Telefunken/Siemens V72 Repair

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AustinStudioGuy

New member
Joined
Nov 12, 2008
Messages
4
Hi everyone,

Can anyone help me out?

Oliver Archut at AMI rewound the transformer for one of my V72s. I have these in a Marquette rack; before I realized that using these with phantom power was a bad idea, the original trafo had died.

Oliver had it for a year and a half, and because of the insane wait and because they felt bad for being so unresponsive he installed the new transformer free of charge and shipped it back to me. The unit came back non-functional. Oliver's message to me was:

"here are two pics of issue that need to be taken care off, the dirt (highlighted squares) on the PCBs need to be cleaned or better the board replaced, the caps in the pic 1,2,3 need to be replaced and the power board need to get the right type of caps, as I said, I can send you a replacement PCB at no charge."

http://i1177.photobucket.com/albums/x356/BigOrangeRecording/004.jpg

http://i1177.photobucket.com/albums/x356/BigOrangeRecording/006.jpg

He sent me a replacement PCB. I'm trying to figure out what the caps are he's talking about. Does anyone here just happen to know the values of these or where to source? I'll include the schematic with this post.

I'm not a tech, so please forgive my ignorance. I am contracting the repair with a qualified tech here in town at the moment but to save him the trouble I'm trying to hunt around for as much info as I can.  Oliver recommended a guy in Arizona named James Gangwer but based on my last experience I just can't have this thing out of the rack for another year and a half.

I'm sure you all know this but just in case the schematic is at http://audio.kubarth.com/rundfunk/index.cgi, just search on the page for Siemens V72.

Any help anyone can offer is sincerely appreciated. Thank you! :)

M.O.
www.bigorangerecording.com

 
I suspect there's more than capacitors that need replacing.

It appears that someone has attempted a variable gain modification, the extra blue capacitor, yellow wire and non-stock resistors are evidence of that.

If you look at the top of the first picture, there's a resistor that has turned black. That's not a good sign and indicates there's something seriously wrong beyond the input transformer.

Take it to a good tech and get it restored to stock.

Regards,
Mark
 
Your V 72's appear to modded.  Cap 1 is 2uF 250 Poly cap, try Solen or better.  2 and 3 are .05 and .025 uf caps.  POI ideally, put any 250V poly cap should be fine.  Actually, you could also test them to see how much resistance they have.  They should't be bad, but if you have less than 1 MegOhm, I would replace. 

I can't understand why he would say you need a new PCB.  Check the blue 2.2uF cap too.  Does that wire from the blue cap go to a pot on the front?  That is a gain control mod that also provides a few dB more gain.


Check those Large PS caps as well. Are they Sprague atoms? 10uF?
 
guavatone said:
I can't understand why he would say you need a new PCB.

Maybe because it's easier to replace it than to clean it. Dirty boards can cause all kinds of random noises in tube gear and the open 'chimney-architecture' of the V72 likes to collect a lot of dirt over decades.

I would have to recheck with an original unit, but my first thought when I saw the pics was 'oops, there's some stuff missing...'.

Is this unit supposed to be modded or do you intend it to be the original circuit? I wouldn't necessarily assume that the caps apart from the lytics have to be replaced.

Michael
 
I can't tell too well from the fuzziness but - picture 2 looks like one side of the 425K terminating resistor hasn't been reconnected to the transformer terminal.  Also, as someone else said, there's a suspect looking resistor on the other side of the board in picture 1.

 
Hi everyone,

Thank you so much for all the replies. This is all really great info.

Biasrocks: I'm under a deadline to have this thing back in service at the studio for some tracking that begins in a few weeks so I went ahead and sent it out to Studio Electronics.

Jensenmann and martthiee_08, man I wish I'd asked here before sending off originally. Your suggestion is appreciated and I'll consider that in the future.

guavatone: Yes, David Marquette modded the units for use with a pot in one of his racks. I've been really happy with it.

Winston: correct. That thing was just hanging loose when I got it back.

desol: I know. Oliver is semi-retired I believe. Still, I wish they'd made that clear before I sent it off to them. Oh well. He appears to really know his stuff. No harm, no foul.

Really appreciate everyone's responses. Thanks again!

:D
www.bigorangerecording.com
 

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