Dumont RA-109 tubes question

[kramden66]

Ok here it is the sams says first and second if are 6AU6 tubes but in the set are 6BC5 tubes , my question is should i leave them or go back to 6au6 tubes ? anyone know if there was a production change or what?

thanks
mike

[Zenith26kc20]

If I remember right, the 6au6 and 6bc5 pin out differently. Pin 2 of the 6bc5 is cathode, supressor and jumper to pin 7
Pin 2 of the 6au6 is supressor, pin 7 is cathode. I'll look at my tube manual tonight to be sure.
My memory is somewhat fresh as I was caught by a 6au6 in the wrong socket lately (but it could be wrong so let me look tonight).

[kramden66]

the horz afc says on the sams 6BC5 but in the set is a 6AG5 , interestigly enough theres hand written tube numbers at the sockets , they match whats in the set like the first and second if and this horz afc , really odd but in the notes in the tube list it does state 6AG5 as alternate but 6BC5 installed in the set ,it says nothing as alternate to the first and second if , i think too on the tube placement chart they list a transformer with the wrong number but its correct in the photo identification and in the scematic.

mike

[kramden66]

So i guess i should ask those with a RA-109 what tubes are in your set for first and second if ?

mike

[kramden66]

ah ha riders tv trouble cures vol 1 says to improve sensitivity replace the first and second if 6au6 tubes with 6bc5 tubes , there are other changes but they were not done to this set , so apparently it will function with those two tubes , the other mod is replace 4th if with a 6bc5 and remove the ground connection from pin 2 of the 4th if , the 6au6 is still the 4th in this set , also replace the last if transformer with a different one , so either dumont or someone else decided to put the two 6bc5 tubes in and that was good enough.

mike

[wiseguy]

I have the same set but "a" version, and the tube complement is the same as you say, the Sams must show the Earlier chassis, my tube chart in the Cabinet does show those Tubes you found

[Tubejunke]

I don't have the set anymore, but I seem to remember many 6AU6 tubes in there along with a few of the others mentioned. I thought that the 6BC5 was called the "reactance" tube, but it's been about a decade. I may still have the schematic somewhere around here. I tend to think whenever I have seen hand written tube #s that some sort of upgrade or modification was done and that was the techs way of noting that for other techs. Great set though, especially if you like em heavy. The power transformer alone probably weighs 20 lbs!

[kramden66]

Thanks i see yours is the sherbrooke , mine is the hanover , good to know that these tubes are right.

mike

[Tubejunke]

You are real lucky I think to have this wonderful set, with a good CRT, and in working order. Keep us posted on your progress.