6N1P Bass DI - Revisited

[rock soderstrom]

Hi Bancho, where are you located? It makes really sense to add this to you forum account. Cheers

 

[bancho]

Heh... sorry  :

 

[rock soderstrom]

Thanks! I am interested in one. Cheers

 

[bancho]

maybe a stupid question but anyway: how much current should the PT take?
I'm thinking to order some custom toroids

 

[CJ]

that cloth wire from Antique Electronic is not easy to strip. they changed vendors, best to use a razor blade or mechanical strippers, if you use needle nose and dikes, the needle nose will slip and you will rip the leads out quicker then you can say ticonderoga,

looking for some 600 volt PVC that does not melt in the oven like the 105 C stuff, but good wire is getting pretty dang expensive, check digikey if you doubt it, evilbay not much better,

shrink pic to 600 x 800

ever hear of the Drive by Truckers? they love those transformers,  ;D

 

[MRecords]

I have some troubles with my DI. I can´t get more than 13dB of gain.

First i had two 220Ohm resistors for each cathode with 2,1V and 9,6mA across it. After increasing them to 470 Ohm i had 2,74V and 5,8mA  but the gain didn´t  changed. For a last try i tied the upper end of the 470Ohm resistors together to recreate the schematic in the first post of this thread. But still no gain change.

B+ is at 170V and plate voltage is 164V.  Can somebody help me out on this one?

thanks

 

[bancho]

So what is good B+ voltage so the gain would be in useful range? Andy you used 190V... measured on unloaded PT?
The price for custom PT is really nice but the manufacturer said the current on primary is 0.08A... is that ok?

 

[CJ]

here is the schematic again,  added transformer wire colors

anybody verify the adj regulator resistors yet?

 

[bancho]

I'm going to make two units in separate boxes - following the sceme provided by CJ.
Yes it would be nice to include the lamp also. I will use the DC for the heaters.
As I said I will get custom PTs with 170V+8V on secondary... I'm just little concerned about 170V regarding the gain as MRecords' had... That's why.
I'm sorry to complicate but I'd like to have proper units

 

[ruffrecords]

I have some troubles with my DI. I can´t get more than 13dB of gain.

That is probably about right for this design.  There is a loss of about 11dB in the transformer. So if you measure 13dB gain then that means the tube is providing about  24dB of gain which is about right. For a bass DI you do not really need any more. Most bass guitars will output around 500mV which will give an output of over 2V which is more than enough for a regular mixer line input.

Cheers

Ian

 

[MRecords]

Thanks Ian and andyfromdenver.

MRecord's post was addressed by IAN, and he mistakenly doubled instead of halved the cathode resistor for parallel operation.

hope that clarifies it.

I always thought that the equivalent to cathodes tied togehter with one 220 Ohm resistor would be 440 Ohm on each of the cathodes.
In CJs schematic 8 mA flow through 220 Ohm which gives 1,76V. I have two resistors on each of the cathodes so 4mA of current through 440 ( i used 470) which is again 1,76V.

Am i wrong?

 

[MRecords]

anybody verify the adj regulator resistors yet?

In my calculation 390 Ohm and 1k5 gives about 6.05V. I would use 250 Ohm and 1k which should give about 6.25V. I´ll try it when i get back home.

 

[bancho]

ok, so 170-0-170VAC 40mA(center tapped, maybe obv.) or 340VAC 40mA (no center tap, bridge rectified) and 8VAC 2-3A (center tapped or not) That should work.

Sorry for my ignorance but why do I need 170-0-170 secondary?
I would make two DIs in two separate enclosures. Each would have its own supply.
I thought the tube is designed for 250V anode voltage and using 170V is kind of being on the safe side.
Another question about the 8V secondary… you said it should take 2-3A current… why if the heater current of the tube is 600 mA ± 35 mA?
And how much current should the primary take? The manufacturer said it is usually 0.08A - is that ok?
I'm sorry if these are obvious things for some of you and right now you are face palming but I'm little confused  ???
Thanks for being patient with me 

 

[ruffrecords]

Sorry for my ignorance but why do I need 170-0-170 secondary?

