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Old 10th December 2004, 11:14 PM   #1
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Default 10-15 mu DHT?

I'm looking for a DHT I intend to use to drive a 300B and require a mu in the range of 10-15. Has anyone any suggestions? The PX25 is perhaps a candidate. The SV572-10 seems a little much, as does a 211. Anyone know of other options available?
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Old 11th December 2004, 12:11 AM   #2
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Default try the other way around

300B driving 845,572-x,211.

The AVVT 8B is as close as you'll get most likely.

If you can give up the DHT, there are a number of non-DHTs with
mu=9 that I've used with spectacular success. My most fave is
the 6W6GT triode wired. My second most fave is the Valve art
KT66. I've used both of these tubes to drive interstages as well
as LC coupling to the output tube and they are amazing.

You can always use a nice, battery powered DHT for the input
stage. The #26, or the 10Y or such. I like the 76.

-- Jim
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Old 11th December 2004, 12:22 AM   #3
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Quote:
300B driving 845,572-x,211.

The AVVT 8B is as close as you'll get most likely.
I know, and I once used to drive my cart before my horse .... ahem. I need the drive volts of a higher mu tube to stay in the 2-stage arena.

Have you any experience with the VAIC tubes? Appreciate your opinion.
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Old 11th December 2004, 12:38 AM   #4
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Smile Small DHT

I don't know if it's enough. But a paralleled 3A5 will give 7-8ma with a mu of 15 at 90 plate volts.
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Old 11th December 2004, 01:13 AM   #5
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Default Re: 10-15 mu DHT?

Konnichiwa,

Quote:
Originally posted by serengetiplains
I'm looking for a DHT I intend to use to drive a 300B and require a mu in the range of 10-15. Has anyone any suggestions? The PX25 is perhaps a candidate. The SV572-10 seems a little much, as does a 211. Anyone know of other options available?
RS241
RS242
YL1130 (triode connected and paralleld sections)

come to mind immediatly, others no doubt exist.

For something real crazy, how about a zero bias high Mu transmitter valve operated at lowish anode voltages?

Sayonara
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Old 11th December 2004, 02:07 AM   #6
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Hey Pete, nice tube, but I suspect it hasn't enough oomph. (BTW, I was born in Regina, raised in Estevan, one not less middle of nowhere, paradoxically, than the other.)

Thorsten, are those RS tubes Telefunken? Und was is es zero bias type tube?
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Old 11th December 2004, 12:07 PM   #7
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Konnichiwa,

Quote:
Originally posted by serengetiplains
Thorsten, are those RS tubes Telefunken? Und was is es zero bias type tube?
They are TFK but not quite zero bias. Gordon Rankin makes a "spud" amp with one of them, around 1 - 1.5 Watt. You can still find them at less than ultra-extreme prices, for how much longer, we will see.

Sayonara
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Old 11th December 2004, 01:59 PM   #8
jlsem is offline jlsem  United States
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Quote:
For something real crazy, how about a zero bias high Mu transmitter valve operated at lowish anode voltages?
Someone over at GM70 Yahoo had good luck with the 3C24.

http://groups.yahoo.com/group/GM70/

John
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Old 12th December 2004, 06:12 AM   #9
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Default direct coupled is how I solved this problem

I dont know of any DHT that can help you out.

You can still remain "two stage" in philosophy by using a direct
coupled driver. Thats exactly what I do. I use a 76 direct coupled
to a 6W6GT. The 6W6 drive an interstage transformer which drives
the 845 in fixed bias.

In this case, you eliminate the phase shifts of a coupling cap or
an additional IT. In my case, the 76 gives me a gain of about 8 and
the 6W6GT a gain of 9. At my 845 op pt, I only need 100V to go
full power, so my amp is about 1.5V sensitive. Had I used a 6SN7/6J5
it would be even MORE sensitive.

Were I to run the 845 up to 800V, then I'd definitely use the 6SN7 as
the new grid swing limits would translate nicely into 250Vp-p of swing
at 2V in, so it would be ideal for CDP direct input.

The directly coupled driver performs flawlessly. 7Hz to 45kHz +/- 1dB.
With direct coupling, its very important to preheat the filaments before
applying B+. The plalte voltage of the 76 provides the proper negative
bias to the 6W6. If it the 76 isnt ready to conduct, the 6W6 will flash.
Further, one must never remove the 76 from its socket. Other than
that, it works as my daily listener.

The design permits easy change to a number of tubes: 26, 37, 76, 6P5GT, 6C5, 6SN7. You will find noticeable variations between
input and driver tubes.

The interstage is an Electraprint 3033-2. It's a 60mA jobber. I run it
at 25mA. You could also use this part with 300b or 6b4g's along with
a #26 is all DHT is clearly a must. There are other tubes that would
make nice input tubes - such as the #30.

You can even forgoe the IT and use LC coupling. This leaves you with
only one capacitor in the signal chain - if you are worried about phase
shifts and stability.

-- Jim
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