I'm currently working on a Farnsworth ET-066 that employs the use of 6 tubes total.
6SS7, 12SA7, 6SS7, 12SQ7, 50L6, 35Z5.

The 6SS7 seems to be almost the same as a 12SK7 so I wonder why the 6SS7 was used?

To keep the filament totals the same... many other six-tube sets of that same generation, used two 12SK7s and a 35L6 for the output tube instead of the 50L6.

Does anyone know a good reason for Farnsworth using the 6SS7 over the 12SK7?
... or was it because one was available before the other was introduced?

Hi Peter

I mentiond this on ARF. The 6SS7 was used where 6 tubes had filaments wired in series. If 12SK7 were in the circuit voltage drop would exceed line voltage. With high line voltage using 2 - 12SK7 would be a good idea. Tubes have the same basing.

They could have used a 35L6 but output is rated slightly lower.

Since 6SS7 is a low power filament tube would have also been used in battery radios.

Norm

:I'm currently working on a Farnsworth ET-066 that employs the use of 6 tubes total.
: 6SS7, 12SA7, 6SS7, 12SQ7, 50L6, 35Z5.
:
:The 6SS7 seems to be almost the same as a 12SK7 so I wonder why the 6SS7 was used?
:
:To keep the filament totals the same... many other six-tube sets of that same generation, used two 12SK7s and a 35L6 for the output tube instead of the 50L6.
:
:Does anyone know a good reason for Farnsworth using the 6SS7 over the 12SK7?
:... or was it because one was available before the other was introduced?

:Hi Peter
:
: I mentiond this on ARF. The 6SS7 was used where 6 tubes had filaments wired in series. If 12SK7 were in the circuit voltage drop would exceed line voltage. With high line voltage using 2 - 12SK7 would be a good idea. Tubes have the same basing.
:
: They could have used a 35L6 but output is rated slightly lower.
:
: Since 6SS7 is a low power filament tube would have also been used in battery radios.
:
:Norm
:
::I'm currently working on a Farnsworth ET-066 that employs the use of 6 tubes total.
:: 6SS7, 12SA7, 6SS7, 12SQ7, 50L6, 35Z5.
::
::The 6SS7 seems to be almost the same as a 12SK7 so I wonder why the 6SS7 was used?
::
::To keep the filament totals the same... many other six-tube sets of that same generation, used two 12SK7s and a 35L6 for the output tube instead of the 50L6.
::
::Does anyone know a good reason for Farnsworth using the 6SS7 over the 12SK7?
::... or was it because one was available before the other was introduced?

Hi Norm and Peter,
I think the two 12SK7s and 36L6GT make for a better design, as it distributes the heat more evenly. 50L6GT gets hotter than 35L6GT.
I suspect that the 6SS7 was used because they had a lot of them or 50L6GT in stock to use up.

Best Regards,

Bill Grimm

Hi Bill

Agree with that. Using a 35L6 would distribute heat better but just about everyone used 50 volt tubes as output in AA5's. Philco used some 35 volt tubes for output along with a series resistor. Some of the lastest series wired radios did use lower voltage output tubes and 18 volt ones for RF & IF.

6BJ6 was also used this way in place of 12BA6.

How would a company have too many 6SS7's if they weren't used very often except in this type of circuit. Agree Philco had way too many #41's so continued to use them into the 1940's.

Norm

::Hi Peter
::
:: I mentiond this on ARF. The 6SS7 was used where 6 tubes had filaments wired in series. If 12SK7 were in the circuit voltage drop would exceed line voltage. With high line voltage using 2 - 12SK7 would be a good idea. Tubes have the same basing.
::
:: They could have used a 35L6 but output is rated slightly lower.
::
:: Since 6SS7 is a low power filament tube would have also been used in battery radios.
::
::Norm
::
:::I'm currently working on a Farnsworth ET-066 that employs the use of 6 tubes total.
::: 6SS7, 12SA7, 6SS7, 12SQ7, 50L6, 35Z5.
:::
:::The 6SS7 seems to be almost the same as a 12SK7 so I wonder why the 6SS7 was used?
:::
:::To keep the filament totals the same... many other six-tube sets of that same generation, used two 12SK7s and a 35L6 for the output tube instead of the 50L6.
:::
:::Does anyone know a good reason for Farnsworth using the 6SS7 over the 12SK7?
:::... or was it because one was available before the other was introduced?
:
:Hi Norm and Peter,
: I think the two 12SK7s and 36L6GT make for a better design, as it distributes the heat more evenly. 50L6GT gets hotter than 35L6GT.
: I suspect that the 6SS7 was used because they had a lot of them or 50L6GT in stock to use up.
:
:Best Regards,
:
:Bill Grimm

35L6 was produced before the 50L6. It is likely that the manufacturer preferred the 50L6 to the 35L6, or perhaps had a huge stock of 50L6 tubes, since the 35L6 seemed to drop out of use. It does have a slight bit more power, though I can't really notice. 6SS7 definitely isn't a common tube.

If you want a definite increase in power and bass, use the 50C6G. I like it, and I like the G shape, too, though it takes up quite a bit more room than the GT tubes, and it looks out of place. If you can obtain a complete set of Zenith AA5 G style tubes, you'll be set to go. Just try not to eat up the 50C6G supply for me. I like them, too.

T.