Using a 12SC7 in place of a 6SC7?

[TubeGeek]

I am beginning to assemble parts to build a 5c3 Deluxe.  I want to experiment with octal preamp tubes. The schematic calls for octal 6SC7's (2) in the preamp.  I thought I had some in my tube stash but it turns out I don't. I have several 6SN7's so now I am on the hunt for a couple 6SC7's.

Looking into this I found that 12SC7's are compatible tubes with the exception of having 12V heaters.  I have a couple 12sc7's and would like to use them if I can.  If it is too much of a pain in the butt I will order some 6SL7's or order some 6SC7's online.

My question is how would/can I wire these tubes for 12V heaters using a 6.3 VAC winding?

[kagliostro]

My question is how would/can I wire these tubes for 12V heaters using a 6.3 VAC winding?

I think that for these tubes you intend 12sc7

if so you must use a 12.6v winding or, at least, a 12v winding

6.3v is too low for this tubes but if you have enough current you can go DC via a voltage doubler

K

[stratele52]

Sorry but your 12SC7 need a 12 volts AC heater voltage. 6SC7 work only on 6 volts.

It is not like "popular" tubes like 12AX7, 12AT7 wich can work on 12 or 6 volts.

Or  add a small 12 volts transformer.

[TubeGeek]

Sorry but your 12SC7 need a 12 volts AC heater voltage. 6SC7 work only on 6 volts.

It is not like "popular" tubes like 12AX7, 12AT7 wich can work on 12 or 6 volts.

Or  add a small 12 volts transformer.

That's what I was wondering. Thanks for echoing my thoughts.

[TubeGeek]

I decided to pull the plug and order a hickok tested, matched pair of NOS GE 6SC7's off ebay.  Haven't purchased tubes on ebay before, hope these will be ok or as stated in the item decription. Sometimes I'm a skeptic.

[printer2]

In your earlier post that disappeared you were saying you wanted to compare the 5E3 to the 5C3. Not sure if you would be interested in comparing the two circuits in the same amp but here is a circuit that switches between the two PI's which is the difference between the circuits using a four pole switch.

[labb]

I have built a couple of the 5B3's with the octal pre amp tubes and really like the sound of them. JFI I had a lot of trouble with the last group of  nos 6SC7's being microphonic. Same with the nos 6SL7's. Ended up trying new production Sovtek and Tung-Sol 6SL7's. The Sovtek's were microphonic. The Tung-Sol's worked out pretty good.

[Willabe]

My question is how would/can I wire these tubes for 12V heaters using a 6.3 VAC winding?

Already been said you can't but....

Look at the heater pins, 7/8, only 2, 1 filliment .

12A_7 has 3 pins, 2 filliments _with_ a CT. 4 and 5 (series) gets you 12.6v, 4/5 and 9 (parallel with CT) gets you 6.3v.


                  Brad      

[stratele52]

My question is how would/can I wire these tubes for 12V heaters using a 6.3 VAC winding?

Already been said you can't but....

Look at the heater pins, 7/8, only 2, 1 filliment .

12A_7 has 3 pins, 2 filliments _with_ a CT. 4 and 5 (series) gets you 12.6v, 4/5 and 9 (parallel with CT) gets you 6.3v.


                  Brad      

!2SC7 don't have same heater than 12A_7 series

[Willabe]

Yes, that's what I was pointing out.

Read the whole post.   


   
                   Brad     

[stratele52]

You are right , Sorry  I can't not easely understand what you write . I'm french speaking


About these heater , long story short that's what I wrote october 3

[TubeGeek]

In your earlier post that disappeared you were saying you wanted to compare the 5E3 to the 5C3. Not sure if you would be interested in comparing the two circuits in the same amp but here is a circuit that switches between the two PI's which is the difference between the circuits using a four pole switch.

Thanks for the info on the PI.  I may experiment with this as I get deeper into the project.  Right now I am more interested in the difference in preamp tubes...noval vs. octal.  A few years ago I built a Weber 5C3P kit for a guy and it sounded nice.  I think lots of what I liked was the octal preamp tubes.  Of course the difference in PI contributed but I'll get into that later on.

[TubeGeek]

I have built a couple of the 5B3's with the octal pre amp tubes and really like the sound of them. JFI I had a lot of trouble with the last group of  nos 6SC7's being microphonic. Same with the nos 6SL7's. Ended up trying new production Sovtek and Tung-Sol 6SL7's. The Sovtek's were microphonic. The Tung-Sol's worked out pretty good.

I have been reading that microphonics is a big issue with these octals.  I hope what I purchased will work for me.  I will try the amp with the NOS tubes and see how it goes.  If all else I can order some of the new reissue tung-sol 6sl7's to try.  Or I could order some Nothern Electric 6sc7's but they are $100 each

[TubeGeek]

My question is how would/can I wire these tubes for 12V heaters using a 6.3 VAC winding?

Already been said you can't but....

Look at the heater pins, 7/8, only 2, 1 filliment .

12A_7 has 3 pins, 2 filliments _with_ a CT. 4 and 5 (series) gets you 12.6v, 4/5 and 9 (parallel with CT) gets you 6.3v.

                  Brad      

Yeah I figured.  I was just hoping for someone to say "oh well that's easy just hook it up this way!"

[Willabe]

You are right , Sorry  I can't not easely understand what you write . I'm french speaking

Your good with me ST.


                    Brad     

[stratele52]

How about the option of running a 12 v filament tranny and taking putting the power tube heaters in series?  Thus you can use those 12SC7s. 

You mean parallele not series  ? 

[TubeGeek]

How about the option of running a 12 v filament tranny and taking putting the power tube heaters in series?  Thus you can use those 12SC7s. 

You mean parallele not series  ? 

Since I have already ordered some 6sc7's, I'll start with this way before going that route but thanks for ideas.

[stratele52]

Two 6CS7 in series on 12 volts is OK