• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

EL34 Baby Huey Amplifier

Hello EL34 Baby Huey builders,

As suggested by SCD in the following thread : http://www.diyaudio.com/forums/tubes-valves/72536-el84-amp-baby-huey-217.html#post5533779 I am starting a new thread specially dedicated to the building of Baby Huey amplifier based on my PCB which has been produced in more than 330 pieces and is still requested by many tube amplifier fans in a possible future Group Buy 4 : http://www.diyaudio.com/forums/group-buys/312869-gb-baby-huey-pcb-42.html :)

I will put in this thread all the information available about the assembly of the EL34 Baby Huey amplifier and some of the auxiliary board that I have used or designed to add some features to the amplifier. I must tell you that I am not in professional amplifier business, this is just a time consuming hobby for me and, as you will see, English is not my first language and I have sometimes difficulties to explain things correctly, sorry for that but at least you will understand easily schematics, pictures, B.O.M., etc... :D

History

All that started about two years ago when I read the http://www.diyaudio.com/forums/tubes-valves/72536-el84-amp-baby-huey-217.html#post5533779 post from "gingertube" ! As I was interested by the shunt feedback concept that I didn't know I wanted to test it and decided to build the simplest version with two PCL86 tubes. Since I am very bad in point to point wiring, I made a small PCB. This amplifier was so good that I decided to continue my quest and, since the ECL86 or PCL86 were unfortunately no more produced, I made a second PCB for the EL84 version which needed a third tube, a 12AX7 (ECC83) for the input stage and added MOSFET with current source to drive the output tubes. This amplifier was very good and I was very satisfied by the MOSFET driver stage, but I was also a little bit frustrated by the limitation in power, about 12 W, and the fact that I could not use different power tubes...

To solve this problem, I made an identical version but with octal socket to accept many compatible tubes from the 6V6 to the KT88 and the EL34 Baby Huey was born ! Following the presentation of this solution on the diyaudio forum some members asked me if I could sell the PCB, I had never done this before but since the moderator move this discussion to the Group Buy forum I have received several request and started a GB1 with a target of 50 boards but finally closed it with 80 PCB ordered :) I had to send them Worldwide and to learn how to make PayPal invoice... Later others readers asked me for more board and I offered a second and "last" GB2 which finished with 120 boards ordered !!!

Later, since there was still a strong demand, I asked Prasi, to whom I have bought a CRC power supply PCB, if he would accept to manage a third GB and he kindly accepted :) He also suggested to make 2.4 mm boards for better rigidity. Now 120 more boards have been ordered and are in production and there is already 20 PCB's in waiting list for a possible GB4 ?

Documentation

In this first post I will enclose some of the latest documents available for building the EL34 Baby Huey and I will add more in next posts depending of your questions.

You will find the updated BOM in the GB letter, the latest schematics, some building recommendations, how to connect and to adjust the amplifier and several pictures showing the PCB assembled on top side (big components go on bottom side), a 6CA7 board fully assembled in test and finally the EL34 Baby Huey in its enclosure nearly finished (two vu-meters are still missing).

More pictures and data will come from all the people who have built this nice small amplifier. It is a very nice project for those who have never made and listen a tube amplifier, but remember there is some lethal high voltage (up to 500 V) and you should be very careful when you work on it :redhot:

Have a nice time building the EL34 Baby Huey...

Best regards,
Marc
 

Attachments

  • Group Buy letter & BOM Aug 22, 2018.pdf
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  • EL34 Baby Huey nearly finished.jpg
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  • Ampli 6CA7 gros plan.JPG
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  • Montage ampli EL34 fini dessus.JPG
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  • Adjusting the Amplifier 27 jan 2018.pdf
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  • Connecting the Amplifier 3 oct 2017.pdf
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  • Building recommendations EL34 Amplifier 27 jan 2018.pdf
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  • Schema EL34 rev. 3 12 july 2018.pdf
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Member
Joined 2014
Paid Member
Thanks Marc for starting a dedicated thread for the EL34 Baby Huey. I am eagerly awaiting to start this project, unfortunately I have to wait several weeks for my output transformers to arrive :(
We all appreciate your time put into the BH project!

