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"WZMAK" - That is, an amplifier on 6P6S, ECC82 and EF86

Pltin74 4992 39

TL;DR

  • A custom tube amplifier built around 6P6S, ECC82 and EF86 evolved from an intended Ampex 2012 clone into a fully original design.
  • Star grounding, a capacitance multiplier instead of a choke, and a corrected negative-feedback resistor solved hum and restored lost output power.
  • The project took almost 4 years, and it adds UL/Pentode switching, an input selector, and GZ34-or-silicon rectification.
  • Pentode mode sounds slightly better than UL, delivers more power, and adds a tube-like compression when listening in full-tube mode.
  • A slight 50 Hz hum remains in tube-rectifier mode, likely from a tiring GZ34 after one sparking incident.
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📢 Listen (AI):
  • #31 21521248
    acctr
    Level 39  
    pawlik118 wrote:
    People, this mistake is already made often enough that it cannot be eradicated in a moment.
    .
    Consider that you probably don't understand self-irony.
    Helpful post? Buy me a coffee.
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  • #32 21521252
    rosomak19
    Level 23  
    If I may, using the subject matter, ask the professionals if a 5k ohm 15W speaker trafo would be good for the PCL805 tubes in PP ?
  • #33 21521271
    Pltin74
    Level 8  
    >>21521252 it would be best to count the operating point from the curves for class AB. As far as impedance is concerned, if you want to get the most out of the pentode I would suggest you draw the curves and see if you get the maximum power. https://valvewizard.co.uk/pp.html - here is how to calculate it
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  • #34 21521361
    rosomak19
    Level 23  
    I generally wanted to go for the easy way and use the circuit from the B&O 608 , or Orgaphon 24 mh .
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  • #35 21521397
    pikarel
    Level 39  
    acctr wrote:
    pawlik118 wrote:
    People, this mistake has been made often enough that it won't be eradicated in a while.

    Consider that you probably don't understand self-irony.

    Let me explain:
    -aut irony would be if the writer referred the word - committed - to one amplifier made and the amplifier would be a dud, play badly and the author would not be happy with it.
    If he has made as many as four amplifiers and still boasts about it as successful constructions - it is simply a mistake of misunderstanding (the other way round) the meaning of the word he used.
    This phrase - I have done something - is newspeak and is used by a certain circle of people on a regular basis; it has simply become fashionable.
    Instead of I did, I made, I built - the opaque I committed .

    And the author's amplifier - if he is happy with it and learned a lot while building it - is a good build, I applaud such DIY.
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  • #36 21521418
    Pltin74
    Level 8  
    >>21521397 as for speech, it's like with everything, without misrepresentation there would be no progress. There is nothing to "explain", let's enjoy life and the wonderful conversation about lamps ;) .
  • #37 21521711
    pikarel
    Level 39  
    Pltin74 wrote:
    >>21521397 as for speech, it's like with anything, without misrepresentation there would be no progress. There's nothing to "explain", let's enjoy life and a great conversation about lamps ;)
    .
    I can even feel it from your speech, this progress (sorry, meant to be fashionable) this progression.
    Wait, wrong; not sorry, but sorry or parda.
    And wrong again; sorry to be trendy, now it's leprechaun.
    I have plunged...

    E there, any spelling and syntax, spelling and grammar; the important thing is to be hepi and enjoy the lajw :)
  • #38 21521756
    Pltin74
    Level 8  
    >>21521711 I recommend melise
  • #39 21523056
    acctr
    Level 39  
    pikarel wrote:
    aut irony would be if the writer referred this word - I committed - to one piece of amplifier made and the amplifier would be a dud, play badly and the author would not be satisfied with it.
    .
    You are standing up for your colleague, you certainly had good intentions, but unfortunately you don't understand self-irony either.
    I suspect that without the ability to recognise it, reading literature more challenging than a t.v. programme is an ordeal for you.
    Recognising auto-irony, tragedy or pathos in a text is part of the requirements of the primary level maths exam, but I won't write that ignorance of such treatments is a cause for shame, because some people do indeed have a problem with it, just as they do with defining left-right.
    Helpful post? Buy me a coffee.
  • #40 21523069
    Pltin74
    Level 8  
    >>21523056 I started this topic to show off my project and to get other forum members' opinions on it - not so that some people, because of whom Elektroda has the reputation it has, can practice their favourite hobby, that is, being - excuse me - a man with a stick you know where. Therefore, please spare yourselves and vent your frustrations elsewhere, not in this thread :) .
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Topic summary

