ECL86 and EM84 Tube Amplifier - PCB

DJCheester 57324 68

TL;DR

Built a low-power stereo tube amplifier using two ECL86s and two EM84 magic-eye indicators, arranged as two separate monoblocks in one enclosure.
Designed custom PCBs in Eagle and GIMP, reused Bambino turntable and ZK120/ZK140 parts, and added a high-voltage rectifier bridge on the amplifier board.
The project used two Bambino output transformers, two mains transformers, and cost about PLN 30 for laminate, connectors, and 3.3k resistors.
After assembly, the amplifier started up with no hum, silence on no input, and the sound was better than expected.
Planned additions include an anode-voltage delay board, stabilizer boards, an audio input selector, and a wooden housing.

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#61 20184338 11 Sep 2022 09:36

mariosvd mariosvd

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Post #61
20184338 11 Sep 2022 09:36

@DJCheester Thanks for the answer.
And what do you think about such a solution:

Thank you in advance for your answer.
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#62 20184351 11 Sep 2022 09:47

DJCheester DJCheester

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Post #62
20184351 11 Sep 2022 09:47

After all, the same is only on yours, there is a divider at the input, two resistors and in mine there is one rest the same.

Compare, best regards ...
#63 20184373 11 Sep 2022 10:13

mariosvd mariosvd

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Post #63
20184373 11 Sep 2022 10:13

Apparently so, but I replaced two diodes connected in series with one and replaced the 330k resistor with a diode.
The question is whether, thanks to the lower voltage drop on one diode, the magic loop will react more quickly?
Kind regards.
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#64 20328230 10 Dec 2022 15:48

mariosvd mariosvd

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Post #64
20328230 10 Dec 2022 15:48

Hello everyone very warmly.
The motive for writing this post is the completion of the construction of my amplifier based on the DJCheester project presented here, for which I would like to thank you very much, because the knowledge I gained here, as well as specific solutions turned out to be crucial.
And I started in 2017 with the purchase of a power transformer and two loudspeakers (which I then had to change) ... then PCB design, enclosures, looking for components ... and so a few years passed.
My amp looks like this:
When making the housing, I was inspired by a photo seen on the web some time ago.
I designed the PCB myself and commissioned them:

The power supply has three circuits:
Anode: for PCL86 and EM84 lamps.
Glows: 6.3V and 14.5V (doubler).
Control: layout delayed switching on of the anode voltage and illumination of PCL86 lamps (they are illuminated from the bottom with an amber LED).

I finally knitted the magic eyes according to the instructions from previous posts:

I changed the input resistor from 56k to 15k, the capacitor from 150n to 100n and connected the input to the speaker terminals. Thanks to this I got the expected effect.

I attach some photos:

The amplifier sounds surprisingly good - sure, it's not DREAM AMP from Noise Reducer, but for its simplicity, you can enjoy the sound of a tube amplifier.
I encourage you to do it, because it's really worth it.
Regards.
#65 20328708 10 Dec 2022 21:02

DJCheester DJCheester

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Post #65
20328708 10 Dec 2022 21:02

Hello

I'm glad that my design was useful, the ECL/PCL86 amplifier sounds nice and for my first amplifier I was also positively surprised.

Buddy, I suggest you start a new DIY topic and share materials for other DIY enthusiasts.

However, over time, the magic eyes began to annoy me and I took them out. The amp is a bit underpowered but other than that it sounds great.

As another amplifier, I used the project from the link below on the EL84

https://majsterkowo.pl/jak-zrobic-wzmacniacz-lampowy-se-el84/

The game is better in my opinion than ECL/PCL86, besides about 5W per channel, not 2W. I recommend trying to build it in the future.

In general, you would need to choose speakers with good efficiency and soft bass suspension for a tube amplifier, then the amplifier will transfer the bass beautifully.

And when it comes to DREAM Reducer, I had the opportunity to listen to it, and I will say that it did not captivate me with its sound, although it plays correctly and is PP, but for me it has a lot of minuses.

Firstly, it's not cheap.
Hits for PP are expensive but if someone can afford ...
PP network transformers are also expensive.
Double the number of lamps so the price does its job.

Secondly, the bass-trebble equalizer - for me, an unnecessary gadget

I compared my EL84 SE with this PP and with my speakers, and to be honest, apart from the power, I didn't notice any differences.

Well, this is my subjective assessment, if someone is "burning" to build PP, I'm not discouraged, once I wanted to do a project on the EL34 for training, but so far the prices are scaring me away and the trouble with getting them.

