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It would be lovely to have everyone here for coffee and records. Might have booze too if I can get the paperwork done for licensing.
Thanks for the explanation about the batteries. I like listening to this equipment and it annoys me that I can’t understand the technicalities, I watch YouTube videos about people mending electronics all the time but I still can’t get a handle on how this stuff works.
Stevethecoffee-
Ok, they aren’t KT88s. They’re 6AS7s which are low impedance twin triode power output valves, so two chunky output triodes in each valve. The KT88 is different. KT88 is a very big single beam tetrode (very similar to a pentode). All 8 of your 6AS7s are probably in parallel, so all 16 output triodes are in parallel and that’s probably why there isn’t a giant output transformer on your amplifier like there normally would be.
It’s an interesting valve. 100-200W from a valve amp would normally use 4x KT88s in class AB push-pull, but it would also need an HT voltage near 700V. Yours is just loads of output triodes stacked in parallel and only needs around 250V so it looks like it might not even have a power transformer and just runs directly on rectified mains voltage. I’d love to have a look inside that thing 👍
Jonny69
Blimey! I said KT66s because they’re normally that tapered shape and KT88s are normally more of a Coke can shape (and size). I’d definitely be up for a forum listening party (and put me down for coffee tasting) if you’d be up for hosting one.
Your 9V batteries are probably for a non transformer-based biasing. It’s an old way of doing it but I’m guessing low noise and probably means you don’t need to use diodes or LEDs to get a simpler but more stable bias voltage.