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 NEW  Matt presents bias and operation data for the 6V6 tube in SE operation - 6V6 Single-Ended (SE) Ultra Linear (UL) Bias Optimization.

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PostPosted: 11 Sep 2018, 09:10 
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Joined: 01 Oct 2017, 23:26
Posts: 6
I seem to have clouded the question with too much information. In my reading I have seen that some builders of tube / SS integrated amplifiers add a zener voltage clamp or turn on delay relay between the tube preamp and SS power amp specifically to deal with a potential voltage spike when the tubes start conducting. I don't understand the mechanism of how this voltage spike would occur when the tubes first start conducting when the cathode warms up and the B+ is already present, and don't have the equipment to measure it so I am not sure if I need to worry about this in my 4S / F5 build.


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PostPosted: 11 Sep 2018, 14:16 
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Joined: 23 Feb 2017, 02:02
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I've designed many valve pre amps, including hybrid, pure valve op amp and classic valve schematics.

The only time you need to be worried about voltage spikes is when you are building a hybrid valve op amp, this means something that uses transistors and valves and inside a op amp.

Classic valve schematics like 4s universal and virtually all valve only schematics you can find online do not have voltage spikes during power on.
I've designed two valve only op amp schematics and they also do not have power on votlage spikes.

If something does give you power on spikes then its likely to be from a hybrid or transitor design, normally cause the output is capacitor couppled this means you will only see the ac votlage spikes.
DC dosen't pass through capacitors.

Only time where dc may pass through a capacitor is when you have one side of the capacitor not ground refrenced by a resistance of 1M ohm or smaller


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PostPosted: 11 Sep 2018, 23:35 
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Joined: 01 Oct 2017, 23:26
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Ok. Thanks to all. My concerns have been relieved and I have a better understanding of what is going on.

After I finish reassembling the amp in it's new case, I will remeasure voltages during startup because the numbers I remember seem a little off. The preamp output capacitor is ground referenced by a 50 kOhm resistor. The volume potentiometer is on the input side of the tubes.

I am quite happy with the sound of the preamp (in combination with the F5) and appreciate the simplicity of the circuit. In order to lower the output resistance of the preamp I ran two triode sections in parallel for each channel (two tubes total) to better match the 50 kOhm input resistance of the F5.


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PostPosted: 12 Sep 2018, 01:19 
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Joined: 06 Jun 2008, 18:23
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Location: Australia
I assume you are aware that HT is always higher until the tube reaches operating temp 20 seconds or so after turn on. The tube being non-conductive when cold there is no load on the PS so the HT floats high briefly.

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Projects: "Grace" - Psvane 6SN7-SE Globe preamp | | "VoXUno" - Single driver MarkAudio 12P speaker | | "Lagoon Take 2" - Single stage tube preamp | Website: retro-thermionic


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PostPosted: 28 Sep 2018, 07:33 
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Joined: 28 Sep 2018, 05:23
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Hi Is this preamp suitable for amplifier control with input impedance of 18 kOhm and 106dB? Thank you very much for your answer.


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PostPosted: 02 Oct 2018, 15:26 
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Joined: 25 Sep 2018, 21:08
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Having difficulties picturing connections regarding the chassis/lift grounding.

Question: How is the signal ground switch wired to chassis and "lift", and how are the signal wires connected to ground so that they can be "lifted" or chassis ground? perhaps a wiring diagram anyone...


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PostPosted: 29 Oct 2018, 14:47 
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Joined: 25 Sep 2018, 21:08
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preamp complete! playing with Tubelab SSE KT88 and Pioneer PLX1000. Sounds great.


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PostPosted: 29 Oct 2018, 17:43 
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Joined: 06 Apr 2009, 10:08
Posts: 1477
Location: US Pacific Northwest
Nice setup! Looks great!

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Matt
It's all about the Glass!
http://www.CascadeTubes.com
Cascade Tubes Blog


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PostPosted: 29 Oct 2018, 17:49 
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Joined: 06 Jun 2008, 18:23
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Location: Australia
I'm being very picky but it is my pet hate; not into raw Al when a spray can can make a huge visual difference. Im sure it all sounds good.

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Projects: "Grace" - Psvane 6SN7-SE Globe preamp | | "VoXUno" - Single driver MarkAudio 12P speaker | | "Lagoon Take 2" - Single stage tube preamp | Website: retro-thermionic


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PostPosted: 29 Oct 2018, 18:16 
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Joined: 25 Sep 2018, 21:08
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Matt, thanks for sharing your design.


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