How to improve this 6B4G push-pull circuit - diyAudio
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Old 4th June 2014, 02:11 PM   #1
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Default How to improve this 6B4G push-pull circuit

hi everyone,

My amp sound good, but there's a lack of musical nuance and low level details that get annoying, Also, the bass is exagerated meaning its a bit too loud.

Compared to a couple of class d I have, the class d has more air, more defined soundstage, more details, more coherancy from bass to low.
however, tube amp has more dynamic, better attack, much better tone and a bigger and fuller sound. the real problem is a too emphasized bass and not enough details.

Ive attached the schematic.

Measurments show no apparent problem, they are not malfunctionning, simply I think the circuit is really simple and could/should be improved for better resolution.

The output transformer and the output transformer are the dynaco a 470. Maybe I should get better OPT?

1- I have been recommended to add a small amount of negative feedback. That would likely help the bass
2- I also been suggested to:
''Might also go with independent cathode resistors (and cathode bypass caps if you end up using them) for the paralleled input triode. I have had some problems with tubes fighting each other if the sections were not perfectly matched. (Symptoms less gain, more distortion, etc.) ''


Any input would be greatly appreciated.

thanks
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Old 4th June 2014, 02:42 PM   #2
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You can change LM317 /it's good for 9 v, but not good idea for good sound/ to resistor, and add cathode bypass cap to input tube.
And no FB, if modes are good and distortions are min.
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Last edited by azazello; 4th June 2014 at 02:51 PM.
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Old 4th June 2014, 02:44 PM   #3
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The choke is too small for choke input from your voltages. If it's the Dynaco choke, it's definitely too small. Poor supply regulation results.

I assume you have the 6B4 heaters wired in-phase for hum cancellation. DC heaters could help. You might try an eternal supply and see.

There are better current sources than the 317. If there's enough gain, you can try some negative feedback.
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Old 4th June 2014, 03:25 PM   #4
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For PP small chock maybe is good...
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Old 4th June 2014, 04:25 PM   #5
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There are a few fellows saying you want less resistance in the power supply for more dynamics so a low DCR choke is in order like 23 ohms or less and 1-2H will do in PP. Edcor has affordable one in 300 mA or so.

Maybe the Williamson circuit maybe better for detail and bass while eliminating the need for SS as no LTP.
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Old 4th June 2014, 05:44 PM   #6
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Yes, the power supply can be greatly improved.

What is the value and DCR of the existing choke?

What is the DCR of the power transformer primary and secondary?
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Old 4th June 2014, 06:48 PM   #7
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problem with this amp, is that it was bought used. All the information I have is written on the schematic.
The power transformer is:
Vintage Tube Amp Power Transformer 512-23629A Baldwi (04/07/2011)...
I do not have any information on the choke. Maybe I'm better off getting another choke?
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Old 4th June 2014, 07:19 PM   #8
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Quote:
Originally Posted by rmyauck View Post
There are a few fellows saying you want less resistance in the power supply for more dynamics so a low DCR choke is in order like 23 ohms or less and 1-2H will do in PP. Edcor has affordable one in 300 mA or so.

Maybe the Williamson circuit maybe better for detail and bass while eliminating the need for SS as no LTP.
is this a suitable choke?
https://www.edcorusa.com/Content/Man...7-2H-300mA.pdf
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Old 4th June 2014, 07:57 PM   #9
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If you unplug the 5AR4 you can measure the DCR of the full transformer secondary on pins 6 & 4 of the tube socket.

You can get the DCR of the primary: Unplug the power cord from AC power, measure across the line and neutral of the AC plug with the power switch on.

You'll have to disconnect one side of choke to measure the DCR. Are there any part numbers at all on the choke? Can you post a photo?

It would really help to know what you already have before just guessing and purchasing a new choke.

Last edited by scott17; 4th June 2014 at 08:01 PM.
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Old 4th June 2014, 08:34 PM   #10
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what is DCR? Resistance in ohm?
sorry for noob question
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