Also worth noting, we are in good hands with Prasi:)
 

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  • Ampli 6V6.JPG
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  • Ampli 6V6 Radio-Tubes.JPG
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Hi Bekim,

These white letters are not white in fact, it is the silver color of the aluminium after the black anodizing has been removed during the panel manufacturing !

This panel is made by Front Panel Express ( Schaeffer AG: Home in Europe), they are quite expensive, about 130 € for the top panel but the quality is superb as you can see on the pictures...

The tough jog is to make the panel drawing on their CAD software, but to help you I can supply my version, of course it should be adapted to your chassis and transformer but all the holes for the EL34 Baby Huey will be done :)

Best regards,
Marc
 

Attachments

  • EL34 Baby Huey rear view.png
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  • Panneau supérieur ampli EL34 - version 20 noire (4 aout 2018).pdf
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Hello Prasi,

At least the back side is finished :)
We were lucky that the chassis was supplied with the big rectangular hole for the main connector already punched therefor we had only to make round holes... I have also put all the label on the top panel and it was not necessary to add text on the rear panel, we have made the same for the front panel :D

Yes I will give more information about auxiliary circuit as announced in the first post. The input selector module is part of 3 PCB designed to add convenient features to the amplifier and to convert a power amplifier in a complete amplifier with 4 inputs selector, volume control, standby power and infrared remote interface. I made the module as small as possible to facilitate their integration into the chassis.

The input selector module use 4 relays to switch input from CD, Tuner, Streaming and Aux. The control unit include a motorized pot with its driver and a MCU driving The 4 relays, 4 LED, and the standby 230 V AC relay, there is also the infrared detector. Finally the mini 5 V Power Supply will include the standby transformer, the 5 V regulator and the standby power relay.

All schematics and PCB are shown below :)

Best regards,
Marc
 

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  • PCB Mini 5V Power Supply.png
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  • Schema Mini 5V Power Supply.pdf
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  • PCB Control panel 2.png
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  • Preampli control unit.png
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  • PCB Input Selector 4 sept 2018.png
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  • Schema Input Selector.pdf
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Hi Prasi,

Thanks for your kind words for the PCB's, coming from you, an expert on PCB, I appreciate a lot :)

Hi Silasmellor,

Here are two pictures of the inside of the amplifier, but it is still a work in progress, when it will be finished I will post more pictures...

For the power supply I definitely recommend the Toroidy transformer TSTA250/001 TSTA 0250/001 - Mains transformer for tubes - Shop Toroidy.pl which fit perfectly the need for this amplifier, if you want to make it visible there is a superb EXPO version with a chrome enclosure (see web). It is also available from TME with very reasonable shipment cost : TSTA 250/001 TOROIDY - Transformateur: toroidal audio | TME - Composants electroniques and the spec are here : https://www.tme.eu/fr/Document/57008aa91b6cc754bad025ca3e7a413f/TSTA-TOROIDY-EN.pdf
I have no interest in these Companies, but I have found that their transformers for power supply and for output are very well built and at a much lower price than other toroid transformer designed specially for audio like Plitron / Amplimo ! I have built my EL34 Baby Huey amplifier with the Hammond 1650N because I had them on my selves since many years and they are quite good, but for my next quad KT120 I have already bought the CFB2000PP : TTG-CFB2000PP - Tube output CFB transformer [2kOhm] Cathode Feedback Push-pull - Shop Toroidy.pl (see picture)...

