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Old 8th October 2003, 03:27 PM   #21
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Default PP?

As your first to design and build you are doing a PP? I think a simple SE is.........simpler, no?

I have not completed a design of a PP but have done some with SE.

Go for it! I would be interested in following this thread if you are able to post curves, loadlines, schemes, etc. Looks like you have plenty of interest and help!

Best of luck!
Rick
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Old 8th October 2003, 03:38 PM   #22
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I NEED TO BUILD!!! I NEED TO BUILD!! I NEED TO BUILD!! I NEED I NEED

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Old 8th October 2003, 04:34 PM   #23
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Default Go for it

Whatever you decide, go for it. If, if it is your first project, a 2A3 wouldn't be bad. Hard to mess it up.

Using Svet KT88s (any KT88 is) is much much much tricker.


Hope the best with whatever design you decide.
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Old 8th October 2003, 05:38 PM   #24
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Sch3matic: Hey! I've been talking about tubes on here lots. I used to gab with colt45 on tubes all the time, that's how I got to know him. Trust me, I don't "not believe in tubes"! I think they're great. I still like transistors as well though. I have respect for both worlds.
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Old 8th October 2003, 09:07 PM   #25
Guiness is offline Guiness  United States
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Default what about this 12b4a schematic?

I am thinking about this one...? Any comments or improvements?
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Old 8th October 2003, 10:05 PM   #26
316a is online now 316a  England
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Default Re: what about this 12b4a schematic?

Quote:
Originally posted by Guiness
I am thinking about this one...? Any comments or improvements?
Ok one point : the power supply . There seems to be a lot of HT wasted in the series resistors to drop from 355V to 200V . Extra heat in both the resistors and the power transformer . I would also recommend a CCS load for the input stage as I find resistor loading to sound 'sludgy' or 'tubey' at times , but all depends on how you wish to flavour the amp . I managed to get away with using a fairly marginal input/driver HT for my 12B4a amp : 220V . I've biased the 6SL7 driver at a puny 1mA using a 1.25V bias point (NimH battery) , holds the anode at about 150V . CCS is a depletion mosfet . Not really enough headroom for my liking but drives the 12b4a into clipping ok

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Old 9th October 2003, 01:26 AM   #27
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I haven't a prejudice against either the 6SN7 or the 12AX7 tube. As a matter of fact I have a number of both. I'm certain that there are very good designs out there (or in Frank's head )for either. The 12B4A design looks interesting enough and I will certainly put it on the list of good designs to build.

Are there any other ideas that anyone would care to share?

Any good 6SN7/2A3 designs?

Joe
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Old 9th October 2003, 02:28 AM   #28
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Default Re: Re: what about this 12b4a schematic?

Quote:
Originally posted by 316a


Ok one point : the power supply . There seems to be a lot of HT wasted in the series resistors to drop from 355V to 200V . Extra heat in both the resistors and the power transformer .
Agreed. With a 5k load, you can probably get away fine with lower current and higher voltage. Not the best operating point but it's not the best suited power transformer either, eh?

Quote:
Not really enough headroom for my liking but drives the 12b4a into clipping ok
Given the relatively low mu, using that 6AU6 in pentode mode might be a good idea too, at least if you want some global NFB (a few dB is good practice anyway), which is probably a good idea given the odd operating point mentioned above.

Tim
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Old 9th October 2003, 02:54 AM   #29
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Hi,

Joe, you mentioned very high efficiency speakers.

Are they full-range large diameter drivers or is it a multi-way speaker?

I'm asking for the mass to move is an important factor in amplifier design choice.

Cheers,
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Old 9th October 2003, 08:20 AM   #30
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Quote:
Any good 6SN7/2A3 designs?
Well I wouldn't claim this one is good but it has enabled my sons WAD 2A3PSE amp to equal my little ECL82SE for sound quality. It's a reworking of the WAD design that makes it a little different. It is still not as good as my 2A3PP designs and they could use a 6SN7 instead of the 6N6P (with a little tweaking)

Not sure I'd call it a begineers amp and it uses a cheap lundahl input transformer as that enabled the changes to stay within budget.

ciao

James
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