Ooh, love this build, Dave! I'll have to check out those Fisher 400 OPTs I have somewhere to see if they'll play nicely here.
Teaser Pics -- Fisher SA-100 clone in progress
- Thread starter dcgillespie
- Start date
Tink -- Thanks for the kind words. For any of you guys that want to give EFB or EFB II a try, I'm happy to help, and glad there is interest to explore it. It really is an excellent way to operate an output stage -- UL with EFB, or pentode with EFB II -- delivering significant improvements over traditional designs.
To be honest, I have really become quite attached this SA-100 clone -- and for many reasons: It really sounds great with a clear, dynamic, and effortless presentation. It operates the tubes very conservatively (@ ~ 80% plate dissipation under quiescent conditions based on Design Center Ratings). And, because of the mechanical layout and low dissipation levels, the whole amplifier runs very cool overall. Even with continuous 8 and 10 hour operating periods, the amplifier only runs comfortably warm, never achieving the blistering hot levels some amplifiers operate at.
For any who might be interested in duplicating the circuit, there should be plenty of general power transformers available to fit the bill, and the Heath AA-100 OPTs can certainly be had if you look for them -- either from a junker, or as pulls that are being parted out. For this project, they have in deed proven to be every bit the equal of the authentic SA-100 OPTs.
Dave
To be honest, I have really become quite attached this SA-100 clone -- and for many reasons: It really sounds great with a clear, dynamic, and effortless presentation. It operates the tubes very conservatively (@ ~ 80% plate dissipation under quiescent conditions based on Design Center Ratings). And, because of the mechanical layout and low dissipation levels, the whole amplifier runs very cool overall. Even with continuous 8 and 10 hour operating periods, the amplifier only runs comfortably warm, never achieving the blistering hot levels some amplifiers operate at.
For any who might be interested in duplicating the circuit, there should be plenty of general power transformers available to fit the bill, and the Heath AA-100 OPTs can certainly be had if you look for them -- either from a junker, or as pulls that are being parted out. For this project, they have in deed proven to be every bit the equal of the authentic SA-100 OPTs.
Dave
Question for you, Dave. If one wanted to keep the pair of 7247s in the circuit as the driver/phase inverter (say, because this hypothetical person had some nice ones stashed away), would your amp otherwise remain unchanged (wiring and tube pinout changes excepted)?
-D
p.s. And no, I've still had no luck finding a pair of good OPTs, but I'm patient.
-D
p.s. And no, I've still had no luck finding a pair of good OPTs, but I'm patient.
Hi Derek -- you can absolutely use the circuit of my clone directly with 7247s, without any changes -- creating the exact tube layout of course that the original SA-100 has. As we all know though, that is only practical for hypothetical people who have some nice ones stashed away!
For the rest of us mere mortals however, the 12AX7/6FQ7 combo works quite well, with the added benefit that the 6FQ7 sections are somewhat heartier than the 12AU7 section of the 7247 tube is, and therefore should last longer. Also, the inverter section is the hardest working part of the driver circuit, causing that tube section to wear out more quickly than the input section does, so even when the heartier 6FQ7 does need to be replaced, you can replace just it and not the 12AX7 portion. With the 7247 configuration, you end up replacing both sections even if one section (usually the 12AX7 half) is still good.
The bottom line is, that since the 12AX7/6FQ7 combo has both sections within each tube operating at the same effective work level, then both sections tend to wear out at the same rate, which is often not the case with 7247 tubes when used in this type of application.
I am hardly trying to trash the 7247, because it is an excellent tube. But it was also a product born out of an effort to improve design efficiencies for equipment manufacturers, in a day when tubes were a dime a dozen so to speak. Today however, that is not the case, which makes a real case for the 12AX7/6FQ7 combo whether you have some nice 7247s stashed away (hypothetically speaking of course) or not!
I'll keep an eye out for an AA-100 junker for you!
Dave
For the rest of us mere mortals however, the 12AX7/6FQ7 combo works quite well, with the added benefit that the 6FQ7 sections are somewhat heartier than the 12AU7 section of the 7247 tube is, and therefore should last longer. Also, the inverter section is the hardest working part of the driver circuit, causing that tube section to wear out more quickly than the input section does, so even when the heartier 6FQ7 does need to be replaced, you can replace just it and not the 12AX7 portion. With the 7247 configuration, you end up replacing both sections even if one section (usually the 12AX7 half) is still good.
The bottom line is, that since the 12AX7/6FQ7 combo has both sections within each tube operating at the same effective work level, then both sections tend to wear out at the same rate, which is often not the case with 7247 tubes when used in this type of application.
