Pentode Posted December 31, 2008 Share Posted December 31, 2008 Hi Dave, I've got a nice little Ampeg B25 currently running with 6L6GC's - I thought it might be fun to try popping a couple of 6550's in there to see how it sounds.... I'm a bit concerned about the screen voltage being a little high for the 6550 and maybe the heater current a bit heavier on the transformer. Whaddya think? Cheers Grahame Quote Link to comment Share on other sites More sharing options...
DHA Posted January 1, 2009 Share Posted January 1, 2009 [quote name='Pentode' post='367469' date='Dec 31 2008, 10:10 PM']Hi Dave, I've got a nice little Ampeg B25 currently running with 6L6GC's - I thought it might be fun to try popping a couple of 6550's in there to see how it sounds.... I'm a bit concerned about the screen voltage being a little high for the 6550 and maybe the heater current a bit heavier on the transformer. Whaddya think? Cheers Grahame [/quote] Hi Grahame, I will check the figures and get back to you. I would think it should be fine but I would be more interested in the output transformers load impedance, I think they are near each other but best to check. Dave Quote Link to comment Share on other sites More sharing options...
Pentode Posted January 1, 2009 Author Share Posted January 1, 2009 [quote name='DHA' post='367707' date='Jan 1 2009, 01:32 PM']Hi Grahame, I will check the figures and get back to you. I would think it should be fine but I would be more interested in the output transformers load impedance, I think they are near each other but best to check. Dave[/quote] Nice one Dave. Thanks very much BTW I've been using one of your VT1 EQ Bass Drives and I'm [u]very[/u] impressed! Grahame Quote Link to comment Share on other sites More sharing options...
Pentode Posted January 8, 2009 Author Share Posted January 8, 2009 On the other hand we could forget about worrying about screen voltages if we tried KT88's........ Still a question mark over the impedance tho'.... Quote Link to comment Share on other sites More sharing options...
DHA Posted January 9, 2009 Share Posted January 9, 2009 [quote name='Pentode' post='367469' date='Dec 31 2008, 10:10 PM']Hi Dave, I've got a nice little Ampeg B25 currently running with 6L6GC's - I thought it might be fun to try popping a couple of 6550's in there to see how it sounds.... I'm a bit concerned about the screen voltage being a little high for the 6550 and maybe the heater current a bit heavier on the transformer. Whaddya think? Cheers Grahame [/quote] It will vary a little betwwen manufactures but a 6550 has a load resistance of about 4K and a 6L6 about 3K8-6K6 in class AB push-pull so if should be okay on that side of things. a re-bais will be a must. 6L6 heater current is 0.9A - 6550 = 1.6A so unless the amp has an overspec'd heater supply then it's not going to work. A KT88 and 6550 are almost the same thing so KT88's will not help. regards Dave Quote Link to comment Share on other sites More sharing options...
DHA Posted January 9, 2009 Share Posted January 9, 2009 [quote name='Pentode' post='367469' date='Dec 31 2008, 10:10 PM']Hi Dave, I've got a nice little Ampeg B25 currently running with 6L6GC's - I thought it might be fun to try popping a couple of 6550's in there to see how it sounds.... I'm a bit concerned about the screen voltage being a little high for the 6550 and maybe the heater current a bit heavier on the transformer. Whaddya think? Cheers Grahame [/quote] Just remember an old Fender Twin I had in to repair years ago, the owners dad swapped the 6L6s for KT66's - took forever to repair. dave Quote Link to comment Share on other sites More sharing options...
Pentode Posted January 9, 2009 Author Share Posted January 9, 2009 [quote name='DHA' post='375101' date='Jan 9 2009, 01:48 PM']It will vary a little betwwen manufactures but a 6550 has a load resistance of about 4K and a 6L6 about 3K8-6K6 in class AB push-pull so if should be okay on that side of things. a re-bais will be a must. 6L6 heater current is 0.9A - 6550 = 1.6A so unless the amp has an overspec'd heater supply then it's not going to work. A KT88 and 6550 are almost the same thing so KT88's will not help. regards Dave[/quote] Nice one! Thanks very much Dave, much appreciated! Grahame Quote Link to comment Share on other sites More sharing options...
Pentode Posted January 9, 2009 Author Share Posted January 9, 2009 [quote name='DHA' post='375107' date='Jan 9 2009, 01:53 PM']Just remember an old Fender Twin I had in to repair years ago, the owners dad swapped the 6L6s for KT66's - took forever to repair. dave[/quote] Ooooops... So what gave? Quote Link to comment Share on other sites More sharing options...
DHA Posted January 9, 2009 Share Posted January 9, 2009 [quote name='Pentode' post='375112' date='Jan 9 2009, 01:55 PM']Ooooops... So what gave? [/quote] quicker to reply what didn't! burnt out wiring and resistors. Quote Link to comment Share on other sites More sharing options...
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