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Post subject: Re: 5E3 Deluxe Build Questions
Posted: Thu Jun 27, 2013 5:30 pm
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BMW2002Ti wrote:
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 may be 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.

Oh, that brings up something else. My filter caps are all 22 mfd. Will that cause any problems?


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Post subject: Re: 5E3 Deluxe Build Questions
Posted: Thu Jun 27, 2013 5:35 pm
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DrewMeyer wrote:
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?


So you used a power tranny with a center tapped heater supply?

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Post subject: Re: 5E3 Deluxe Build Questions
Posted: Thu Jun 27, 2013 5:36 pm
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BMW2002Ti wrote:
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.


+1

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Post subject: Re: 5E3 Deluxe Build Questions
Posted: Thu Jun 27, 2013 5:39 pm
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DrewMeyer wrote:
BMW2002Ti wrote:
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 may be 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.

Oh, that brings up something else. My filter caps are all 22 mfd. Will that cause any problems?


Should be fine. Rectifier tubes do have a max cap size they like to see (not sure what it is for a 5Y3GT), but what you have is not that big of a difference. BMW probably knows the value by heart. :lol:

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Post subject: Re: 5E3 Deluxe Build Questions
Posted: Thu Jun 27, 2013 5:42 pm
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bluesky636 wrote:
DrewMeyer wrote:
BMW2002Ti wrote:
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 may be 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.

Oh, that brings up something else. My filter caps are all 22 mfd. Will that cause any problems?


Should be fine. Rectifier tubes do have a max cap size they like to see (not sure what it is for a 5Y3GT), but what you have is not that big of a difference. BMW probably knows the value by heart. :lol:

Alright, good to know. And yes, the PT I have has a center tapped heater supply. Is there a good chance the 5Y3 will solve my issue? I want to know before I order one so I can add other components to my order at the same time just to save on shipping in the long run if I end up needing a new cap or something.


Last edited by DrewMeyer on Thu Jun 27, 2013 5:51 pm, edited 1 time in total.

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Post subject: Re: 5E3 Deluxe Build Questions
Posted: Thu Jun 27, 2013 5:48 pm
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Drew,

Yeah, 22mfd is fine. For both a good 5Y3GT and a GZ34. First stage is most critical, in terms of the health of your tube rectifier.

Maybe, best to post a photo of your breadboard layout. To see what components you are using. As Bluesky asked, you do have the 5VAC CT grounded, correct? You need this, to run a tube rectifier.


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Post subject: Re: 5E3 Deluxe Build Questions
Posted: Thu Jun 27, 2013 5:52 pm
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BMW2002Ti wrote:
Drew,

Yeah, 22mfd is fine. For both a good 5Y3GT and a GZ34. First stage is most critical, in terms of the health of your tube rectifier.

Maybe, best to post a photo of your breadboard layout. To see what components you are using. As Bluesky asked, you do have the 5VAC CT grounded, correct? You need this, to run a tube rectifier.

Sorry, I'm bad with acronyms and amp terms. What's the 5VAC CT?


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Post subject: Re: 5E3 Deluxe Build Questions
Posted: Thu Jun 27, 2013 6:26 pm
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DrewMeyer wrote:
BMW2002Ti wrote:
Drew,

Yeah, 22mfd is fine. For both a good 5Y3GT and a GZ34. First stage is most critical, in terms of the health of your tube rectifier.

Maybe, best to post a photo of your breadboard layout. To see what components you are using. As Bluesky asked, you do have the 5VAC CT grounded, correct? You need this, to run a tube rectifier.

Sorry, I'm bad with acronyms and amp terms. What's the 5VAC CT?


I think BMW means the 6.3 volt heater center tap. The 5 volt heater for the rectifier is not center tapped.

