Weird Heater Supply Problem - And other solutions!

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marshallnoise
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Re: Weird Heater Supply Problem - And other solutions!

Post by marshallnoise » Thu Nov 02, 2017 1:15 am

Well, I made every change suggested and I have the same problem as before. These are 6L6WGS power tubes and I have -30ma on each tube so I think my bias is on point.

But I did notice that turning the bias trim pot definitely increased the noise significantly. Dropping the bias voltage towards 0 reduced the noise but it was there still.

Grounding out 2 and 7 on the first two preamp tubes makes the amp silent.

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Re: Weird Heater Supply Problem - And other solutions!

Post by Littlewyan » Thu Nov 02, 2017 4:02 am

Don't turn the bias voltage to 0 as you're running the valves real hard and they could red plate!

So increasing the bias voltage makes the noise louder? Can you please upload a new photo of the wiring? Are the bias caps the right way round? Negative side on the bias rail?

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Re: Weird Heater Supply Problem - And other solutions!

Post by marshallnoise » Thu Nov 02, 2017 4:01 pm

Littlewyan wrote:
Thu Nov 02, 2017 4:02 am
Don't turn the bias voltage to 0 as you're running the valves real hard and they could red plate!

So increasing the bias voltage makes the noise louder? Can you please upload a new photo of the wiring? Are the bias caps the right way round? Negative side on the bias rail?
I didn't jam on it like that. I just let it idle at that and ran the bias pot all over the range and observed the change in sound.

The 120hz buzz is always there, but it gets louder and more intense the more negative voltage I give it.

ImageBias by Paul Abbott, on Flickr

Pretty sure I got it wired up correctly.

I was thinking that it might be smart to do a false center tap on the HT as well then I can run a more traditional bias supply, right?

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Re: Weird Heater Supply Problem - And other solutions!

Post by Littlewyan » Thu Nov 02, 2017 4:14 pm

Sorry I meant a photo of the whole amp.

I've never seen a virtual centre tap on the HT and I don't think it's wise.

Try pulling V1 to see if the noise is still there. If so, pull V2, then V3. That will help us isolate it.

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Re: Weird Heater Supply Problem - And other solutions!

Post by marshallnoise » Sun Nov 05, 2017 10:17 pm

Ha! I think I got it figured out. Funny how this thread has come full circle.

Turns out my heater artificial center tap was the issue. I had the two 100 ohm resistors grounded to a lug that was attached to the power transformer. I moved that ground off that lug to the ground of the 50uf/50uf cap can that goes to the 10k 2w resistors near the power supply section.

Bam, just normal noise.

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Re: Weird Heater Supply Problem - And other solutions!

Post by neikeel » Mon Nov 06, 2017 6:05 am

marshallnoise wrote:
Sun Nov 05, 2017 10:17 pm
Ha! I think I got it figured out. Funny how this thread has come full circle.

Turns out my heater artificial center tap was the issue. I had the two 100 ohm resistors grounded to a lug that was attached to the power transformer. I moved that ground off that lug to the ground of the 50uf/50uf cap can that goes to the 10k 2w resistors near the power supply section.

Bam, just normal noise.
:thumbsup:
Neil

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Re: Weird Heater Supply Problem - And other solutions!

Post by Littlewyan » Mon Nov 06, 2017 8:49 am

How bizarre! Glad you got it sorted. Now crank that thing and enjoy it 8)

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Re: Weird Heater Supply Problem - And other solutions!

Post by marshallnoise » Mon Nov 06, 2017 10:49 am

Littlewyan wrote:
Mon Nov 06, 2017 8:49 am
How bizarre! Glad you got it sorted. Now crank that thing and enjoy it 8)
Not until I secure those cap cans! Haha

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Re: Weird Heater Supply Problem - And other solutions!

Post by marshallnoise » Wed Nov 15, 2017 3:07 am

I have to tidy up a few things yet, but I have settled on the Thundertweak/Ace Pepper Top Fuel 50 setup. The only differences are a 100k nfb instead of 56k and I left the stock 33k slope resistor. I think I will be using a three way switch though for different voicing options based on that slope resistor. The 47k the layout calls for us very cocked wah type sound but it would be very useful. I would put a 39k in there as an option too.

The Top Fuel 50 has .1uf caps over the phase inverter and the one next to it is switched to a .1uf too. Then the V1B cathode is a 4.7k with a 100mf bypass cap. I took that to mean .1uf and loved the thick rich time I am getting.

ImageTop_Fuel_Plexi_50 by Paul Abbott, on Flickr

ImageTop side by Paul Abbott, on Flickr

I drilled the holes for the pots too close together for chicken head knobs so I am going to have to find something else there. Love the look though!

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Re: Weird Heater Supply Problem - And other solutions!

Post by neikeel » Wed Nov 15, 2017 3:54 pm

Glad it is sounding good 8)

100uF is not 0.1uF (mF = uF in different shorthand)

Where are your filter caps :wink:
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Re: Weird Heater Supply Problem - And other solutions!

Post by marshallnoise » Wed Nov 15, 2017 4:26 pm

neikeel wrote:
Wed Nov 15, 2017 3:54 pm
Glad it is sounding good 8)

100uF is not 0.1uF (mF = uF in different shorthand)

Where are your filter caps :wink:
Haha, I am not showing you yet. Lest I get one of these: :palm:

Strange the layout I posted showed a 100mf value over the V1B 4.7K resistor. Either way .1uf sounds damned good.

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Re: Weird Heater Supply Problem - And other solutions!

Post by marshallnoise » Thu Nov 16, 2017 11:26 am

One of the last pieces of the puzzle for me is getting the 110v lamp working without destroying the bulb.

Is there a simple wiring diagram for 110v bulbs out there?

https://www.amazon.com/gp/product/B0080 ... UTF8&psc=1

I tried bouncing 110v off the on switch to the bulb and it lit up for a few minutes then melted. :stars:

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Re: Weird Heater Supply Problem - And other solutions!

Post by marshallnoise » Thu Nov 16, 2017 5:02 pm

And to answer my own question: I forgot to add a current limiting resistor. The interwebz says 220K in series should do fine. So I will wire that in and see how it goes.

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Re: Weird Heater Supply Problem - And other solutions!

Post by marshallnoise » Wed Apr 03, 2019 12:54 am

To close this thread out: The last thing I did fixed the amp. This thing kills.

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