I am hardly trying to trash the 7247, because it is an excellent tube. But it was also a product born out of an effort to improve design efficiencies for equipment manufacturers, in a day when tubes were a dime a dozen so to speak. Today however, that is not the case, which makes a real case for the 12AX7/6FQ7 combo whether you have some nice 7247s stashed away (hypothetically speaking of course) or not!
I'll keep an eye out for an AA-100 junker for you!
Dave
Hi Derek -- you can absolutely use the circuit of my clone directly with 7247s, without any changes -- creating the exact tube layout of course that the original SA-100 has. As we all know though, that is only practical for hypothetical people who have some nice ones stashed away!
For the rest of us mere mortals however, the 12AX7/6FQ7 combo works quite well, with the added benefit that the 6FQ7 sections are somewhat heartier than the 12AU7 section of the 7247 tube is, and therefore should last longer. Also, the inverter section is the hardest working part of the driver circuit, causing that tube section to wear out more quickly than the input section does, so even when the heartier 6FQ7 does need to be replaced, you can replace just it and not the 12AX7 portion. With the 7247 configuration, you end up replacing both sections even if one section (usually the 12AX7 half) is still good.
The bottom line is, that since the 12AX7/6FQ7 combo has both sections within each tube operating at the same effective work level, then both sections tend to wear out at the same rate, which is often not the case with 7247 tubes when used in this type of application.
I am hardly trying to trash the 7247, because it is an excellent tube. But it was also a product born out of an effort to improve design efficiencies for equipment manufacturers, in a day when tubes were a dime a dozen so to speak. Today however, that is not the case, which makes a real case for the 12AX7/6FQ7 combo whether you have some nice 7247s stashed away (hypothetically speaking of course) or not!
I'll keep an eye out for an AA-100 junker for you!
Dave
Hypothetical, of course!
And thanks for keeping an eye out for a junker - I owe you one (well, actually, I owe you at least a wheelbarrow full of one, if not a small U-Haul)!
-D
For any of you that were following the larger picture of this effort, the installation and documentation of performance from the installation of EFB in a fellow AKer's Fisher SA-100 is now complete over on the Fisher forum. With that effort now closed out as well, I hope to be able to get started on my next article on EFB (a Tronola publication) soon, which will be presented in somewhat of a cookbook form.
There are currently 3 different regulators in the EFB family, and between the original Dynaco installation, my clone build, and now installation in the Fisher, all three have been put to good use. You can find the Fisher thread here:
http://www.audiokarma.org/forums/showthread.php?t=476431
Thanks to all who have followed along, and Happy Holidays to everyone!
Dave
There are currently 3 different regulators in the EFB family, and between the original Dynaco installation, my clone build, and now installation in the Fisher, all three have been put to good use. You can find the Fisher thread here:
http://www.audiokarma.org/forums/showthread.php?t=476431
Thanks to all who have followed along, and Happy Holidays to everyone!
Dave
Missing solid state device
I am looking to build a version of Dave G's SA100 clone. I can't find any reference to the solid state device that is mounted on the side wall of his
masterpiece and seems integral to the device. The drawing show 2 devices in the power supply and none in the amp while the pictures show 3...what am I missing?
I am looking to build a version of Dave G's SA100 clone. I can't find any reference to the solid state device that is mounted on the side wall of his
masterpiece and seems integral to the device. The drawing show 2 devices in the power supply and none in the amp while the pictures show 3...what am I missing?
Attachments
jazbo8
Well-Known Member
Thanks for the clarification...that's the EFB (LM337) device. The other picture shows two devices..one is the MOSFET near the pots and the other
in the upper right is not shown on the circuit. The voltage rectifier bridge is also not shown but that is straight forward. What is the device in the upper right hand corner?
in the upper right is not shown on the circuit. The voltage rectifier bridge is also not shown but that is straight forward. What is the device in the upper right hand corner?
Attachments
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Hi Glen -- Good eyes! In the middle pic of the post that Jaz dug up, the bridge rectifier and 3-T regulator up next to the power indicator uh, well, it just got gone. As an idea, it ended up on the cutting room floor, and so never ended up in the final version that the schematic represents. Those components were removed, and hopefully don't appear in any of the other pics.
Thanks for pointing it out and asking about it. That is amp is my daily driver, getting more play time than anything else. It just seems to have the right combination of performance, power, and pure enjoyability. By the way, the reissue Gold Lion tubes I installed in that unit when it was finished are now approaching 1700 hours of use, with all still capable of (on average) > 96% of their original as new power output capability........
Dave
Thanks for pointing it out and asking about it. That is amp is my daily driver, getting more play time than anything else. It just seems to have the right combination of performance, power, and pure enjoyability. By the way, the reissue Gold Lion tubes I installed in that unit when it was finished are now approaching 1700 hours of use, with all still capable of (on average) > 96% of their original as new power output capability........
