[AMRadio] Johnson Valiant Audio Driver Xfmr - Wake Up Call

[Peter Markavage]

Add another 12AU7 and just direct couple it. Common way to do it in many
Hi-Fi amplifiers.

Pete, wa2cwa

On Tue, 23 Oct 2007 00:03:37 +0000 w0ng at comcast.net writes:
> Greg,
> 
> Thanks for the advice. I'll check out the AES website. I'm thinking 
> you're referring to the Hammond 124D or 124E interstage driver xfmrs 
> they sell.
> 
> My Valiant uses the 12AU7 driver tube just like your Ranger but mine 
> feeds a pair of 6146's whereas your Ranger uses 1614's. I'm not 
> enough of an expert at this to know if the impedance, etc. at the 
> modulator grid is the same in both 6146 and 1614 modulators or not. 
> Because of my lack of specific knowledge on this, choosing the 
> correct replacement driver xfmr is a mystery to me for sure. 
> 
> The driver xfmr in my Valiant does have a center-tapped secondary, 
> but from some info I found on the Peter Dahl website, they say the 
> primary DC resistance is 230 ohms (12AU7 parallel driver plates) and 
> the secondary DC resistance is 800 ohms C.T. (PP 6146 modulator 
> grids).  I haven't yet found anything online that matches that 
> particular spec. Guess I'll have to keep looking. Any other 
> suggestions appreciated.
> 
> 73
> Bill
> w0ng