Hi All,
I have a TO Clipper here full of loctal tubes. Each has a funny little code below the part number. The schematic indicates that this is a date stamp of some kind. It says that 1LD5 with date codes before 'F6E' June 1946 have microphonc problems. I have some microphonc problems.
I was wondering how one reads these date codes. Does anyone know?

Best Regards,

Bill Grimm

:Hi All,
: I have a TO Clipper here full of loctal tubes. Each has a funny little code below the part number. The schematic indicates that this is a date stamp of some kind. It says that 1LD5 with date codes before 'F6E' June 1946 have microphonc problems. I have some microphonc problems.
: I was wondering how one reads these date codes. Does anyone know?
:
:Best Regards,
:
:Bill Grimm
:
Any takers? I googled this and all I got was a PDF that is quite confusing.

A lot of date codes are in Lud Sibley's book "Tube Lore". F6E would be an RCA code for Nov-Dec 1946, OEM (original equipment manufacturer).

Beginning in 1947 Sylvania and RCA both used open date codes for week and year. "7-26" would be the 26th week of 1947. 13, 26, 39 and 52 usually indicate that the code only changed once per quarter.

:A lot of date codes are in Lud Sibley's book "Tube Lore". F6E would be an RCA code for Nov-Dec 1946, OEM (original equipment manufacturer).
:
:Beginning in 1947 Sylvania and RCA both used open date codes for week and year. "7-26" would be the 26th week of 1947. 13, 26, 39 and 52 usually indicate that the code only changed once per quarter.
:
Hi Alan,
Thank you for the information.
One question, is the 1946 signified by the 6 or the F?

All the Best,

Bill Grimm

The F. Numbers indicated two-month units, 6 for Nov-Dec. Previous years were K, H and V for 1943, 44, 45.

Hi Bill

1LD5 is used as 1st audio amplifier in battery radios. Tubes used in this position, in battery radios, will all be microphonic to some extent.

Tubes have a filament wire which is held tight by a small spring. Due to high gain between this tube and speaker there will be microphonic sound when this tube is tapped.

It becomes a problem when speaker vibrations causes a continous ringing sound. Extent of microphonics will change with different tubes but 1U5, 1S5, 1H5, 1LH5 will also give this noise.

Norm

:Hi All,
: I have a TO Clipper here full of loctal tubes. Each has a funny little code below the part number. The schematic indicates that this is a date stamp of some kind. It says that 1LD5 with date codes before 'F6E' June 1946 have microphonc problems. I have some microphonc problems.
: I was wondering how one reads these date codes. Does anyone know?
:
:Best Regards,
:
:Bill Grimm
:

I agree. The 1S5 det/amp tube socket in my G500 T/O is isolated from the chassis by rubber grommets.
It will ring if you tap it, but is OK in normal operation.

:Hi Bill
:
: 1LD5 is used as 1st audio amplifier in battery radios. Tubes used in this position, in battery radios, will all be microphonic to some extent.
:
: Tubes have a filament wire which is held tight by a small spring. Due to high gain between this tube and speaker there will be microphonic sound when this tube is tapped.
:
: It becomes a problem when speaker vibrations causes a continous ringing sound. Extent of microphonics will change with different tubes but 1U5, 1S5, 1H5, 1LH5 will also give this noise.
:
:Norm
:
:
:
:
::Hi All,
:: I have a TO Clipper here full of loctal tubes. Each has a funny little code below the part number. The schematic indicates that this is a date stamp of some kind. It says that 1LD5 with date codes before 'F6E' June 1946 have microphonc problems. I have some microphonc problems.
:: I was wondering how one reads these date codes. Does anyone know?
::
::Best Regards,
::
::Bill Grimm
::
:

Hi Norm and Walt,
I hadn't thought about why thesy seem to get microphonic, but once you described the process it makes perfect sense. If that filament is tight you can get a good resonance at some audio frequencies, something not seen on tubes like 6SQ7.
This also explains why you need the extra elements on a first audio tube, to dampen oscillations, just like in an IF tube.

All the Best,

Bill Grimm