Well time has come for me to try and build an 807 amp. I have 2indentical power and OPT x-formers, and 4 identical chokes to work for this circuit. They should be a good match for this schematic.
807 Amps
Not entirely sure of the impedence of the opt's but should be 9k-10k, also has a CT'd tertiary winding.....which i'm not entirley sure what for, its seperate from the primary windings. Any thoughts or ideas.
Thanks
Jeremy
807 Amps
Not entirely sure of the impedence of the opt's but should be 9k-10k, also has a CT'd tertiary winding.....which i'm not entirley sure what for, its seperate from the primary windings. Any thoughts or ideas.
Thanks
Jeremy
Both the original Williamson amplifier and the The Musician's Amplifier (your schematic) used OPT's with a 10K primary impedance. The Williamson amplifier in America has a looong history. The original Heath WM-1 is a near direct copy of the Musician's design, and each succeeding amplifier just represented the latest version of the amplifier. Of greatest importance is the need to address stability -- both on the low end and high end. Williamson amplifiers demand very high quality OPTs, and will hardly work with just any transformer lying around. There were numerous stories of "breathing woofers" (low frequency instability), and burned out tweeters (high frequency instability) from poor copies of the design -- and they were all true. It took Heath to reissue their W-3M and W-4M amplifiers as the W-3AM and W-4AM amplifiers to finally produce decently stable amplifiers.
All that being said, the Williamson design has many virtues as well. Triode outputs, low output impedance, wide frequency response, class A operation, and low distortion. With proper attention to stability at both ends of the spectrum, they can be very nice amplifiers in deed. I have my own version of the design using triode EL34s and Heath W-4 output transformers. Both low and high frequency stability is excellent, and the sound is superb through my Cornwalls.
Dave
All that being said, the Williamson design has many virtues as well. Triode outputs, low output impedance, wide frequency response, class A operation, and low distortion. With proper attention to stability at both ends of the spectrum, they can be very nice amplifiers in deed. I have my own version of the design using triode EL34s and Heath W-4 output transformers. Both low and high frequency stability is excellent, and the sound is superb through my Cornwalls.
Dave
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Jeremy,
Either the tertiary winding is for the screen grids or (more likely) it's for cathode feedback. Determine the % of the primary the tertiary winding is and report back.
The linked schematic employs triode wired "finals", in Williamson style circuitry. By today's standards, PSU energy storage is very small. It's quite safe to increase the value of C10 and C11 to 15 μF. C12 should be 40 μF. for good bass performance. C8 and C9 are known as death caps. and they must be eliminated. Build with a proper, safety grounded, 3 wire power cord.
Either the tertiary winding is for the screen grids or (more likely) it's for cathode feedback. Determine the % of the primary the tertiary winding is and report back.
The linked schematic employs triode wired "finals", in Williamson style circuitry. By today's standards, PSU energy storage is very small. It's quite safe to increase the value of C10 and C11 to 15 μF. C12 should be 40 μF. for good bass performance. C8 and C9 are known as death caps. and they must be eliminated. Build with a proper, safety grounded, 3 wire power cord.
For these purposes, you can think of the 807 as a 6L6 with a top cap. The Musician's Amplifier was very popular in the day (807s were dirt cheap) and there were a lot of happy builders. Good, solid design.
Many of the Williamson stability issues were OPT related, many were from the RC coupling time constants being insufficiently staggered. The latter is an easy fix. The former just takes money.
Many of the Williamson stability issues were OPT related, many were from the RC coupling time constants being insufficiently staggered. The latter is an easy fix. The former just takes money.
How do i figure ou the % of the primary the tertiary winding is? How does cathode feedback work? I'm thinking i'll build as is and eliminate the line caps, and use a line filter in thier place and a ground plug, and try using the tertiary windings later after i get all the bugs worked out.
Thanks
Jeremy
Jeremy --
Determine your ultimate goal. If it is to build the original Williamson amplifier, then first determine if your OPT is capable of performing well with that design. You will need the specifications of your transformer to determine that. The requirements of a Williamson transformer are readily available on line. If your transformer is appropriate, the tertiary winding is not needed for that circuit.
