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#1
Posted to rec.audio.tubes
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71A amp
Hi RATs,
I finally got my 71A amp up and running and in a proper chassis. It's a push-pull design with transformer coupled 56s driving the 71As. It has transformer input with a pair of Newcomb microphone transformers. Really nice sound, zero hum in Klipsch Cornwalls. I used, at Al Marcy's suggestion (thanks Al) Blumlein Garters. I found the bass to much improved over a standard bias method. Nine tubes and sixteen transformers for 2 watts/channel :-). I posted a photo on alt.binaries.pictures.radio. I will have a web page up tomorrow. Happy listening! Raymond |
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#2
Posted to rec.audio.tubes
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71A amp
Hey Raymond:
Congratulations! My server won't let me access binaries anymore. Do you think you could email a pic? I'm really happy with my transformer input, interstage coupled 6J5PP 6B4G. Standard cathode bias, though. Bass is decent through my T-Line speakers, but I've downloaded the Blumlein circuit as I admire it's elegance and might put it to use in some other project. Andrew Raymond Koonce wrote in message ... Hi RATs, I finally got my 71A amp up and running and in a proper chassis. It's a push-pull design with transformer coupled 56s driving the 71As. It has transformer input with a pair of Newcomb microphone transformers. Really nice sound, zero hum in Klipsch Cornwalls. I used, at Al Marcy's suggestion (thanks Al) Blumlein Garters. I found the bass to much improved over a standard bias method. Nine tubes and sixteen transformers for 2 watts/channel :-). I posted a photo on alt.binaries.pictures.radio. I will have a web page up tomorrow. Happy listening! Raymond |
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#3
Posted to rec.audio.tubes
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71A amp
I posted a web page with additional photos and commentary. Take a look
at http://www.timebanditaudio.com/71A/71a.html. Best regards, Raymond dre7 wrote: Hey Raymond: Congratulations! My server won't let me access binaries anymore. Do you think you could email a pic? I'm really happy with my transformer input, interstage coupled 6J5PP 6B4G. Standard cathode bias, though. Bass is decent through my T-Line speakers, but I've downloaded the Blumlein circuit as I admire it's elegance and might put it to use in some other project. Andrew Raymond Koonce wrote in message ... Hi RATs, I finally got my 71A amp up and running and in a proper chassis. It's a push-pull design with transformer coupled 56s driving the 71As. It has transformer input with a pair of Newcomb microphone transformers. Really nice sound, zero hum in Klipsch Cornwalls. I used, at Al Marcy's suggestion (thanks Al) Blumlein Garters. I found the bass to much improved over a standard bias method. Nine tubes and sixteen transformers for 2 watts/channel :-). I posted a photo on alt.binaries.pictures.radio. I will have a web page up tomorrow. Happy listening! Raymond |
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#4
Posted to rec.audio.tubes
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71A amp
Raymond Koonce wrote: I posted a web page with additional photos and commentary. Take a look at http://www.timebanditaudio.com/71A/71a.html. Best regards, Raymond Very nice work Raymond. I'd probably go broke if I limited myself to making 2W amps, but then if I only made wooden boats then I'd also go broke. In 2009, much technology which radiates the skill of its maker is only for those who fall asleep when they see a mass made article, like say a fibreglass boat, or a modern house that resembles a plastic chook pen. I cannot understand why bass would be better with Garter biasing though. Effectively each output cathode has a cap to 0V. But there is twice the normal Rk used, so Iadc regulation would be better. Its OK for class A. And if one tube begins to conduct more Iadc than the other as it ages, then its rise in Ek causes half that rise on the other tube's grid, and that raises the Ek and then the Eg of the original tube. I'm not sure sure the Garter is worth the extra heat and B+ lost because you have a higher Ek than normal, but in this case the waste is negligible because its only a 2W amp. The Garter is at least better than having a common Rk and Ck for both cathodes IMHO, although Williamson didn't think so. But then he had some adjust pots to trim his amps dc and ac. These went up in smoke when a KT66 or an 807 decided to slowly die. Leak just used individual Rk