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Old 5th November 2009, 03:45 AM   #101
kevinkr is offline kevinkr  United States
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Hi Lars,
Where can I get the 26 model and symbol you are using?
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Old 5th November 2009, 06:28 AM   #102
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Kevin,

DHT models: Composite Tube Models

I have also made a 6B4G model from the included 2A3.

Made the "triodeh.sym" myself in LTSpice. Can mail it if you need it.

The "gyrator" can of course be cascoded using two FETs.

Last edited by revintage; 5th November 2009 at 06:35 AM.
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Old 5th November 2009, 06:48 AM   #103
CFT is offline CFT  United States
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Hi Lars,

Does LL1676 fit 26 tube nicely? It doesn't seem to have high enough inductance at the primary, does it?
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Old 5th November 2009, 07:37 AM   #104
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Originally Posted by CFT View Post
Hi Lars,

Does LL1676 fit 26 tube nicely? It doesn't seem to have high enough inductance at the primary, does it?
No, probaly too small as you say. Better suited with tubes as eg. 12B4 and 6n6p.
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Old 5th November 2009, 08:03 AM   #105
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Quote:
It doesn't seem to have high enough inductance at the primary
Where did you get that info? I talked to Per Lundahl a while ago and he was reluctant to give any specific figures.

My guess is you can count on at least 200H. Can measure mine if this is of major interest. Compare it to its smaller brother 1544A that is said to be 80k. The 1676 has enough core to give 5,5V out in 4:1.
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Old 5th November 2009, 08:13 AM   #106
CFT is offline CFT  United States
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Quote:
Originally Posted by revintage View Post
Where did you get that info? I talked to Per Lundahl a while ago and he was reluctant to give any specific figures.

My guess is you can count on at least 200H. Can measure mine if this is of major interest. Compare it to its smaller brother 1544A that is said to be 80k. The 1676 has enough core to give 5,5V out in 4:1.
A sheer guess

Will be interested to know your measurement, actually interested in them as well
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Old 5th November 2009, 10:51 AM   #107
Richard is offline Richard  Australia
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Hi Guys,

Iím stoked that my 26 preamp works. I just finished wiring up one channel for testing, it sounds great and Iím surprised that there is not much hum at all, but microphonics is another matter. This is my second scratch built valve project, the first being a 6N2P lampizator for my CD player. I must admit I thought I was being a hero trying the 26 without much experience, but all the info and excellent advice offered on this site as well as Kevinís write up on his 26 pre helped with proper planning and building. So a big thank you for all the advice and to Andy for raving about DHTís in preamps almost everywhere on the net. I simply had to build one.

Iím using the 2 Hammond 150H chokes as plate loads and a 0.22uF output cap similar to Gary Pimmís 26 pre. Iíve built the prototype on a wooden chassis that also will allow me to try that Hashimoto transformer later. Itís a 3 chassis preamp at the moment, power supply, filament supply and preamp.
Filament supply is 6V XF 1N5822 diodes Ė 16000uF Ė 1R Ė 16000uF Ė Lm1086 ccs.

Iíll post some pictures later.

Rich out
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Old 5th November 2009, 10:52 AM   #108
Richard is offline Richard  Australia
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45 & Kevin,

Thank you for the advice on transformer loading and other options, Iíll experiment with step-ups in my setup first.

Just one quick query, should I load the secondary of the 20K:600 XF with a 600 ohm resistor or just leave it open?

Cheers,

Rich
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Old 5th November 2009, 11:24 AM   #109
45 is offline 45  Italy
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Quote:
Originally Posted by Richard View Post
45 & Kevin,

Thank you for the advice on transformer loading and other options, I’ll experiment with step-ups in my setup first.

Just one quick query, should I load the secondary of the 20K:600 XF with a 600 ohm resistor or just leave it open?

Cheers,

Rich
I would leave it open if you get a smooth high frequency response.
In this case the load will be the input impedance of your power amp. If you have a typical 47K (+ some pF's that matter for high frequencies) the low frequency cut-off should be well below 20Hz anyway.
The 600 ohm resistor (or other values) would serve as equalizer if you don't get a smooth high frequency response. Also distortion could change substantially with or without additional load resistor.
However off-band peaking could not not be a problem. It would be a problem with feedback.....
Try different solutions, listen to them and choose what you like!

Cheers,
45

Last edited by 45; 5th November 2009 at 11:37 AM.
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Old 5th November 2009, 02:41 PM   #110
fingerx is offline fingerx  Hong Kong
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Hi Richard, Would you mind telling me the value of the resistor on 1086 CCS ? or better the formula is, I think that's simple though..
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