I've been re-doing a Howard-256 that uses a 6D6 as the 1st IF amp.

http://www.nostalgiaair.org/Resources/224/M0009224.htm

I had a questionable 6D6 in the set that seemed rather weak.
Replacing it made a nice improvement but I also noticed somewhere that a 6d6 could be replaced with a 78 as well.

Since I have quite a few of both these tubes I tried a 78.
With the 78 tube I get equally good apparent results as with a good 6D6.

Other than the obvious "orig schematic design" is the best advice...
What is the better tube to use here?
....Meaning ...will one tube perform much better than the other tube? ... or are they "practically" about equal?

I can't see any particular difference in the manuals that jumps out at me.
.. though it says that 6d6 is the same as a 6K6 and the 78 is the same as a 6F6.

So if the schematic calls for the 6D6 ... will the 78 be only a temp substitute or will it be just fine to leave it in the radio?

Try this site, I think you might find the plate impedances are the only difference.
Lewis

:I've been re-doing a Howard-256 that uses a 6D6 as the 1st IF amp.
:
:http://www.nostalgiaair.org/Resources/224/M0009224.htm
:
:I had a questionable 6D6 in the set that seemed rather weak.
:Replacing it made a nice improvement but I also noticed somewhere that a 6d6 could be replaced with a 78 as well.
:
:Since I have quite a few of both these tubes I tried a 78.
:With the 78 tube I get equally good apparent results as with a good 6D6.
:
:Other than the obvious "orig schematic design" is the best advice...
: What is the better tube to use here?
: ....Meaning ...will one tube perform much better than the other tube? ... or are they "practically" about equal?
:
:I can't see any particular difference in the manuals that jumps out at me.
:.. though it says that 6d6 is the same as a 6K6 and the 78 is the same as a 6F6.
:
:So if the schematic calls for the 6D6 ... will the 78 be only a temp substitute or will it be just fine to leave it in the radio?
:

:Try this site, I think you might find the plate impedances are the only difference.
:Lewis
:oops, didn't list the site.

http://radioremembered.org/outimp.htm

Lewis

:
:
:
:
:
::I've been re-doing a Howard-256 that uses a 6D6 as the 1st IF amp.
::
::http://www.nostalgiaair.org/Resources/224/M0009224.htm
::
::I had a questionable 6D6 in the set that seemed rather weak.
::Replacing it made a nice improvement but I also noticed somewhere that a 6d6 could be replaced with a 78 as well.
::
::Since I have quite a few of both these tubes I tried a 78.
::With the 78 tube I get equally good apparent results as with a good 6D6.
::
::Other than the obvious "orig schematic design" is the best advice...
:: What is the better tube to use here?
:: ....Meaning ...will one tube perform much better than the other tube? ... or are they "practically" about equal?
::
::I can't see any particular difference in the manuals that jumps out at me.
::.. though it says that 6d6 is the same as a 6K6 and the 78 is the same as a 6F6.
::
::So if the schematic calls for the 6D6 ... will the 78 be only a temp substitute or will it be just fine to leave it in the radio?
::

Hi Peter

In my opinion 78 is better than 6D6. Have no idea why they came out with 6D6?

A 78 is shorter and better shielded. It won't go into osillation as easily. Sometimes 78 will operate without a shield while 6D6 usually requires shielding. 6D6 being taller has higher capacity between leads which can also cause oscillation.

Due to difference in internal capacity interchanging between these tubes may require alignment.

Norm

::Try this site, I think you might find the plate impedances are the only difference.
::Lewis
::oops, didn't list the site.
:
:
:http://radioremembered.org/outimp.htm
:
:Lewis
:
:
:
::
::
::
::
::
:::I've been re-doing a Howard-256 that uses a 6D6 as the 1st IF amp.
:::
:::http://www.nostalgiaair.org/Resources/224/M0009224.htm
:::
:::I had a questionable 6D6 in the set that seemed rather weak.
:::Replacing it made a nice improvement but I also noticed somewhere that a 6d6 could be replaced with a 78 as well.
:::
:::Since I have quite a few of both these tubes I tried a 78.
:::With the 78 tube I get equally good apparent results as with a good 6D6.
:::
:::Other than the obvious "orig schematic design" is the best advice...
::: What is the better tube to use here?
::: ....Meaning ...will one tube perform much better than the other tube? ... or are they "practically" about equal?
:::
:::I can't see any particular difference in the manuals that jumps out at me.
:::.. though it says that 6d6 is the same as a 6K6 and the 78 is the same as a 6F6.
:::
:::So if the schematic calls for the 6D6 ... will the 78 be only a temp substitute or will it be just fine to leave it in the radio?
:::

I like the taller 6D6, but the 78 is definitely shielded better. The 6D6 only has shielding on the top and bottom. The 78 is completely enclosed, like a 12SK7 or 1LN5.

T.

Thanks a lot yoooze guyz... appreciate it. Got it.

:Thanks a lot yoooze guyz... appreciate it. Got it.

I started servicing during WWII when for some reason parts were hard to come by. Ever since I have considered a 78 and a 6D6 as the same. Ditto 77/6C6.

Bruce

Thanks Bruce

:Thanks Bruce

Hey Peter no thanks necessary. I gain a lot from yours posts but never have the courtesy to say thanks.

Bruce