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Old 18th January 2013, 08:18 PM   #141
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I'm envisioning a need for diamonds...
Be careful...that only works a finite number of times in a lifetime before it becomes prohibitably expensive.....After 28 years of marriage I have used them all up!
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Old 20th January 2013, 01:52 AM   #142
Magz is offline Magz  United States
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Here's a slightly different version of the 833 schematic, using a gentle 3dB of local feedback to lower the output impedance and increase the damping factor a bit.

Full power is now 181W at 3.5V input...it will make my preamp feel more needed...

I think this is the one I'll build. Probably.


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Old 20th January 2013, 02:51 AM   #143
Magz is offline Magz  United States
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Actually, it turns out that the above schematic sims very well with the feedback removed and everything else the same, so I'll just make it switchable. Best of both worlds...
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Old 21st January 2013, 12:27 PM   #144
Magz is offline Magz  United States
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Originally Posted by Magz View Post
Here's a slightly different version of the 833 schematic, using a gentle 3dB of local feedback to lower the output impedance and increase the damping factor a bit.

Full power is now 181W at 3.5V input...it will make my preamp feel more needed...

I think this is the one I'll build. Probably.


.
Turns out I can eliminate C3 from the above schematic without any harm...one less capacitor!

After some further optimization I've obtained the following output figures from the sim:

200Wrms at 2.5V input with 0dB feedback
192Wrms at 3.3V input with 3dB feedback
156Wrms at 4V input with 6dB feedback

Anything past that and the 6E5P runs out of steam.

My 26 preamp can easily supply the 4V needed, so that's not an issue. So it looks like I'll make it with switchable feedback and experiment to find which is best. Now just waiting for the iron...
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Old 21st January 2013, 01:58 PM   #145
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I predict your heating costs dropping ;-) very impressive!
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Old 21st January 2013, 02:06 PM   #146
iko is offline iko  Canada
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2300V B+ ... scary!
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Old 21st January 2013, 03:25 PM   #147
Magz is offline Magz  United States
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Originally Posted by ikoflexer View Post
2300V B+ ... scary!
Agreed. I plan to exercise the utmost caution both in assembly and use. For example, although heater supplies may be acceptably moved to a separate power supply unit depending on space considerations and hum, the ultra-HT will ONLY be in the amp chassis, so no umbilical electrocution cords will be used. I'd like to keep the path as short as possible within that chassis - Xfrmer to rectifier to chokes/caps/to 833 anode, with the appropriate high voltage wire of course. Double insulation in addition to safety earth grounding is a consideration as well. Of course the 833 will have a shield of some sort around it, most likely a ventilated tempered glass tube, to limit access.

I do not undertake this lightly, lest someone undertake me in short order.
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Old 12th August 2013, 07:52 AM   #148
mogliaa is offline mogliaa  United Kingdom
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Default 4-65a SE Amp finished!

Glad to have reached the end of this long project. A fantastic amp built experience and so far I'm amazed with the performance of this amp. I've only listened to it no more than 2-3 hours. Need further burn-in, but I'm very happy with it!

My initial goal was an all DHT class A2 SE amp based on Michael's design. I ended up with a crazy idea of a 46 driver in filament bias. You realised it's crazy when you see the size of the power supplies. The investment paid off. The driver can do 200Vpp @ 0.09% running at about 35mA which provides a great driving capability to the 4-65a thanks to the mu-follower gyrator load.
What surprised me so far are the bass and dynamics of this amp. Clearly I wasn't used to having 10W of single-ended power, but know I can get more than the 2W of my 45 SE to play that music that needed a tad more power. I'm not playing it loud at all. So far I did a quick run through jazz (e.g. Coltrane, Mingus, Davis), classical and rock music to test some favourite songs to listen to subtle characteristics of the amp. I will probably make some further comments in the future but overall can say it has a deep bass, fantastic dynamics and sweet tone.

A remarkable note is the quietness of this amp. Can get no hum whatsoever on the FE167E speakers. See my THD measure below. All filaments are DC using Rod Coleman regulators (highly recommended) and not easy to achieve this with the 6V/3.5A heaters

here are some pictures if you are interested:
4-65a SE Amp: testing it finally! | Bartola Valves

And the 4-65A running cherry red to keep the getter healthy:
4-65a SE Amp: cherry anodes | Bartola Valves

I have some slight improvement to make to the Salas SSHV2 regulator which I will post on the other thread.

Special thanks to Michael Koster (design), Rod Coleman (regulators and crowbar protection help) and Thomas Mayer (transformers).

Thanks
Ale
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File Type: jpg IMG_1154.jpg (173.3 KB, 212 views)
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Old 12th August 2013, 04:23 PM   #149
eboz is offline eboz  United States
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Quote:
Originally Posted by mogliaa View Post
Glad to have reached the end of this long project. A fantastic amp built experience and so far I'm amazed with the performance of this amp. I've only listened to it no more than 2-3 hours. Need further burn-in, but I'm very happy with it!

My initial goal was an all DHT class A2 SE amp based on Michael's design. I ended up with a crazy idea of a 46 driver in filament bias. You realised it's crazy when you see the size of the power supplies. The investment paid off. The driver can do 200Vpp @ 0.09% running at about 35mA which provides a great driving capability to the 4-65a thanks to the mu-follower gyrator load.
What surprised me so far are the bass and dynamics of this amp. Clearly I wasn't used to having 10W of single-ended power, but know I can get more than the 2W of my 45 SE to play that music that needed a tad more power. I'm not playing it loud at all. So far I did a quick run through jazz (e.g. Coltrane, Mingus, Davis), classical and rock music to test some favourite songs to listen to subtle characteristics of the amp. I will probably make some further comments in the future but overall can say it has a deep bass, fantastic dynamics and sweet tone.

A remarkable note is the quietness of this amp. Can get no hum whatsoever on the FE167E speakers. See my THD measure below. All filaments are DC using Rod Coleman regulators (highly recommended) and not easy to achieve this with the 6V/3.5A heaters

here are some pictures if you are interested:
4-65a SE Amp: testing it finally! | Bartola Valves

And the 4-65A running cherry red to keep the getter healthy:
4-65a SE Amp: cherry anodes | Bartola Valves

I have some slight improvement to make to the Salas SSHV2 regulator which I will post on the other thread.

Special thanks to Michael Koster (design), Rod Coleman (regulators and crowbar protection help) and Thomas Mayer (transformers).

Thanks
Ale
Ale,

Congrats on the job well done! I am curious as to know what capacitors you ended up using in the mu-follower coupling?

Regards,
-MW
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Old 12th August 2013, 04:58 PM   #150
mogliaa is offline mogliaa  United Kingdom
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Hi Michael,
Thanks, it doesn't look as nice as yours though!
Which cap do you mean? It's DC coupled so I guess you are refering to the gyrator cap? It's an 1uF/630V LCR one...
Ale
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