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Old 20th May 2009, 05:56 AM   #791
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Join Date: Oct 2004
Location: Adelaide South Oz
Adamus,
Just live with it. EL84 tolerate over voltage very well in fact some guitar amp folks run them up over 400 volts (but with 2K2 screen resistors).

My fixed bias monoblocks are running at +350V without any signs (sounds!!) of stress.

Lars,
Without changing the BH scheme I'm limited with the current I can draw through the front end diff amp to around 600uA to 700uA maximum per side. Changing the feedback taps from the anodes (via 47K) to the Ultralinear taps (via 10K) actually helps a little here. I can draw a little more current. The 6BR7 happened to be something I picked up a batch off cheap and the (knowledgeable) supplier claims they are better than EF86. I certainly have some premium grade E180F on the shelf as well, they are used, ex a Hewlett Packard Pulse Generator, but measure 100% on the AVO MKIII. Will look at some plate curves to see if they might be better, keeping in mind my operating current limitations. Thanks for the suggestion. Work on this is "on-hold" while I repair (and part rebuild) some JADIS JA80 Mono blocks for a local chap. I want to keep the basic BH scheme. Triode diff amp limitations and all it seriously leaves all the amps I've compared against (the JADIS, Amplifons etc.) for dead, by comparison they all seem to "dumb down" the music compared to the BH.

Cheers,
Ian
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Old 20th May 2009, 01:49 PM   #792
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Location: utica n.y.
Why not try 6973's They sound better and will take more abuse(designed for jukebox duty) 24 watts max PP
Here is the pdf.
http://www.pmillett.com/tubedata/HB-...t_2/6973.PDF:D
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Old 20th May 2009, 11:45 PM   #793
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Thanks for pointing out that tube (the 6973).
While (here in Oz) NOS RCA are going for A$79 I see that ElectroHarmonix have new production 6973 for A$30 which is only A$2 more than the JJ EL84. I'm going to grab a couple of the EH 6973 for comparison purposes.
Cheers,
Ian
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Old 21st May 2009, 01:08 AM   #794
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Hi Ian,

Ive decided after a long hard think to make your first Baby Huey design (with feedback alterations) my first build, mainly because of the detailed help that has already been given on the build.

So I am comprising a parts list etc, and am interested on your thoughts about OP transformers. I am just looking at some Sowter OPTs; whats your opinion on having a cheaper 2 channel transformer compared to a having one per channel? Obviously there is a big price difference, but is the performance that much more noticeable?

Cheers mate

Charlie
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Old 21st May 2009, 01:24 AM   #795
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Location: Adelaide South Oz
Charlie,
The baby Huey was designed specifically to work well with cheaper output transformers. It works very well with Hammond 1608 and similar. Having said that, like any other tube amp the better the output transformer the better the sound of the final product. I'm not a fan of the 2 channel output transformers, they always appear that they have been designed down to a size and price rather than designed up to a standard. If you go with Sowter then the U064 would be fine. I don't believe it would be worth the (1/2 again) extra price for the UA23 BUT it would certainly be a little better, particularly in the bottom end.
Cheers,
Ian
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Old 21st May 2009, 02:02 AM   #796
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Hi Ian,

Thats what attracted me to your design for a first build, and with everything in consideration I think spending the extra cash would be worthwhile in the long run.

Im sure ill be picking your brain again in the future, if you'll have me.

Thanks for you help

Cheers

Charlie
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Old 21st May 2009, 07:24 AM   #797
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No worries Charlie,
The basic Baby Huey (at the risk breaking an arm trying to pat my own back) is a damn good amplifier. I do repair work for a lot of the local HiFi Tube Nutters and see some weird and wonderful amps from time to time.
Recently I have worked on a Dynaco ST70, a Chinese Music Angel 845 SET Amp, a Polish? Amplifon WL25 and some French JADIS JA80 Monoblocks. It doesn't go quite as loud as some of those but it kicks their butts sound wise.
I think you should be happy with a BH.
Cheers,
Ian
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Old 22nd May 2009, 11:43 PM   #798
rhone is offline rhone  Australia
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Great thread, this!
I'm seriously considering building the "bub" and have a parochial question.
Hammond seems to be the common choice for power trafo. Now, their universal transformers are configured for 115 or 230 Volts, right? For those of us in Australia our AC is specified at 230V+/_ x% which in practice means I always get 240-250V from the wall.
Doesn't this mean all the secondaries on the Hammond will be above their rated voltage? In particular I'm concerned about the heater windings. Can anyone from Oz tell me what voltage a Hammond universal has on it's 6.3V secondaries? Or tell me why I'm concerned about nothing?
Rod
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Old 25th May 2009, 03:14 AM   #799
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Rod,
Hammond 300 Series which is what we use here in Oz has tapped dual 0 - 100, 110, 120 primaries such that they can be wired for 100, 110, 120, 200, 210, 220, 230, 240 Volts. Wire it for 240V and you won't have any problems. I've used quite a few Hammond 300 Series Power Transformers for various projects.
Cheers,
Ian
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Old 27th May 2009, 01:52 AM   #800
rhone is offline rhone  Australia
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Thanks Ian.
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
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