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Old 20th September 2011, 03:10 AM   #21
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Default Just found this too

Building something better with a Chinese SE EL34B Amp DIY Kit

So, I reckon I might just make a silly offer and see if it fly's with the seller - the objective with me is learning something, and this is a pretty cost effective way to get a toe in the water.

We'll see how we go!
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Old 20th September 2011, 09:49 AM   #22
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Originally Posted by planet10 View Post
For an amp like this it would, IMO, be a mistake to go to the higher power OPTs, the appropriate ones are ~$70/pr.

dave
Yes, that's the ones I mean ... But the power transformer cost about 80$ and the shipping must be around 20$ in USA ... There is tax too ... And I forget the little choke too ...

I count both three transformers, not just the OPTs ...

Last edited by Alain Poitras; 20th September 2011 at 09:51 AM.
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Old 20th September 2011, 01:25 PM   #23
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Default silly offer accepted

Er, I guess I own one of these kits now.

'Make an offer' accepted so I guess I better start reading the tweaking thread a bit more throughly...
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Old 20th September 2011, 02:08 PM   #24
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Originally Posted by ttan98 View Post
sorry my mistake, it is pentode----> higher distortion and o/p impedance than triode or ultralinear hence more feedback is required.
True, but IMO pentode is still better . First the grid cut-off voltage is more negative so you avoid class A2 (grid current), second the grid is easier to drive anyway, and third - feedback can just be Schade or from the anode to the drivers cathode.

I use heavy feedback in mine from anode (GU50) to an SRPP driver (6N2P) and it sounds much better than it did in triode mode

I'd avoid ultralinear and global feedback - no good can come from them
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Old 21st September 2011, 08:03 AM   #25
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Originally Posted by Globulator View Post
True, but IMO pentode is still better . First the grid cut-off voltage is more negative so you avoid class A2 (grid current), second the grid is easier to drive anyway, and third - feedback can just be Schade or from the anode to the drivers cathode.

I use heavy feedback in mine from anode (GU50) to an SRPP driver (6N2P) and it sounds much better than it did in triode mode

I'd avoid ultralinear and global feedback - no good can come from them
With a Shade feedback, the pentode curves become more like a triode curves, it work very well with JFETs and MOSFETs too ... But there is a little loss of power because some of the output current is spend in the driving tube. A 6dB global feedback can help very much too to get less distortions and a better frequency response ...
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Old 21st September 2011, 08:09 AM   #26
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Hokay then, well what are the options for constructing an amp starting from here?

I guess I can run with any sort of SET or SEP setup, but is there any other possible designs?

Front runner is this schematic c/o VictoriaGuy thread, but I'd be happy to see if anyone has alternate suggestions...
Click the image to open in full size.

Are there other reccommended schematics?

Oh, and i read something about solid state regulation of heater voltage as being advantageous in terms of removing hum? Any thoughts there?

Last edited by aspringv; 21st September 2011 at 08:10 AM. Reason: extra queries.
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Old 21st September 2011, 08:15 AM   #27
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Originally Posted by aspringv View Post
Er, I guess I own one of these kits now.

'Make an offer' accepted so I guess I better start reading the tweaking thread a bit more throughly...
Congratulations ...

Just assemble the kit the way it should be and measure the DC voltages at every points with no signal and write them on the schematic, check also the OPT impedance ratio ... Then you will have help from all the "tubes experts" of this forum for the tweaking ...
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Old 21st September 2011, 08:21 AM   #28
Tarzan is offline Tarzan  Belgium
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Hi,
Have a look here: Lo Spaccio di Nova di Novarria Marco
and specific here: http://www.enovaz.it/categorie-1517/...-chitarra.aspx

It's in Italian but a very summier Englisch translation is available.
Click the Union Jack...
Cheers,
Tarzan
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Old 21st September 2011, 08:23 AM   #29
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Great, well I'll update the thread when I take delivery and get cracking with the original design.

Cheers all!
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Old 21st September 2011, 08:46 AM   #30
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Quote:
Originally Posted by aspringv View Post
Hokay then, well what are the options for constructing an amp starting from here?

I guess I can run with any sort of SET or SEP setup, but is there any other possible designs?

Front runner is this schematic c/o VictoriaGuy thread, but I'd be happy to see if anyone has alternate suggestions...
Click the image to open in full size.

Are there other reccommended schematics?

Oh, and i read something about solid state regulation of heater voltage as being advantageous in terms of removing hum? Any thoughts there?
This is almost same but it have a global feedback, a very good thing to add on your's ... This one also have the 6CA7/EL34 triode connected, much less power ...

But the parts values, voltages and currents of your's will be differents, to implement a good global feedback, you will have to mesure the amplifier overall gain or have the schematic run on a Spice simulator, that is the easy way ...

Personnally, I will not use a bypass capacitor on the driver tube to make an additional local feedback that make the distortion much lower than with just a global feedback, but the stage will also have less gain ... The two triodes use for the SRPP can be use a different way too, in a Schade circuit with an additionnal preamp stage for example, to get more gain ... Three differents kinds of feedback together are much better then none at all ... It is like day and night ...

Last edited by Alain Poitras; 21st September 2011 at 09:11 AM.
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