✨ A DIY tube amplifier project based on 6P6S, ECC82, and EF86 tubes evolved over four years from an intended Ampex 2012 clone to a custom design due to issues with input pentode gain and power output. The builder addressed hum problems by implementing a star ground topology and replacing a choke with a capacitance multiplier. Output transformers from P. Ogonowski were used in a push-pull configuration. The amplifier features a minimalist front panel with visible screws and 3D-printed transformer covers made from PET-G material, chosen for heat resistance up to 80°C. The design includes a fixed bias phase inverter circuit, which sparked discussion about potential risks of tube aging and distortion. The input selector switch is located on the rear for aesthetic reasons. Component choices such as the negative feedback resistor and volume potentiometer were discussed, with suggestions to use quality parts like an Alps 50k potentiometer. The project also touched on tube equivalences and differences, clarifying that PCC88 and ECC88 tubes share characteristics except for heater parameters. The community exchanged advice on circuit improvements, transformer impedance matching for PCL805 tubes, and practical construction tips. The thread concluded with encouragement for DIY tube amplifier building and a focus on enjoying the process and sound quality.
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FAQ

TL;DR: This DIY tube amp took 4 years to develop, then about 1 month to build after redesign, and its creator says "the sound? Even better". This FAQ helps builders of 6P6S/ECC82/EF86 push-pull amplifiers solve hum, bias, feedback, rectifier, and transformer-choice questions fast. [#21514922]

Why it matters: The thread shows how small choices in grounding, feedback, rectifier mode, and bias filtering can decide whether a tube amplifier sounds powerful and quiet or hums at 50 Hz.

Topic Option 1 Option 2 Practical effect
Output stage mode UL Pentode Pentode gave more power and more "tube hoarseness" to the builder.
Rectification GZ34 tube Silicon bridge Silicon was quieter in daily use; GZ34 added voltage drop and character.
PSU smoothing Choke Capacitance multiplier The builder chose the multiplier to avoid a heavy, expensive choke.
Input selector location Front panel Rear panel Rear placement kept the front visually minimalist.

Key insight: The biggest lesson is that hum and lost output power did not come from one dramatic flaw. They came from small implementation details: feedback resistor value, star-ground execution, and bias-supply filtering.

Quick Facts

  • The amplifier evolved from an Ampex 2012 idea into a custom push-pull design using 6P6S, ECC82, and EF86, after the original input pentode gain proved too high for the intended source levels. [#21514922]
  • Output transformers are commercial units from Mr. Ogonowski, confirmed by the builder when asked whether the amplifier is push-pull. [#21515365]
  • The reported lost power was traced to a wrongly chosen negative-feedback resistor; after correction, the builder says output returned to the expected level, citing 12 W from the datasheet discussion. [#21517044]
  • The remaining hum is 50 Hz and is mainly heard in tube-rectifier mode; after adding an extra capacitor and returning that ground to the star point, the hum was reduced but still audible very close to the speakers. [#21520337]
  • The 3D-printed transformer covers use PET-G, with 3 mm walls and quoted softening around 80°C; the builder reports no visible deformation in use. [#21520337]

How did the design evolve from an Ampex 2012 clone into a custom 6P6S, ECC82 and EF86 tube amplifier?

It started as an Ampex 2012 clone, then became a custom design when the builder found the input pentode gain too high for the intended signal levels. He had already bought the tubes, transformers, and parts, so he redesigned the amplifier around those components instead of forcing the original schematic. He later confirmed that the final circuit was entirely his own design rather than a close Ampex copy. [#21517470]

What causes 50 Hz hum in a tube amplifier with a GZ34 rectifier, and how do star grounding and power-supply filtering help reduce it?

50 Hz hum here came from power-supply grounding and filtering details, not from the audio path alone. The builder first reduced hum with careful star grounding and a capacitance multiplier. Later, he identified another issue: the multisection capacitor shared ground with the amplifier section on the PCB before returning to the star point. After adding an extra capacitor with its return taken to the star, hum dropped, but remained faintly audible in GZ34 mode when standing very close to the speakers. [#21520337]

What's the difference between UL and pentode mode in a 6P6S push-pull amplifier, and how does each mode affect sound and power?

In this build, pentode mode gave more output power and a stronger tube character than UL mode. The builder described pentode mode as having more power and a slight "tube hoarseness," while UL sounded a little more restrained. He also noted that the effect becomes more pronounced in full-tube operation, because the GZ34 adds voltage drop that further compresses the sound. [#21514922]

How do you choose the negative feedback resistor value in a tube amplifier when the gain is too low to reach the expected output power?

Choose the feedback resistor so the amplifier keeps enough closed-loop gain to reach the target output. In this project, the builder lost power because the negative-feedback resistor value was wrong. After changing it, the amplifier recovered the expected performance. He later clarified that the real issue was insufficient gain to drive the stage to about 12 W from the datasheet. That makes the feedback network a power-limiting element when set too aggressively. [#21517044]

What is a star ground in tube amplifier construction, and why is it used to fight hum?