and Ck. I like this the best because its simple, and bias change in one tube doesn't change anything very much in the other tube. But because we now have had solid state sinjce 1947, we can use a few devices to make elegant bias management circuits which stop smoke occuring and allow visual monitoring of bias balance condition. Patrick Turner. dre7 wrote: Hey Raymond: Congratulations! My server won't let me access binaries anymore. Do you think you could email a pic? I'm really happy with my transformer input, interstage coupled 6J5PP 6B4G. Standard cathode bias, though. Bass is decent through my T-Line speakers, but I've downloaded the Blumlein circuit as I admire it's elegance and might put it to use in some other project. Andrew Raymond Koonce wrote in message ... Hi RATs, I finally got my 71A amp up and running and in a proper chassis. It's a push-pull design with transformer coupled 56s driving the 71As. It has transformer input with a pair of Newcomb microphone transformers. Really nice sound, zero hum in Klipsch Cornwalls. I used, at Al Marcy's suggestion (thanks Al) Blumlein Garters. I found the bass to much improved over a standard bias method. Nine tubes and sixteen transformers for 2 watts/channel :-). I posted a photo on alt.binaries.pictures.radio. I will have a web page up tomorrow. Happy listening! Raymond |
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#5
Posted to rec.audio.tubes
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71A amp
On May 5, 6:32�am, Patrick Turner wrote:
I cannot understand why bass would be better with Garter biasing though. Hi RATs! The idle current balances at a point halfway between the points each tube would operate at, without garters. This reduces residual current through the halves of the output transformer primary - minimizing magnetic corruption of the core. I try to hear first and understand later  Here is Broski's further musings: http://www.tubecad.com/2009/04/blog0163.htm He doesn't think listening first is worthwhile, neither His firsteffort was modeling on a software testbench. It is a big planet. Garters prolly are worthless against swine flu. Happy Ears! Al PS After a quarter century in the AZ sun, this endless TX cloud cover and thunderstorms are an interesting change. Many of the locals ignore SAD, but us sunspots see their stress. Not a happy bit of knowledge. Thank fate for ears |
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#6
Posted to rec.audio.tubes
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71A amp
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#7
Posted to rec.audio.tubes
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71A amp
On May 5, 2:01*pm, "Staring at old audio chassis as a hobby
 "wrote: It is a big planet. Garters prolly are worthless against swine flu. Heretic! Clown! Troll! Screech! (signed) Lottie Offah-Lotta |
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#8
Posted to rec.audio.tubes
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71A amp
Patrick Turner wrote:
Raymond Koonce wrote: I posted a web page with additional photos and commentary. Take a look at http://www.timebanditaudio.com/71A/71a.html. Best regards, Raymond Very nice work Raymond. I'd probably go broke if I limited myself to making 2W amps, but then if I only made wooden boats then I'd also go broke. In 2009, much technology which radiates the skill of its maker is only for those who fall asleep when they see a mass made article, like say a fibreglass boat, or a modern house that resembles a plastic chook pen. I cannot understand why bass would be better with Garter biasing though. Effectively each output cathode has a cap to 0V. But there is twice the normal Rk used, so Iadc regulation would be better. Its OK for class A. And if one tube begins to conduct more Iadc than the other as it ages, then its rise in Ek causes half that rise on the other tube's grid, and that raises the Ek and then the Eg of the original tube. I'm not sure sure the Garter is worth the extra heat and B+ lost because you have a higher Ek than normal, but in this case the waste is negligible because its only a 2W amp. The Garter is at least better than having a common Rk and Ck for both cathodes IMHO, although Williamson didn't think so. But then he had some adjust pots to trim his amps dc and ac. These went up in smoke when a KT66 or an 807 decided to slowly die. Leak just used individual Rk and Ck. I like this the best because its simple, and bias change in one tube doesn't change anything very much in the other tube. But because we now have had solid state sinjce 1947, we can use a few devices to make elegant