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Author Topic: VF 14 Low Plate Voltage Update  (Read 3023 times)

sheltsound

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VF 14 Low Plate Voltage Update
« on: March 25, 2011, 11:55:26 pm »

In my last post I reported that the plate voltage measurement on my VF-14 was down to 24 volts. The noise floor was high and the mic sounded weak. All my resistor values and power supplies were fine. I was able to snag another supply and the results  were the same. Not wanting to believe my tube was finished I experimented a bit..As soon as I removed the plate voltage from g3(suppressor/screen grid normally tied to the plate) , the  plate voltage bounced back to 31.5 volts!.The noise floor is once again acceptable and the mic sounds like my 47.. warm and bright and big. So now the plate and g2 are connected, g3 is open, B+ is 105v... heater voltage at 36v cathode bias at 1.15 v... A second life for the VF14???  Fingers crossed...

What is the typical  DC resistance of the BV8 transformer output winding strapped for 200ohms...?


Steve Addabbo
www.shelterislandsound.com
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sheltsound

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Re: VF 14 Low Plate Voltage Update
« Reply #1 on: April 24, 2011, 02:20:19 am »

I continue to use the mic and it sounds great.. I just used it for three and a half days for ambiance for an incredible 17 year old violinist..

But I have discovered the mic is a U47a with the Gn8 transformer(hence the low dc resistance, 2 ohms, of the output winding  compared to a U47, 17 ohms). I always wondered why this mic never had the output level of my U67..and thanks to an old post on this forum I learned  the difference between a U47 and a U47a. I had the pleasure ?? of meeting Stephen Temmer (Gotham Audio NY) in the days I worked for Sterling Sound.We had 10 Neumann cutting lathes.. and yes he was as arrogant as folklore has it.. And now I have to decide whether to change out the output transformer..I'm leaning towards doing it.. Thanks Mr. Temmer you weren't always right..

Thank you Klaus for a great forum..

Steve Addabbo
www.shelterislandsound.com
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klaus

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Re: VF 14 Low Plate Voltage Update
« Reply #2 on: April 24, 2011, 03:09:24 am »

... however, if you are still using the K47 capsule that was the stock original capsule for that model, the mic's overall output drop with the BV8b is not all that dramatic, and can be made up with a bit of gain in a (good) mic pre. You might want to consider that before you devalue the mic further with an after-market transformer.
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Klaus Heyne
German MasterworksŪ
www.GermanMasterworks.com

sheltsound

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Re: VF 14 Low Plate Voltage Update
« Reply #3 on: April 24, 2011, 02:14:32 pm »

I'll leave it stock...it still sounds great..I'm not a fan of fixing what isn't broken..If the tube degrades further I will find another VF 14 but for now it's still the best vocal mic I have..Thanks for the reality check!!

Steve Addabbo
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