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Old 31st December 2005, 03:26 PM   #1
pixpop is offline pixpop  United States
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Default What I have: 4 Tubes. What I need...

Through a mistake I made in ordering some replacement tubes for my HP 200CD Oscillator, I now have these 4 homeless NOS tubes:

2x 6SH7 (Branded KEN-RAD)
2x 6AU5 GT (Branded RCA)

I have the following projects on my list of things to do, and wondered if any of these tubes are good choices for any of these projects:

An RIAA preamp for MM cartridges.
A line stage
A 2 way active filter for bi-amping

Thanks,

Neil
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Old 31st December 2005, 05:29 PM   #2
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Neil,

The 6AU5 data sheet suggests suitability in voltage regulator service. Regulated B+ definitely has its place in preamps, particularly phono sections.

With DC on the heater, the 6SH7 might make a good 2nd gain block in a passively equalized phono preamp. Perhaps 6922 sections in the 1st gain positions. Be sure to buffer the line level O/Ps. 5687 or ECC99 cathode followers seem about right, but JFETs could work out too.
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Old 31st December 2005, 07:40 PM   #3
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The 6AU5 can be used as an output tube, but the screen voltage needs to be lower than the plate - perhaps regulated? The 6SH7 is a linear pentode, good for a gain stage. Mu about 35 triode connected. GE data sheet says "not recommended for high gain audio amplifier due to hum." I'm sure it would be fine at line levels.

I take it your 200CD is the later one with 6AU6 and 6CW5?
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Old 31st December 2005, 08:06 PM   #4
pixpop is offline pixpop  United States
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Quote:
I take it your 200CD is the later one with 6AU6 and 6CW5?
I'd have to open it up again to be sure, but what I can say is that these tubes dont fit. The tubes in the oscillator are more miniature, with finer pins, and these replacements don't fit. I later found out that the oscillator didn't need new tubes anyway. I just had to fix a problem with the attenuator and now it works fine.

It's a beautiful thing, and also acts as a ballast to keep my bench stable during earthquakes ;-)

But it sounds as though, if I want to build a phono stage, I'd be better off choosing some other tube. That's OK.
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