bias management circuits which stop smoke occuring and allow visual monitoring of bias balance condition. Patrick Turner. dre7 wrote: Hey Raymond: Congratulations! My server won't let me access binaries anymore. Do you think you could email a pic? I'm really happy with my transformer input, interstage coupled 6J5PP 6B4G. Standard cathode bias, though. Bass is decent through my T-Line speakers, but I've downloaded the Blumlein circuit as I admire it's elegance and might put it to use in some other project. Andrew Raymond Koonce wrote in message ... Hi RATs, I finally got my 71A amp up and running and in a proper chassis. It's a push-pull design with transformer coupled 56s driving the 71As. It has transformer input with a pair of Newcomb microphone transformers. Really nice sound, zero hum in Klipsch Cornwalls. I used, at Al Marcy's suggestion (thanks Al) Blumlein Garters. I found the bass to much improved over a standard bias method. Nine tubes and sixteen transformers for 2 watts/channel :-). I posted a photo on alt.binaries.pictures.radio. I will have a web page up tomorrow. Happy listening! Raymond Thanks Patrick, I build these things because I like to do something with my hands and I love to listen to music. Triodes do it best, IMO. I sure couldn't make any money building these. This one took months of Saturdays to get right (the chassis, not the circuit, it was fairly easy). The small output transformers I used apparently saturate easily with any unbalanced DC. Since 71As are getting like hen's teeth, matched pairs are even harder to find. The Blumlein circuit eliminates the DC offset and prevents the core saturation, allowing the bass response to improve. I like the use of separate filament transformers for each 71A, which allows me to use the CT of each one for the bias network. Your electronic knowledge as a professional is much greater than mine as a hobbyist, so I can't pretend to design these solid state bias circuits. I'm sure they work better than what I've done, but this works for me. Best regards, Raymond |
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#9
Posted to rec.audio.tubes
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71A amp
I build these things because I like to do something with my hands and I love to listen to music. *Triodes do it best, IMO. Yes but if it doesn't do it accurately why bother? Building time intensive but bad things is a waste of time. Build good things. *I sure couldn't make any money building these. *This one took months of Saturdays to get right (the chassis, not the circuit, it was fairly easy). The small output transformers I used apparently saturate easily with any unbalanced DC. * Wouldn't buying a transformer made for a single ended circuit have been much more sensible? It isn't as though they are terrifically expensive. |
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#10
Posted to rec.audio.tubes
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71A amp
That is absolutely beautiful, Raymond. Congratulations! On Sun, 03 May 2009 19:11:19 -0400, Raymond Koonce wrote: Hi RATs, I finally got my 71A amp up and running and in a proper chassis. It's a push-pull design with transformer coupled 56s driving the 71As. It has transformer input with a pair of Newcomb microphone transformers. Really nice sound, zero hum in Klipsch Cornwalls. I used, at Al Marcy's suggestion (thanks Al) Blumlein Garters. I found the bass to much improved over a standard bias method. Nine tubes and sixteen transformers for 2 watts/channel :-). I posted a photo on alt.binaries.pictures.radio. I will have a web page up tomorrow. Happy listening! Raymond -- Jesla Using Opera's revolutionary e-mail client: http://www.opera.com/mail/ |
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#11
Posted to rec.audio.tubes
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71A amp
Thanks Jeff. Take a look at the web page at
http://www.timebanditaudio.com/71A/71a.html. Raymond Jeff wrote: That is absolutely beautiful, Raymond. Congratulations! On Sun, 03 May 2009 19:11:19 -0400, Raymond Koonce wrote: Hi RATs, I finally got my 71A amp up and running and in a proper chassis. It's a push-pull design with transformer coupled 56s driving the 71As. It has transformer input with a pair of Newcomb microphone transformers. Really nice sound, zero hum in Klipsch Cornwalls. I used, at Al Marcy's suggestion (thanks Al) Blumlein Garters. I found the bass to much improved over a standard bias method. Nine tubes and sixteen transformers for 2 watts/channel :-). I posted a photo on alt.binaries.pictures.radio. I will have a web page up tomorrow. Happy listening! Raymond |