If the transformer is not appropriate, and your goal is simply to build an 807 amplifier, then your transformers could still likely perform well, although using tertiary FB within an output stage using a triode connection provides diminished returns since the stage gain is so low. However, a triode design also allows transformers of unknown origin to perform to their best capabilities. Therefore, if your transformers are not appropriate for use in the Williamson design, then use a triode design that favors local feedback (of which tertiary is a form of) and much less global feedback. Stability will be enhanced, and performance will be very good.
To determine the % of of the primary winding that the tertiary winding represents, drive the full primary winding with 100.0 volts AC from a variac (using caution of course), and then measure the voltage of the full tertiary winding. If the tertiary winding produces 50.0 vac in this scenario, then the tertiary winding represents 50% of the turns ratio of the primary winding, meaning that for every volt developed across the primary, .50 vac will be developed at the tertiary winding. Perform this test with no load connected to the transformer, and preferably, out of circuit if the transformer is currently installed in some other application.
Dave
Determine your ultimate goal. If it is to build the original Williamson amplifier, then first determine if your OPT is capable of performing well with that design. You will need the specifications of your transformer to determine that. The requirements of a Williamson transformer are readily available on line. If your transformer is appropriate, the tertiary winding is not needed for that circuit.
If the transformer is not appropriate, and your goal is simply to build an 807 amplifier, then your transformers could still likely perform well, although using tertiary FB within an output stage using a triode connection provides diminished returns since the stage gain is so low. However, a triode design also allows transformers of unknown origin to perform to their best capabilities. Therefore, if your transformers are not appropriate for use in the Williamson design, then use a triode design that favors local feedback (of which tertiary is a form of) and much less global feedback. Stability will be enhanced, and performance will be very good.
To determine the % of of the primary winding that the tertiary winding represents, drive the full primary winding with 100.0 volts AC from a variac (using caution of course), and then measure the voltage of the full tertiary winding. If the tertiary winding produces 50.0 vac in this scenario, then the tertiary winding represents 50% of the turns ratio of the primary winding, meaning that for every volt developed across the primary, .50 vac will be developed at the tertiary winding. Perform this test with no load connected to the transformer, and preferably, out of circuit if the transformer is currently installed in some other application.
Dave
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It seems that Williamson is good choice, I had made few ones and the one with 807 works really fine Williamson amplifier with 807 tubes
Good luck!!!
Good luck!!!
OK and the results are.... 125 volts on the primary. tertiary winding shows 25volts ct would show 12.5-0-12.5, and secondary shows 2.2. Show it would be 5%? Core dimensions 1 1/2H X3 3/16L X 3 3/4 W.
Ultimate goal is just to utilize some of this iron on my shelf. I'm not set on anything, just got a little time to spend... Idea was to use 807's, volt meter and current meter to make an amp that looked like a piece of broadcasting equipment. But i'm all for getting the most out of this iron. Power x-former was somehting like 450 VDC at 200 ma. BUt i'd have to go check that again, and that was using a 5U4 rect. choke look a little small, probly about 5-6 H @ 150-200 ma.
Thanks
Ultimate goal is just to utilize some of this iron on my shelf. I'm not set on anything, just got a little time to spend... Idea was to use 807's, volt meter and current meter to make an amp that looked like a piece of broadcasting equipment. But i'm all for getting the most out of this iron. Power x-former was somehting like 450 VDC at 200 ma. BUt i'd have to go check that again, and that was using a 5U4 rect. choke look a little small, probly about 5-6 H @ 150-200 ma.
Thanks
With 25 vac on the tertiary from 125 vac on the primary, that would provide 20% FB from the tertiary winding. With the numbers you have provided for the secondary, the turns ratio of the primary to secondary is 56.82 : 1. For the primary to represent a 10K load, you would need to load the secondary with a 3.1 ohm load. Is there only one secondary tap available, or were there others you did not measure? Using this transformer with a conventional 8 ohm load would reflect nearly 26K back to the output tubes, although a 4 ohm load would work reasonably well.
Do you know the origin of this OPT? What kind of equipment did it come from (for example, hi fi, or public address)? What tubes were originally used with it? What power output did it provide? Do you have a circuit for what they came out of? Knowing these things can be most helpful in determining its capability. Additionally, do you know for a fact that the tertiary winding is in fact a winding for that was originally used for that type of service? Or (for example) was it a balanced line output of a public address amplifier?
Once you can get beyond determining what basic level of quality the transformers represent and their basic specifications, then it becomes much easier to choose a circuit they would be happy and perform well in.
