[denny9167]

I'm needing a 6V4 for an FM-1 rebuild,but I have a pair of 6CA4 tubes that are very similar in design,I do know they draw more heater current,and take a larger input capacitance. Will this tube work in it's place?

[Bill Thomas]

Denny,

Considering the cost of a new 6V4/EZ80 is *usually* well under $20.00 for a GOOD quality NOS tube, I would avoid trying to substitute a 6CA4 in its place.  The additional filament current will increase the load on the Power Transformer significantly.  Since new Power Transformers for the FM-3 are non-existent, this seems like "false economy" to me.

This is ESPECIALLY true if your FM-1 has the Multiplex module installed.  The 6CA4 will push the load on the Power Transformer beyond its normal loading.  As you know, heat is the enemy of the FM-3.  The additional load of the 6CA4 will make things even hotter.

Bottom line:  I would hold out for a 6V4/EZ80.

Make sense?

Bill Thomas

[denny9167]

Denny,

Considering the cost of a new 6V4/EZ80 is *usually* well under $20.00 for a GOOD quality NOS tube, I would avoid trying to substitute a 6CA4 in its place.  The additional filament current will increase the load on the Power Transformer significantly.  Since new Power Transformers for the FM-3 are non-existent, this seems like "false economy" to me.


Thanks Bill, I have other uses for the 6ca4's so it won't be a problem.

This is ESPECIALLY true if your FM-1 has the Multiplex module installed.  The 6CA4 will push the load on the Power Transformer beyond its normal loading.  As you know, heat is the enemy of the FM-3.  The additional load of the 6CA4 will make things even hotter.

Bottom line:  I would hold out for a 6V4/EZ80.

Make sense?

Bill Thomas

[denny9167]

Denny,

Considering the cost of a new 6V4/EZ80 is *usually* well under $20.00 for a GOOD quality NOS tube, I would avoid trying to substitute a 6CA4 in its place.  The additional filament current will increase the load on the Power Transformer significantly.  Since new Power Transformers for the FM-3 are non-existent, this seems like "false economy" to me.

This is ESPECIALLY true if your FM-1 has the Multiplex module installed.  The 6CA4 will push the load on the Power Transformer beyond its normal loading.  As you know, heat is the enemy of the FM-3.  The additional load of the 6CA4 will make things even hotter.

Bottom line:  I would hold out for a 6V4/EZ80.

Make sense?

Bill Thomas

Would there be a way to put a series resistor in the filament curcuit,to limit current draw,would this effect the 6ca4's output?

[baldrick]

If you limit the current on the filament you won't get proper heating of the cathode...
If you want to use a 6CA4 then you'll need a small filament transformer.  There may be enough space below the chassis for one.
But you can get current production 6V4s which are just as good as NOS:http://thetubestore.com/nos-6v4.html

[denny9167]

If you limit the current on the filament you won't get proper heating of the cathode...
If you want to use a 6CA4 then you'll need a small filament transformer.  There may be enough space below the chassis for one.
But you can get current production 6V4s which are just as good as NOS:http://thetubestore.com/nos-6v4.html

I thought that might be the case,but wanted to make sure,thanks