• 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.

6V6 line preamp

diyAudio Chief Moderator
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Hi Salas, the same 6922 preamp sounds much better with an ECC82 (NOS-Mullard) at the input.

But I plan to refine the 6V6 preamp and get a couple of more tube brands, Tungsol and maybe JJ . EH also has them but I'm not sure how they will sound.

I will also complete my 6SN7 tube preamp which has been lying in storage for a very long time ! All octal !

EH 6V6 were rather sharp tonally in my trials. They are clear and fast though if that is what's missing in a speaker with tubby low mids and there is a cloth tweeter or mylar compression driver to keep them in check for HF sharpness.
 
diyAudio Chief Moderator
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About JJ I liked their 300B for the price but I did not like their novals. They always had left me an arid feeling in the mids. About their octals I don't know.

P.S. Nice to know you will progress it. We will be happy to know your final config and valve picks plus pictures of your build, the resilient board mounting etc.
 
diyAudio Chief Moderator
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Best the Russians do in that factory is labeled "Genalex" promoted and priced accordingly by Western investor. EH is like their branded plain vanilla production one step above Sovtek labeled.
Midway there are the other old labels they bought for brands use and make so called new production copies of their iconic types. https://www.youtube.com/watch?v=feIkWtC6GTI
 
Thanks nicoch58 .
I'll bite the bullet and buy them. Might take a while to actually get them in my hands. Will get a good board ready with shock mounting included !

Now I have to try my board with close to V+ = 300 V and see what happens.
EL34's are waiting to be checked out too ! :)
The dc heater circuit isn't ready yet for that test !
 
Used another traffo to up the supply voltage. Now I get a supply of + 262 Volts.
Plate voltage of 118.3 V and 117.5 V
Plate current of 11.15 mA and 11.28 mA

I think it sounds clearer . Must be operating in a more linear region. Sound is nice and tight . Good LF and good HF. Mids are very nice.

Maybe we should compare the EL84 also ? :)
Might be less microphonic. However the 6V6 didn't seem to be affected audibly with microphony on playback provided it isn't on a badly resonant surface. Tapping the tube directly is 'wow' ! :)

However one needs protection ( mute or relay cut out) till the tube comes up to operating voltage before turning on the power amp. About one minute I think. Otherwise you will get a very loud pop . If it's too early you will get a whole lot of other noises and dangerous speaker cone movement.
Better to incorporate the relay in the preamp itself. Turning off the heater last (!) helps to bring down the HT really fast ! Otherwise it takes ages with a high bleeder resistor.
 
diyAudio Chief Moderator
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Staffan, since you got a boatload of tubes stash, if you maybe see some 6F6 around try test a good pair in your preamp by the way. Because an American friend who's an old hand in tubes wrote me that they are compatible to this circuit and very good.
 
Ok. Yes I would guess there is maybe 10-20 of 6f6 and about the same with GT. 6k6 maybe 10, dunno there is some unsorted cubic meters still to sort. Problem no 1 is that the boat owner got a back surgery yesterday and still in hospital for another week or so. No 2 is that finding them. We know they are not among the sorted boxes easy to reach but in the cargo area. No 3 is that my workbench is torn to peices and all my instruments stached on top of eachother. I guess we could dig up some and do a kitchen work in a week or two if your very curious. A little tip that I could do easyer is 6g6g since I have a bunch at home. Also 6aq5 (think I sent you a matched pair?) and about 50 different 6v6. What jig did you have in mind and what do you want to measure?