• 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.

EL84 Amp - Baby Huey

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ArthurDK

Member
Joined 2009
This is one thing I havnt tried myselv yet, but normally you will get approx. 1.4 * 300v out of your dual rectified PS with your PT, if you use a relatively large first cap ( minus the power drop over the tube rectifier ), but if you go directly into the choke in and L-C configuration, you should only get 1.4 * 300v (minus drop) * 0.9, according to what I read.

I have thought about using that techniq to get 6.3v rectified heater voltage out of an unused 5v heater winding.

Maybe another user have tried to go L-C after the rectifier ?

Best regards
Arthur.
 
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ArthurDK

Member
Joined 2009
OK, I have to try it out. That would then vaste too much voltage in this application.

But then you can vary the voltage out, by varying the first cap in a C-L-C input configuration. The output would according to Morgan Jones be: ´Rectified mean value DC´ minus half the ripple voltage, page 301-302 in the 3rd edition.

I havn´t tried that either.

Arthur
 
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oldtexasdog

Member
Joined 2011
6L6 said:
Some people might say that the primaries of your output transformers are too high, but they will work just fine. Plus, you have them, and using what's on hand is always a good thing!

Your power transformer is great.

Go for it!
Click to expand...

Thanks-I will be getting started on this in the next couple of weeks-I'll use the old Motorola HS 711B chassis as it has a lot of room and is already set up for EL84's.
 
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sharkey22

Member
Joined 2008
Hello all. This is my first go at building a power amp, I've built a couple of tube pre/phono stages using the join part a to Part b "i dont really know what i am doing" method both of which work rather well..

Could one of you knowledgeable people tell me the necessary power mA for the high voltage winding on the power transformer, I am building my power supply and 2 amplifiers to the original schematic in the baby huey thread. ECC83/EL84 tubes.

Thanks....... Ian
 
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gingertube

Member
Joined 2004
A rating of 200mA is enough for 2 channels.
4 EL84 (2 per channel) idling at around 35 to 40 mA each = 160mA. A bit of overhead to handle the peaks.

ASIDE: After months of intermittent listening/tweaking I finally screwed the bass plate on the 6SL7/6V6 version, this weekend just passed.
To get the last "drop" of performance out of it I added 10 Ohm + 2u2 zobels across the 4 Ohm speaker taps to correct the speaker impedance vs frequency characteristic. That makes the amps's job a little easier.

Cheers,
Ian
 
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sharkey22

Member
Joined 2008
RE:post number 800

rhone said:
I'm working out exactly what I need for the build (fixed bias version) and have a few basic questions. I've built a few valve circuits but don't have much experience with the SS stuff. I mean, all the bits are so SMALL :)
Anyway, the pots: 100R and 50k. Single or multi turn? Cermet?
The 12AX7 gridstoppers (1k5): I've got plenty of 1k, do they need to be that bit bigger?
The 2u2 cap. between the 50k pots: An 'audiophile' 400v polyprop type? A mylar?
Rod
Click to expand...


Hi Ian, I am slightly confused, having been trawling through this very tnformative thread for a while now. I cannot see which components the poster of this message is refering to. (the pots: 100R and 50k. Single or multi turn? Cermet?
The 12AX7 gridstoppers (1k5), 2u2 cap. between the 50k pots).

He is making reference to a fixed bias layout, what would be the advantage of this and could you point me towards the schematic?



By the way I have just finished constructing the 2 CCS's for the ecc83's but only had green LED,s to hand. Does green make any difference, what current should it provide?

cheers. Ian.
 
R

rhone

Member
Joined 2005
sharkey22 said:
Hi Ian, I am slightly confused, having been trawling through this very tnformative thread for a while now. I cannot see which components the poster of this message is refering to. (the pots: 100R and 50k. Single or multi turn? Cermet?
The 12AX7 gridstoppers (1k5), 2u2 cap. between the 50k pots).

He is making reference to a fixed bias layout, what would be the advantage of this and could you point me towards the schematic?



By the way I have just finished constructing the 2 CCS's for the ecc83's but only had green LED,s to hand. Does green make any difference, what current should it provide?

cheers. Ian.
Click to expand...
Hi Ian,
That was my post you quoted and, yes, it's the fixed bias version which has some extra components. That amp is currently doing good service in my system. Circuit is at post 431 page 44 of this thread. Somewhere in the thread are some comments Gingertube made comparing the two versions. IIRC the fixed bias version sounds slightly better, but I'm sure you'd be happy with the simpler to build original version.
 
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gingertube

Member
Joined 2004
Guys,
Something has happened to my notifications and I'm not getting emails when someone posts to this thread anymore. I need to look through the last few pages to catch up with what you've been doing.

The 100 Ohm pot is in the cathodes of the 12AX7 diffamp. It allows balancing of the diffamp. Adjust it for equal anode voltages on the 2 12AX7 triodes. A simple single turn job will do.

The 50K are the bias set pots. I always like to use 10 or even 20 turn pots for these.

If using Green LED for the current source reference (on the bottom transistor of the cascode current source) then there will be about +1.8V at the transitor base and about 1.2V at the emitter. Try a 820 Ohms resistor from the transistor emitter to negative supply. That should give you 1.2 / 820 = 1.5 mA current source.

Cheers,
Ian also (gingertube)
 
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sharkey22

Member
Joined 2008
Help required for tube rectified Power Supply.
Does anyone have a suitable schematic including transformer voltages/current requirements, rectifier type, choke, resistor and cap values. I intend having a transformer constructed that will provide for both Solid State and have an option for a valve rectifier. I'm afraid my knowledge / ability isn't up to all the workings out.
Any info will be much appreciated.

Ian
 
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