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Old 10th February 2005, 07:44 PM   #1
lcleven is offline lcleven  Canada
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Default Van der Veen 70W tube Amp DIY

Has anyone built the DIY Menno Van der Veen 70w or 100w tube amp which uses the Plitoron torroidal power and output transformers. I am thinking about using this design for my first tube amp project and was wondering what the DIYers out there have to say about this amp. My current system is bi-amped with 100W and 200w solid state amps with an active crossover. The tube amp would be used to drive two PHL 1240 mids and Raven R2 ribbon tweeter in a MTM with an overall sensitivity of abot 95 dB. I would use a 200w solid state for the 12" Lambda bass driver. The info on the Van der veen's tube amp can be found at Plitron.com. Thanks
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Old 10th February 2005, 08:04 PM   #2
VT67 is offline VT67  Belgium
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Some 5 years ago I've built the 100W version.
I did substituted the EL34 with the KT66 from Valve-Art.
Until today I'm still very happy with this design.
Have look at my website.

Cheers

GeWa
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Old 10th February 2005, 09:28 PM   #3
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I built the 40 w and 100 w Radio Bulletin versions a long time ago, EL84 and EL34,even had a talk with Menno once.

Both really nice amps, i did Menno's Mosfet 20 watt Class A amplifier too, also a design in Radio Bulletin.
Quite often the transformers are offered on the web here in Holland, the original Amplimo's(ILP).
I can not think of someone around knowing more on transformers and transformers for tube amplifiers than Menno van der Veen.
Many of the old transformer companies are gone, and a lot of the knowledge.
Even have a bunch of his articles in Radio Bulletin, including the ones on the 40 and the 100 watters.
Menno works for both Plitron in Canada and Amplimo here in Holland i think.
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Old 10th February 2005, 09:51 PM   #4
VT67 is offline VT67  Belgium
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Hoi Jacco

Before I started building the amp I first bought me this one together with Menno's book.

Cheers
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Old 11th February 2005, 05:30 AM   #5
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Default Yep - I built a pair just recently

I built the 100W versions using 4 x Winged C Svetlana EL34s.

I started off with them in Ultralinear Mode and found I had two problems.

Problem #1 - Slight bursts of HF Oscillation just after the postive peak of a sine wave. This was cured by increasing the 150R screen resitors to 1K. I reported this to Menno and he has put a note on his web pages to the effect that this mod should be "Standard".

Problem #2 - The Output Impedance of the basic amp (no global feedback) is 12 Ohms. There was some "colouration" of the sound as the output power followed the speakers impedance curve.

To cure problem #2 I rewired the output into triode mode. Output Impedance dropped to just less than 5 Ohms. Output power dropped to 40W BUT full power bandwidth is 12 Hz to 150 kHz

If you build the 70W version you can bias the output tubes a little higher and this will drop the output impedance to probably about 4 Ohms or just less.

In this arragement these mono-blocks have become my favourite amp(s). I have an 845 SET and a Hugh Dean AKSA 55 Nivarna Plus (Solid State) which these amps have displaced.

Have a look on the Photo Gallery above about the second to last page for the Gingertube "Menno Bricks" for some pics.

P.S. My speakers are VAF Research DCX s with a nominal impedance of 6 Ohms (95dB sensitivity). If your Speakers are less than 4 Ohms or if you are using Electrostatics then the Output impedance will probably be a bit high.

Oh - one last thing I pulled the 12AU7 and am using ECC99 in its place. I thought that gave me a slight improvement.

One problem with the design is that the Output Tube grid resistors are reasonably high and is in fact too high for anything except EL34s. Don't be tempted to use 6550s or KT88s. In any case the tube separation really only suits the skinny EL34s. I haven't checked data sheets to see if the KT66 that someone above suggested is a SAFE substitution or NOT.

I RECOMMEND that you use the "Winged C" Svetlana EL34s and not try to substitute cheaper alternatives.

I also did 2 other mods which I have no idea if they helped or NOT.
1) A 2uF/900V Polypropylene (from Rarefaction in Melborne Australia) directly across the high voltage at the Output Transformer Centre Tap connection to 0V.
2) A 100K 3W Metal Film bleed resistor across that cap.

I suggest that you put the electrolytic caps on the back (the tracks side) of the PCB just to keep them a bit further away from the heat of the tubes. Also put the bias pots and the bias measure resistors in each output tube cathode on the back of the board so that when the board is screwed down into its chassis you can get at the bias measuring points and the adjustments.

Due to the 250V AC Oz Mains Voltage my rail voltage was 480V instead of 450V so I backed off the OPutput Tube bias currents from 50mA to 45mA to keep anode dissipation at 22.5 Watts.

Good Luck
Ian
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Old 11th February 2005, 06:12 AM   #6
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Default After thought

As an after thought -

100W or even 70W is WAY more than you need for driving Mids and Tops.

Have a look at Menno's UL40-S2 kit from Amplimo instead. Mennos web pages describe how to convert this design to his "Super Triode" configuration if desired.

Cheers,
Ian
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Old 11th February 2005, 11:07 PM   #7
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Default Re: Van der Veen 70W tube Amp DIY

Quote:
[B]Has anyone built the DIY Menno Van der Veen 70w or 100w tube amp which uses the Plitoron torroidal power and output transformers.

Hi there........Yes...I've built one and never again..(this is only my opin)........I binned the toroidal output transformers....and redesigned the amp..using convential trannies.Why ? I found circuit unstable at low frequencies with massive amounts of 2nd harmonic thd and sloppy sounding mid....also output impedance sensitive.........hallmarks of a completely badly designed amp. Each toroidal o/p tranny (which had strip cores) had poor balancing circuitry which couldn't handle the steep sided BH curve when driven hard........resulting in skewed BH curve around the H axis. The bass sounded like a closet in it's finals.

Sorry to put cold water on your ideas !

rich
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Old 14th February 2005, 07:55 AM   #8
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I love the post by richwalters (someone not afraid to say what he thinks about the emperor's new clothes)!

I have avoided using toroidal OPTs because (a) they're expensive; (b) I understand that they are easily prone to DC saturation if the OP tubes are not precisely balanced (even if they are balanced to start with, they probably won't be with the passage of time); and (c) they just don't look as nice, to me, as the more traditional E-I design.
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Old 14th February 2005, 09:00 AM   #9
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Quote:
Originally posted by jacco vermeulen
I can not think of someone around knowing more on transformers and transformers for tube amplifiers than Menno van der Veen.
He certainly is knowledgable on transformers... i had the opportunity to listen in on a couple conversations between him & Bill Perkins -- althou a lot went over my head, it was clear both of these guys knew a lot about transformers.

dave
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Old 14th February 2005, 09:10 AM   #10
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It's never my interest to offend anyone......but when a <newamp design> designed in the last century turns up on my bench which has inbuilt inherent problems, I'm quick to flick it into a design that works........motto.....keep it simple. who wouldn't ??

rich
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