jp6l6 Posted March 24, 2010 Share Posted March 24, 2010 The KT66 has higher heater current draws than the 6l6 / 5881 which is from the same family and I'm wondering if the original power transformer of the Blues Custom could feed KT66's. These tubes sound warmer than 6l6's and were used in the legendary Marshall JTM45 Bluesbreaker. I really would like to try this so that if anybody already has a background about the question it would be kind of him (her ???) to share his experience[cool] . Link to comment Share on other sites More sharing options...
carverman Posted March 25, 2010 Share Posted March 25, 2010 The KT66 has higher heater current draws than the 6l6 / 5881 which is from the same family and I'm wondering if the original power transformer of the Blues Custom could feed KT66's. These tubes sound warmer than 6l6's and were used in the legendary Marshall JTM45 Bluesbreaker. I really would like to try this so that if anybody already has a background about the question it would be kind of him (her ???) to share his experience[cool] . I would be cautious with trying those in an amp designed for the 6L6 series. The heater current is 50% greater (1.3 amp vs .9 amp per tube). Thats a extra load of almost an amp on a power transformer 6.3 volt winding. If you can find the specs from Epiphone on the current capacity of the power transformer used, you will be better informed on whether the transformer can still deliver the extra current. Depending on the guage of wire used and current rating of the 6.3 v winding in the power transformer, you may be able to run the KT66 for a very short time as an experiment. it is very possible that a heater voltage drop can occur if the heater winding can't deliver the required current, so the tube will not be able to operate at it's full power potential, because the cathode will run at a much lower temperature. Lower temperature means less electrons being released from the cathode and getting to the plate. However, if you are planning to run the amp for prolonged times..3 to 4 hrs, you should stick to the 6L6GC rather than risk frying the 6.3 winding on the transformer. Link to comment Share on other sites More sharing options...
m-theory Posted March 25, 2010 Share Posted March 25, 2010 The PT might be able to supply the required current for that heater, though that remains to be seen, but the wiring and resistors in line may not be up to the task, and you may well end up smoking something between the PT and the tubes. At the very least, even if you can get them to run without melting something, you'll want to scope the amp to get the bias dialed in properly. Then, of course, you also have the dilema of locating acceptable KT66 tubes to use, which may turn out to be the most difficult part of the entire project. Link to comment Share on other sites More sharing options...
jp6l6 Posted March 26, 2010 Author Share Posted March 26, 2010 To be the most careful about that point, I got a serious discussion with an amp technician from Tube Town today. Following him, the 5A heating current fits good to use KT66. After looking at the schematic, I think there is no bias pot in the BC30. It seems to be an autobias amp. Don't forget it works in class A in the 15W triode setting. Link to comment Share on other sites More sharing options...
carverman Posted March 26, 2010 Share Posted March 26, 2010 To be the most careful about that point' date=' I got a serious discussion with an amp technician from Tube Town today. Following him, the 5A heating current fits good to use KT66.After looking at the schematic, [b']I think there is no bias pot in the BC30. It seems to be an autobias amp. Don't forget it works in class A in the 15W triode setting[/b]. That shouldn't be a problem, if it's cathode biased. As far as heater current..which is an issue with whether the power transformer can sustain delivering the extra current of long periods of time without delivering hot spots on the heater winding, and you still want to go with a KT66, then go with a Tungsol KT66, which has the same heater current as the 6L6 ..then you don't have to worry. Note, that if you have those "bear trap" base retainers on the BC30, these may not work with the larger based KT66, and you may have to remove them. The octal base used on most of the power tubes has sufficient socket/pin retention to keep them from vibrating with the low bass frequencies from the cabinet, and if it's just guitar lows, it shouldn't be too much of a problem. Read the info on the Tungsokl KT66 here.. http://thetubestore.com/kt66reviews.html Link to comment Share on other sites More sharing options...
jp6l6 Posted March 27, 2010 Author Share Posted March 27, 2010 It's not the first time I'd have to remove "bear trap" base retainers. Amps conceptors arent all that clever... I have a Hayden Peacemaker 40W that features four EL84 and when I wanted to fit Mullard tubes into the amp these were really larger than original and TAD tubes so that it was impossible to fit the Mullard tubes and I've been obliged to remove the base retainers... Thank you for infos about Tung Sol tubes. Link to comment Share on other sites More sharing options...
