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Old 27th January 2013, 08:50 AM   #71
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I'll take a better spectrum of the 6n1p later.

I've not heard these tubes driving a gm70, but on just distortion levels at the required swings there are better tubes out there. thats not to say that once in the amplifier they wont work well...
I have a little development project that will probably end up a DHT pp with 6b4g's or somesuch at the output, but has 12av5 in at present. as drivers i tried almost all the drivers i've tested, and a pair of not great testing (0.6% @64vrms 6p52p worked best, at least for distortion.
Click the image to open in full size.

Thats at 1W, an order of magnatude lower than my 6e5p/gm70 at 1W.

enzo

Last edited by enzoastro; 27th January 2013 at 08:53 AM.
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Old 27th January 2013, 09:05 AM   #72
mogliaa is online now mogliaa  United Kingdom
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Enzo,
I tried 6N6P as well and not good at all to drive large signals. However, there are many out there who praise its sound and qualities as a driver. Having said that, I haven't listened to this one, so cannot comment further.

Have you tried 4P1L? It beats 65eP at least based on my experiments...
Ale
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Old 27th January 2013, 09:33 AM   #73
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I'm having a go at designing a direct coupled 4p1l to gm70 at the moment, it, i'm afraid looks much like a copy of your transmitter tube design, but it looks like i have to have either 2 dropping resisters dissipating 850v x 28ma or a third power supply.

I'll try and post a basic design, perhaps you could give me some advice? I'm trying to keep the chassis as cool as possible, it has a very quiet cooling fan which keeps the important things cool, pp caps and ptx.

The only 4p1l testing i did was a very quick and nasty test by feeding one channel of my preamp into the other channel. I bypassed the second channels ht regulator (250v) to give it 330v. The results weren't great. but this was filiment bias and i didnt get a chance to optimise it.

Did you get some figures with a 4p1l @ 200vp-p?

enzo
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Old 27th January 2013, 11:02 AM   #74
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The sticking point with this design is providing the gyrator with ~400v so that the driver tube has enough headroom to swing 180vp-p+ and the mu output gives 70-90v bias whilst keeping it as simple and cool running as possible.

I'd rather not have resistors dropping 850v from the gm70ht so the other option i thought of was to provide a third ps of 100v to sit abouth the 300v supply and feed the gyrator from that.
If i used my preamp ps for the 300v supply i'd have room for a 100v supply in the gm70 chassis.
If the ps look basic thats due to my build method, get it going with cheap bits, then optimise.

Click the image to open in full size.

Click the image to open in full size.


enzo
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Old 27th January 2013, 04:59 PM   #75
mogliaa is online now mogliaa  United Kingdom
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Yes, the downside of using the gyrator instead of a choke is that it doesn't store any energy so you will need the full swing voltage plus about 25-50V headroom to ensure the FET operates efficiently.
You can feed the CCS fet which set the gyrator voltage from your 300V reference.
A floating 100V will be better to feed the gyrator FET.
65eP will do a great job here, as well as later 4P1L in triode and filament bias. Perhaps the latter in your chassis is a bit more complex as also you need another DHT supply and DC regulators, etc.

I will measure the 4P1L at 200Vpp when get some time next week
cheers,
ale
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Old 27th January 2013, 05:41 PM   #76
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Thanks for that Ale, my preamp filliment supply tx are 100w @ 18 v to feed each of the 2 v + 12 v bias (2x6.3v heaters) @ 600ma, definatly dont have the space for that in my chassis, and at 25kg its already quite heavy to hang off the wall. perhaps I'll make more space in my external ps box, no chance i could run another Coleman reg from each existing filliment ps?

enzo
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Old 27th January 2013, 08:40 PM   #77
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Quote:
Originally Posted by mogliaa View Post
Enzo,
I tried 6N6P as well and not good at all to drive large signals. However, there are many out there who praise its sound and qualities as a driver. Having said that, I haven't listened to this one, so cannot comment further.

Have you tried 4P1L? It beats 65eP at least based on my experiments...
Ale
So, how Lampizator do it??
MALPA a owner of this Lampizator GM70 amp informed the sound quality is great:
Lampizator GM70 amp
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Old 27th January 2013, 09:25 PM   #78
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I've not heard that amplifier, but i'm sure its great.

It may sound great in that amplifier, it may even produce great figures.

See my post above where a pair of 6j52p that did 0.6% @67rms ( not great in the company of other tubes in this thread) produced lower distortion (0.05% @ 1W!) than any of my other driver tubes.

I'm just trying to find optimum operating points and the lowest thd tubes, another variable is in what context they are used.

I have been suprised that only one triode i've tested competes with the strapped pen and tetrodes, the 6c45pi, and that seems to have fallen from favour.

p.s if i was doing a 6c33 amp i'd go straight to a 6e5p :-)

enzo

Last edited by enzoastro; 27th January 2013 at 09:28 PM.
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Old 27th January 2013, 10:03 PM   #79
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Enzo,
I would test the sound of these drivers tubes, not a DHT test chart if I was building a amp.
Distortion is not important in tube amps and mainly in SETs, as the distiortion is pleased to the ear(even order harmonics).
Good luck
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Old 27th January 2013, 10:19 PM   #80
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Well my Quad 11's measure much better than my GM70 but they don't sound as good. But of course they use ooodles of feedback to do it. I would like an amplifier that measures well as well as sounds good. sound is what we build them for after all.

I'd like to think i prefer tube amps for reasons other than excess distortion. Perhaps I'm deluding myself, though i did read a thread where a guy measured in room the distortion from a dht amp and a ss amp and the dht measured better. perhaps cancelling in the speakers?

enzo
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