v72 repair

honkytonk · Feb 17, 2020

Bonnie1 said:
Hello Honkytonk,
This tread was brought to our attention...
To confirm from the pic's those are indeed not the original transformers, they appear rewound. Difficult to determine from a picture if the inductor or power transformer meet original specifications, the input transformer definitely does not. To my knowledge Tab-Funkenwerk founded by Oliver Archut (RIP) is the only company that correctly rewinds and manufactures new V72, V76 input transformers and inductors etc... (according to original specifications).
Following Oliver's lead TAB continues to provide these products and services (Inputs are very laborious and not cheap) you can email [email protected] for more info.

Disclaimer..... I work at TAB and am not trying to sell or promote our products, just offering information that there are proper solutions available.

-dennis

btw, there are more than a few V-series units working in Norway that use our rewound transformers....

Thanks, interesting. I will contact you.

MatthisD · Feb 17, 2020

honkytonk said:
No, they are not working preamps. I bought them some years ago for later racking. Though I got them for a "not working price", I was told they were all original. I was prepared for surprises and here they are ...-.). However, the v72 preamp is a fantastic preamp when it works, so I would like to go ahead and see if I can make them work oneday.

That is unfortunate. You should first establish whether the power transformer is going to work. Then theres the tubes to test because ef804 are expensive to replace. If you can tick the box in those areas then I would look at solutions to the missing transformers.

AndreasSchwarz · Feb 18, 2020

honkytonk said:
the part to the left on first photo

This is a plate choke (BV 621 E 4040; M42 core, stack height 22mm, RDC ca. 12 kΩ, L > 220 Henry), similarity the CKV72/1

Andreas

AndreasSchwarz · Feb 18, 2020

honkytonk said:
This is the input transformer? The right part of the first photo .....

This is an 1:5+5 input transformer (Siemens BV 621 E4041; M42 stack height 15 mm, iron core, primary 4,3 Henry) with a terrible frequency response.

Andreas

AndreasSchwarz · Feb 18, 2020

honkytonk said:
the part in the middle of the first photo

This is an output transformer (M42 core) from Rohde & Schwarz; data unknown - but you can measure.

Andreas

johnheath · Feb 18, 2020

honkytonk said:
Hi John
Thanks for replay!
I have been looking at the Sowter. Did you build a diy v72?
Regards
Bjorn

Hi...

Yes, I did some years ago... it's still in use and it works very well.

Unfortunately I cannot reach any measurements I did back then. This due to tha fact that I am currently working in Africa.

I will recall using a Sowter 9610 as an input transformer which hasn't the same ratio as the one in an original V72.

But for the others i used the ones recommended from Sowter.

Best regards

/ John

honkytonk · Feb 18, 2020

AndreasSchwarz said:
This is an 1:5+5 input transformer (Siemens BV 621 E4041; M42 stack height 15 mm, iron core, primary 4,3 Henry) with a terrible frequency response.

Andreas

Thanks for very useful info, now I understand more about these v72`s. A project not quite succsessful.

panman · Feb 18, 2020

I have used Sowter 1960 input-trafos a few times in my V72:s and my V72-builds. When all the rest is original, I hardly hear a difference between Sowter and original.

honkytonk · Feb 20, 2020

I want to thank you all guys for enlighten me about these v72 preamps, and how to start bringing them up to working condition.
Sowter and Tab-T. has replacements for transformers and choke. I will go for one of these alternatives, or a mix?

The input transformer from Tab-T. is very expensive, output T. and choke do not vary so much in price. Maybe difference on sound, but probably nobody has ever tested side by side and not seeing which pre is playing?

My experience with diy projects is limited to racking / cabling up preamps / comp modules in working condition. I need help to get these v72´s up and going.

So I am looking for somebody to help me. Maybe one of you guys could do this? Or can recommend a clever diy / company?
I will of course pay for the job.

I can install the replacement transformers in the v72´s, so more or less cabling / testing is left to be done.

panman · Feb 20, 2020

I`ve sent you aPM.

MatthisD · Feb 20, 2020

honkytonk said:
The input transformer from Tab-T. is very expensive

I don't know the price but it is a very complex coil or set of coils to make. The transformer core is physically much much larger than a typical input transformer core which substantially increases the cost. If you have experience using V72 and are expecting your units to compare then you shouldn't overlook the difference between the Tab and the other options available.

honkytonk · Feb 20, 2020

MatthisD said:
I don't know the price but it is a very complex coil or set of coils to make. The transformer core is physically much much larger than a typical input transformer core which substantially increases the cost. If you have experience using V72 and are expecting your units to compare then you shouldn't overlook the difference between the Tab and the other options available.

Can imagine the Tab input transformer is more complex than the Sowter and the cost will be approx 500 euros, maybe more with shipping and taxes. The Sowter approx 60 UK pounds ......
About the sound, I have to trust others experiences.
I have used v72 for many years. Maybe not possible to create the exact original v72 sound with "copy" transformers, but still the result can be an interesting sounding preamp. This aspect compared to how much the project will cost totally.

mjrippe · Feb 20, 2020

I just uploaded my personal copy of the Telefunken schematic with notes and a drawing of the terminal board with components and voltages. Helpful for anyone servicing these modules. Please share freely.

https://groupdiy.com/index.php?topic=45156.msg942656#msg942656

mjrippe · Feb 20, 2020

I have only replaced the input transformer once, with a Sowter 1960e. It worked perfectly and tested to original spec in the amp. https://analogaudiorepair.com/2013/02/26/telefunken-v72s-transformer-replacement/

MatthisD · Feb 20, 2020

mjrippe said:
I have only replaced the input transformer once, with a Sowter 1960e. It worked perfectly and tested to original spec in the amp. https://analogaudiorepair.com/2013/02/26/telefunken-v72s-transformer-replacement/

Do you know where that original input transformer went to?

mjrippe · Feb 20, 2020

MatthisD said:
Do you know where that original input transformer went to?

If you mean the defective one, it went back to the client.

MatthisD · Feb 20, 2020

I wondered if it had been sold on or if it was gathering dust somewhere in your parts storage possibly.

leadbreath · May 24, 2020

I can testify to the Sowter - quality transformers. Had a client with missing iron and installed some Sowter inputs and sounded fabulous!

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