Thordarson or holldarson
 

Are these 2 flyback companies the same having the same item made the same. Because some flybacks have wax donuts and others have the newer plastic and silicone donut’s

I have wondered the same question. I had tried searching for acquisition information but could not find anything. My guess is that at some point Thoardarson purchased Halldorson, they shared part numbers but still kept separate branding.

ISTR some Sam's where the parts sub list had a single Thordarson/Haldorson column with a single number for both brands, but maybe I'm remembering wrong.

Best way to tell is by EIA numbers on the part.
EIA #'s are one to 4 place numbers with each mfg having a ##.
Example is #343 for Zenith. It can be any brand but if you see
#343 on the CRT you know Zenith built the CRT.
Other info you can find on parts is.

Week & year date codes, 4 places. example 4578 is 45th week, 1978.
OEM part ##'s.
MFG part ##'s .
Run ##'s
Values.
All can be useful ! AND fun :banana:

Now someone that has the list of EIA ##'s please post. I cant find it any more. I knew many but age is slowly eating away at my brain list !

73 Zeno:smoke:
LFOD !

There are a few lists of EIA codes at this site:

https://www.ecianow.org/eia-source-codes

I found Gramer-Halldorson listed with an EIA code of 596. Thordarson's EIA code is 238.

It's interesting that they used very similar graphics on their boxes (from eBay auctions):

https://i.ebayimg.com/00/s/NzY4WDEwM..._id=880000500F

https://i.ebayimg.com/images/g/0CkAA...FxO/s-l400.jpg

TNX 4 that link Sean. I saw that box & said "boy that looks like a Thordarson box !". Aah the memories:D.
When I scrolled down any doubt about it went away.

73 Zeno:smoke:
LFOD !

The switch from wax to silicone could have been due to a change in UL requirements.

It seemed to be an over time change to me. There was an in-between time where vulcanized rubber was used...It had a tendency to become conductive and cause arc overs on CTC-16 and later RCAs.

As anyone can tell you, klingonized is always better! :D

Lol.