[mordy]

Appears I have the exact same tubes as you, same numbers and all - they've been in my collection for a good part of a year now, and I agree, I think they sound wonderful - btw, how did you date them?

The M-R designation means that these tubes were rationed during WW2 and it existed between 1942-1945.
"The tube was manufactured during WW2 for “Maintenance and Repair” of civilian radios. During WW2, military need for vacuum tubes created a large shortage of tubes that could be purchased by civilians."
I haven't found a guide to Hytron codes, but usually the first digit is the year, so 1943 seems accurate.
The A could mean January.
That leaves us with the 5 - don't know.

 

[shwnwllms]

Appears I have the exact same tubes as you, same numbers and all - they've been in my collection for a good part of a year now, and I agree, I think they sound wonderful - btw, how did you date them?

Seller had them listed as 1943, @mordy post seems to confirm this

A could mean week
5 could be month

ie 1st week of June 1943

Or A is January like Mordy said and the 5 is some sort of internal production code

 

[g0ldl10n]

The M-R designation means that these tubes were rationed during WW2 and it existed between 1942-1945.
"The tube was manufactured during WW2 for “Maintenance and Repair” of civilian radios. During WW2, military need for vacuum tubes created a large shortage of tubes that could be purchased by civilians."
I haven't found a guide to Hytron codes, but usually the first digit is the year, so 1943 seems accurate.
The A could mean January.
That leaves us with the 5 - don't know.

In regards to the 'M-R' markings, I never knew that is what it meant, very interesting and good to know.

 

[mordy]

Seller had them listed as 1943, @mordy post seems to confirm this

A could mean week
5 could be month

ie 1st week of June 1943

Or A is January like Mordy said and the 5 is some sort of internal production code

Seller had them listed as 1943, @mordy post seems to confirm this

A could mean week
5 could be month

ie 1st week of June 1943

Or A is January like Mordy said and the 5 is some sort of internal production code

As far as I know US manufacturers did not use the month/week codes, unlike many European factories. The month was skipped and only the week indicated - as an example 1964-26 which would mean the 26th week (June) 1964.
UNLESS it is a GE tube - then the two digit number indicates the month:
The month codes are: 04, 09, 13, 17, 22, 26, 30, 35, 39, 43, 48, and 52. These represent January through December, respectively.
Confusing, eh?

 

[raindownthunda]

These 1943 Hytron 6C5’s are sounding mighty fine

As far as I know US manufacturers did not use the month/week codes, unlike many European factories. The month was skipped and only the week indicated - as an example 1964-26 which would mean the 26th week (June) 1964.
UNLESS it is a GE tube - then the two digit number indicates the month:
The month codes are: 04, 09, 13, 17, 22, 26, 30, 35, 39, 43, 48, and 52. These represent January through December, respectively.
Confusing, eh?

I picked up a pair of these Hytron's a few years back and realized I and haven't tried them in my new amp. They do sound pretty great! Very smooth and sweet while still having good clarity. Definitely rotation-worthy.

The date codes on both are different but they look the same otherwise.

One has: 1A5
The other has: 9A4
Neither have the "MR" designation.

They also have the markings:
SC
966
A

 

[triod750]

They also have the markings:
SC
966
A

American 'OTK' marking. SC is Signal Corps and 966A might be the unit. I think @mordy told me this in 1943

 

[mordy]

I picked up a pair of these Hytron's a few years back and realized I and haven't tried them in my new amp. They do sound pretty great! Very smooth and sweet while still having good clarity. Definitely rotation-worthy.

The date codes on both are different but they look the same otherwise.

One has: 1A5
The other has: 9A4
Neither have the "MR" designation.

They also have the markings:
SC
966
A

Since these tubes have the military markings JAN (Joint Army and Navy) and the Signal Corps quality control markings it explains the absence of MR which means that the MR tubes were set aside for maintenance and repair of civilian equipment.
1A5 could be May 1941.
9A4 - since these tubes first came out 1935 it is possible that 9 = 1939 and the 4 = April.

 

[triod750]

I read somewhere on Wikipedia last year that MR meant Manufacturers Replacement during that same period. This could mean the same thing that Mordy describes and a slight misunderstanding.

 

[g0ldl10n]

Since these tubes have the military markings JAN (Joint Army and Navy) and the Signal Corps quality control markings it explains the absence of MR which means that the MR tubes were set aside for maintenance and repair of civilian equipment.
1A5 could be May 1941.
9A4 - since these tubes first came out 1935 it is possible that 9 = 1939 and the 4 = April.

Unless I am reading this wrong, did the JAN labeling/marking system not come until after 1943 though?

https://www.radiomuseum.org/forum/us_navy_equipment_designations_until_194353.html

 

[shwnwllms]

Does anyone know if 6P5 takes the same adapter as 6J5 / 6C5?

Looks like the 6P5 is basically a successor to a 76 with an octal base. Anything else I should be aware of with this type of single triode?

http://vinylsavor.blogspot.com/2019/06/tube-of-month-6p5.html

 

[LobalWarming]

Does anyone know if 6P5 takes the same adapter as 6J5 / 6C5?

Looks like the 6P5 is basically a successor to a 76 with an octal base. Anything else I should be aware of with this type of single triode?

http://vinylsavor.blogspot.com/2019/06/tube-of-month-6p5.html

Yes, same pinout as 6J5/6C5/6L5. Lower amp factor like the 76. The 6P5Gs I've rolled are sweet and balanced. Like a 76.

 

[mordy]

Unless I am reading this wrong, did the JAN labeling/marking system not come until after 1943 though?



https://www.radiomuseum.org/forum/us_navy_equipment_designations_until_194353.html

Thanks for the clarification! Did some reading and indeed, the JAN designation started 1942-43.
Here is a wartime Hytron ad that seems a little strange:

 

[mordy]

Since these tubes have the military markings JAN (Joint Army and Navy) and the Signal Corps quality control markings it explains the absence of MR which means that the MR tubes were set aside for maintenance and repair of civilian equipment.
1A5 could be May 1941.
9A4 - since these tubes first came out 1935 it is possible that 9 = 1939 and the 4 = April.

I picked up a pair of these Hytron's a few years back and realized I and haven't tried them in my new amp. They do sound pretty great! Very smooth and sweet while still having good clarity. Definitely rotation-worthy.

The date codes on both are different but they look the same otherwise.

One has: 1A5
The other has: 9A4
Neither have the "MR" designation.

They also have the markings:
SC
966
A

Looks like the interpretation of the date codes has to be revised since the JAN designation went into use around 1943.
So here is another (educated/uneducated?) guess:
1A5 = January 1945 Factory A
9A4 = September 1944 Factory A.

 

[shwnwllms]

Yes, same pinout as 6J5/6C5/6L5. Lower amp factor like the 76. The 6P5Gs I've rolled are sweet and balanced. Like a 76.

Thanks, I was just reading up on them. I had my eye on a pair or two but the consensus on this thread seems to be the 6J5/6C5 are mainly preferred over 6P5. I can’t help but wonder if it’s due to the lower amp factor μ 13.8 (equivalent to 76) versus 6J5/6C5 μ 20 (equivalent to 6SN7)

 

[nwavesailor]

I bought several pairs of 6P5G when I first starting using 6J5's in a Garage 1217 amp! They were good and inexpensive but nothing terribly exciting, IMO.