Advice on old input xformer

[Gavin Pursinger]

I have 4 of these xformers from a shelf at a salvage store.
I believe them to be US army shielded input xformers
50-10k. I would like to build a tube pre(s) with them...maybe stereo or quad. I am not a math guy and like to pre plan chassis cut/drill...don't mind experimenting. CAN I USE THESE TO FEED 50 OHM TLM49 OR 200 OHM U47 CLONE INTO A 6SL7 ??? If not what tube would LOVE to se
this hit its grid... ?

 

[emrr]

I'm gonna assume 100M is the old version of 100K here. It's not that critical, anything 15K to 120K is found amongst pre's.

100 may have poor response with a 200 ohm mic, OK with a 50.

Both of those mics will probably need 20dB input pads with ANY tube pre if there's any loudness to the source, so it's not an issue with the right input pad values.

 

[Gavin Pursinger]

Thx EMRR

I forgot old school used 'm' instead of 'k' sometimes...that makes waaay more sense. Should I use 100k audio pot off the secondary? I am not sure of a formula for pots to grid...or would 500k or 1 Meg. Does it depend on the xformer secondary or grid of 1st tube ?
Thx for you insight

 

[emrr]

You generally don't use a pot there, a 100K pot would reflect real 100R to the source, and a 1M pot would have problems losing treble.

 

[Gavin Pursinger]

So...hit the 1sr rube straight off the xformer and pot its output to the 2nd tube...yes ?
Thank for your help