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Old 10th June 2011, 06:51 AM   #1
neskor is offline neskor  Serbia
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Default Best input DHT tube?

Any suggestion for DHT input tube for 10Y IT 300B amplifier?
Beside 26
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Old 10th June 2011, 08:12 AM   #2
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This is really up my street. I've been experimenting with different DHT small tubes for 3 years in 300b SETs. In terms of input tubes I found I liked in approximately this order:

26 - my preferred option for tone and overall magic
10Y - capable of great clarity and dynamics, but I missed the 26
01A - very good, but not as magical as 26 or clear as 10Y
30sp (VT67) - surprisingly good, less microphonic than 30
46 - usually a driver tube, but very neutral with good tone
1G6G/GT - surprisingly good but very microphonic, so needs special mounting

I went with the 10Y for ages in different contexts but came back to the 26.

The implementation matters here. On the basis of listening tests I gave up resistor loads and solid state loads and went for a transformer/plate choke. 26 needs a high inductance load like 200H or more, and this is most easily found in a plate choke. I currently use a cheap solution - two Hammond 156C chokes of 150H, in series making 300H. It does the job fine, though clearly there will be more expensive and sophisticated options. I don't use a cathode bypass because I use filament bias, and the cathode resistor is just 10 ohms. I preferred filament bias to battery bias on the grid which would be my second best option. But I do use choke input plus a Rod Coleman boards for the filament - only works when it's super clean.

Like you I planned on using 10y as a driver, but when I started matching the 10Y up with interstages I surprisingly found that I preferred the tone quality of the 46. Usefully this sounded very good with the cheap but excellent Hammond 126C without cathode bypass, and also with the much more expensive Lundahl LL1692A. So I went with that. I was surprised not to be using the 10y because in AB listening tests in various other contexts it seemed to sound better than the 46. So it's really a case of getting the alchemy right.

Andy
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Old 10th June 2011, 08:20 AM   #3
neskor is offline neskor  Serbia
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Thanx Andy!
I was waiting for your answer
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Old 10th June 2011, 07:59 PM   #4
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I'm using 8025a in my preamp, it is a great sounding DHT that tube can be used as driver as well for 300b. the tube has white filament like 10Y.

best
karsten
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Old 10th June 2011, 08:20 PM   #5
neskor is offline neskor  Serbia
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it looks cool
Click the image to open in full size.
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Old 10th June 2011, 09:06 PM   #6
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Hi!

I always use step up input transformers with all DHT amps and stick to 2 stages. Of course this requires a preamp with low enough output impedance to drive the input transformer

Thomas
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Old 10th June 2011, 09:09 PM   #7
neskor is offline neskor  Serbia
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What kind of input transformer?
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Old 10th June 2011, 09:15 PM   #8
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Hi!

Lundahl LL7903 works nicely for me

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Old 10th June 2011, 09:16 PM   #9
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Quote:
Originally Posted by 211hojbjerg View Post
I'm using 8025a in my preamp, it is a great sounding DHT that tube can be used as driver as well for 300b. the tube has white filament like 10Y.

best
karsten
Holy Cow! Never seen that one. What a cool tube. What's your operating point - is it happy with around 250v on the plate?

I couldn't see any curves. Doesn't look too expensive.

Andy
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Old 10th June 2011, 09:17 PM   #10
neskor is offline neskor  Serbia
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I have LL1636, can I use that?
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