• 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

I used to always use regulated DC for tube amp projects. However, I recently built a 12au7-EL84 parafeed hp amp and since the circuit was so simple I decided to try AC. I carefully twisted and dressed the leads and to my surprise there was not a bit of hum at all, and this is on 300 ohm headphones driven from a nominal 400ohm tap on the primary of a 4K output transformer. Perhaps the EL84 is better than most tubes for AC heater induced hum?
I think ac filaments may often be blamed for hum caused by other sources. I know from experience that power transformers can induce hum into output transformers and this source is sometimes hard to isolate. I may try AC first on the BH which makes it easy with the PCBs.
 
@ silvercosworth & bandol83,

silver cosworth, could you show how you have this wired.

@ bandol83, is running heaters in AC a recommended practice for tube amps.

Newbie trying to get it right,

Thanks,

Myles

This.

I think Marc and other tubey folks could do us ultra newbies a favour by showing some power supply designs and schematics as well as recommending some commonly available power tranny. Considering this is probably the most expensive and also the most dangerous part of the build, we need to get it right.

This is my first tube amp build as I am a SS guy, while I have built a few SS amps, mostly involved dual secondary tranny and have no more than 50V DC. I do have a bit of electronic knowledge, mostly from uni and only textbook theory, this centre tapped transformer thingy is doing my head in, such as how do I get 275v from a 550v CT transformer.:confused:

Although this toroidy power transformer looks awesome, it's designed for 115/230v primary. Our 240v nominal main here down under can vary a lot especially at night time, I once measure it and get 257v. :mad:
 
It may take some time but I am happy to draw out what I end up doing.

Really for this amp pcb you just need some careful thought around the heaters.
B+ and the bias voltage are taken care of on board....the referenced Toroidy transformer provides all voltages necessary.

I think Marc did a hand sketch in one of his posts...ill see if I can find it.

This.

I think Marc and other tubey folks could do us ultra newbies a favour by showing some power supply designs and schematics as well as recommending some commonly available power tranny. Considering this is probably the most expensive and also the most dangerous part of the build, we need to get it right.

This is my first tube amp build as I am a SS guy, while I have built a few SS amps, mostly involved dual secondary tranny and have no more than 50V DC. I do have a bit of electronic knowledge, mostly from uni and only textbook theory, this centre tapped transformer thingy is doing my head in, such as how do I get 275v from a 550v CT transformer.:confused:

Although this toroidy power transformer looks awesome, it's designed for 115/230v primary. Our 240v nominal main here down under can vary a lot especially at night time, I once measure it and get 257v. :mad:
 
Totally agree that DC heating is the way to go whenever possible, considering space needed in the chassis for the converter board. Success rate will definitely higher in terms of keeping hum to a minimum.

Connection wise, i simple connect the 6.3Vac line to the BH board, i didn't bother to twist them and i did not ground any of the terminals, so its kind of floating ground for the ac heater line. I will put in my dc/dc converter board once i complete my bench testing, and into a proper chassis.

Currently out of town, will post more pics when i m back home.

Good luck with all your builds...
 
Hi EmeryBB,

I am glad to learn that it is your first tube amplifier, be careful with the high voltage :) I have seen that several builders are making their first tube amplifier with the EL34 Baby Huey, I think that is because of the availability of a PCB ! Most tube amplifiers in the past were built with point to point wiring and they didn't use semiconductors at all. With the Baby Huey architecture including current source and MOSFET drivers, it was obvious that a PCB should make the building much easier :D

Regarding your question about power supply there is a good design guide on Hammond : Design Guide For Rectifier Use - Hammond Mfg. For a long time I have used Hammond transformer they offered good quality at reasonable price compare to some "boutique" transformers, I am using a 1650N for my EL34 Baby Huey, but their price have increased and I have found that toroidal transformer offered better specifications in the book of Menno van der Veen ( Menno van der Veen, audio electronic research & consultancy ) but Plitron and Amplimo were very expensive at that time and I was very pleased to discover TOROIDY which offer toroidal transformer at a lower price :D

For the heater, it is exact that a good wiring with twisted wire will not generate hum, but with a PCB I haven't twisted pair :eek: therefor it is safer to use DC however it will not hurt to use AC and you will hear the difference by yourself...

