I bought an old Knight KN-720 amp as a donor to build a new amp from. The amp is a PP 6V6GT design. The picture shows the transformers, basically it is a 620VCT power tranny and two output trannies with 190 ohms between taps.
I am looking for some recommendations/links/schematics for an amp I can build using this iron. No need to reuse any of the original tubes, not even the rectifier. I am not picky about power required as I will build efficient speakers. I am not resistant to silicon and would likely put an SS regulator in no matter what the original design called for. Not afraid of a complex design, as a matter of fact I would probably prefer it. Does not even have to be an integrated amp, I can drive it with this preamp:
http://www.diyaudio.com/forums/showthread.php?postid=601590#post601590
So as you can see, I am wide open to suggestions. I am more looking for a "this amp is a killer" recommendation than "this amp is a good starter" advice. I just don't know enough about tubes & transformers to know what I can build with those output trannies!
I am looking for some recommendations/links/schematics for an amp I can build using this iron. No need to reuse any of the original tubes, not even the rectifier. I am not picky about power required as I will build efficient speakers. I am not resistant to silicon and would likely put an SS regulator in no matter what the original design called for. Not afraid of a complex design, as a matter of fact I would probably prefer it. Does not even have to be an integrated amp, I can drive it with this preamp:
http://www.diyaudio.com/forums/showthread.php?postid=601590#post601590
So as you can see, I am wide open to suggestions. I am more looking for a "this amp is a killer" recommendation than "this amp is a good starter" advice. I just don't know enough about tubes & transformers to know what I can build with those output trannies!
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Just guessing here- this is probably a 8K plate-plate opt (you should verify this!). Besides 6V6, it should work very nicely with 6BQ5/EL84. And there's a TON of designs out there with that tube; I'm building one myself at the moment. Figure a solid 10-12 watts in pentode or UL mode. If you want something a bit more challenging, a pair of 6BL7/6BX7 should give you 10 watts of pure triode.
The Bevois Valley amp in Morgan Jones's "Valve Amplifiers" is a nice, simple, classic design, and has the benefit of a full engineering analysis in the accompanying text.
edit: I see that this tranny doesn't have UL taps, so you'll need to decide between pentode and triode.
The Bevois Valley amp in Morgan Jones's "Valve Amplifiers" is a nice, simple, classic design, and has the benefit of a full engineering analysis in the accompanying text.
edit: I see that this tranny doesn't have UL taps, so you'll need to decide between pentode and triode.
LB,
Those O/P trafos were used with 6V6s and there is no reason to change. However, you could use EL84s.
Surf on over to Audio Asylum (www.audioasylum.com). Search the Tube DIY Forum archives for posts by "Poindexter". Poinz has an elegant triode wired PP 6V6 circuit that's exactly what you need.
On the PSU front, the higher voltage SS rectification yields would give you the headroom you need for regulation. Even though they are costly, use 1200 PIV Silicon Carbide (SiC) Schottky diodes, as they are DEAD QUIET.
Those O/P trafos were used with 6V6s and there is no reason to change. However, you could use EL84s.
Surf on over to Audio Asylum (www.audioasylum.com). Search the Tube DIY Forum archives for posts by "Poindexter". Poinz has an elegant triode wired PP 6V6 circuit that's exactly what you need.
On the PSU front, the higher voltage SS rectification yields would give you the headroom you need for regulation. Even though they are costly, use 1200 PIV Silicon Carbide (SiC) Schottky diodes, as they are DEAD QUIET.
I have a Leak Stereo 20 with an 8K OPT, and by far the best sound I've had from this is using two pairs of 6S4A triodes in push-pull. These are very cheap and plentiful in NOS, and genuine triodes, not triode strapped pentodes, and they're also easy to drive because their amplification factor is around 16 and they're good for 8.5w dissipation. Also the heater requirement is modest - .6amp, and since they run at 20mA in existing EL84 designs, two of them neatly slot in for single EL84s or 6V6s. Plus you get about double the output of a single EL84 in triode. I run them in fixed bias and drive them from a diff pair of 6BK7 (a ECC88 type) with one of Morgan Jones constant current sinks underneath. If you listen to classical music or jazz, the grand piano sound is particularly good and realistic, which is a joy to me since I listen a lot to that. I have a circuit I can email. Andy
Thanks for all your leads.
In reviewing the amps you guys referred to, I noticed that my OPT's are noticeably smaller than those used in the amps you mentioned. Does that impact best tube choice in some way? What I mean is would that steer me towards the EL34 which some say has better bass, in order to offset what is likely weak bass from my OPT's? Or just the opposite: give up on making a fullrange amp and use the 6V6 to make a smoother midrange + tweeter amp?
In reviewing the amps you guys referred to, I noticed that my OPT's are noticeably smaller than those used in the amps you mentioned. Does that impact best tube choice in some way? What I mean is would that steer me towards the EL34 which some say has better bass, in order to offset what is likely weak bass from my OPT's? Or just the opposite: give up on making a fullrange amp and use the 6V6 to make a smoother midrange + tweeter amp?
Andy,
I would be interested in seeing that schematic if you get a chance. My email is dan636@yahoo.com
I've built guitar amps but want to build a good stereo amp soon.
Thanks, Dan
I would be interested in seeing that schematic if you get a chance. My email is dan636@yahoo.com
I've built guitar amps but want to build a good stereo amp soon.
Thanks, Dan
According to the Sams parts list, the output transformers are 8400 Ohms to 4 and 8 Ohms. They are rather small, so that will limit the bass. Triodes will give a little more low end, but transformer saturation will be the real limit.
Build it! But leave room for better transformers if you decide to upgrade later.
Build it! But leave room for better transformers if you decide to upgrade later.
OK, after mulling it over I think I would like to use triode strapped SV83's. I think I will only build the output stage and use my already completed 6922 preamp to drive it. This will leave me a lot of flexibility to try different front ends in the future.
With the huge number of EL34 schematics out there, I thought I would have an easy time finding exactly what I wanted, PP triode strapped, CCS bias. I have not found one like this so far. What's up with that? Is CCS bad for the EL34?
Another question is that I have been told to strap the screen grid to the plate with a resistor. Is the screen grid G2 or G3? Here's the pinout:
With the huge number of EL34 schematics out there, I thought I would have an easy time finding exactly what I wanted, PP triode strapped, CCS bias. I have not found one like this so far. What's up with that? Is CCS bad for the EL34?
Another question is that I have been told to strap the screen grid to the plate with a resistor. Is the screen grid G2 or G3? Here's the pinout:
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