Dave
Thanks Dave....That explains why its not on the final schematics. I am going to try my hand at building this amp from scratch....except shrink it down to the SA100 size. I want to use it in a console so real estate is limited.
I have a junk Heathkit AA100 and I'm using the output transformers and also the Power Xfmr...its a little different but believe it should work....with the choke its going to be the heaviest amp out there!
Regards,
Glenn
I have a junk Heathkit AA100 and I'm using the output transformers and also the Power Xfmr...its a little different but believe it should work....with the choke its going to be the heaviest amp out there!
Regards,
Glenn
Dave, correct me if I'm wrong, but you were unable to find room for a choke on the 'stock' SA100 just plain due to lack of real estate. Glen, as such, you may want to consider perhaps just a small dimensional 'increase' so as to allow for some additional 'build room'. IIRC, Dave indicated that the SA100 was perhaps the most 'crowded' amp he'd ever worked on. For being such a 'big' performer.....it really is a 'small' package. If need be, I can measure the SA100 I have and provide the original chassis specs. From there, you may want to try to add an inch or two in each direction. If you don't have room for that in your console....then maybe some other options may have to be considered....like a separation between 'amp' and PS? Just a thought. WC
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Thanks WC. The dimensions on the Fisher SA100 are 12.56 x 6.75 x 7.125 inch / 319 x 171 x 181 mm . I have acquired a 13"x7x2" Hammond case to test if I can get close. That's the max length I can do. I am looking at changes to Dave's components to see what I can shrink...for instance I acquired a can cap 50/50/50/50 500v and plan to undermount two other caps that are 33uF 500v to match Dave's design. That cuts out 2 can caps on the top. Fisher mounted 4 pots on the back to save top space and I'm looking at that vs Dave's design. Only concern I have is interference between tubes because my spacing is limited...would like to keep test points and adj pots for output tubes on top. Dave also used a separate ground wiring setup (UL Requirement?) I assume to cut out multiple ground attachments to the case although the case must be grounded at some point but I haven't found that yet. I still have a blank canvas so I'm rearranging components for best fit. Agree that trying to retrofit the Fisher would be a tough task. Doing this as a learning experience and challenge...first effort at building a tube amp. Thanks for the advice.
Glen, you're inspiring me! I may attempt to tag on to your efforts in following. So, hopefully you'll begin a separate 'build-thread', and when you do, please PM me with a link. I'm in process of building my #4 version of Dave's little SE EL84 amp....but I too have a couple of the AA100s here, and I bought them specifically as 'donors' for a project such as this. I was about to tear the OTs off one and put them on to an amp I built out of a Baldwin Organ 'donor'. But, maybe I'll just wait to see how your progress and go from there. Good luck... Tom D.
Hi Tom
I will post pics if I get it to work...layout takes experience like Dave G's but I'll make an amateur attempt and post pics if it works...following Dave's layout as much as I can but as I indicated space is limited so changes have to be made. Thanks to Dave G for his quality posts...they are really an asset to the board and this effort. Thanks
I will post pics if I get it to work...layout takes experience like Dave G's but I'll make an amateur attempt and post pics if it works...following Dave's layout as much as I can but as I indicated space is limited so changes have to be made. Thanks to Dave G for his quality posts...they are really an asset to the board and this effort. Thanks
This is such an amazing project that I still read through it in awe....even over 2 years later. And, at some point I hope to 'emulate' Dave's efforts.....as to 'duplicate' them is simply beyond my capability. But....an incredible build! Talk about integrating the latest cutting edge technology for 'tube' performance while still retaining that 'vintage' tube concept...... If I weren't so adsorbed everywhere else.... including the little SE amps, I'd jump in to this pond with both feet. But, probably best I still hang on the edge, as my 'swimming' skills are still being developed!! WC
rockdoc
Active Member
Dave,
I have two SA-100 amps; one in good shape, waiting to be restored. The other in tough shape, with a thin layer of rusty corrosion inside the chassis. I'm considering using the OPTs from the rough one to do a clone, to get out of this chassis. Or, should I get an AA-100 for those OPTs? Are they better? Has anyone done a clone using the Fisher trannies?
Thanks for these fascinating threads!
Steve
I have two SA-100 amps; one in good shape, waiting to be restored. The other in tough shape, with a thin layer of rusty corrosion inside the chassis. I'm considering using the OPTs from the rough one to do a clone, to get out of this chassis. Or, should I get an AA-100 for those OPTs? Are they better? Has anyone done a clone using the Fisher trannies?
Thanks for these fascinating threads!
