Plate capacitors on Laney outputs

Repairs, trouble shooting, modding and so on.

Plate capacitors on Laney outputs

Postby neikeel » Sat Jun 06, 2015 8:37 am

Maybe should have asked a more philosophical question here than on misc Brits on PP.

Two Laneys one 100w SG the other a 60w LBO. Both late 69/early 70.

The 100 has 0.01uF caps between plates and ground bus:

Image

The 60 had 0.022uF between plates and blob of solder on chassis (i.e. same but less elegant). The 60 had carbon between pin 3 and pin 2 with blown cap (I removed both). Will replace sockets and up the screen resistors to 1k5. and redo heaters.

Image

Any body explain this too be, seems that it would bleed off certain frequencies to ground as a resonance mod but on the plates (why not just put cap in NFB line , much less stressed?)

Allegedly a mod done to Tony Iommis Laneys but how much of that I believe............ :roll:
Neil
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Re: Plate capacitors on Laney outputs

Postby dai h. » Sat Jun 06, 2015 12:03 pm

Park 1210 "Rock Head" shows (2n?--bit hard to read) caps from plate(s) to ground:

Image

seems that it would bleed off certain frequencies to ground


That's what it looks like to me (I suppose you'd want to use high voltage ones here since ACV can be high at plates).

(check out the "smooth cap examples" schematic(maybe this is the idea)--you need to open it or save it to see the right side where the plate is) :

http://el34world.com/Forum/index.php?topic=8579

re: resonance:

(If you mean "resonance" as in low freq boost) I'm not sure if this would do anything as far as that. (My understanding) a LF boost "resonance" mod inhibits lows from being fed back (by using series C in line with feedback small enough to not allow the usual lows to be fed back) thus increasing lows (the "regular" high freq presence works same way by shunting highs to ground before they can reach the PI).
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Re: Plate capacitors on Laney outputs

Postby neikeel » Sun Jun 07, 2015 6:20 am

Thanks Dai, makes more sense now, thanks for the link = a much happier me!
Neil
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