• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

power transformer

I downloaded the PSUD software from duncanamps and simulated the power supply.
i realized that if i put a 220V secondary i will not get 312V after rectifier under load, but around 288V because of the transformer regulation.

i think i will need a 240V secondary.
i am right?
 
That sounds more realistic to me (240v). I've done quite a bit of modeling with PSUDII, and that sounds more like what I'd expect, too, using a solid-state (diode) rectifier.

BTW: Don't worry about being 10 volts higher or lower than stock, on your final B+ voltage. It will still work fine, as long as you adjust bias to compensate, and make sure the capacitors can handle the voltage.

Regards,
Gordon.
 
Hi,
i got at antique radios the service manual for the uS version (my version).

The schematic looks the same as the one i have, even same resistors and caps values, but the voltages and currents not.

the ransformer listed in service manual is

320V 150mA.

the others windings are almost the same as i calcukated before.

after rectifier in the schematic are 330V and 75mA ( in my other schematic says 312V and 150mA and i'm pretty sure about the 150mA because i simulated it in multisim).

if i calculate the voltage after rectifier it should be 451V, so to have 330V there is a drop of 80V in selenium rectifiers and transformer regulation.
i think this is too much. also have to consider the schematic rates the filter caps at 350V

maybe the designers of grundig take advantage of an undersized trasformer to get 330V?

maybe because of this the guy in this page saya the transformer is somethin "delicate", and should be used with the 240V primary tap in german version?
http://www.tube-classics.de/TC/GermanTubeHifi/Poweramps/Grundig NF2/NF2.htm
 
The selenium rectifier would drop some voltage, yes... but 80v? I don't know, if that much.

If they were using transformer regulation/sag as part of their voltage dropping, then it might be better to use a stouter transformer of lower voltage.

I'd still be looking for a stout transformer with a 240-250v secondary, I'd think. That, with some good modern silicon or Schottky diodes, and you should have a much more robust power supply.

Regards,
Gordon.
 
update,

i ordered 2 pairs of jj el84's ( i cancelled my first order because they where out of stock)
i need onlu 1 pair, but i think there is no harm having a spare pair.

also i ordered 2 jj100+100uF 500v caps
i ordered mallory 150 to replace paper caps.
i'm still thinking what to do about the power transformer.
i think it will be 240V and 200 or 250mA.
 
Thanks GordonW
i also made some simulations with PSUD2.
i think 240V(322V after rectifier) should be ok, because 330V is a little high for the EL84.
since in my german schematic shows 312V after rectifier instead of 330V, a voltage between these 312 and 330 should be ok. i only have to adjust the bias properly.
i looked at edcor homepage and the XPWR065-240 should be ok.
this has a primary for 240V, but in chile voltage is 220V, and sometimes is less. that should give me 230V.

That should be my B plan, because i will need another transformer for the second 6,3V tap to run the tuner tubes. and also i will need another tap for bias if i don't want to modify the circuit.

I will try to made a custom transfomer. i found several people near me that can make the transformer for $50.

I have a question about caps.

i found replacements for paper caps, also for the big can caps, but i need some axial electrolytics to replace the little electrolytic caps.
what do you use for this?
 
Update:

I have a new transformer.

And i have new Questions. This transformer have an extra wire for shield.
Should i connect this to chassis?
 

Attachments

  • P1030322 (Large).jpg
    P1030322 (Large).jpg
    84.6 KB · Views: 5
Alfonsol said:
I am in chile.
i have an error, the voltage for the bias sfter rectifier is -16V, the have a resistor divider to achieve -11V

i posted some pictures.
the cabinet is in good shape, only some discoloration on the top.
the tape recorder works, and the turntable works.
Click to expand...

The bias winding is going to be more then 12V if you have -16 as the raw output which should be pretty close. Knowing the circuit resistance and layout would get us closer to what that bias tap should be. You can easily source a separate small transformer to supply this tap and then used the transformer Tom mentioned above with another 6.3V smaller heater transformer to get this all to work.

Kind of complicated but doable.
 
Alfonsol said:
Thanks GordonW
i also made some simulations with PSUD2.
i think 240V(322V after rectifier) should be ok, because 330V is a little high for the EL84.
since in my german schematic shows 312V after rectifier instead of 330V, a voltage between these 312 and 330 should be ok. i only have to adjust the bias properly.
i looked at edcor homepage and the XPWR065-240 should be ok.
this has a primary for 240V, but in chile voltage is 220V, and sometimes is less. that should give me 230V.

That should be my B plan, because i will need another transformer for the second 6,3V tap to run the tuner tubes. and also i will need another tap for bias if i don't want to modify the circuit.

I will try to made a custom transfomer. i found several people near me that can make the transformer for $50.

I have a question about caps.

i found replacements for paper caps, also for the big can caps, but i need some axial electrolytics to replace the little electrolytic caps.
what do you use for this?
Click to expand...

If you can get a custom transformer wound for $50 I'd be jumping at that offer. The shipping from the US for all this will probably cost you half of that.
 
You must log in or register to reply here.
Back
Top Bottom