The main voltage is not critical for this design, with a 115/230 VAC transformer you can have 120/240 VAC main it will increase your output only by about 4% which is not critical for high voltage and bias, for heaters, it may reduce the life of the tubes, but if you are using the DC/DC converter you can adjust it to 6.3 VDC exactly :)

I put again the quick hand sketch I have published in post 15 !

Best regards,
Marc
 

Attachments

  • Cablage EL34 Baby Huey 05092018.pdf
    513.2 KB · Views: 476
So as i was going through some old project i came across a pair of Edcor CXPP60-6K OPT's. I was going to order something around 4K but since i am not using these other ones for anything right now i figure i would put these in and budget some other stuff for the build...coupling caps...connectors...etc...

BONUS!!!
 
Sounds good. You must have some deep parts bins for a pair of output tranys to hide! You’ll get a little less power with the higher Z transformer if you use the same B+voltage but you’ll have a lower Z out.

I know right? I went berserk building amps and preamps for a while. Took a little break and wanted to build again. I have a nice little el84 pp amp but have never built a higher power tube pp amp...
 
I hear you! I’m saving up parts for 2 PP builds- el84 and the BH with KT88/6550. I already have a PPPkt88 triode mode amp that I want to rebuild to use a feedback scheme similar to the BH and have UL/triode but who knows where that sits on the project stack. I’ve recently gone on a SS First Watt binge and am now shifting back to tubes but first up is an ACA. So much fun and not enough time for everything!
 
Lol...same here.

Moskido build and my favorite a hot rod dual output F5. That amp shakes the house...lol.

Aleph J and F5turbo V3 monoblocks - My aim is to have different power levels of SS and Tube amps available for different speaker projects. The BH boards are perfect for a general purpose tube integrated amp. I’d like to have a preamp output as well as a switchable HP filter for using it with subs.
 
Member
Joined 2014
Paid Member
I am pleasantly surprised with how fast Edcor got my OPT’s out to me! I was ready for the 6-8 week lead time, but they were delivered in less than 3 weeks. Sweet!!
I can start the Baby Huey sooner than expected :)
 

Attachments

  • A317D2A0-0AD8-4593-BD99-277B3F087593.jpg
    A317D2A0-0AD8-4593-BD99-277B3F087593.jpg
    1,019.7 KB · Views: 1,306
Can i confirm that the all the heaters of the 4 tubes run on 6.3 V ?
the total current requirement is 760 ma x2 ( 1520 ma ) + 3ooma x2 (600ma).
ie approx 2.2 amp??
Can i buy one or two ac adapter rated for 5 amp to power all the 8 heater filament per stereo set ?
will this do the job ?
https://www.lazada.com.my/products/...53330496547_508092447_125126796&utm_campaign=[SSC-000000000000-00000-00000-0]:%20Smart%20Shopping%20Campaign&utm_term=[SSC-000000000000-00000-00000-0]:%20Smart%20Shopping%20Campaign_xxmo0000000at0000_c_pla-453330496547&adjust_tracker=t2v78t_5n20iw&adjust_campaign=1032211143&adjust_adgroup=54400014687_c_pla-453330496547&adjust_creative=453330496547_508092447_125126796&tracker_limit=1000000&ef_id=W6htkQAABBX9MD6X:20180924045233:s
 
Are you using EL84 for outputs? With EL84 you would need 6.3 volts at 760max2 +300ma for the 12ax7 = 1820ma For each board

If you are building for el34/kt88 you need 1.6ampx2 +300ma = 3.5amps For each board
If you wanted to try the biggest tubes like KT120/150 they draw close to 2 amps each so 4.3 amps maximum for each board.