Redd 47 AC Heater terminations w.differring tubes-EF86 and E88cc-need 6v-each.

[devonhaas]

.I have just finished a -tedious turret board- built Redd 47 -not dissimilar to the La2A layout, that 'photographs extremely well', but using this 460 volt transformer with a 6.3 volt secondary, fails to supply 6.3-7. volts  to 'Two' tubes', namely, the E88cc and the EF86.  I have 2.5 amps of current available, but have not been able to reconcile how to terminate- this' often 'overlooked topic.  I build Microphone systems with OB2's that sound better than Neumann.. but when it comes to providing  "AC" 6.3 voltage to -two 'differing tubes'  such as is found on the REDD 4 7,  I can only get 3.5 volts on both.  I have only done DC discreet choke fed shunt regulation for filament and have no experience in AC heater  design with different tubes. 1. First attempt - simple parallel- ( load to pin 4 and 5- both tubes..)no ground ref.. gave me a steadily changing '5-7volt' on the E88cc and '4- 5.1 volts' on the EF86(receiving current last..).  2. Second shot, I changed to the Guitar Amp approach where you short 4 to 5 and then use "9" on the E88cc as the other terminal.. with the same on the EF86- except using pin "7". 3.  Third attempt, I -now have 3.5 volts --across load , with E88cc pins 4 and 5 tied together, other lead to "9" , with the EF86  simply going to pins 4 and 5-  however with a ground reference.There is no center tap, so I built out two 5 watt Ohmite resistors to signal ground and took my 7 volts from there.  Also, can I not 'clamp' this with some simple voltage clamp at 6 volts?  Across the load?..The transformer is "6K49VG"  Hammond(La2A) and is capable- more so than I (ha..) with a 460 volt secondary @50ma/[email protected] WITH CT for B+.  I have great B+ voltage at 294volts and I'm using an AMI Tab Funkenwerk BV8r at .6.5:1 for input and output- since they are around..  Input secondary load resistor is 63k. Output is 10k  over secondary.  Any help with this Multiple  Tube AC Heater dilemma would be appreciated!

 

[gyraf]

The "E" in ECC88 and EF86 designates 6.3V parallel heating.

If you have 6.3V AC available, simply connect to this.

As for possibly-needed hum nulling, look at how it's done in guitar amps (or other preamps) - it's a pot across the heater ac, wiper goes to ground.

Jakob E.

 

[ricardo]

.. gave me a steadily changing '5-7volt' on the E88cc and '4- 5.1 volts' on the EF86(receiving current last..)

I don't understand your various connecting schemes but if one tube is getting less heater than the other, your heater wiring needs to be MUCH thicker.  This is probably where you are losing your volts.

 

[ruffrecords]

You should wire these tube heaters in parallel. The e88cc heaters are different to the those of the ecc series. They just connect to pins 4&5. Pin 9 is a screen which should be connected to 0V. So wire transformer to ef86 pin 4 then the e88cc pin 4. Wire other side of transformer to ef86 pin 5 then to e88cc pin 5.

Cheers

Ian

 

[gyraf]

You mean different from the ECC81-82-83 series. But ECC88 and E88CC are the same, only the latter is a selected/hq version.

Jakob E.