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Old 26th June 2003, 03:48 PM   #1
Guiness is offline Guiness  United States
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Default Help with new amp ideas...

It has been along time since I gotta chance to read and post on this forum. But I just settle down again in a new town. So now I have the time to start a new project. I have some nice 96db sensitivy full range speakers that I would like to build a nice 5w or so amp for. Either PP or SE. I also would like to stay away from the more standard tubes. Like the 2a3 and so on. Do you guyz have any ideas? Preferably a nice schematic too!
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Old 26th June 2003, 04:36 PM   #2
Joel is offline Joel  United States
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Welcome back Guiness.

Well, at the risk of shameless self-promotion... you could try my 6AQ5/6DV4 push-pull amp. See the "10W ultralinear amp..." thread. It has unusual tubes (a Nuvistor, and gas tubes), and performs well (20-20kHz, -2dB/+0dB respectively), and puts out a clean 4 watts (I overestimated the driver's swing initially).
Very few parts too.

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Old 26th June 2003, 09:12 PM   #3
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Since a nuvistor is rather expensive, you could go with a 6C4 instead. Some minor mods to the circuit and it should work out great.

As for self-promotion, Revision 3 (6L6GC SE) works great, for as much power output.
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Old 27th June 2003, 01:05 PM   #4
Joel is offline Joel  United States
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Tim,
Only problem with using a 6C4 is the plate resistance is nearly twice that recommended for the interstage transformer. Lundahl claims highest fidelity with a driver Rp of 3.5k or less.
So.... you could run two 6C4's in parallel - but then you'd have a lot of needless current running through the primary, and you'd have the "no parallel anything" crowd after you.

This is what I struggled with during the initial design, and why I went with the nuvistor finally. I don't know many other tubes that have an Rp of 3k ohms, Ip of 10mA or less, decent gain, and high linearity... but I'm open to suggestions! As you know from the other thread, they aren't swinging as much voltage as I would like.

Also, I picked up three 6DV4's from eBay for $9 each. So, I wouldn't really put them in the expensive category.

Joel
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Old 27th June 2003, 01:28 PM   #5
316a is offline 316a  England
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Default Ra 3.5k

Quote:
Originally posted by Joel
Tim,
Only problem with using a 6C4 is the plate resistance is nearly twice that recommended for the interstage transformer. Lundahl claims highest fidelity with a driver Rp of 3.5k or less.
So.... you could run two 6C4's in parallel - but then you'd have a lot of needless current running through the primary, and you'd have the "no parallel anything" crowd after you.

This is what I struggled with during the initial design, and why I went with the nuvistor finally. I don't know many other tubes that have an Rp of 3k ohms, Ip of 10mA or less, decent gain, and high linearity... but I'm open to suggestions! As you know from the other thread, they aren't swinging as much voltage as I would like.

Also, I picked up three 6DV4's from eBay for $9 each. So, I wouldn't really put them in the expensive category.

Joel
6C4 is half a 12AU7 Ra 3k , 6DJ8 should do the trick , 6S45 even less , plenty more types are out there !

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Old 27th June 2003, 06:22 PM   #6
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Quote:
Originally posted by Joel
Tim,
Only problem with using a 6C4 is the plate resistance is nearly twice that recommended for the interstage transformer. Lundahl claims highest fidelity with a driver Rp of 3.5k or less.
Ah, didn't know that.

Quote:
This is what I struggled with during the initial design, and why I went with the nuvistor finally. I don't know many other tubes that have an Rp of 3k ohms, Ip of 10mA or less, decent gain, and high linearity... but I'm open to suggestions! As you know from the other thread, they aren't swinging as much voltage as I would like.
I'd say 6DJ8 but apparently that's too much current as well.. Looks like 5k at 10mA, 100V (-2Vg).

Quote:
Also, I picked up three 6DV4's from eBay for $9 each. So, I wouldn't really put them in the expensive category.
Good deal!

Tim
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Old 28th June 2003, 06:55 PM   #7
Fuling is offline Fuling  Sweden
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What about a pair of Sovtek monoplate 6B4Gīs in SE??
Practically the same thing as 2A3 but at least they are called something else
They are IMHO easier to use than 2A3īs due to the 6,3V filaments and octal sockets.

I use them in my "flagship" amp and they do sound sweeeeet if I may say. A bitch when it comes to filament induced hum, but nothing that some DC canīt handle...
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Old 28th June 2003, 11:38 PM   #8
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Hi,

Quote:
A bitch when it comes to filament induced hum, but nothing that some DC canīt handle...
The advantage of the 2A3 is that you can run it from an AC heater supply without the hum problem a 6B4G would have.

If ever you feel inclined to try out the difference on a DHT between a DC or AC supply you may find both do sound different to the point you'd believe you're listening to different tubes.

As you stated elsewhere that you didn't lile SS devices mixed in with tubes you may want to try this.

Cheers,
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Old 29th June 2003, 06:44 AM   #9
Fuling is offline Fuling  Sweden
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Iīve read at more than one place that 2A3īs are just as prone to humas 6B4G. Havenīt tried 2A3 myself though.

Yes, I know what I wrote about SS devices in tube amps but the hum was slowly driving me mad so something had to be done.
That "something" turned out to be unregulated choke filtered PSUīs for the filament.
The hum decreased quite a bit but itīs still not completely gone, so I will add more capacitance and if necessary more inductance too.

While Iīm at it I will check the HV supply too, since I think the filter caps there may be a bit on the low side.
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Old 6th July 2003, 07:33 PM   #10
Joel is offline Joel  United States
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Guiness? Did you pick an amp?
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