Dave
Do you know the origin of this OPT? What kind of equipment did it come from (for example, hi fi, or public address)? What tubes were originally used with it? What power output did it provide? Do you have a circuit for what they came out of? Knowing these things can be most helpful in determining its capability. Additionally, do you know for a fact that the tertiary winding is in fact a winding for that was originally used for that type of service? Or (for example) was it a balanced line output of a public address amplifier?
Once you can get beyond determining what basic level of quality the transformers represent and their basic specifications, then it becomes much easier to choose a circuit they would be happy and perform well in.
Dave
For your possible interest.
The 807 Application Report - all you ever wanted to know about using 807.
http://www.retrovox.com.au/STC807.pdf
Cheers,
Ian
The 807 Application Report - all you ever wanted to know about using 807.
http://www.retrovox.com.au/STC807.pdf
Cheers,
Ian
The power x-former seems a bit over kill for this project. Hi-V secondary tests.
515VDC @ 50ma
513VDC @100ma.
Resitors get too hot to leave them on for long, I think this x-former is capable of about 200ma, and about 500 VDC at that current, don't have a resistor/s capable of handling the heat. Perhaps i'll use these on a better suited project.
I do have a Hammond 6.6K p-p with UL taps, as well as some salvaged x-formers from a homebrew x-mitter.
T1
325-0-325 @ 400 ma, is whats wrote on it, and thats what the voltage measures AC with no load.
T2
400-0-400, @ 500ma wrote on it, test 400-0-400 ac no load.
T3 hammond
300-0-300 @200ma
515VDC @ 50ma
513VDC @100ma.
Resitors get too hot to leave them on for long, I think this x-former is capable of about 200ma, and about 500 VDC at that current, don't have a resistor/s capable of handling the heat. Perhaps i'll use these on a better suited project.
I do have a Hammond 6.6K p-p with UL taps, as well as some salvaged x-formers from a homebrew x-mitter.
T1
325-0-325 @ 400 ma, is whats wrote on it, and thats what the voltage measures AC with no load.
T2
400-0-400, @ 500ma wrote on it, test 400-0-400 ac no load.
T3 hammond
300-0-300 @200ma
New Output Transformers?
Hello,
I am considering building a stereo original Williamson amplifier with 12SN7’s and 1625’s. The 1625 is an 807 with a different base and 12 volt heaters.
My question; are current production (new) output transformers made for this amplifier?
Thank you all.
DT
All just for fun!
Hello,
I am considering building a stereo original Williamson amplifier with 12SN7’s and 1625’s. The 1625 is an 807 with a different base and 12 volt heaters.
My question; are current production (new) output transformers made for this amplifier?
Thank you all.
DT
All just for fun!
New Output Transformers?
Hello,
I am considering building a stereo original Williamson amplifier with 12SN7’s and 1625’s. The 1625 is an 807 with a different base and 12 volt heaters.
My question; are current production (new) output transformers made for this amplifier?
Thank you all.
DT
All just for fun!
Hello,
I am considering building a stereo original Williamson amplifier with 12SN7’s and 1625’s. The 1625 is an 807 with a different base and 12 volt heaters.
My question; are current production (new) output transformers made for this amplifier?
Thank you all.
DT
All just for fun!
Hellyeah. You can get Hammonds (I used these myself, but can't say I recommend them anymore as there seems to be quality assurance issues with Hammond lately) or Edcor's (not audiophool expensive, and they are pretty good). Or you could go with Lundahl's (pricey) James (pricey) One Electron (pricey) Magnaquest (pricey). Electraprint is another possibility (more than Edcor's, but better, and not such budget busters).
Lots of OPTs made for 807s & Co.
Hello Miles Power,
Thank you for the heads up!
I have used Edcor transformers before and was happy with how they perform. I went shopping for Williamson output transformers and did not have any likely suspects. They have their standard Push–Pull but none with 10000 ohm output impedance. Do you know of any custom brew transformers they have “designed” and built for other customers? Or any recommendations for selection of Edcor transformers for this application?
DT
All just for fun!
Thank you for the heads up!
I have used Edcor transformers before and was happy with how they perform. I went shopping for Williamson output transformers and did not have any likely suspects. They have their standard Push–Pull but none with 10000 ohm output impedance. Do you know of any custom brew transformers they have “designed” and built for other customers? Or any recommendations for selection of Edcor transformers for this application?
DT
All just for fun!
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