• 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

I know I never got around to building my BH, but I still want to. Summer is usually the time I build anything, hanging out in the AC, hiding from the heat. Winter is for skiing :) !!

Anyway, I was thinking of a PPP 6P15P (rough equivalent to EL83) version of the BH with ~5k OPT's. The 6P15P looks good, is easy to drive (low bias voltage) and is very cheap. I have loads and loads of 12AX7 types to play with. So what do you think? Can a 12AX7 type drive PPP EL83 type tubes, or is higher gm needed from the phase splitter/driver?

Just thinking...
 
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rogon,
A bit confusing, sorry. The new power supply drawings show the " local for each channel" power supply decoupling components, ignore the duplicates on your markup. That is,
the 2K2 and 1000uF from the -70V are deleted and the point you have marked -33V comes direct from the power supply where you will see that this supply has 4K7 + 220uF decoupling instead. Hope that clears this up.

Cheers,
Ian

Sorry to dredge up post 1356 to 1358 but I've built my 6V6 sometime ago and want to increase the -ve supply from -48v to -70v.

My question is: Can I use the -70v supply (might actually be closer to -80v in my case) for the 6SL7 cathode CCS also? To do so would significantly simplify matters for me :)

Cheers
Andrew
 
Hi,
quick question: Can any one spot glitches on this one,
or
is this schematic architecture conform to the original hand drawing?
Thanks
J.
 

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Hi Ian
Im trying to change the pre/driver stage in a Sunsui AU70 to an ecc83 diff.
The thing is I am getting a lot of distortion at lowish level.
The power stage is fixed bias at 12.7V, 1K stopers, 300K load, catode feeback from opt, anode voltage is 420V,
grid 2 is 300V, driver is 285V anode with 150K load, no ccs at this- time 560 ohm catode for 1ma, 2nd grid has 220 ohm to ground.
Any sugestions to what is wrong?
 
asddd,
For some reason I'm not getting notifications on posts to this thread anymore, I only just noticed your post.

I take it that you are replacing the 6AN8 pentoder + triode concertina splitter with a 12AX7 LTP to make this amp Baby Huey'ish.

To get you going join the 2 off 12AX7 cathodes together and wire them via a 15K resistor to the -18V point or if easier via a 27K resistor to the -37V point. If using the -18V point then you may want to reduce the 6K series resistor to say 4K7 to get back to the -18V after the extra load current has been added. Once that works you can then add a real CCS in place of that resistor.

Hope this helps,
Cheers,
Ian
 
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I'm trying to make a list of parts and get a handle on costs for my own BH build. Is it still considered Ok to use the Hammond 1650E output xfmrs, and 270FX for Pwr? Those 1650s run almost $100 ea, so I want to be sure I'm right.

Also, out of curiosity, what is it about a Blackgate cap that takes 100 hrs to burn in?

Thanks all...
 
Since you are in the US I would be looking for a pair of Dynaco Z-565 Output Trannies
OR
cheaper option - Edcor CXPP25-MS-8K
https://www.edcorusa.com/cxpp25-ms-8k

I don't know why Blackgates take 100 hours to break in - in fact I did'nt believe the stated "break in" times until I experienced it for myself.

Anyway Blackgates are now difficult to find and expensive.
Elna Silmic II are a good alternative.

Cheers,
Ian
 
Thank you!
If I may, since I have NO experience in either theory or spec comparison: If cost were no option - what would you choose? First: between those two - then a "good" one. I've read the majority of the thread, and I can see that there's little wisdom in going cheap at the goal. I can do this once, but not over and over for comparison. I want "good-approaching-great" transformers. I won't be buying others to play with for quite some time...
Thanks!