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Post by Chris on Jul 7, 2014 19:45:46 GMT
I realise they are interchangeable with the 6550/KT88 variants but I've a feeling it's more to do with whether the amps transformers can handle them?
I use 6550s and KT88s no problem(and really shouldn't get MORE valves) but I would like to know how to be able to tell.
All answers much appreciated.
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Post by John on Jul 7, 2014 19:47:44 GMT
I think you right but hopefully someone like Nick (Lurcher) be along to give you a better response
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Post by lurcher on Jul 7, 2014 20:26:52 GMT
Well, the biggest question is can the heater supply handle the extra current.
KT88 - 1.6A per valve
KT120 - 1.7A to 1.95A (not sure why there is such a range)
But worst case thats an extra 20%, without knowing the mains transformer spec its anyone’s guess if it will be happy with that extra load.
The second part is will it draw more current through the output transformer. The transformer itself should be ok, and without increasing the B+ voltage you probably wont get much of a difference. If its self bias it should settle at about the same point, if its fixed bias, you can bias them to give the same current. Again, the amp may handle more current, but without knowing the internal spec its not easy to say.
So a long winded "depends".
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Post by Chris on Jul 8, 2014 4:17:50 GMT
Cheers!
Plenty valves anyway and as it seems possible to damage equipment I don't think I will bother.
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Post by RFGumby on Jul 13, 2014 4:12:55 GMT
I believe I've only had one situation where I preferred the KT-120 anyway. And they were designed with that tube in mind.
I think I'd avoid trying them unless necessary. Check to see how hot the trannys run with the original tubes, that might give an idea of the amount of headroom required for the added heater and idle currents of the 120's. But still...
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