AK47 (REDD47 ) documents

[mitsos]

Hi, I just saw your post..  Did you ever find your answers?

1- I use a secondary center tap power transformer (HV secondary and heater)
Do I need to plug them to ground or keep them floating ?

2- What voltage I have to set B+ ?

3- I use cinemag 75101 as input trafo and cinemag cm-9661 as output trafo both have dual primaries. Can you tell me the better way to plug them.

1.  With a Center-Tapped secondary, tie it to ground and use only two rectifier diodes (the ones with cathode towards the 68R.  See the image of the PSU silkscreen I posted, of the four B+ rectifiers, just install the ones marked in red.

2.  About 300V. With 3x 100V zeners in ZD1-3, you should max out around 320V.

3. Well, with the inputs, you can tie the pads to a switch to choose impedance (and input trafo gain).  I've never used that output, but it's the same ratio as what the original is supposed to have been, so it should work fine wired 30K:600.  If in doubt email cinemag, David Geren is very helpful. 

 

[manulaf]

Hi !

Thank you !

Can I keep HV's center tap floating ? Or it's a bad idea ?

 

[mitsos]

No, for full wave rectification, use the two diodes marked in red above and connect the CT of your B+ winding to one of the ground connections of the connectors next to it (AC input for the 48V multiplier). 

 

[manulaf]

Hi thanks !

I use a 125-0-125V secondary. It's mean that with full wave rectification I will have +/- 175Vdc. Am I right ?
Can I use a Full bridge rectifier to have my 320Vdc ? Do I have to ground center tap in that case ?

Thanks for your help

 

[Deepdark]

Hi thanks !

I use a 125-0-125V secondary. It's mean that with full wave rectification I will have +/- 175Vdc. Am I right ?
Can I use a Full bridge rectifier to have my 320Vdc ? Do I have to ground center tap in that case ?

Thanks for your help

With 125-0-125, you will get 125V x 1.414 = 177V. That is in full wave rectification. The way it works, both side of the secondary don't sum up, they split each cycle between each other. A redd47 need about 290-300V B+.  So you would be better off to get a transformer of, around 300-0-300 or , at least 250-0-250, so you'll get 353V after rectification.

 

[moamps]

I use a 125-0-125V secondary....Can I use a Full bridge rectifier to have my 320Vdc ?

Yes, you can use it, you will get about 340-350V after rectifier and first capacitor. 

......Do I have to ground center tap in that case ?

No.

 

[manulaf]

Great ! thanks very much !

 

[manulaf]

Hi !

I finished my redd47 and it's work great, lot of headroom, nice sound.
Everythings work fine and the tow channel work the  same way. But Something strange happen to the left channel after 2-3 hour running, I noticed that this channel overload before the right channel ( 5-6 db less headroom).
Sawp the tube and nothings change
Maybe it's can help but if I remove ground wire of the output transformer, the sound become cleaner with more level.
Maybe a ground issue ?


I add the fine gain option but it just add 2 or 3 db, not very usefull actually.


Thanks for your help.

 

[mitsos]

Hi !

I finished my redd47 and it's work great, lot of headroom, nice sound.
Everythings work fine and the tow channel work the  same way. But Something strange happen to the left channel after 2-3 hour running, I noticed that this channel overload before the right channel ( 5-6 db less headroom).
Sawp the tube and nothings change

hmm, not sure what to say, but if it happens after it's been on for some time, maybe it's heat related.  They look identical in the pic, so I would go over both channels very carefully.  Compare voltages when it's OK and when it's acting funny.

Also, when it's acting strange, maybe listen to the signal after each stage to see if it's V1 or V2, etc.  It's usually something simple. 

Maybe it's can help but if I remove ground wire of the output transformer, the sound become cleaner with more level.
Maybe a ground issue ?

Not sure, I usually don't ground the output, but for preamps you have to ground pin 1 of the inputs so phantom will work.

I add the fine gain option but it just add 2 or 3 db, not very usefull actually.

This control is for close-matching gain between two channels for stereo use. 

I'm finishing up my last two PCBs today, so let me know if yo uget this fixed or need me to check something on mine.

good luck!

 

[manulaf]

Not sure, I usually don't ground the output, but for preamps you have to ground pin 1 of the inputs so phantom will work.

Is it Ok  if I don't ground the primary output tansformer ?

 

[mitsos]

Not sure, I usually don't ground the output, but for preamps you have to ground pin 1 of the inputs so phantom will work.

Is it Ok  if I don't ground the primary output tansformer ?

No, I should have been more clear.  I meant I don't usually connect the output XLR pin 1 to circuit ground, but direct to the case. Input XLR pin 1, I do connect to circuit ground for phantom.

The output transformer primary gets connected between the output cap and ground. Without the ground connection you should have no output, or just lots of noise. 

 

[kosi]

I'm selling 2 pcbs, if anyones interested
https://groupdiy.com/index.php?topic=65455.0