new (old) amp day
- Thread starter dbw
- Start date
please, oh please tell me he used the big blue Sprague TVA ATOM filter caps... please....
Nice shape!
The KT-66 is whats know as a kinkless tetrode (KT). The "kink" being a weird spike in the performence curve of any higher amperage tubes (power tubes) at the time. That spike would make the tube go critical mass, or in the tube jargon "runaway", on its own, even when the operating environment of the circuit was considered satisfactory. Like drinking from a strychnine laced well, all it took was one wrong low frequency thump and "out go the lights". The problem was due to unexpected secondary electron emission, which, was controlled in the KT tubes by spacing the elements in the tube at very precise points - for the first time, calculated mathematically. This allowed higher performance and reduced secondary emission. Soon after, the beam power tube came along, with its beam forming plates, which also nixed the secondary emission very well. The secondary emission thing is like a sort of internal feedback within the tube, not a good thing, hence once you reach a threshold on that feedback, you cant stop it unless you power down. The tube dies quickly, but quite painfully.
The beam tubes became popular in the USA, the KT type popular in England and Europe. I dont think the US companies copied the British tube design performance, but the Brits, seeing the larger market, designed a line of KT type tubes to "emulate" popular US made beam power tubes. Hence, the KT-66 is a 6L6 wannabee.... with a really cool flavor all its own.
I'm not big on the Chinese Valve Art. Mo betta is the BIG base Russian imported by EH - just check your matching with any KT-66, they tend to run all over the place.
Nice shape!
The KT-66 is whats know as a kinkless tetrode (KT). The "kink" being a weird spike in the performence curve of any higher amperage tubes (power tubes) at the time. That spike would make the tube go critical mass, or in the tube jargon "runaway", on its own, even when the operating environment of the circuit was considered satisfactory. Like drinking from a strychnine laced well, all it took was one wrong low frequency thump and "out go the lights". The problem was due to unexpected secondary electron emission, which, was controlled in the KT tubes by spacing the elements in the tube at very precise points - for the first time, calculated mathematically. This allowed higher performance and reduced secondary emission. Soon after, the beam power tube came along, with its beam forming plates, which also nixed the secondary emission very well. The secondary emission thing is like a sort of internal feedback within the tube, not a good thing, hence once you reach a threshold on that feedback, you cant stop it unless you power down. The tube dies quickly, but quite painfully.
The beam tubes became popular in the USA, the KT type popular in England and Europe. I dont think the US companies copied the British tube design performance, but the Brits, seeing the larger market, designed a line of KT type tubes to "emulate" popular US made beam power tubes. Hence, the KT-66 is a 6L6 wannabee.... with a really cool flavor all its own.
I'm not big on the Chinese Valve Art. Mo betta is the BIG base Russian imported by EH - just check your matching with any KT-66, they tend to run all over the place.
mayfly
Epic Member
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Yep, they are supposed to be reversed. The caps are actually stacked on top of eachother in parallel with a voltage divider to effectively double the voltage rating. That is, we take two caps of value C rated at voltage V, and we make them look like one cap rated at 2V. Sadly, this decreases the capacitance to C/2, but in the late fifties/early sixties you did what you needed to do with the caps you had to work with :icon_thumright:
Return of Guitlouie
Senior Member
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Hey DBW! I have a 66 Bassman head, looks a lot like yours. Ok, no it doesn't, it's beat to hell, but it works and sounds grand. It is actually next on my list of projects. I have recently started talking to a guy here in NC who was a lead designer at Carr amps for ten years. He said that if I trusted him, he would hot rod this thing for me. He has some great ideas, and I'm trying to work out with him just what I'm going to do. I'll try to keep you posted about what we do, and how it works out! Love the Bassman!
Superlizard
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Looking at the pics, that amp's too clean for hotrodding, even with the (necessary) maintenance... looks
great on the outside as well.
You might wanna consider keeping it stock, so you can hold onto it as a player *and* an investment.
Besides, if you need more gain, just stomp on a box. :icon_thumright:
great on the outside as well.
You might wanna consider keeping it stock, so you can hold onto it as a player *and* an investment.
Besides, if you need more gain, just stomp on a box. :icon_thumright:
dbw said:
I disagree, but I may be wrong, I think anything from the 60's is a collectable, people didn't start collecting stuff till the late 80's.
I think you should keep it as is, and if possible, un-mod it, ie....find original caps and parts and make as original as possible,
If you wanna mod something, build from scratch
I'm not going to mod the hell out of it or anything.
I strongly disagree about finding "period" parts or not doing safety mods.
Those old filter caps have a limited lifetime, and most of them have probably failed by now (it's been 44 years)... modern electrolytics will last much longer. More caps will fail over the years as they age, so they'll be replaced with modern caps too.
If the 44-year old death cap fails, my guitar will connected to 120VAC wall power. A 3-prong plug mod makes the amp WAY safer.
The original screen resistor can catch fire. Why keep a "vintage" carbon resistor that's worth less than nothing and can destroy your amp when you can install a 50-cent part that will last forever?
What should I cannibalize a cord from? Maybe I'll just buy an extension cord and cut off one end.
Alfang said:
I strongly disagree about finding "period" parts or not doing safety mods.
Those old filter caps have a limited lifetime, and most of them have probably failed by now (it's been 44 years)... modern electrolytics will last much longer. More caps will fail over the years as they age, so they'll be replaced with modern caps too.
If the 44-year old death cap fails, my guitar will connected to 120VAC wall power. A 3-prong plug mod makes the amp WAY safer.
The original screen resistor can catch fire. Why keep a "vintage" carbon resistor that's worth less than nothing and can destroy your amp when you can install a 50-cent part that will last forever?
What should I cannibalize a cord from? Maybe I'll just buy an extension cord and cut off one end.
Superlizard
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Technically, in the vintage amp world, replacing ancient caps and doing stuff like 3-prong grounded power cord (replacing the death cap) isn't considered modding, but
an accepted necessity.
It's when doofy schmoes do things to vintage amps like cut a hole in the chassis for an extra 12AX7 t00b gain stage or put a Master Volume circuit (complete with hole cut in faceplate)
that are considered mods... and bad ones at that.
an accepted necessity.
It's when doofy schmoes do things to vintage amps like cut a hole in the chassis for an extra 12AX7 t00b gain stage or put a Master Volume circuit (complete with hole cut in faceplate)
that are considered mods... and bad ones at that.
jackthehack
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What did you pay for that?
That's a lot cleaner than similar amps I've seen 20 years ago...
DO NOT fudge WITH TRYING TO MOD THAT!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
That's as perfect an updated Blackface Bassman as probably exists in the world, don't you dare; it doesn't need ANY mods beyond a 3 prong grounded plug for safety....
That's a lot cleaner than similar amps I've seen 20 years ago...
DO NOT fudge WITH TRYING TO MOD THAT!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
That's as perfect an updated Blackface Bassman as probably exists in the world, don't you dare; it doesn't need ANY mods beyond a 3 prong grounded plug for safety....
