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Old 21st January 2011, 06:25 PM   #831
vgeorge is offline vgeorge  Greece
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Merlin,
this is something that you have to try for yourself and decide.
What kind of transformers do you have on hand now?
If you have some volts to spare you can try Salas shunt.
With a 180-0-180 trafo you can go either with choke input and passive filtering and get around 130V B+ or cap input, with a small first cap and depending on your rectifier, and get around 180 - 200V and regulate down with SSHV. These are rough calculations, you can use PSUD2 for more accurate results.
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Old 21st January 2011, 06:31 PM   #832
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Hi!

Quote:
Originally Posted by merlin el mago View Post
I want to use 26 preamp with my SS Erno Borbely 75WRMS class A amps & eventually for my Sennheisers HD600 as heaphone amp, can I use it or I have to forget in the applications that I want?
Check the input imoedance of your SS amp. You can simply do this my measuring with a multimeter with the amp switched off. SS amps often have low input impedances like 10-20k. Not good at all with a preamp with a Zout of 7k!


Quote:
Originally Posted by merlin el mago View Post
It's a good idea to use a super shunt regulator like Salas between the psu & the anode choke or will be better only the anode choke?
Matter of taste. If you ask 3 people you will get 5 opinions. I prefer the purely passive approach with my DHT linestage. As little SS as possible (just the filament rectifiers)

Thomas
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Old 21st January 2011, 07:43 PM   #833
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Hi Thomas,

What's your estimate for the Z out of a 26 into a LL1660/5mA in 4.5:1?

Andy
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Old 21st January 2011, 08:47 PM   #834
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Hi Andy,

neglecting copper losses in the transformer this is calculated as follows:

rp of the tube divided by the square of the turns ratio.
That is 7000 Ohms / SQR(4.5) This is roughly 350 Ohms

Best regards

Thomas
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Old 22nd January 2011, 07:42 AM   #835
CFT is offline CFT  United States
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Quote:
Originally Posted by andyjevans View Post
So I'm thinking "DHT system" not DHT preamp. Thomas has a good point - put the preamp stage in the amplifier. I'm going to try exactly that - it makes good sense. And Thomas has another good point - the LL1660 will sound better in 4.5:1. My solution to that is simply this - don't use a 26, use a 10Y. Keep the 26 for the input of the amp and direct couple it to the driver stage, like another 10y.

Different ways of doing it - I'm saying this in favour of the idea of using nothing except DHTs. That's what's given me the best sound.
After my second 26 preamp was complete (see earlier posts ->#622), I also had the 112-A driven 45 amp built, using a pair of Noguchi C-core nano crystal output trans (parafeed), Rod Coleman's filament regs, and lots of trans used as input, loading, and interstage, thus becoming quite heavy as it consists of 11 irons altogether....

Initially I was thinking of building the parafeed 26 preamp for my Linkwitz Pluto, and call it a day, thereafter just enjoy the music, but because I already had certain parts on hand including a few pairs of full rangers, so I decided to build the DHT amp too, and it indeed sounds great
(photo showing 01As, not 112-As)

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Old 22nd January 2011, 07:50 AM   #836
CFT is offline CFT  United States
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The rectifier tube is an 83, thus two switches on panel as one needs to periodically turn on the pre-heat switch first before pumping in the HV....

Voltage more constant as current draw fluctuates I understand.....

BTW, I wondered how different it would be if 10y is used as driver instead of 112-A....
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Old 22nd January 2011, 09:04 AM   #837
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Wow - CFT, that's nice work. I bet it sounds wonderful!

I think you'd get a noticeable increase in quality with a 10Y - I'd recommend it. I have some if needed.

Do you use filament bias at all? I'm getting good results with that, assuming you have a really good filament supply like Rod's or some nice chokes for choke input, or for overkill a choke input supply followed by Rod's filament board or another choke as Thomas uses.

Alternatively, battery bias like Kevin uses?

Andy
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Old 22nd January 2011, 09:16 AM   #838
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Here's mine - it has a separate power supply. Glow tubes on the left for the input tubes. I use a modular chassis with several interchangeable top plates, with rackmount parts as you can see. All my chassis are 2U and usual rack width. Lundahl transformers underneath.

Andy
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Last edited by andyjevans; 22nd January 2011 at 09:19 AM.
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Old 22nd January 2011, 10:12 AM   #839
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Quote:
Originally Posted by vgeorge View Post
Merlin,
this is something that you have to try for yourself and decide.
What kind of transformers do you have on hand now?
If you have some volts to spare you can try Salas shunt.
With a 180-0-180 trafo you can go either with choke input and passive filtering and get around 130V B+ or cap input, with a small first cap and depending on your rectifier, and get around 180 - 200V and regulate down with SSHV. These are rough calculations, you can use PSUD2 for more accurate results.
Quote:
Originally Posted by Vinylsavor View Post
Hi!


Check the input imoedance of your SS amp. You can simply do this my measuring with a multimeter with the amp switched off. SS amps often have low input impedances like 10-20k. Not good at all with a preamp with a Zout of 7k!



Matter of taste. If you ask 3 people you will get 5 opinions. I prefer the purely passive approach with my DHT linestage. As little SS as possible (just the filament rectifiers)

Thomas
@vgeorge
Thanks for the input.

@Thomas
Bad news, my SS Borbely amps are less 10K input impedance so can't match with the 26 preamp? can I use the 26 preamp like a headphone amp for Sennheiser HD600?
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Old 22nd January 2011, 10:23 AM   #840
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Quote:
Originally Posted by merlin el mago View Post
@Thomas
Bad news, my SS Borbely amps are less 10K input impedance so can't match with the 26 preamp? can I use the 26 preamp like a headphone amp for Sennheiser HD600?
This only means you can't use it with a 1:1 output transformer or with LC or RC coupled output. With a Lundahl 1660 4.5:1 it will easily drive your SS amp.

Thomas
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