Don't make the error of thinking TQ stuff was substandard especially the later ones when they had $ from the sale to Tek. The D83 and D75 are the same scope just the D75 is in horizontal format and has a bit smaller CRT than the D83.
These with plugins are a dream to service and I had a D83 for several years. (sold long ago

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My D83's display was as crisp and sharp as any CRO I've seen and considerably better than most.
Yes they have their weak points like any TE but due to the design of using 'off the shelf' componentry they're relatively simple to keep running.
Main area to watch is EHT (NOT PDA) where the high resistance caps drift or go open and along with that will be many of the Ecaps that are getting a fair age now.
The D83 is probably the only CRO I'd want if I was to keep one.
In good running condition yours is worth at least $1/MHz and with a pair of cheapy 100 MHz probes ($15) and the manual on CD a few $ more.
If you have repair experience these are a good scope to learn about CRO's because of their (relatively) simple design, construction, linear PSU and an excellent manual.
Whack the covers off and pull the plug-ins and have a look around before you give up on this one.
Start a repair thread, I'll help and probably bd139 too. We both like TQ stuff.
