The 12AX7/EL34 Prototype: Power Supply wiring and Testing!

Today we finish wiring the power supply, the output tubes and power up the amp for the first time. This is obviously a work in progress but I wanted to share my though process and let you see how much time I am spending making sure this amp is as perfect as I can make it right out of the gate.
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[@acghifiaudio-vinyland78rpm53]

Built my first el34 amplifier in the beguinning of the 90’ and I still enjoy it. You can double voltage of capacitors by using two in serie in the rectifier filter, a old cheap trick. But probably you know already. Will follow this build. Thank you!

[@frankgeeraerts6243]

Hello Steph .....The octal pin 6 is not used in case of the EL34/6CA7 . You can use it to connect/mount the screen resistor from the screen tap 4 to the pin of 6 and connect the wire ( UL tap ) from the transformer to 6......resistor between 4 and 6. Your ampolifier build looks very nice and clean, it will sound good ( with the right transformers )...this is proven circuit that sounds very well. Some will use the 5751 instead of the ECC83 ......this can create an option to tune the amp to one's personal taste . Have a nice day Kind regards

[@greenlanternseven]

Hello Steph ...thank you for helping me with the capacitor value as my electronic repair friend reassured me of the .1 uF 250v that you helped me figure out as it was originally .0.1k 250v ...now I can order , thanks Steph

[@SkunkieDesignsElectronics]

Glad I could help!

[@EskWIRED]

I am excited to hear about the results of your listening tests. I would be especially interested to hear why you prefer one design over another, and especially, the strong points and weak points of each design.

[@SkunkieDesignsElectronics]

Will do!

[@herbieschwartz9246]

That long ground wire running across the chasse may induce thermal and vibration loads on each terminal connection. I suggest putting a loop in the wire to eliminate that stress.

[@ThePerkri]

Very excited to see this come together! Wish I had the resources to build one with “proper” transformers/choke, but for now, it’ll have to be built with the repurposed ChiFi SE EL34 amp I was gifted.

[@Maria-EstherEsparza]

I’d suggest stacking two 1st HV filter stage 630V caps in series (with a pair of HV equalization resistors across) instead of just that one cap. The *peak* voltage of spikes coming from the rectifier can be much higher than expected, and potentially well above the 630V rating of the single capacitor, and thereby cause shortened capacitor life and failures.

[@bob_mosavo]

Thanks, Steph👍

[@paulgood2218]

Looks like a great start!!

[@alanm.thornton4055]

A) Congrats on business stuff! 2) I am really excited for this series. I have wanted to take the winter to learn to build a tube amp, and this is the one I want to try! C) those channel locks, are legit BADASS!! I saw them and was just about to say WHERE DO I GET THOSE! and you said they are dinosaurs. Remember: "retro-vintage-up cycled" is cool now.

[@SkunkieDesignsElectronics]

Hehe, yeah I love them!

[@nevillegoddard4966]

Nice, simple wiring layout so far Stephe! I've probly said it before, but bending over the top of the unused mounting lug on the tagstrips for strength is a GREAT idea! It also takes away the 'temptation' to use anything other than a single earth star earth point, & so ensures no hum from earth loops. Probably not quite close-up enough for an instructional build-video, but certainly good enough for most potential builders of your amp to get a pretty good idea of the internal wire routing though! The 12V DC rated angel-eye halo power indicator led must be pretty efficient to require an additional dropping resistor, given it's only gonna be running on less than 9V DC after the rectified 6.3V AC! But of course, you don't want the led too bright, lighting up your loungeroom do you? It's an unexpected bonus that a number of different valve types could be used in this amp. It's gonna be fascinating to see how the sound compares with all the different permutations of O.P.T's, preamp, & O.P valves that is available now.

[@SkunkieDesignsElectronics]

Yeah this is NOT a build video by any means and the layout may change!

[@frankgeeraerts6243]

One of the options for upgrading is indeed the components choice........... For example , replace the sand cast cathde rersistors with NI ( ayrton /penny windings ) resistors.....They are NON inductive ........there are also other Ni resistors with good wattage .

[@ericlane5949]

Hi Stephe! Looking great! I’m sorry if you’ve addressed this in another video and i missed it but what are the advantages to using a film cap instead of the usual electrolytic at the 5ar4? The extra-high voltage there? Never seen that before. Thx!