Best regards
Marc
 

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  • Transfo TOROIDY.JPG
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  • 6CA7 Toroidy.JPG
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  • Inside view 2 21 Aug 2018.jpg
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  • Inside view 1 17 Aug 2018.jpg
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Some more precision about the PSU (see attached diagram) :

1) The EL34 Baby Huey PCB include already the rectifier, the capacitor and the resistor filters for the high voltage, the input current source, the output bias and the driver voltage :)
2) Even if you can supply the heater directly from the 6.3V AC outputs of the power transformer, I recommend to use a 6.3V DC approach to have no hum at all from the 50 or 60 Hz main. Today DC/DC converter are so cheap that it should be an error not to take advantage of them, but don't hesitate to take a big one, like 20 A, because their specification are very exaggerated :rolleyes: : 1 PC DC 300 W 20A CC CV Courant Constant Reglable Step Down Converter Tension Buck Z09 Drop ship dans Circuits integres de Composants electroniques et Fournitures sur AliExpress.com | Alibaba Group
3) It is always recommended to use a main filter like a Schaffner FN2010-3/06 (for 230 V line) to cancel the industrial noise carried on the main : https://www.mouser.fr/ProductDetail...fRZG4TNX9kK14J18U2hN1pqcTd4bmJM5LusW4m3t3Ww==
4) A CTN resistor will also be a good decision to protect the power transformer and the capacitors during power up...
5) The third 6.3 V output can be used to generate auxiliary power supply for devices like the 1.999 V voltmeter used to test bias. Again with the low price of these voltmeter it is a better solution than to connect multi-meter to test points, and it solve the problem of location of these test points :D
6) Of course, if you are using the standby module, the transformer must be connected via the power on relay !

Best regards,
Marc
 

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  • Cablage EL34 Baby Huey 05092018.pdf
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  • DC DC Converter 20 A.JPG
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  • 6 CA7 Baby Huey Toroidy.JPG
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Chokes

Hi,
I have used the Hammond 159v in each channel instead of R27 10 ohms 4w resistor and I am very happy with the results. Also, I recommend using 500v caps in the power supply section if using 275v ac supply. This is because, at the initial start of the amplifier the dc voltage goes higher than the nominal 400v caps, it is only for a little time but I feel this degrades the cap ability to filter, also when the amplifier is stabilized around 385v dc, this value is in my modest opinion very near the nominal limit of the psu caps. I changed them to 500v ones and also no regrets. Absolutely silent amp.

Read carefully the info regarding the 500v caps because their value are little bit different than the 400v counterparts, I think this is due to limitations in size. I ordered wrongly the same mf value but in 500v and they didn’t fit in the pcb so I had to install them outside and used cables to the pcb solder points.

I am going to make some photos during this weekend to show the inners of my build. I am going to make another set of pcbs but using boutique parts to check if the sound can be improved but it’s very difficult because it is a really very good amp. Thanks Marc and Gingertube and everybody who have made this possible.

Regards,

Jorge
 
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Hey Marc, thanks for the info that is perfect. I am already a fan of toroidy PTs, which I’ve used for a couple of projects so that seems like sound advice. Being new to tube amps (only built a Bassman 5f6 so far), what is the preferred way to rectify the 6,3v tap for the heaters?
 
Member
Joined 2014
Paid Member
Hi,
I have used the Hammond 159v in each channel instead of R27 10 ohms 4w resistor and I am very happy with the results. Also, I recommend using 500v caps in the power supply section if using 275v ac supply. This is because, at the initial start of the amplifier the dc voltage goes higher than the nominal 400v caps, it is only for a little time but I feel this degrades the cap ability to filter, also when the amplifier is stabilized around 385v dc, this value is in my modest opinion very near the nominal limit of the psu caps. I changed them to 500v ones and also no regrets. Absolutely silent amp.

Hi Jorge,

Thanks for the detailed information! I had very good results substituting the resistor for a choke in a Tubelab SSE.
I also have Mundorf Tubecaps rated at 550v that I will try with the Baby Huey, they are very large :eek:

Regards,
Vunce