6N1P Bass DI - Revisited

[Spencerleehorton]

Ah sorry just read above and it looks like we need in the range of 95H - 175H on the primaries.
My inductance meter only goes up to about 30H!!

 

[ruffrecords]

If you go back a few posts CJ says the primary inductance of his is 175H but he said a Lundahl someone wanted to use with a primary inductance of 95H should be OK. The impedance of 95H at 20Hz is almost 12K ohms which is plenty for a 9K6 nominal primary. Fortunately inductance is proportional to turns squared so doubling the turns will quadruple the inductance.

Cheers

Ian

 

[Spencerleehorton]

Ok, thanks Ian, just need some power transformers now as just done turret board layout and have most of the bits

 

[Spencerleehorton]

Nope all my calculations are wrong!! Forgot some steps!!! Been a while!!

0.25 and 0.14 won’t get me where I need, pretty sure on the smaller bobbin 0.2mm will be better, will find out!!

 

[Spencerleehorton]

Is there a winding sheet!!!

 

[Spencerleehorton]

CJ has very kindly sent me winding spec for EI75 so I can wind one.

Have gone for a 6N1P tube over the 5963 or the 12AU7 as it’s better on bottom end.

 

[MicDaddy]

Is there a winding sheet!!!

i have an old one laying around somewhere but i think it's for EI100
good on CJ, he's quite the asset to the community

Have gone for a 6N1P tube over the 5963 or the 12AU7 as it’s better on bottom end.

A few years back I was getting boxes of hundreds NOS 6N1P from Ukraine for very little money, not sure if those are still available now or not.

 

[CJ]

I had a friend tell me that the best 6n1p tubes are the ones that have a brand name that starts with a V but I forget the name.

Edit: looked it up on evilbay it is voskhod.

 

[Spencerleehorton]

I’ve found a voskhod and saved it!!

Here are my calculations for doing a power txf!!!

Power tx

Multiply core
2.4 x 2.4 = 5.76
42 / 5.76 = 7.29 core answer = ohms per wind
Pri
230v x 7.29 = 1676

Pri = 1676 turns on 0.61mm swg 23(1amp)
230 / 170 = 1.35

1676 / 1.35 = 1241

2x170v = 1241 T on 0.213mm swg 35 (110mA)
230 / 8 = 28.75

1676 / 28.75 =

8v = 58T on 0.61mm swg 23 (1amp)

Don’t know if I’m close here?

Could someone help please point me in the right direction!!

 

[Egor Reshetnikov]

6nip

лол

 

[CJ]

fixied it thanks!

and Voskhod means sunrise in Russian. hopefully not a nuclear sunrise because i believe there is a rocket printed on that tube

 

[Murdock]

Does someone know what the actual plate impedance of the 6N1P in this circuit is?
I have a big chunky transformer here with the right ratio and a gap. But I think it is more a 2k2:200 transformer... I’ve tested various resistors in series with my generator and 3k Ohm gave me -3dB at 15 Hz. -3dB in the upper region was a good 150KHz.

 

[CJ]

6N1P runs at about 160 volts and combining the two sections in parallel there is 8 ma.

160/.008 =20k

Check your primary inductance at 20 Hz and 20 v rms.

300 henries will load the tube at about 40k which will give you great bass response.

Measure your primary current with the secondary open at 20 Hz and 20 v.

If you are at 1 ma or below then you should have made in the shade with KoolAid.

 

[Murdock]

6N1P runs at about 160 volts and combining the two sections in parallel there is 8 ma.

160/.008 =20k

Check your primary inductance at 20 Hz and 20 v rms.

300 henries will load the tube at about 40k which will give you great bass response.

Measure your primary current with the secondary open at 20 Hz and 20 v.

If you are at 1 ma or below then you should have made in the shade with KoolAid.

Thanks for the info CJ!
Wow, 20K... that’s a lot.
I thought it’s more in the 8k region.
Wouldn’t 20k plate impedance be like 1k5 ohm on the secondary with a 3.6:1 transformer?
My signal generator can “only” output 10Vrms...at what source impedance should I measure the current?
Is 20Vrms at the primary the level one can expect with that circuit and common bass guitars?
That’s like 6v on the output, right?

 

[ruffrecords]

According to the "datasheet" the nominal plate resistance of the 6N1P is 4400 ohms. You have two in parallel so that is about 2K2. This is the incremental plate resistance as opposed to the static plate resistance which CJ gave. The incremental plate resistance is essentially the small signal output impedance of the tube; the one you would use in its equivalent circuit. We are not strictly small signal because this DI can have some serious plate excursions and the data sheets do not give the variation of plate resistance with plate current so the value at the actual operating point will be different. Oh, the joys of using obscure Russian tubes with minimal data - not to mention those data sheets that quite erroneously equate the 6N1P with an ECC88 - they are totally different tubes.

Anyway, 2K2 is not a bad starting point. I definitely think it is worth trying your transformer - as long as you re sure it is gapped and can take the dc current.

Cheers

ian

 

[Murdock]

Thanks for the info Ian!
That sounds good! Especially because I asked myself what I should do with that transformer for quite some time.
Concerning the gap. I’m not 100% sure it has one but the lams are not interleaved but all stacked on top of each other. If it has a gap, it is quite small. It’s also varnished.
Here is a picture of this heavy hitter. Core size is 72mm x 64mm and 28mm high.

 

[MicDaddy]

@Murdock not advice but I'd try it. I seem to recall winding/building some with no gap and can say they didn't burn the house down. Cannot recall performance but they made one hell of an electro magnet with DC applied
I think i tried interlacing them with no gap for science, maybe a better for no DC but the transformer passed audio

 

[CJ]

Yeah you want the dynamic plate resistance, doh on me.

Even without a paper gap you will still have a natural air gap.

It varies with lam size. The bigger the lam, the bigger the natural air gap.

Do try the ammeter in series with the generator. Or if unable take a primary DC resistance.

This will give you a rough idea of how many turns are on the primary.

Some transformers might have 50 henries and they call it 2 k, others might have 200 henries and they call it 2 k.

 

[Murdock]

I tried the ammeter in series with the generator. With 10V output and 600ohm source I got around 1.35mA current. So around 60H, right?
Primary DC resistance is around 1k2 Ohm.
Reactance is about 7k5 so it should barely be enough for 2k2 plate impedance. Probably a slight drop at 20Hz. But whose playback system goes so low anyway, right?
I will give it a try. Finally a project where I can put this chunk of steel to good use.
Thanks alot!

 

[ruffrecords]

At what frequency did you measure the reactance? Remember good old steel lams have inductance which actually increases at low frequencies so it may be OK down to 20Hz.

Cheers

Ian