[@SkunkieDesignsElectronics]

One is the high voltage rating without having to double up caps. Also this solen cap sounds really sweet as I found out when I tried to swap this for a Wima film cap which I covered in another video, it really delivers some good bass. Honestly I do need to try swapping in a high voltage electrolytic and see if that changes the sound signature.

[@MojoMedicineMan]

Now that's cool 👍

[@Maria-EstherEsparza]

What is your main B+ voltage feeding your output transformer?

[@SkunkieDesignsElectronics]

430VDC

[@kubockferre5532]

hi it would be cool to do a vidéo to show how to test ripple on tube power supply with oscilloscope .thanks

[@SkunkieDesignsElectronics]

Ripple of what? The AC heater or? I mean the output of this amp is silent, even with 105db speakers.

[@kubockferre5532]

i mean hi voltage supply ,i know your amp is silent its just for learning with a scope ,thanks

[@RobertKohut]

Nice!! 🙂

[@DavidDellarosa-j7s]

Hi. I’m really enjoying your channel. I just ordered a Reisong A12 that is going to be delivered tomorrow. This is my first tube amp. I’m going to do your mods and I just have a quick question. In a lot of your videos you highly recommend the JJ EL34L tubes. On the Tubes and More site they sell a JJ E34L (It doesn’t say EL34L) which has a higher grid voltage than a standard EL34. Is this the tube that you recommend for the A12? If so I assume I should buy a matched pair, correct? Sorry if these sound like silly questions, but I want to make sure I order the exact tubes that you recommend. Your videos are GREAT. Thanks so much.

[@SkunkieDesignsElectronics]

www.tubesandmore.com/products/vacuum-tube-e34l-jj-electronics

[@DavidDellarosa-j7s]

Thanks so much for the quick reply! 👍

[@frankverschoof8083]

For comparison: when calculating heatsink's (who does that, 5hese days?), you can add 30% more power if the heatsink is black

[@SkunkieDesignsElectronics]

Interesting!

[@jimmyfreeman1622]

I'm in AWE !

[@herbieschwartz9246]

Have you considered toroidal transformers?

[@SkunkieDesignsElectronics]

Nah, I know some people like them, I like old school EI iron.

[@herbieschwartz9246]

But have you tested them back to back? Something you like or are most comfortable with, might not be the best.

[@SkunkieDesignsElectronics]

If someone wants to send me some, sure I'll test them. I'm already testing a bunch of different transformers, there is a limit...

[@kubockferre5532]

hi skunkie i tried to put dc with the 6.3 volts but it dont works , my voltage drop to 4.5 v so i got 7 amp to my transformer , all my tubes have need 2.4 amp . Do you put your capacitor and your diode bridge reférenced to ground or not .thanks

[@nevillegoddard4966]

@@kubockferre5532 You might have gotten away with using a 5600uF or so filter capacitor across your rectifier, instead of having to go way overboard with a 7A transformer. 2.4A is quite a lot of ripple current the capacitor is required to smooth. A much too small capacitor here may even overheat! By the way, you never mentioned the current-rating of the transformer you used that only gave you 4.5V. Chances are, that even with a 7A transformer, you'll STILL need a large filter capacitor! Yeah, I forget if Stephe was using a centre-tapped 6.3V winding or not. If so, the centre-tap would be earthed. Even without a centre-tap, each end of the 6.3V winding can be connected to earth via 100 ohm resistor, to create a 'virtual' earthed centre-tap.

[@SkunkieDesignsElectronics]

This DC is ONLY for the LED on the power switch. This is not DC tube heaters.

[@kubockferre5532]

ok i understand why now @@SkunkieDesignsElectronics

[@nevillegoddard4966]

@@@SkunkieDesignsElectronics Oh riiight! He's used the led 'power supply' for heaters! Gotcha! I never thought of THAT scenario! This guy should NOT be building this amp! He obviously has no idea. Even I heard you say the little rectifier & cap are for the led power lamp! Smh!

[@Maria-EstherEsparza]

Is that a capacitor-input or a choke-input HV power supply? If it’s a choke-input design, then a single 630V-rated HV cap should be okay.

[@SkunkieDesignsElectronics]

Cap input.