Vintage JTM-50 - S/11295 - 1968 - what it it worth? How to rennovate (if at all)

[StuC]

Where did you see those pics!!!
Yes def Partridge

looks like TG9624?
Do you know where they were used Stu? Not one I recognise.

My eyes aren't that good, I can't make it out.

 

[redfish]

I posted my thoughts on the old Plexi Palace forum. This is only what I came up with after looking at dozens of amps of different makes, so it's by no means definitive, but it seems to fit.

Usually, there's a part number and a batch number. It seems to me that the part number follows the pattern T(X)(1234) where T presumably stands for transformer, X is a letter denoting the decade when the part was designed and 1234 is a four digit number.

The second number takes the form (X)(1)(234) where again X is the decade, but this time the decade in which the transformer was made. The first digit appears to be the year in that decade and the last three digits a batch or job number.

The relevant decade letters are G for the '60s and H for the '70s. Prior to 1967, it's rare to see any codes on the transformers. '67 and '68 codes are usually hand written with a paint marker, later ones are stamped.

So for example, TG5479 H1422 would point to a '60s designed part produced in 1971.

wow thats cool ... great detective work

 

[redfish]

Screenshot 2021-04-10 At 09.38.52

• redfish
• Apr 10, 2021

OT Number

 

[redfish]

I might have to take it out again to get a good pic ... but this seems to show TG9624 athough the 'G' is a bit too blurry to tell for sure on this pic

 

[redfish]

 

[Ned B]

I posted my thoughts on the old Plexi Palace forum. This is only what I came up with after looking at dozens of amps of different makes, so it's by no means definitive, but it seems to fit.

Usually, there's a part number and a batch number. It seems to me that the part number follows the pattern T(X)(1234) where T presumably stands for transformer, X is a letter denoting the decade when the part was designed and 1234 is a four digit number.

The second number takes the form (X)(1)(234) where again X is the decade, but this time the decade in which the transformer was made. The first digit appears to be the year in that decade and the last three digits a batch or job number.

The relevant decade letters are G for the '60s and H for the '70s. Prior to 1967, it's rare to see any codes on the transformers. '67 and '68 codes are usually hand written with a paint marker, later ones are stamped.

So for example, TG5479 H1422 would point to a '60s designed part produced in 1971.

Thanks! I actually remember that post as I was an avid PP member. These are pictures of my SA212 transformers. Are the TG numbers the model and the H numbers the date code? Sorry, Redfish...not intending to hijack your tread!

 

[StuC]

Yes, H2 would be 1972 if I figured it out correctly. Don't see many 50s with the original PT, does it run hot?

 

[alpha al]

Well I would certainly remove that death cap, it is call that because if it leaks and if in some situation you would be the ground, through your guitar or a microphone, well it could kill you..

Not possible if it's "Earthed" (grounded) properly.

 

[Seanxk]

Not possible if it's "Earthed" (grounded) properly.

And it is.....

Red, can you read off any letter codes on the Brown cap please, they will be capitols XXX.
I have a curious finding, will post later.

 

[redfish]

which brown cap Sean?

 

[Seanxk]

which brown cap Sean?

The .05uf 1000v Hunts cap next to the Bulgin and P/T

 

[redfish]

The .05uf 1000v Hunts cap next to the Bulgin and P/T

I cant read it on any of my pics or video - would have to open her up again - will post what I find when I get round to opening up again

 

[TAZIN]

And it is.....

Red, can you read off any letter codes on the Brown cap please, they will be capitols XXX.
I have a curious finding, will post later.

Hunts
A74 (series)
0.05uF 1000v
DC Wkg
H Y? (date code)

 

[Ivan H]

Hunts
A74 (series)
0.05uF 1000v
DC Wkg
H Y? (date code)

I could be way off base here, but through using modern 1,000V (& greater) capacitors, my understanding is that an X rated capacitor will fail closed, or "short" while a Y rated capacitor will fail open. Not at all sure when these designations came into use, but is it possible the H Y designation has something to do with this?
My JMP50 has this same 1,000V Hunts capacitor mounted between the HT fuse holder & ground. Cheers

 

[TAZIN]

I could be way off base here, but through using modern 1,000V (& greater) capacitors, my understanding is that an X rated capacitor will fail closed, or "short" while a Y rated capacitor will fail open. Not at all sure when these designations came into use, but is it possible the H Y designation has something to do with this?
My JMP50 has this same 1,000V Hunts capacitor mounted between the HT fuse holder & ground. Cheers

I believe the three letter sequence to be a manufacture date code. A similar type date code was used on their electrolytic capacitors. So, if true then I'd expect the code to be either 'H YN' or 'H YD'.

 

[StingRay85]

I posted my thoughts on the old Plexi Palace forum. This is only what I came up with after looking at dozens of amps of different makes, so it's by no means definitive, but it seems to fit.

Usually, there's a part number and a batch number. It seems to me that the part number follows the pattern T(X)(1234) where T presumably stands for transformer, X is a letter denoting the decade when the part was designed and 1234 is a four digit number.

The second number takes the form (X)(1)(234) where again X is the decade, but this time the decade in which the transformer was made. The first digit appears to be the year in that decade and the last three digits a batch or job number.

The relevant decade letters are G for the '60s and H for the '70s. Prior to 1967, it's rare to see any codes on the transformers. '67 and '68 codes are usually hand written with a paint marker, later ones are stamped.

So for example, TG5479 H1422 would point to a '60s designed part produced in 1971.

Great info. Now I need to check my own Partridge codes

 

[StuC]

I could be way off base here, but through using modern 1,000V (& greater) capacitors, my understanding is that an X rated capacitor will fail closed, or "short" while a Y rated capacitor will fail open. Not at all sure when these designations came into use, but is it possible the H Y designation has something to do with this?
My JMP50 has this same 1,000V Hunts capacitor mounted between the HT fuse holder & ground. Cheers

As TAZIN said, it's a date code. I checked the one in my JTM50 as it's out of the cabinet and it's H TU.

 

[Seanxk]

As TAZIN said, it's a date code. I checked the one in my JTM50 as it's out of the cabinet and it's H TU.

Yes it's a date code, Stu is it a Hunts or an Erie, is there a type space between those letters or are they equi spaced.

 

[StuC]

Hunts. It's spaced like that: H TU, so tempting to see the H as the year, which would make it week 46 of 1962. It could be week 24 of 1966... I haven't yet found one with a middle digit that would confirm which way around to read these. I've only come across H and Y as the first letter in Marshalls.

 

[Seanxk]

Interesting, yes the spacing makes it confusing, but 62 could be from the first batch ( they probably didn't use that many) or more likely 66 I think, let's see what others come up with.