Line output transformer for 201A

[Fei]

Those of you who have done 201a tube line stage, which output transformer is your favorite?

 

[kmtang]

Hi Fei,

The plate resistance of the 201a tube is 10~11K and the Mu = 8.

I would suggest the Monolith SL-02/20 (2:1) or SLX-01/10 (4:1) line transformer. The SLX-01/10 is better match with the 201a but the gain will be less.

Anyway, what is the gain you need for this line amp????

Johnny

 

[sser2]

UTC A-25, or even better HA-133. Single plate to line, 8 mA DC in primary. Both have permalloy cores.

 

[kmtang]

UTC HA-133 is 15K : 600 ohm (5:1). When it is used with the 201a, the overall gain would only be 1.6.

 

[sser2]

True. But this is LINE stage, it has to be 600R out.

 

[kmtang]

True. But this is LINE stage, it has to be 600R out.

I don't think it has to be 600 ohm. Most of tube power amp's input impedance is about 100K. The line amp output impedance can be 10K or more.

 

[euro21]

"The line amp output impedance can be 10K or more."
In practice not more than few kOhm.
If you use it with SS amp (sometimes lower input impedance than 10k), even below 1K suggested.

 

[euro21]

Those of you who have done 201a tube line stage, which output transformer is your favorite?

Loading 01a family IMHO the most problematic thing.

Even with high/er/ capacitance load (variable impedance at higher side) causes trouble due to the tube's limited slew rate capacity.
It also occurs in the lower side if you use inductance.
It's no coincidence that using of source follower is the proven solution.

Few years ago the slew rate problem of the 01a was discussed here, and Ale's blog too.