily handle the extra capacitance & you may get better isolation between each stage.

Good luck! Keep us posted!

:D

Thanks, very informative post! That's the circuit I used for the components on the board, but I used a different layout for the heater wiring due to the PT I bought. I'm running it with a 12AY7 in the V1. I'm using a GZ34 rectifier, would a 5Y3GT work better? Also, I don't know all my terms, so by power supply rail do you mean the caps highlighted in green on this layout: http://members.shaw.ca/carlgigun/5e3_layout_labeled.jpg (Sorry about links, I can't embed pictures on my computer).


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Post subject: Re: 5E3 Deluxe Build Questions
Posted: Thu Jun 27, 2013 2:52 pm
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DrewMeyer wrote:
Thanks, very informative post! That's the circuit I used for the components on the board, but I used a different layout for the heater wiring due to the PT I bought. I'm running it with a 12AY7 in the V1. I'm using a GZ34 rectifier, would a 5Y3GT work better? Also, I don't know all my terms, so by power supply rail do you mean the caps highlighted in green on this layout: http://members.shaw.ca/carlgigun/5e3_layout_labeled.jpg (Sorry about links, I can't embed pictures on my computer).


Can you show us how you wired your heaters?

Using a GZ34 will give you a higher B+ voltage which may not be compatible with the power tubes you are using.

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Post subject: Re: 5E3 Deluxe Build Questions
Posted: Thu Jun 27, 2013 4:22 pm
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bluesky636 wrote:
DrewMeyer wrote:
Thanks, very informative post! That's the circuit I used for the components on the board, but I used a different layout for the heater wiring due to the PT I bought. I'm running it with a 12AY7 in the V1. I'm using a GZ34 rectifier, would a 5Y3GT work better? Also, I don't know all my terms, so by power supply rail do you mean the caps highlighted in green on this layout: http://members.shaw.ca/carlgigun/5e3_layout_labeled.jpg (Sorry about links, I can't embed pictures on my computer).


Can you show us how you wired your heaters?

Using a GZ34 will give you a higher B+ voltage which may not be compatible with the power tubes you are using.

As in a picture of the wiring or a layout? The layout I used was this one by weber: http://taweber.powweb.com/store/5e3_layout.jpg (I posted the cieratone one earlier by mistake). What will a higher B+ voltage do?


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Post subject: Re: 5E3 Deluxe Build Questions
Posted: Thu Jun 27, 2013 5:26 pm
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Drew, Higher B+ will most likely push the 6V6GT's into a different class "A" operating curve, than using the lower B+ 5Y3GT. Having a cathode-biased output stage will compensate--- to a point --- for the increased B+. You definitely change the tone and response of the amp, by upping the voltage parameters.

You also change the plate voltages on the input and PI stages. And this maybe part of "coupling" oscillation issue. With lower value capacitance filter stages than most GZ34 amps (16 mfd stages instead of 20 mfd). And higher plates voltages on those 12AX7 --- you prolly have inadequate filtering and isolation plus too much gain.

Try a 5Y3GT, in you have one and see if that helps the problem.


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