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I threw this hypothesis up on the PP forum a while back. It appears to me that the bottom number on Partridge transformers is some kind of date/batch code (the top number being the part number).

'60s tranny codes begin with G, '70s with H, then the first numerical digit is the year. This seems to hold on most amps I've looked at, including Sound City, Laney & Orange Matamp.

Examples (amps dated from other components e.g. mustard caps, pots, filter cans):

'67 DR506 code G7807
'68/'69 SC 100 Mk3 G8543 & G8544
'69/'70 DR103 s/n 727 codes G9486 & G9487
'71/'72 Laney Supergroup H1947 & H1948
'72 Laney 60W H2574
'80 DR103 H9683

Now here's one that throws a spanner in the works - my DR103 s/n 1489 which we just decided is 1970 has H1037 and H1038... very early '71 after all?

Does this seem reasonable, or am I barking up the wrong tree?

It does seem intuitive.
I will have to go through my amps and record the tranny #'s

Maybe we can prove your theory and have another valuable tool!

There are a lot of transformer codes listed in Mark's Registry:

http://mhuss.com/Hiwatt/RegAmps.php

Someone who's got time and interest could populate a spreadsheet with that info for starters.

Dave

I skimmed through Mark's registry and the theory seems to hold.

Ahhh...a theory!

I shall organize a symposium at once.

Mike
Living for Theory Since 1955

I think it has to remain a hypothesis until it's proven? I could be wrong though, I often am...

BTW, I noticed Ian Frankish's (PP member) set, which he custom ordered from T&R (as they are now) are coded K8xxx. If they skipped I for the '80s and used J, could be those were made in '98? I wonder when he bought them?

I believe you are correct. my earlier post should read, "your Hypothesis seems to hold!"

after further review, I have found some discrepencies...........so I have to revise my opinion to uncertain.....

Care to elaborate?

I have seen a handful of amps that certainly seem to be original and authentic that don't seem to follow suit.

A huge percentage do follow suit, but some don't.

shrugs shoulders...........

I have not forgotten this thread or Hypothesis.
The only discrepencies seem to be with the year 1970.
G9 seems to go directly to H1

I do believe this hypothesis to be valuable..........I would rely on it 99% of the time.

Only time and more HIWATTs will tell...........

My #249=1968 yet my Partridge code is G6469 suggesting 1966,any ideas?.

Exactly!
I believe your amp to be a 1967 rather than a 1968.
Very nice!
Glad you found The Vintage HIWATT Forum!

You can also refine the date of manufacture further by checking the pot and cap date codes, as shown here:
http://mhuss.com/Hiwatt/dates.html

--mark

my dr203 trans are h2 and it has 72 caps in it also the theory works in this instance.