• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

211 Preamp

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hacknet

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Joined 2002
#1
i`ve heard of a couple of people enjoying a 211 as a preamp. but, i can`t seem to find any 211 preamp schmatics online.

any one know any?

looking at the datasheet, the 211 seems to have a rather high plate resistance. is this okay for preamp without an output transformer?
 
#5
hmm.. thats kinda crap...

in this case, can anyone recommend a tube i can impliment in a simple manner which is generally know for its dynamics and drive?

i`m using a 6900 now and it seems okay. i`m just looking for something more...😉
 
#6
analog_sa said:


Not unless it's used as a cathode follower
Click to expand...


The 211 has a relatively high plate resistance for a power tube, but it's still lower than many of the tubes people like to use for pre-amps, including the 6SN7. Of course, to get the 211 up to a plate voltage/current where it's going to be happy will pretty much force the use of choke loading or the B+ will need to be in the several kV range :bigeyes:

Peace
 
#10
`ve heard much about choke loads but i`ve never tried... i think i`ll do so soon
Click to expand...

You owe it to yourself before embarking on adventurous high-voltage 211 plans. Choke loading sounds better than any resistor to my ears - more dynamics, better rhythmically, a more interesting sound in general. Just decide upon current and inductance and get on of Lundahl's plate chokes from Martin Electronics - you don't really need to buy expensive chokes to get great sound.
 
#12
hmm.. i`ll put that top of my list to get a pair of chokes...


analog_sa: wow, you know martin😎 okay... i actually have a custom trafo winder in mind.

whats to keep in mind when picking a choke other than current capabilities? any special cores to look out for?

BTW, how do you determind the required inductance?

is it through the reactance of a choke to ac at the lowest freqency i want to achieve?
 
#13
is it through the reactance of a choke to ac at the lowest freqency i want to achieve
Click to expand...

Exactly. So this reactance may be sufficient for a low Rp tube but not for a high Rp.

Nickel content is always good. Not so essential as for interstage transformer but still desirable. Your winder presumably has experience with plate choke winding geometry and knows how to achieve low parasitic capacitance. I mostly use two Lundahl chokes - 1667 and 1668 and between them they cover a large variety of possible tubes. A good friend of mine compared my Lundahls to his Bartollucis and couldn't qiote decide which was better.
 
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