Well, in the DIY EL84 project, you can use the same transformers as are used in Bambino, so recovery.

TG2.5 will approach EL84 because it has taps that allow you to use these transformers, it's about TG2.5-1-666 and network TS40/29/676

My amplifier cost about PLN 200, I mean EL84, i.e. two speaker transformers + mains + EL84x2 and ECC83 tubes.

Regards and good luck to all builders...
#66 20331092 12 Dec 2022 13:39

sq3evp sq3evp

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Post #66
20331092 12 Dec 2022 13:39

It's not bad for the cost.
Do you have any way to check the lamps? He has several - once there was an idea to build a simple tube amplifier, but there was no motivation.
I have to put together what I have - I probably miss tube transformers. Lamps should also be checked.
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#67 20331482 12 Dec 2022 17:41

DJCheester DJCheester

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Post #67
20331482 12 Dec 2022 17:41

Hello, to check the type of lamps, it does not work or "by ear" to assess whether the lamp is playing and whether the sound is clear wacniacz is enough, however, in lamps it is useful to know the parameters and wear of the lamp, measuring the parameters and comparing them with the catalog data of the checked lamp.

A great solution once appeared in the journal Elektronika Praktyczna - a microprocessor meter for electron tubes.

Although the topic and idea of building a vacuum tube meter was born on the trioda.pl forum, below is the link to the topic.

http://www.forum-trioda.pl/viewtopic.php?t=12209

In the AVT store there is a board and a microprocessor for this meter - you have to assemble the rest of the parts yourself.

https://sklep.avt.pl/avt5229.html

It is worth buying another plate for mounting lamp sockets

https://sklep.avt.pl/avt1694.html

I will admit that I built this meter - it works great, elements that are difficult to access today can be replaced with others available today.

I built an attachment for the meter to extend the measurement capabilities. But that's a thought for a separate topic.

Regards...
#68 20332593 13 Dec 2022 11:16

sq3evp sq3evp

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Post #68
20332593 13 Dec 2022 11:16

DJCheester wrote:

A great solution once appeared in the journal Elektronika Praktyczna - a microprocessor meter for electron tubes.

Although the topic and idea of building a vacuum tube meter was born on the trioda.pl forum, below is the link to the topic.

http://www.forum-trioda.pl/viewtopic.php?t=12209

In the AVT store there is a board and a microprocessor for this meter - you have to assemble the rest of the parts yourself.

https://sklep.avt.pl/avt5229.html

It is worth buying another plate for mounting lamp sockets

https://sklep.avt.pl/avt1694.html

I will admit that I built this meter - it works great, elements that are difficult to access today can be replaced with others available today.

Curious, maybe I'm replacing an entire research station?
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#69 20332615 13 Dec 2022 11:25

DJCheester DJCheester

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Post #69
20332615 13 Dec 2022 11:25

Hello.

It has a catalog with the parameters of over 100 tubes, most of them for audio applications because it was created with this in mind, the processor controls a very extensive power supply where, depending on the choice of a particular tube, anode and grid voltages are given. Three anode catalog voltages and lower and higher are set to outline the slope of the characteristic, calculates the gain and internal resistance as I remember correctly, so this meter replaces the test stand, of course it also has the option of working in manual mode and working as a power supply you set the voltages yourself and you can test a lamp not from the catalog.

As for me, this is a great device, of course, when using it, you should think about testing tubes, especially in manual mode.

I suggest reading about 100 pages on the triode and the documentation from the AVT website, you will know exactly what the meter measures, and after the measurement, we can compare the measured parameters with the catalog data, so we can immediately see if the lamp parameters differ significantly from the catalog ones.

Regards...
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Topic summary

✨ The discussion revolves around the design and construction of a tube amplifier utilizing ECL86 and EM84 tubes. The author shares their experience of building a low-power stereo amplifier using recycled components from old turntables and tape recorders. Key topics include the design of the PCB using Eagle and GIMP, the importance of delayed anode voltage for tube longevity, and the challenges faced with filament voltage and hum issues in the amplifier. Participants provide suggestions for improving the design, including the use of PCL86 tubes, voltage stabilization, and grounding techniques to reduce hum. The conversation also touches on the aesthetics of PCB design and the practicalities of tube selection and testing.
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FAQ

TL;DR: ECL86 prices have risen to ≥ PLN 40 per tube, yet builders report “sound better than expected” [Elektroda, pawelr98, #17830223; DJCheester, #17829065]. A twin-monoblock SE amplifier with EM84 indicators, recycled Bambino transformers and ~250 V DC rails can cost under PLN 200.
Why it matters: It lets hobbyists taste real tube sound without boutique budgets.

