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swapping 6SL7 with 6SN7

ke4mcl

ke4mcl

Super Member
Banned
i just resuscitated a western electric hoot and holler box. i think its a 10D model. uses a 6SL7, 25L6, and a 25 something rectifier. the 6SL7 tests kinda flat and i have loads of 6SN7's laying around. from what i read they are very similar tubes. same pinout. 6SL7 has higher gain which i think i can do without. 6SN7 draws 300mA more heater current though. in my app the filaments are in series just like an old AA5 radio. it has a ballast tube to make up the rest.

can i use a 6SN7 in place of a 6SL7 despite the different heater draw?
 
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in a series string, the heater draw has to be matched. Carefull with that amp, it probablt has a hot chassis (connected to the AC line).
 
No, heater current must match. A 12SN7 should be OK, though...

Input and output of this box are isolated by audio transformers. But chassis is connected to the power line by a 50-year-old capacitor - don't operate this with the back removed...
 
kinda looks like im stuck rumaging for a 6SL7. i dont want to get into rewiring the amp anymore than i have to.

as far as safety, im aware its a hot chassis. im used to working on AA5 radios and immediately noted the lack of power transformer. i replaced 2 of the 3 lytics in the unit. the big filter cap is a pain. i brought it up on the variac and its playing ok, just has some distortion on high freq peaks, maybe from the flat 6SL7. the big filter cap will get replaced when i find something suitable.

btw...
anybody got a schematic for this amp?
 
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