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Old 29th August 2006, 08:47 AM   #1
neg2led is offline neg2led  Australia
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Default Tube Hybrid Amp.

Hi all,
I want to make a tube hybrid, and i was looking for a bit of advice.

Am i correct when i say a tube hybrid is effectively a tube pre-amp and a MOSFET power amp?

If so, has someone made one that is fairly simple, preferably requiring only one or two tubes?

Thanks in advance,

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Old 29th August 2006, 11:29 AM   #2
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Default Heres a one tuber!

Single mosfet amp

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Old 29th August 2006, 12:01 PM   #3
Ryssen is offline Ryssen  Sweden
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Here is one that is turning in to a hybrid.
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Old 29th August 2006, 12:22 PM   #4
heater is offline heater  Finland
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Check the nice simple htbrids here http://www.wdehaan.demon.nl/hybrid/

I built the "Design Using 5687 Tube". I love it.

If high voltages worry you try the battery tube version.
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Old 29th August 2006, 01:04 PM   #5
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Hybrid is a pretty broad term, when applied to trasistors and tubes. It just means a mixture of the two and can be a tube preamp with SS power amp, as you describe, or it can be the other way around. Many people value the sound of tubes in a power amp because they tend to have a more gentle overload character that an SS amp. Preamp sstages are often seen as OK with either tubes or SS, since overload is usually virtually impossible. Let's be honest, these days a lot of music sources (CD, DVD, cassette tapes, radios, etc.) use SS.
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Old 29th August 2006, 01:23 PM   #6
Sherman is offline Sherman  United States
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Default VB GC

Valve-buffered gainclone. About as simple as you can get for a hybrid. Build a "gainclone" with LM3886 ot LM3875 chips. Then just add a cathode follower front-end with a 6922 tube.

Search the Chipamp forum for 'valve buffered' or 'tube buffered'.
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Old 30th August 2006, 02:12 PM   #7
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Careful when loading a tubes' plate with a MOSFET gate. The MOSFET's Crss capacitance can be large and is guaranteed to be non-linear. See other discussions about this effect in other threads.
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Old 30th August 2006, 06:04 PM   #8
Sherman is offline Sherman  United States
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Quote:
Originally posted by Brian Beck
Careful when loading a tubes' plate with a MOSFET gate...
Very true, but that is the main reason for using a cathode follower. Extremely low output impedance and relative immunity to capacitive loads (within reason of course ). One could even go with a White Cathode Follower and have even more margin, though that would require two dual triodes of course. The 6DJ8 family is well suited to that sort of duty.
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Old 30th August 2006, 06:21 PM   #9
Ryssen is offline Ryssen  Sweden
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Quote:
Careful when loading a tubes' plate with a MOSFET gate...
So you mean that a 6C45 as voltage amp wont do the job?
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Old 30th August 2006, 07:09 PM   #10
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Depends what you mean by "do the job". I guess you could say that a any SS amp will "do the job".

But the RC time constant of a 6C45 plate looking into the horrendously non-linear capacitance of a MOSFET gate will still produce phase shift in the audio band, and non-linear phase shift at that. Some people won't mind the resultant sound. More etch. More zip. As we discussed in another thread, one solution is to increase the MOSFET's drain voltage way up to 100 or 200 volts, reducing and flattening Crss. The other solution, better in my view, is to use a CF or even a White follower.
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