"Star ground" is a grounding layout that brings separate return currents to one common point, reducing shared impedance and hum coupling. The builder used a very carefully executed star topology to fight mains-frequency noise. That matters because shared ground paths can let power-supply ripple enter sensitive input or bias circuits. In this thread, moving returns toward the star point was part of the successful hum-reduction strategy. [#21514922]

What is a capacitance multiplier in a tube amp power supply, and when is it used instead of a choke?

"Capacitance multiplier" is a power-supply filter stage that uses an active device to imitate a much larger capacitor, lowering ripple without a large inductor. The builder chose it instead of a choke because a choke would have been heavy and expensive. In this amplifier, that substitution was part of the solution for hum, alongside careful star grounding. [#21514922]

Which output transformers were used in this build, and how suitable are Mr. Ogonowski transformers for a 6P6S push-pull amplifier?

This amplifier uses push-pull output transformers from Mr. Ogonowski. The builder confirmed both the push-pull topology and the transformer source directly. The thread does not give primary impedance, bandwidth, or power rating, so it does not prove exact electrical matching. It does show practical suitability: the amplifier was completed, ran, and delivered the expected output after feedback correction. [#21515365]

Why would someone place the input selector on the back panel of an amplifier instead of the front?

The builder put the input selector on the back purely for appearance. He wanted a minimalist front panel and said the rear selector does not get in the way during use. That choice trades some convenience and labeling clarity for a cleaner faceplate. Other users questioned the ergonomics, but the builder kept it because the visual result matched his design goal. [#21518736]

How long does it typically take to build a DIY tube amplifier like this one once the design is finalized and all parts are ready?

In this case, the finished redesign took about 1 month to build once the design was settled and all parts were available. The builder also said the whole project stretched across almost 4 years because he used it as a learning process and repeatedly corrected mistakes. That gives a realistic split: weeks for assembly, years if the design is still evolving. [#21518155]

How should the bias supply for Grid 1 be filtered in a fixed-bias tube amplifier to avoid injecting AC ripple and hum?

Filter the Grid 1 bias supply with a capacitor to ground and return that ground cleanly to the star point. One reviewer noted missing filtering after diode D2 or near resistors R19 and R20 would leave large AC voltage on the bias network. The builder later confirmed the working design already had those capacitors and further reduced hum by adding another capacitor with a direct return to the star. 1. Add the filter capacitor. 2. Keep the bias return separate. 3. Tie it at the star ground. [#21520337]

What is a phase inverter in a push-pull tube amplifier, and why does its biasing method matter for long-term stability?

"Phase inverter" is a driver stage that creates two equal, opposite-phase signals for a push-pull output pair, so both output tubes share the waveform symmetrically. In this thread, one user accepted the stage would work with the shown values but warned that fixed phase-inverter bias is less forgiving than autobias. He pointed to aging high-value resistors and tube wear as long-term risks, because drift can push one half toward cutoff and raise distortion. [#21518834]

How do PCC88 and ECC88 differ, and how is that comparison different from ECL86 versus PCL86 or EL84 versus PL84?

PCC88 and ECC88 differ only in heater parameters, not in the triode system itself. One poster stated that for dual triodes, the differences are only in the glow parameters. Another user added that ECL86 and PCL86 are also identical in characteristics and differ only in heater requirements, while EL84 and PL84 are a genuinely different pair electrically. So PCC/ECC and ECL/PCL are heater variants, but EL84/PL84 is not the same kind of substitution. [#21518055]

What should you check before using 3D-printed PET-G transformer covers inside a hot tube amplifier chassis?

Check the material, its softening temperature, wall thickness, and whether the part visibly deforms in service. The builder used PET-G, not PLA, and stated that PLA softens around 50°C while PET-G softens around 80°C. He also used 3 mm walls and reported no distortion after use. That makes PET-G more appropriate here, but only if the cover stays below its thermal limit in the real chassis. [#21520337]

How do you calculate the right output transformer impedance for PCL805 tubes in push-pull class AB, and when is 5 kOhm suitable?

Use the tube curves and the class AB operating point, then check whether the load line reaches the intended maximum power. The builder answered that directly when asked about a 5 kOhm / 15 W speaker transformer for PCL805 in push-pull. He did not give a blanket yes. He said the correct method is to plot the curves, choose the operating point, and verify that the chosen impedance lets the pentode deliver the target power without violating the selected conditions. [#21521271]

What is a 'pseudo rectifier tube' made from diodes plus a power resistor, and how does it compare with a real GZ34 and a silicon bridge?

A pseudo rectifier tube is a diode rectifier with a series power resistor added to imitate some voltage drop of a real tube rectifier. The builder mentioned it as a future experiment: "two diodes + a power resistor." In this amplifier, the real GZ34 added sonic character through voltage sag, while the silicon bridge was quieter in daily use and did not wear like a tube. A pseudo rectifier aims for a middle ground between those two behaviors. [#21514922]
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