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Old 2nd February 2008, 03:27 PM   #1
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Default Build a VT100?

Hello fellow forum members...


Question: Since I moved into a larger home, I need some more power to listen to music at levels I'm accustomed to. 35 wpc isn't cutting it anymore.

I have some experience doing mods and refurbishing my Dynaco ST70 (VTA driver board, SDS lab power supply), but admit that theory and circuit design are not my strong points.

Having said that, I've looked (and listened) to some fine gear and was wondering about the possibility of building a cloned AR VT100. Seems like it has enough power and would be a good match for my system requirements. I have no idea where I would source OPT, maybe Lundahl?

Any input appreciated.
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Old 2nd February 2008, 06:22 PM   #2
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Do you really want to get involved with parallel push pull? A project of acquisition and overhaul of a vintage Harman/Kardon Citation II will yield an amp that O/Ps 60 WPC continuously and 120+ WPC instantaneously. That's plenty of power. Also, the O/P trafos in the "Duece" are among the very finest ever made. Dyna O/P "iron" aint bad, but compared to the Freed stuff H/K used, it's guano.

Jim McShane, AKA Mr. Citation, has everything needed to get a "Duece" back into tip-top shape.
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Old 4th February 2008, 05:06 AM   #3
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Quote:
Originally posted by Eli Duttman
Do you really want to get involved with parallel push pull? A project of acquisition and overhaul of a vintage Harman/Kardon Citation II will yield an amp that O/Ps 60 WPC continuously and 120+ WPC instantaneously. That's plenty of power. Also, the O/P trafos in the "Duece" are among the very finest ever made. Dyna O/P "iron" aint bad, but compared to the Freed stuff H/K used, it's guano.

Jim McShane, AKA Mr. Citation, has everything needed to get a "Duece" back into tip-top shape.
One thing ELI perhaps didn't make clear is that a properly working/restored Citation II sounds a heck of a lot better than you'd suspect for the vintage, and IMO sounds way better than the VT100 which is needlessly complex.
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Old 4th February 2008, 03:14 PM   #4
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Correct me if I'm wrong - I thought to hear a significant increase in volume that I would need roughly 3 times the power of my current amplifier.

I suspect my modded Dyanco is pushing closer to 40 wpc, so a Citation with 60 seems like it won't be enough increase for me notice.
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Old 4th February 2008, 03:55 PM   #5
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Despite the fact that the steady state power output difference between the Citation II and the ST-70 is in theory less than 3dB, the Citation has a lot more headroom over all, as Eli points out it is quite capable of producing more than its rated power on music. I've had both heavily modded ST-70's and Citation II, and the Citation II is a lot more dynamic, and has far better extension on the bottom end and top end, and plays way louder with a given speaker..

Frankly my old modded Citation II managed to sound louder and more dynamic on real program material driving a pair of Magnepan MQ1.4 and later a pair of 1.6QR than a 250wpc highly regarded solid state stereo power amplifier I owned at the time.
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Old 4th February 2008, 08:22 PM   #6
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Thanks for the input, Kevin.


If I chose to go down the path of building a cloned VT100, where would I source OPT? Jensen? Lundahl?

TIA
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Old 4th February 2008, 09:14 PM   #7
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Quote:
Originally posted by petera77
Thanks for the input, Kevin.


If I chose to go down the path of building a cloned VT100, where would I source OPT? Jensen? Lundahl?

TIA
I'd probably choose Electra-Print or one of several others frequently recommended here. (Heyboer, or Onetics)
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Old 8th February 2008, 05:21 PM   #8
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Another question....


I'm trying to determine the correct characteristics for the output transformers in this amp.

Because I'm not good at reading circuits, I'm struggling a little bit. OK, a lot.

Near as I can tell, the 6550 like around 5K ohms of plate resistance. Would a Lundahl LL1620 be a good fit, given the circuit design of the VT100?
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Old 8th February 2008, 05:26 PM   #9
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I don't remember the exact pp primary z of the VT-100 opt, but my 120W PPP amplifier used a 3.2K transformer at 500V.. Typical values for a 4 tube PPP could run from about 1.6K to 3K or so depending on class of operation, operating point, and configuration. (Pentode/UL/Triode)
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Old 8th February 2008, 06:17 PM   #10
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Thanks Kevin.

Assuming PP in class AB operation (I think this is the correct topology of the VT100), does the LL1623 look like a btter fit to you?

This stuff is hard.....but fun.
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