Because that creates the desired HT voltage

I would make two DIs in two separate enclosures. Each would have its own supply.

OK

I thought the tube is designed for 250V anode voltage and using 170V is kind of being on the safe side.

It can be run at up to 250V but that does not mean you have to. The typical output is 2V rms. This means the primary of the output transformer has to swing by 8Vrms which  is about 11V peak. This means the anode only has to swing down to  159V and up to 181V. Raising the HT to 250V is unnecessary and only result in more dissipation in the tube and a need for a larger mains transformer.

Another question about the 8V secondary… you said it should take 2-3A current… why if the heater current of the tube is 600 mA ± 35 mA?

As a rule, the transformer needs to be able to provide an ac current into the rectifier that is about 1.6 times the required dc output  current - so it needs to be able to provide 960mA; nearly 1 amp. If you had two in the box you would need 2A

And how much current should the primary take? The manufacturer said it is usually 0.08A - is that ok?

You need to add up the total primary VA and multiply by 1.1 to allow for the transformer efficiency. This is the VA in the primary. What current that represents depends on the mains voltage.

Cheers

ian

 

[bancho]

OK... I did some homework and re-read some of the basics  and thigs are much more clear now  :
Thanks everybody!
but... I still have a question though: I there really any benefit using the PT with center tap on secondary (either for HT or heater)?

 

[bancho]

I'm sorry but there is still something that bothers me...
On the sowter page there are some basic principles about calculating the specs for power transformer.
If using two diodes for rectifying we use this formula: Vac = Vdc x 1.41
If using rectifier then we use this formula: Vac = Vdc x 0.71 which suggest that the voltage actually builds up (?). We are using rectyfier bridge here. Does the smoothing network really drops the voltage so much that  we get around 170V for HT (considering 340V secondary without center tap and the bridge)?

As this is my first tube build I would like to make things in a proper way without frying anything

 

[PRR]

> On the sowter page

Look *carefully* how they are specifying "VAC" for the center-tapped 2-diode case.

 

[bancho]

> On the sowter page

Look *carefully* how they are specifying "VAC" for the center-tapped 2-diode case.

I understand that in full wave case the secondary is just "half efficient" comparing to the bridge case...
I also believe other members made this DI with great results... I'd just like to understand where/if the drop from 340V to 170V happens (in the bridge version).
You can also post some link directing to the explanation. Thanks!

 

[PRR]

> You can also post some link

Your question. You could have posted the link to "the Sowter page" so others would not have to re-hunt what you found.

> understand where/if the drop from 340V to 170V happens (in the bridge version).

ok, so 170-0-170VAC 40mA(center tapped, maybe obv.) or 340VAC 40mA (no center tap, bridge rectified)

This appears to be incorrect (and also un-refuted). Thank you for spotting this. The 340VAC single winding FWB will give 480V DC, which is distressingly high. You need an >450V first cap. You can drop 300V with much bigger hotter dropping resistors, but that is inelegant. If you do not *know* this will give way-high voltage, it may be trouble. (Andy should check my math; then if valid edit his post.)

170-0-170VAC 2-diode makes 240V DC.
Single 170VAC with FWB makes 240V DC.

Dropping resistors will get you into the 160V-220V range suitable for the amplifier. Ohm's Law is a friend.

 

[bancho]

Hi everybody... the more I check this and previous thread about this DI more confused I'm becoming... in the previous schematics there were two 200R and 470uF (each on its half of the tube) and now in the new one just one. Also the current was twice as big as now. Is this really ok? I know CJ said this is corrected regarding to the measurements... did anyone tried this version? Compare to the previous one?
I have to know this because depending on the current (which is now also different - half the previous one) I'll know how much voltage drop will be on the resistors - so I can choose the correct secondary voltage (the difference between 170V and 200V secondary is quite big).
Am I complicating too much? Should I just build it and see what happens? 


p.s.: what happened wit andy's posts?  ???