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AC701 substitute
Author: Posted by Kevin Ink
Date: 07/04/2001
Re: AC701 substitute
Author: Posted by Oliver
Date: 07/04/2001
Forums / Archive / Thread
Is anyone familair with the tube used in the old Lomo mics? I was
told it can used as a replacement in Neumanns for the AC701. Does
anyone have a data sheet for the AC701? Thanks, Kevin
Hello Kevin,
I don't know anything about the old Lomo mics, but there are three
tubes that are identical in sound and electric values. The AC701 was
only made by Telefunken in Ulm Germany, the last scheduled
production run around 1979 was canceled because Western
Germany boycotted the Olympic games in Moscow and because of
that Neumann lost the deal supplying the microphones for the
games. Today there are some 701 on the market but they climbing
in price. As an alternative there are three different tubes that work
and sound the same. RFT Funkwe rk Erfurt in east Germany ma de
the AC761, identical system but grid and plate are reversed, heater
voltage is the same, but there are same as rare than the Ac701.
Than there are the EC70/71 two UHF sub miniature triodes that were
made by Telefunken and other western companies as well
EC70/6778 and EC71/5718. Those tubes are very similar to the
AC701, u=20/27 Ri=3.65/4.65 with better interelectrode
capacitance than the AC701. The y fit without a problem in any Mic
that asks for an AC701, with minor modification in the cathode set
up, the 6.3V filament is no problem at all. Most Neumann power sup.
have a potentiometer to adjust the filament from 10 to 3V. Aside the
different heater and pin layout the nice price of about $5.00 is way
better than the $100 that the AC701 goes for these days. Here is the
AC701 data: Bp= 80V Ug= -1.5V Ip = 2.1mA S = 2.8mA/V u = 22
Ri= 8.5 k Ohm Max. Values Bpc = 250V Bp = 120V Pmax = 0.8W I
max = 5mA
If you read german I can send yo u the Telefunken Data sheet a nd
application information....
Best regards,
Oliver
Re: AC701 substitute
Author: Posted by Ulrich Thielem ann
Date: 07/19/2001
Wow! Thanks again very much for your expert information. I will go
and look for these tubes which I need for my KM56 and KM54
microfones. Ulrich
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