• 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

External Power Supply Option

Hello All,

I am pleased to see that there is a lot of tweaking on the EL34 Baby Huey PCB :)
That was the purpose of this layout : to put everything on a single PCB, including all power supply circuitry, therefor it could be easy to build a tube amplifier by only adding the transformers, but still to give a lot of flexibility for those who will try to test different solutions, like different output tubes, different output transformer wiring and of course different power supply...

The most recommended modification is to use DC power supply for heaters instead of AC to have a silent amplifier (no hum) as several builders have confirmed, but, as I have just answered in th GB thread, it is totally possible to use an external power supply with bigger capacitors and even a choke to power the EL34 Baby Huey :D In that case you can connect the DC high voltage to the AC connector and the diode bridge will connect the good polarity to the capacitors, it is the safer method with a small price to pay : you will loose 2 V in the diodes !

If you have enough knowledge of electronic circuits, you may even remove ALL the UF4007 rectifiers and to replace D1 and D3 with two jumpers, AC2 will become the positive input and AC1 will be the negative input, but in this case you should be careful to connect the B+ correctly :bomb:

In all case always refer to the schematic and check twice before to do the last solution because if you reverse the polarity you will kill you amplifier :redhot:

Don't hesitate to put your questions on this forum it case of doubt, it may help others.

Best regards,
Marc
 
Some more precision about the PSU (see attached diagram) :


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


Best regards,
Marc
I send you a pm for more explication in french ,it feels good to write in French from time to time :)
 
Hi,

The EL34 Baby Huey enclosure is nearly finished (see Picture) and now the final wiring will start... The holes for the vu-meters have been made and the last problem to solve is the hole for the infra-red detector, since the pin are on the side and not on the back like a LED and the front panel is 6 mm thick, it is not evident to mount it :confused:

If you have any suggestion, they are welcome :)

Best regards,
Marc
 

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Hi,

The EL34 Baby Huey enclosure is nearly finished (see Picture) and now the final wiring will start... The holes for the vu-meters have been made and the last problem to solve is the hole for the infra-red detector, since the pin are on the side and not on the back like a LED and the front panel is 6 mm thick, it is not evident to mount it :confused:

If you have any suggestion, they are welcome :)

Best regards,
Marc

Marc, Can you enlarge only the back side of the hole? I have sometimes done this on thick panels to allow for the mounting of RCA jacks or switches that do not have a long enough thread to reach through the thickness of the chassis. It is not for the faint of heart, because if you make a mistake you could ruin the panel.

Brian
 
Hello,:)




I made a counterbore with a strawberry of 8 with my old drill press.:cool:


The IR cell is in place.;)


For information, a view of the area of 220v and DC power circuits.



The mechanical part and chassis integration is now complete, now place to wiring ....:rolleyes:





Regard,


Philippe
 

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Last edited:
KT66

OK, it is a little bit putting the cart before the horse, I am looking at using KT66 (or similar) tubes because I have a pair of Hammond 1650FA transformers I can use - are there any components that would need to be changed? Also, any idea of how much power I would lose against using EL34's (with something like the 1650N transformers)?
 
The Hammond 1650FA are 7k6 Raa, 25 watt rated.
They don't really suit KT66. Could be made to work with B+ of 390V and Screen Voltage of 270V in Class A Push Pull for 30W output, Tetrode connected, but the BH Board is not really set up to provide that lower screen voltage.

Possibly some JJ 6V6S (which have higher voltage rating than many 6V6) would work with the 1650FA, output would likely be 15 Watts.

Cheers,
Ian
 

PRR

Member
Joined 2003
Paid Member
Any of the 25W tubes can work with 7k6 25W, with B+ near 400V.

It is an unusual condition. Commercially you want a lower Z and B+ to save a few cents.

Since most big tubes are scaled for lower Z, you have the awkward condition that Vg2 does not need to be as high as Vplate, but a reduced Vg2 is more than just a dropping resistor.

7027 data shows several close suggestions, any of which can be used with other tubes with small bias change.
 
KT66

Grumpish, gingertube,

"Tetrode connected, but the BH Board is not really set up to provide that lower screen voltage"

The EL34 Baby Huey PCB can be used without difficulties with lower screen voltage :)

As I have already explained this is a very flexible PCB, you can use it very easily with just external transformers and take advantage of the on board rectifiers and CRC filtering, but you can also use an external power supply with high voltage connected to the main input (if you leave the diodes it will protect the amplifier against a wrong connection !) and a lower voltage can be applied to the screens inputs that are already protected by a 270 ohm 2W resistor :c_flag:

Otherwise if you want to buy a new output transformer, you can use the TOROIDY TTG-EL34PP, at 6.6 k it will fit the KT66 or the EL34 and it is only 70 US$ :D

Best regards,
Marc
 

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Hi EmeryBB,

Yes, the TTG-KT88PP is very good for the EL34 Baby Huey, it is 4k which is perfect for EL34, 6550 or KT88 of course. They are used with good result by Philippe who made the mechanical for my Baby Huey( see post 2076 ): EL84 Amp - Baby Huey

I recommended the TTG-EL34PP because it can fit both KT66, 6L6, and EL34 but I think 4k is better for EL34 and bigger tube, on my amplifier I am using 4.3k Hammond 1650N transformer...

Rgds,
Marc
 
Hi EmeryBB,

Yes, the TTG-KT88PP is very good for the EL34 Baby Huey, it is 4k which is perfect for EL34, 6550 or KT88 of course. They are used with good result by Philippe who made the mechanical for my Baby Huey( see post 2076 ): EL84 Amp - Baby Huey

I recommended the TTG-EL34PP because it can fit both KT66, 6L6, and EL34 but I think 4k is better for EL34 and bigger tube, on my amplifier I am using 4.3k Hammond 1650N transformer...

Rgds,
Marc

Thanks Marc.
 
OK i think my plan for DC heaters is developing.

Using 1 of these Tubacad H-PS1 regulators per channel H-PS-1.

Feeding each one will be one of these Antek 50VA wired in series to feed the regulator 10V @ 8A AS-0505

Most likely going Edcor for the OPT's but still struggling to find a power transformer. Edcor will do a custom one 275V @350mA and 60V @ 100mA for $60 but require a 1 time setup fee of $180. Maybe they would waive the fee or reduce it if a few people ordered one.