ic TL783 for G9 pre

[tony dB]

hi,

does the ic TL783 (HT) for G9 pre has to be 245 volt? Can not get them at my local store, neither do i score the tubes there, so will have to order elsewhere anyway.

Any help here is appreciated!

Cheers,

Tony

 

[sismofyt]

There's no 245V version, Jakob's design is 'cheating'. The TL783C can take a maximum potential difference between input and output of 125V. As long as you stay below that it can regulate much higher voltages. It won't be short circuit proof though.

It can be a little bitchy too. It doesn't work without load, that can be catastrophic when using them for phantompower supplies. Not many mics like 70VDC. I _always_ load them with at least 20mA, no matter what resistor divider design I use for the ADJ terminal. Also, don't bypass that terminal, it tends to oscillate.

I have never used them in a B+ supply, I don't trust them enough. When tube gear with solid state devices break down, it's almost always the sand that burns up. Just ask Audio Research :green:

TL783C datasheet:

http://focus.ti.com/lit/ds/symlink/tl783.pdf

Enjoy :grin:

 

[tony dB]

Thanks Sismofyt,

the TL 783 CKC will work, that's what was offered to me.

 

[tony dB]

just rereading your post, what would be a safer option to you? :roll:

 

[sismofyt]

Well, if you absolutely want it regulated, try some tubes. They rarely fail. The WE300B was used as a power voltage regulator/pass element for nuclear rockets... or so the urban myth goes :wink:

A simple design with a string of zeners and a 6AS7G works nicely:

 

[tony dB]

wow :shock:
this will be difficult to put in a 1" housing using the pcb's i've already have!

I was more thinking of a substitute for the TL 783 or are all these considered high risk?

Anyone here who already blew them up?

 

[sismofyt]

There is no sub for the TL783C. There is a 400V VB408, but it's 40-50mA max and I don't know how well it works.

Space is at the bottom of my list. Sound and durability at the top :wink:

Maybe a discrete regulator with a MOSFET will be more tough :? You could also use a smaller tube, maybe a 6BX7.

VB408 datasheet:

www.st.com/stonline/books/pdf/docs/6421.pdf

 

[flyingfader]

Hi TonydB,

I've used with sucess a LM317 to replace a TL183 in a similar psu design, no problem until Vi/o stay within 35v max, should work fine,but don't forget to replace zeners D3,4,5 with one zener 35v.

Fly

 

[tony dB]

thanks Fly!

No disrespect to Sismofyt or anyone but i would like to stay as close as possible to the original pcblayout and concept until i get the G9 a bit more in the fingers/mind, Hotrodding is for later date, i've ordered enough parts and pcb's to build 6 G9's leaving some improvisation possible and trannieswapping too.

I was just curious if the TL783C where such a bad components?

Cheers,

Tony

 

[sismofyt]

They're not bad, they're touchy, like most silicon used in such an app. If they go, they can short the in/out terminals, which would probably kill the mics, if the TL783C is used for a phantompower PSU. In the Gyraf, the preamp won't die I think.

Unless you wan't to re-design the PSU, just go with the original design. I don't think using a LM317 will be better.

Tube regulators seem to be almost bombproof, at least in my experience.

 

[sismofyt]

That VB408 does look a bit interesting. I guess it's designed to be used in switchmode PSU or directly rectified mains voltage. Needs to be tough to do that. It can handle an electrostatic discharge of 2kV and has a power dissipation of 89W. No ripple suppression data. 40mA will only be enough for one Gyraf channel, maybe not even that.

Not the same pin outs as the TL783C though..

 

[tony dB]

understood :thumb:

 

[gyraf]

The TL783 is actually a very forgiving component - even in a non-standard application like the G9 PSU. If you don't short it's output, it will simply not fail you. I've not had one single TL783 failing me yet, and according to my books I've used some 180 of these over the last four years. And they are all set up to regulate from 120 to 250V HT supplies.

Actually I think that if you can avoid accidental shorting, you won't get a better HT regulator than this one. And I've tried a few.

Jakob E.

 

[sismofyt]

I've replaced a few over the years, in different PSUs, mostly phantompower supplies. I've seen 'em both go open and short input to output.

 

[gyraf]

Yep, I've changed some also - but always because they were not properly protected from input/output voltage differences (specially in TL Audio gear, I think?). Fit the diode and the zeners across it whenever you replace them. This ensures that re-re-replacement won't be necessary..

Jakob E.

 

[sismofyt]

Yup, TL Audio gear. They also don't like being mounted away from the PCB with wires, they oscillate easier than other Vregs. Maybe because of the MOS design? I dunno...

What other high voltage Vregs have you tried Jakob?