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#12
Posted to rec.audio.tubes
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71A amp
Raymond Koonce wrote:
Hi RATs, I finally got my 71A amp up and running and in a proper chassis. It's a push-pull design with transformer coupled 56s driving the 71As. It has transformer input with a pair of Newcomb microphone transformers. Really nice sound, zero hum in Klipsch Cornwalls. I used, at Al Marcy's suggestion (thanks Al) Blumlein Garters. I found the bass to much improved over a standard bias method. Nine tubes and sixteen transformers for 2 watts/channel :-). I posted a photo on alt.binaries.pictures.radio. I will have a web page up tomorrow. Happy listening! Raymond Beautiful job Raymond. I like the copper chassis! Sal |
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#13
Posted to rec.audio.tubes
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71A amp
Sal Brisindi wrote:
Raymond Koonce wrote: Hi RATs, I finally got my 71A amp up and running and in a proper chassis. It's a push-pull design with transformer coupled 56s driving the 71As. It has transformer input with a pair of Newcomb microphone transformers. Really nice sound, zero hum in Klipsch Cornwalls. I used, at Al Marcy's suggestion (thanks Al) Blumlein Garters. I found the bass to much improved over a standard bias method. Nine tubes and sixteen transformers for 2 watts/channel :-). I posted a photo on alt.binaries.pictures.radio. I will have a web page up tomorrow. Happy listening! Raymond Beautiful job Raymond. I like the copper chassis! Sal Thanks Sal. It's a lot of work, but it sure looks nice when it's done. Raymond |
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#14
Posted to rec.audio.tubes
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71A amp
Very niced Raymond! Any idea how your PP 71A amp would sound compared to a
SE 71A amp? Thanks. Gerry "Raymond Koonce" wrote in message ... Hi RATs, I finally got my 71A amp up and running and in a proper chassis. It's a push-pull design with transformer coupled 56s driving the 71As. It has transformer input with a pair of Newcomb microphone transformers. Really nice sound, zero hum in Klipsch Cornwalls. I used, at Al Marcy's suggestion (thanks Al) Blumlein Garters. I found the bass to much improved over a standard bias method. Nine tubes and sixteen transformers for 2 watts/channel :-). I posted a photo on alt.binaries.pictures.radio. I will have a web page up tomorrow. Happy listening! Raymond |
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#15
Posted to rec.audio.tubes
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71A amp
Hi Gerry,
Thanks for the kind words. I've never heard a SE 71A amp, but the output power is only 800mW or so. I'm getting 2 whole watts from a pair. The sound is very good, IMO. Maybe the transformer coupling/splitting? The Blumlein Garter circuit really made a distinct change in the bass response by eliminating any DC offset in the OPT. Best, Raymond GerryE123 wrote: Very niced Raymond! Any idea how your PP 71A amp would sound compared to a SE 71A amp? Thanks. Gerry "Raymond Koonce" wrote in message ... Hi RATs, I finally got my 71A amp up and running and in a proper chassis. It's a push-pull design with transformer coupled 56s driving the 71As. It has transformer input with a pair of Newcomb microphone transformers. Really nice sound, zero hum in Klipsch Cornwalls. I used, at Al Marcy's suggestion (thanks Al) Blumlein Garters. I found the bass to much improved over a standard bias method. Nine tubes and sixteen transformers for 2 watts/channel :-). I posted a photo on alt.binaries.pictures.radio. I will have a web page up tomorrow. Happy listening! Raymond |
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#16
Posted to rec.audio.tubes
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71A amp
On May 4, 12:11*am, Raymond Koonce wrote:
Hi RATs, I finally got my 71A amp up and running and in a proper chassis. *It's a push-pull design with transformer coupled 56s driving the 71As. *It has transformer input with a pair of Newcomb microphone transformers. Really nice sound, zero hum in Klipsch Cornwalls. *I used, at Al Marcy's suggestion (thanks Al) Blumlein Garters. *I found the bass to much improved over a standard bias method. *Nine tubes and sixteen transformers for 2 watts/channel :-). *I posted a photo on alt.binaries.pictures.radio. *I will have a web page up tomorrow. Happy listening! Raymond That's a thing of beauty, Raymond. Congratulations! It must have a very high Dunker Factor (weight/power ratio). Andre Jute Mo' iron is betta iron! |
