I know the feeling. I have a lot of 6L6GC tubes saved from when I used them in guitar amps. But I don't think they're what I want to use for a hifi amp.
Ian (the designer of the Baby Huey) will likely have better advice than I can give, but I think EL34 would work pretty well if you run them with low plate and screen voltage so that they run with a grid-cathode bias of only about -20V.
The problem with the 12AX7 driver is that it can't swing a whole lot of volts into the output stage. It does well enough for a pair of EL84, but EL34 would be a challenge. Since 7591 is only slightly more difficult to drive than EL84, it might be worth investigating.
Anyway, I have no right to talk about this in any kind of depth. I haven't built a Baby Huey, although I do have all the parts. I need to get started already...
Re: 7591EH - I tried one set, and they seemed OK.
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Actually, you can use the 6L6-oids for HiFi. Mixed lNFB (as in this design) and gNFB can definitely tame 'em, and they'll give excellent sonic performance. Pents aren't a difficult load, nothing like power triodes.
I'm interested in building the Baby Huey. Over the winter I completed my first scratch built tube amp, so I'm very much a novice. Now I'm looking for another project and this looks like a good one.
According to post #1 it is suitable for beginners. The 1565 posts are a bit overwhelming and hopefully I don't miss something important in one of them.
Would the recommendation for someone like me, to stick with the original schematic on post #9? What caps are recommended for the Blackgate caps listed? Hopefully something that can be sourced from a place like Mouser.
Thanks.
-Brad
According to post #1 it is suitable for beginners. The 1565 posts are a bit overwhelming and hopefully I don't miss something important in one of them.
Would the recommendation for someone like me, to stick with the original schematic on post #9? What caps are recommended for the Blackgate caps listed? Hopefully something that can be sourced from a place like Mouser.
Thanks.
-Brad
Brad: I haven't been on the forum or posted in awhile, but I can give some relevant info here I hope....
The BH was my first project, I built the original schemo version and still have them..they were an awesome learning experience...I recommend them for that..you even build your own constant current sources, very good learning, and they sound great. The outputs in the original are cathode bias so trouble free no adjustment needed. The later evolution adds fixed bias options and some other mods like mosfet followers IIRC...I'm planning on updating mine when I have a spare minute or two.
Build the original and then update....you will learn lots, and Ian and others can help when required.......read the thread......
OK and thanks for the feedback, I'm excited about this project and hope to learn a lot.
Brad-
OK, I'll just get some good quaility audio grade caps.
I have some diodes from past projects and the diodes for rectifier for the CCS are not called out. What would be recommended? I have almost no experience with solid state.
Thanks Ian! I sure appreciate you taking the time in answering my rookie questions.
Here is my next question, The power transformer that I'm planning to use has a 275V secondary winding.
Can I just adjust the 220K ohm and the 47 Ohm resisters to dial in to the 300-330V B+
or would it be better for me to try and use an additional 38V secondary in series with the 275V
( the 38V 150mA tap is a bit hidden behind the blue wires in the photo).
I have order most of the parts and I'm getting pretty excited about building this.
-Brad
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Just Use the 275-0-275.
That will give a B+ which is a bit high (probably around +350V to 360V).
The 47 Ohms resistors were reduced to 4R7 which is noted on thread somewhere. Not sure which 220K you mean but it won't affct the B+ (which ever it is).
I am assuming that you are building the basic BH with the CCS Bias blocks on the output tube cathodes. For that higher B+ then change the current set resistors in the Bias blocks from 16 Ohms up to 22 Ohms. That will set idle currents to 29.5mA and keep output tube dissipation within limits.
The tranny rating of 180mA is a little light but should be OK.
Cheers,
Ian
That will give a B+ which is a bit high (probably around +350V to 360V).
The 47 Ohms resistors were reduced to 4R7 which is noted on thread somewhere. Not sure which 220K you mean but it won't affct the B+ (which ever it is).
I am assuming that you are building the basic BH with the CCS Bias blocks on the output tube cathodes. For that higher B+ then change the current set resistors in the Bias blocks from 16 Ohms up to 22 Ohms. That will set idle currents to 29.5mA and keep output tube dissipation within limits.
The tranny rating of 180mA is a little light but should be OK.
Cheers,
Ian
Ian, Yes I'm building the basic Baby Huey version with the CCS Bias block.
I'll change my schematic to reflect the 4.7 Ohms on the B+ and 22 Ohms in the bias blocks.
Here is the schematic of the power supply I'm using and where the 220K resistor I'm referring to. It is the resistor in the RC circuit of the B+.
Is the schematic not the current one?
-Brad
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Trying my best to go through the previous posts, there sure are a lot of them and at times hard for me to determine what version Baby Huey is being discussed.
Would my power transformer having higher B+ and lowish amperage be suited for using a choke filter? I have a 18H, 285 ohm choke out of a Hammond tone cabinet. When I run the simulation it puts the B+ at 315V .
-Brad
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Ian,
I don't have the specs on the choke other than the resistance and inductance. I found the schematic online and to me it looks like it was originally used with about 50mA going through it, I will nix the choke idea.
On the BH power supply schematic you have the separate 4.7R voltage dropping resistors after the capacitor filter going into each channel.
Is the use of 2 resistors done primarily to reduce the wattage size that would be needed? Can I just increase these resistors and get the B+ down closer to the 330V you recommend? By my calculations using 330 ohm 5 watt resistors in each channel would get it close.
-Brad