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RE: TL-404 , more than one version for impedance taps?

Posted by mwiebe (A) on January 23, 2023 at 06:02:14

In Reply to: TL-404 , more than one version for impedance taps? posted by Ian L on January 13, 2023 at 12:33:05:

Ian,
I feel your pain. There were two TL-404 core sizes and a variety of tap, insulation and wire options. And given the requests for tap info for these I'll assume most have nothing written on the core like mine. So yes there was more than one tap scheme for these.

The short answer is to tap hop until you get the best sound. Or if you have the ability determine the tap impedance more empirically. One additional issue is the MGM studio spec many were built to used three different gauges of wire, so use of DCR to help needs that warning.

Here is the info Mike sent me for mine which appears to be how a few of these were made.
#1 black ground
#3 orange 4 ohms
#4 yellow 10 ohms
#5 white 50 ohms
#6 green 200 ohms
#7 red 500 ohms
#8 blue 5000 ohms (goes to plate of tube)

Not all units have the four ohm tap.
PRI (1-8) dcr is approx 88 ohms
MOL 100 vrms @ 25 hz
MOL 125 vrms @ 30 hz

Nominal impedance ratios (with respect to the full winding) of the various taps are as follows;
terminal #3 is 1250:1
terminal #4 is 500:1
terminal #5 is 100:1
terminal #6 is 25:1
terminal #7 is 10:1

I use mine with the EXO-010 plate choke.
Good luck they are worth sorting out.
Matt

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