Members SnaxSlingerAns Posted May 22, 2009 Members Share Posted May 22, 2009 So if I'm reading this correctly...I can stick a quad of 6550s in my Cobra, bias it up and Go, without ANY internal modification and teh transformers can handle it, no problem, right? -Ans- Link to comment Share on other sites More sharing options...
Members Eric Hellstyle Posted May 22, 2009 Members Share Posted May 22, 2009 So if I'm reading this correctly...I can stick a quad of 6550s in my Cobra, bias it up and Go, without ANY internal modification and teh transformers can handle it, no problem, right? -Ans- that's what he said you can e-mail them again Link to comment Share on other sites More sharing options...
Members SnaxSlingerAns Posted May 22, 2009 Members Share Posted May 22, 2009 that's what he said you can e-mail them again I tried, the personal addy doesn't work now, but I sent the email to the framus support addy. I'm assuming that even with all the extensive modding you've done, you've not tried this theory out on your Cobra eh? -A- Link to comment Share on other sites More sharing options...
Members TheEsupremacy Posted May 22, 2009 Members Share Posted May 22, 2009 So if I'm reading this correctly...I can stick a quad of 6550s in my Cobra, bias it up and Go, without ANY internal modification and teh transformers can handle it, no problem, right?-Ans- I dunno about this info man...I'd be careful here.Framus/Warwick's support is well...you can read. Link to comment Share on other sites More sharing options...
Members Eric Hellstyle Posted May 22, 2009 Members Share Posted May 22, 2009 I tried, the personal addy doesn't work now, but I sent the email to the framus support addy. I'm assuming that even with all the extensive modding you've done, you've not tried this theory out on your Cobra eh? -A- I started liking el34's actually, I still have the 5 years old stock tubes one pair started to redplate about 8 months ago, so I'm running 50 watt only Link to comment Share on other sites More sharing options...
Members Eric Hellstyle Posted May 22, 2009 Members Share Posted May 22, 2009 so... what issues did you find? still waiting for an answer :poke: Link to comment Share on other sites More sharing options...
Members EdgeOfDarkness Posted May 22, 2009 Members Share Posted May 22, 2009 ummm most 6l6 pins are wired different than el34/kt88 pins are they not ? Link to comment Share on other sites More sharing options...
Members nakedzen Posted May 23, 2009 Members Share Posted May 23, 2009 I asked this from London Power and here's what they answered: If this is a fixed-bias amp with adjustable bias then it is safe to make tube swaps. You should check that the new tube is idling at a safe current for its type. Link to comment Share on other sites More sharing options...
Members knucklefux Posted May 23, 2009 Members Share Posted May 23, 2009 tell ya what...ask framus what the MAX grid to bias resistor value is for a KT88, and then ask them what their grid to bias resistor value is. i'll save you the wait....cobras have 220K? g-b resistors, and the absolute MAX g-b resistor you can use with a KT88 is 100k?. Link to comment Share on other sites More sharing options...
Members nakedzen Posted May 23, 2009 Members Share Posted May 23, 2009 i'll save you the wait....cobras have 220K? g-b resistors, and the absolute MAX g-b resistor you can use with a KT88 is 100k?. What about 6550's? And why is this? Link to comment Share on other sites More sharing options...
Members knucklefux Posted May 23, 2009 Members Share Posted May 23, 2009 What about 6550's? And why is this? i'd have to look at the specs, but i imagine they're pretty similar. as for why, i'm not going into it here because i don't feel like typing that much. that information IS readily available on the web, though. Link to comment Share on other sites More sharing options...
Members Eric Hellstyle Posted May 23, 2009 Members Share Posted May 23, 2009 tell ya what...ask framus what the MAX grid to bias resistor value is for a KT88, and then ask them what their grid to bias resistor value is. i'll save you the wait....cobras have 220K? g-b resistors, and the absolute MAX g-b resistor you can use with a KT88 is 100k?. a lot of old Marshalls had 150k the Ibanez Thermion has 220k the board layout of the Cobra makes this a pretty easy resistor swap, anyway I lost interested on trying this cause I already have a lot of trouble trying to tame the excessive punch of the Cobra I guess 6550's would be overkill... and I don't think my building structure could handle that Link to comment Share on other sites More sharing options...
Members nakedzen Posted May 26, 2009 Members Share Posted May 26, 2009 Not to start an argument here, but here's a second opinion from London Power:The tube manufacturer's spec for grid circuit resistance is 100k for fixed-bias with a 6550. However, most amp manufacturers are not even aware of this spec - unless they read the appendix in our books - and design all their amps with 220k grid-leaks. For most tubes this is fine. If you change to 100k, there will be a slight roll-off of bass. This is often found to be an improvement. If you wish to retain the stock frequency response, bump the coupling caps from the driver tube by a factor of 2.2 to keep the time constant the same. There will also be a slight reduction in gain from the driver tube using 100k grid-leaks for the output tubes instead of 220k. Link to comment Share on other sites More sharing options...
Members nodachi Posted May 26, 2009 Members Share Posted May 26, 2009 so, can i stick my kt77's in the cobra or not? Link to comment Share on other sites More sharing options...
Members nakedzen Posted May 26, 2009 Members Share Posted May 26, 2009 so, can i stick my kt77's in the cobra or not? Of course, they're a direct replacement for EL34's. Link to comment Share on other sites More sharing options...
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