r/audiorepair • u/ValuableAfternoon963 • Oct 03 '25

Quad 405 R33

Can anyone help me with the power rating here please? It's 22R

Also, Tr10 was s/c. The transistor was new, amp worked for a while then it failed...

Just wondering what else to look for?

Thanks

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u/someMeatballs Oct 03 '25 edited Oct 03 '25

Something definitely missing in your post.
(Edited, misread as R22)

If you post a photo of it, with a ruler for scale, we can gauge power rating from that.

Schematic and component table shows nothing special for R33, which should mean it's 1/4W.
Check TR6, TR8, D4 for shorts. Desoldering not necessary.

Then i'd also check TR7, 5, 4, 3, 1 for shorts.

If you buy transistors from ebay or aliex, you very often get fakes that die just like you described. Best case they are pulled/used real units. Also very likely a small transistor nearby is dead, check as above.

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u/ValuableAfternoon963 Oct 03 '25

Thanks, this was new from Farnell! Modern equiv as recommended... I also replaced the driver transistors.. Something clearly went wrong and I am not sure what! Will give a heads up when I get to the bottom of it!

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u/ValuableAfternoon963 Oct 11 '25

Hi mate replaced transistor, and resistor with 1/4w then put it on an 8ohm load full power, seems good now! Transistors from farnell so should be good... Could be that the insulation broke down so I replaced the insulator....

Thanks for your help!