jefrs Posted April 27, 2010 Share Posted April 27, 2010 The octals have their own 5A heater winding in the BC30, there should be plenty of power. Triode or tetrode mode (no, they are not pentodes as stock) it runs in Class AB: it is a push-pull amp, it cannot run in continuous Class A, that's a popular misconception, very misleading. The cathode bias is a compromise since triode and 'pentode' (beam-tetrode) have different requirements. It is cathode self-biased which means it can in theory take any 6V6/6L6/EL34/KT88 etc provided they can take the HT. However it will not automatically output more power just by changing bottles, just power handling capability, you would have to completely re-bias for more current. Grid biasing is possible as the transformer has the tap - see SoCal50 schematic. It is pre-wired with g3 pin1 to cathode so it will take EL34 (a true pentode) without modification. Link to comment Share on other sites More sharing options...
Nailgun Posted February 17, 2011 Share Posted February 17, 2011 Why yes I have. The KT-66's have raised the bar quite a bit, The BC30 now has a much deeper growl and crunch, but still has the chime and bell if you want. The stock 6L6wxt+ just don't have the warmth of the KT-66. Link to comment Share on other sites More sharing options...
jp6l6 Posted February 17, 2011 Author Share Posted February 17, 2011 Since I asked these questions, after reading again the shematics that confirmed there's a heating circuit that may deliver 5A, I made a very simple biasing circuit and use KT66 tubes without any problem. It provides, to me, more interesting tones. At last, I fit new speakers into the amp (Eminence "The Wizard", from the red coat series) to get more sensitivity and it gives enough volume for some scenes. I think I'll also swap the output transformer for a Mercury or a real Marshall. I do it as a game too and foud a four spring reverb for peanuts on ebay, coming from a high end amp Huges & Kettner. Hope you'll excuse my English isn't that good but I'm a native French speaker from Belgium. Link to comment Share on other sites More sharing options...
Nailgun Posted February 17, 2011 Share Posted February 17, 2011 I think the Marshal trans is a haybor (not sure how to spell the name) As for the BC30 the guy that designed it said the trans would handle the KT-66 heater no problem. I think the KT-66 is a good start with tone, I will never cut any caps.. Link to comment Share on other sites More sharing options...
jp6l6 Posted February 18, 2011 Author Share Posted February 18, 2011 I think the Marshal trans is a haybor (not sure how to spell the name) As for the BC30 the guy that designed it said the trans would handle the KT-66 heater no problem. I think the KT-66 is a good start with tone, I will never cut any caps.. Actually I spoke about the output transformer that highly influes the tone but it doesn't concern the point about the heating. Link to comment Share on other sites More sharing options...
wildschwein Posted February 23, 2011 Share Posted February 23, 2011 About 18 months ago I contacted Gibson and asked if you could drop KT66s into the BC-30. The short answer is you can and heater current is no problem. The copy of the email is below: I said: "Hi, I recently purchased a BC30 amp and have seen some comments on online guitar forums that state that the amp's designer (Pyotr Belov) has said it would be okay to use KT66 tubes in the power section. As I am aware that most KT66s draw more heater current than regular 6L6s or 5881 tubes I just thought I'd ask if it is possible to find out if the transformer on the BC30 is up to the task. Kind regards, Canaan Perry." ...and the reply was: "Hello, Yes – the KT66 is interchangeable with the 6L6. Although the output is higher on the KT, the transformer can handle it. I would recommend using KT66-C. Thanks. Best regards, Bob Burns" Of course the KT-66C is a Chinese KT-66 tested and sold by Groove Tubes. So, I guess the recommendation is for a Chinese KT66. Haven't tried it yet myself because I really dig the sound of my Svetlana Reflektor-marketed 6L6GCs. When they're worn out maybe I'll try a set of KT-66 bottles but as noted above you have to add some spring retainers, as the beer traps won't hold them. Link to comment Share on other sites More sharing options...
jp6l6 Posted February 23, 2011 Author Share Posted February 23, 2011 Thanks a lot. When I asked Gibson Europe, they answered they only may give the schematics... This is why I studied the whole amp. Link to comment Share on other sites More sharing options...
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