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Post subject: Re: 5E3 Deluxe Build Questions
Posted: Thu Jun 27, 2013 6:31 pm
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bluesky636 wrote:
DrewMeyer wrote:
BMW2002Ti wrote:
Drew,

Yeah, 22mfd is fine. For both a good 5Y3GT and a GZ34. First stage is most critical, in terms of the health of your tube rectifier.

Maybe, best to post a photo of your breadboard layout. To see what components you are using. As Bluesky asked, you do have the 5VAC CT grounded, correct? You need this, to run a tube rectifier.

Sorry, I'm bad with acronyms and amp terms. What's the 5VAC CT?


I think BMW means the 6.3 volt heater center tap. The 5 volt heater for the rectifier is not center tapped.

Is that the green/yellow wire? If so, then yes, it is grounded.


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Post subject: Re: 5E3 Deluxe Build Questions
Posted: Thu Jun 27, 2013 7:09 pm
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Yep, that's the 6.3VAC center tap. Like the guys are saying , your power rail is set-up for a 5Y3 GT. I think you'll find that tube change will bring the amp into focus. The only thing you might consider are the (2) 56k resistors in the PI circuit. It's best if they are matched. So you could measure what you have in there. Art

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Post subject: Re: 5E3 Deluxe Build Questions
Posted: Fri Jun 28, 2013 5:56 am
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Yes, the 6.3 VAC tap, not the 5VAC. Sorry.

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


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Post subject: Re: 5E3 Deluxe Build Questions
Posted: Fri Jun 28, 2013 6:49 am
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bluesky636 wrote:
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.


I had a similar issue with the little five watter I built. That amp is true point to point, no turret board only components to terminal strips and wire. It was similar to Bill's example I had too long a connection in the tone stack. The oscillation only appeared with the bass control dimed. I reconfigured it and the problem disappeared.

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Post subject: Re: 5E3 Deluxe Build Questions
Posted: Fri Jun 28, 2013 10:07 am
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aclempoppi wrote:
Yep, that's the 6.3VAC center tap. Like the guys are saying , your power rail is set-up for a 5Y3 GT. I think you'll find that tube change will bring the amp into focus. The only thing you might consider are the (2) 56k resistors in the PI circuit. It's best if they are matched. So you could measure what you have in there. Art

Oh that would be fantastic if a simple tube swap solved the problem. Also, right now I've got chinese filter caps in it. Would it be a good idea to swap those out for F&T caps or will that not make much of a difference?


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Post subject: Re: 5E3 Deluxe Build Questions
Posted: Fri Jun 28, 2013 2:03 pm
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DrewMeyer wrote:
aclempoppi wrote:
Yep, that's the 6.3VAC center tap. Like the guys are saying , your power rail is set-up for a 5Y3 GT. I think you'll find that tube change will bring the amp into focus. The only thing you might consider are the (2) 56k resistors in the PI circuit. It's best if they are matched. So you could measure what you have in there. Art

Oh that would be fantastic if a simple tube swap solved the problem. Also, right now I've got chinese filter caps in it. Would it be a good idea to swap those out for F&T caps or will that not make much of a difference?


While F&Ts may last longer, they are not going to change the sound in my opinion. I have stuck with the supplied caps in both my Weber kits.

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Post subject: Re: 5E3 Deluxe Build Questions
Posted: Fri Jun 28, 2013 4:10 pm
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bluesky636 wrote:
DrewMeyer wrote:
aclempoppi wrote:
Yep, that's the 6.3VAC center tap. Like the guys are saying , your power rail is set-up for a 5Y3 GT. I think you'll find that tube change will bring the amp into focus. The only thing you might consider are the (2) 56k resistors in the PI circuit. It's best if they are matched. So you could measure what you have in there. Art

Oh that would be fantastic if a simple tube swap solved the problem. Also, right now I've got chinese filter caps in it. Would it be a good idea to swap those out for F&T caps or will that not make much of a difference?


While F&Ts may last longer, they are not going to change the sound in my opinion. I have stuck with the supplied caps in both my Weber kits.

But you don't think they might be the cause of my problem?


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