Quick Facts

• Output power: Approx. 2 W / channel in single-ended mode [ECL86 Datasheet]. • Anode rail used: 250–300 V DC [Elektroda, DJCheester, post #17829065] • Heater options: 6.3 V (ECL86) or 14.5 V via doubler for PCL86 [Elektroda, DJCheester, post #18772160] • Typical DIY spend with salvaged parts: PLN 100–200 [Elektroda, DJCheester, post #18772160] • Selenium stacks can overheat and emit toxic fumes—replace with a silicon bridge [Elektroda, pawelr98, post #17830876]

What power can I expect from a single-ended ECL86 stereo build?

The datasheet shows 2 W RMS per channel into 5–7 Ω with 250 V anode supply and 5 % THD [ECL86 Datasheet]. Builders of this thread confirm “low-power” but room-filling results [Elektroda, DJCheester, post #17829065]

Can I substitute cheaper PCL86 tubes?

Yes. Add a simple voltage doubler or current-source heater to raise 6.3 V to about 14.5 V; the rest of the circuit stays unchanged [Elektroda, DJCheester, post #18772160] PCL86 NOS cost PLN 10–15, 70 % less than ECL86 [Elektroda, pawelr98, post #17830223]

How do I kill hum in this amplifier?

Twist heater wires and keep them away from inputs. 2. Symmetrize or reference the 6.3 V winding to ground through two 100 Ω resistors [Elektroda, zworys, post #17973071] 3. Check the filter cap; a dry 2×50 µF can raise ripple dramatically [Elektroda, tytka, post #17972710] Residual hum can be cut below 5 mV with fresh capacitors.

Do I really need a delayed anode-voltage board?

Not for small bottles: “For these lamps there is no need to use delayed anode switching” [Elektroda, zworys, post #17831896] Delaying adds life margin but adds parts; many builders power heaters and anodes simultaneously without issues [Elektroda, ak44, post #17829720]

Which transformers from Bambino or ZK recorders will work?

Use TG2.5-1-666 (output) and TS40/29/676 (mains). The TG2.5 primary matches the ECL86 plate impedance; the TS40 secondary gives ~250 V AC and 6.3 V heaters [Elektroda, DJCheester, post #18772160]

My amp squeals loudly after power-up—what’s wrong?

You likely wired the feedback in phase. Swap either the primary or secondary leads on the output transformer to restore negative feedback [Elektroda, Krzysztof Kamienski, post #17971976]

How can I fine-tune EM84 magic-eye sensitivity?

Decrease the 56 kΩ input resistor to 15 kΩ or lower, and experiment with the 150 nF capacitor (range 22–100 nF). Smaller C values give faster, treble-weighted response; larger give slower bass emphasis [Elektroda, mariosvd, #20129431; DJCheester, #20129627].

Is the original selenium rectifier safe to keep?

No. Age increases its internal resistance and failure releases toxic fumes. Replace it with a silicon bridge plus a series resistor to drop excess voltage [Elektroda, pawelr98, post #17830876]

What mains-voltage adjustment is necessary?

Bambino transformers were designed for 220 V. Modern 230 V lines raise heater voltage to about 6.6 V. Insert a 0.22 Ω–0.47 Ω, 5 W resistor in series with the 6.3 V winding to restore spec and protect valves [Elektroda, pawelr98, #17830223; DJCheester, #17830511].

Quick 3-step fix for positive feedback (how-to)

Power down and discharge capacitors. 2. Identify the two primary leads of the output transformer. 3. Swap them; if squeal persists, revert primary and instead swap the two secondary leads to the feedback network. Success is immediate.

How can I test tube health without laboratory gear?

Build the AVR-based tube tester (AVT-5229). It stores parameters for 100+ audio tubes, applies catalog plate and grid voltages automatically, and reports gain, transconductance and internal resistance [Elektroda, DJCheester, post #20331482] Quote: “It replaces a full research station.”

What total budget should I plan for?

Using salvaged transformers and sockets, builders finished a stereo unit for roughly PLN 100–200 including new EL84 or ECL86 pairs [Elektroda, DJCheester, post #18772160] New boutique parts can push costs above PLN 500.

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