FPIII experimenters ?

[iain42]

A friend has  a stash of 76 and 56 tubes that he would let me have. Has anyone tried these tubes with the FPIII? Are these good tubes to use? The tubes look really cool but looks aren't everything.

Any info appreciated

Thanks

[Grainger49]

I swapped my 12AT7 tubes in my Paramours for 76 drivers.  The voltages were good for a drop in on the B+ and a cathode resistor change to get the operating point right.  Remember that the 76 is a single triode the 12AU7 is a dual triode.  You will have only one stage of amplification.  I'll dig up some information from PJ that will help you with the operating point.

[iain42]

I swapped my 12AT7 tubes in my Paramours for 76 drivers.  The voltages were good for a drop in on the B+ and a cathode resistor change to get the operating point right.  Remember that the 76 is a single triode the 12AU7 is a dual triode.  You will have only one stage of amplification.  I'll dig up some information from PJ that will help you with the operating point.

Thanks!

[Grainger49]

From PJ

[iain42]

From PJ

[Grainger49]

6SN7s are drop in replacements when you change out the socket.  By that I mean no resistor values need to be changed, but you would want to replace some when doing the conversion.  And that is the tube that was probably in mind when the FP III tube socket holes were made large enough for octal tubes.

As for using 4 - 76 tubes, that would look cool!  I don't know what the FP III power supply can handle.  Hopefully Doc or PJ or PB will answer.

[iain42]

6SN7s are drop in replacements when you change out the socket.  By that I mean resistors need to be changed.  And that is the tube that was probably in mind when the FP III tube socket holes were made large enough for octal tubes.

As for using 4 - 76 tubes, that would look cool!  I don't know what the FP III power supply can handle.  Hopefully Doc or PJ or PB will answer.

I love the look of triodes in the morning. 4 76's and an 0D3 would look wicked cool.

This might be a common question but what are the other tube drop in replacements that just require resistor changes?

[Grainger49]

  .  .  .  This might be a common question but what are the other tube drop in replacements that just require resistor changes?

I think there is a post already, maybe a sticky, that addresses other tubes.  It is a carryover from the old forum.

[Paul Birkeland]

You can indeed build the FP-3 circuit with the 27/37/56/76.  I built a 27 Foreplay a long time ago that I still have, but it requires a 2.5v transformer with quite a bit of secondary current.  The PT3 in the FP-III is not up to it.   There is indeed a post that has been put up here (maybe in legacy products?) that refers to the variants that can be run. 
-Paul