Steve
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rockdoc
Active Member
Hi Steve,
Here is the link to Dave's project build:
http://www.audiokarma.org/forums/showthread.php?t=665735
Also, for what it's worth, here are links to the 5 versions that I built, starting with the latest version first:
http://www.audiokarma.org/forums/showthread.php?t=674944
http://www.audiokarma.org/forums/showthread.php?t=673825
http://www.audiokarma.org/forums/showthread.php?t=670448
http://www.audiokarma.org/forums/showthread.php?t=669302
http://www.audiokarma.org/forums/showthread.php?t=667852
I don't know how you feel about retaining the 'originality' of Dave's build by doing it on the actual Magnavox 8600 chassis, and if that's important to you, then by all means have at it. However, I'd just mention that all 5 of my builds thus far have been either on chassis of 'other' manufacturer's SE Console amps.....or as in #3 and #5, they were both on 'new' chassis. I'm about to embark on #6 and #7, and I think both will be built on 'new' chassis' as well. However where I used the 8" X 12" for the first two, I think I can carve that down to a 6" X 10" in these last 2 builds, mostly owing to the fact that I'm going to use the AES OTs in both of them. I do have an 'original' 8600, and not sure yet if I'll just keep it 'as is'..... or convert it. However, while I greatly respect those who do the conversions on the OE chassis, I have to say that I think having the extra room in a replacement chassis is a real benefit.
Dave did the EFB mod on my SA-100, and one of his 'concerns' was the real estate limitations in the original chassis. Due to that limitation, there was just no way that he could include the addition of a 'choke' in the power supply...which was part of what he did in his 'clone'. So, I kind of took my que from that, and after reading his original thread on this 8600 project, and looking at the shoe horning that was done in squeezing in the additional parts, I decided to save that project for last on my end, as I'm just not all that good at that kind of detail work........ yet!! I'm getting better, as noted by the fact that my last 'build' looks pretty good as compared to the other 4.
Anyway....... good luck with your SA-100 clone! I have a couple AA-100s, one of which I plan to use as a 'donor' for an SA-100 clone myself. One question that I'd planned to ask Dave (and maybe he'll read it here) is: Would the PT in the AA-100 make a suitable PT for an SA-100 clone as well...... or is it necessary to find something else due to inappropriate HV levels in the secondary of the AA-100 PT? Right now, I see that PT as being one of my limitations in getting started on that project.
Take care, WC
Here is the link to Dave's project build:
http://www.audiokarma.org/forums/showthread.php?t=665735
Also, for what it's worth, here are links to the 5 versions that I built, starting with the latest version first:
http://www.audiokarma.org/forums/showthread.php?t=674944
http://www.audiokarma.org/forums/showthread.php?t=673825
http://www.audiokarma.org/forums/showthread.php?t=670448
http://www.audiokarma.org/forums/showthread.php?t=669302
http://www.audiokarma.org/forums/showthread.php?t=667852
I don't know how you feel about retaining the 'originality' of Dave's build by doing it on the actual Magnavox 8600 chassis, and if that's important to you, then by all means have at it. However, I'd just mention that all 5 of my builds thus far have been either on chassis of 'other' manufacturer's SE Console amps.....or as in #3 and #5, they were both on 'new' chassis. I'm about to embark on #6 and #7, and I think both will be built on 'new' chassis' as well. However where I used the 8" X 12" for the first two, I think I can carve that down to a 6" X 10" in these last 2 builds, mostly owing to the fact that I'm going to use the AES OTs in both of them. I do have an 'original' 8600, and not sure yet if I'll just keep it 'as is'..... or convert it. However, while I greatly respect those who do the conversions on the OE chassis, I have to say that I think having the extra room in a replacement chassis is a real benefit.
Dave did the EFB mod on my SA-100, and one of his 'concerns' was the real estate limitations in the original chassis. Due to that limitation, there was just no way that he could include the addition of a 'choke' in the power supply...which was part of what he did in his 'clone'. So, I kind of took my que from that, and after reading his original thread on this 8600 project, and looking at the shoe horning that was done in squeezing in the additional parts, I decided to save that project for last on my end, as I'm just not all that good at that kind of detail work........ yet!! I'm getting better, as noted by the fact that my last 'build' looks pretty good as compared to the other 4.
Anyway....... good luck with your SA-100 clone! I have a couple AA-100s, one of which I plan to use as a 'donor' for an SA-100 clone myself. One question that I'd planned to ask Dave (and maybe he'll read it here) is: Would the PT in the AA-100 make a suitable PT for an SA-100 clone as well...... or is it necessary to find something else due to inappropriate HV levels in the secondary of the AA-100 PT? Right now, I see that PT as being one of my limitations in getting started on that project.
Take care, WC