advice on an EL84 Push pull Amp schematic

One of the pp El84 amp I looked at before Settling on SE was "Baby Huey" which was discussed alot on this very forum. It is definatly on the list for future amp projects



http://www.diyparadise.com/simpleel84.html


It is a good, simple shcematic, the only reason I haven't built it is because I have no PP Iron....yet

Colin,
Self recommendation is NO recommendation at all
BUT
have a look at this:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=72536

I've designed several EL84 Amps and built several designs from other folk including the highly regarded "Bevois Valley" by Morgan Jones. If you think the "Baby Huey" is a bit complicated then the "Bevois Valley" is a great amp and a liitle simpler and will certainly be better than the schematic you posted..

The amp shown in the thread above is the best sounding of the lot and its what I'm using on my HiFi in preference to some very expensive tube and Solid State Amps I own.

Cheers,
Ian

Colin,
Use the corrected schematic that Bas posted on Post #9 of the baby Huey thread with:
delete the 4700uF caps from the bias networks shown on the 2nd page.

There isn't an ideal power transformer from the Hammond range.

For UK folk I suggest a SOWTER M028 (approx 82 UK pounds) power tranny (there may be cheaper options but it was difficult for me to search UK suppliers from down under).

Check price of SOWTER U064 as an alternative to the Hammond 1608 Output Transformers.

More expensive options would be Hammond 1650E or SOWTER UA23 - these are likely to be a bit better but whether the additional cost is justified or not I don't really know.

Once its built and running, experiment with the 16K resistor which cross couples the 220K / 47K networks between the outpuut tube anodes and the diff amp anodes. I'm running 27K in my amp now.

Hope this is of help.
Cheers,
Ian

Colin,

FWIW, I don't like the circuit you posted at all. Pentode mode without NFB of some kind is (IMO) highly questionable.

Ian's "Baby Huey" is nice. Another simple design is the "El Cheapo" project I've been involved in. "El Cheapo" is set up for 12AQ5s and the 6AQ5/EL90. However, the EL84 is easier to drive than the 'AQ5. So, the 12AT7/ECC81 splitter/driver in "El Cheapo" would be fine with EL84/6BQ5 "finals". No preamp is needed.

"El Cheapo" project here.

Colin and Others,
I waded through Eli's thread - A very nice piece of work, a lot of attention to parts selection and things like snubbers and surge current limiters. These are things which have not yet been addressed in the Baby Huey design. That is the El_Cheapo is a more mature design.
In addition you can get parts kits for it.

If you don't want to wade thru' the lot go direct to page 18 post number #259 in Eli's link above for the final? schematics.

I'm obviously biased BUT I think the Baby Huey has the capacity to be better BUT it probably wants a higher level of basic understanding of tube stuff do all of the things which have been done for you in Eli's design.

Cheers,
Ian