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#17
Posted to rec.audio.tubes
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71A amp
Andre Jute wrote:
On May 4, 12:11 am, Raymond Koonce wrote: Hi RATs, I finally got my 71A amp up and running and in a proper chassis. It's a push-pull design with transformer coupled 56s driving the 71As. It has transformer input with a pair of Newcomb microphone transformers. Really nice sound, zero hum in Klipsch Cornwalls. I used, at Al Marcy's suggestion (thanks Al) Blumlein Garters. I found the bass to much improved over a standard bias method. Nine tubes and sixteen transformers for 2 watts/channel :-). I posted a photo on alt.binaries.pictures.radio. I will have a web page up tomorrow. Happy listening! Raymond That's a thing of beauty, Raymond. Congratulations! It must have a very high Dunker Factor (weight/power ratio). Andre Jute Mo' iron is betta iron! Hi Andre, Thanks! It was a lot of work getting the chassis built. To me, that's the most challenging part of a project. The wiring is easy. The breadboard that I built this on was made from the cases of old computer power supplies with appropriate holes punched to mount the sockets. I haven't weighed it yet, but I'll estimate 35 pounds, so 4 watts (2 per side) divided into 35 pounds gives a Dunker of 8.75. Not too bad, I get about 6 wpc from my SE 300Bs which weigh in at 60 pounds, a DF of 5 :-) Raymond |
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#18
Posted to rec.audio.tubes
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71A amp
On May 3, 7:11*pm, Raymond Koonce wrote:
Hi RATs, I finally got my 71A amp up and running and in a proper chassis. *It's a push-pull design with transformer coupled 56s driving the 71As. *It has transformer input with a pair of Newcomb microphone transformers. Really nice sound, zero hum in Klipsch Cornwalls. *I used, at Al Marcy's suggestion (thanks Al) Blumlein Garters. *I found the bass to much improved over a standard bias method. *Nine tubes and sixteen transformers for 2 watts/channel :-). *I posted a photo on alt.binaries.pictures.radio. *I will have a web page up tomorrow. Very nicely done - a great deal of effort for those couple of watts, but if ever any speakers deserved such, those would be the Cornwalls. Please see my direct e-mail when you get the time. Thanks! Peter Wieck Melrose Park, PA |
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#19
Posted to rec.audio.tubes
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71A amp
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#20
Posted to rec.audio.tubes
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71A amp
The garter circuit just isn't terribly good. Fixed bias with a good
solid supply is the best, overwhelmingly, asfety relay can be provided if you like. I wonder how this amp measures. Without repeatable measurements I have no opinion on any amp because very terrible amps can " sound good" to some people who like infidelious sound. Especially through Cornwalls, which are a rude speaker in many situations. Proper tweaking of the Cornwall can improve things quite a bit=the Avedon T35 EV tweeter needs to go-but still it's raw. |
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#21
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71A amp
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#22
Posted to rec.audio.tubes
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71A amp
I wonder how this amp measures. Without repeatable measurements I have no opinion on any amp because very terrible amps can " sound good" to some people who like infidelious sound. Especially through Cornwalls, which are a rude speaker in many situations. Proper tweaking of the Cornwall can improve things quite a bit=the Avedon T35 EV tweeter needs to go-but still it's raw. Hi, That amp is very nice looking, especially the night time shot. As for the comment above, measurements and a nickel may make one believe an amp should sound better then another. But, in the real world, many times an amp, which shows up with poor specs in testing, sounds better to the human ear when playing actual music. A case in point is the DHSET amp. Most SET amps, that use minimal or no feedback, have specs that say they should sound less then perfect when compared to push pull amps. But, I have heard and built several SET amps that just plain sound amazing. You need to actually hear an amp before you can judge it. Specifications are not the last word in an amplifier's performance when playing music. Your ears are. I just happen to have a radio with push pull 71A's and transformer coupling. Before I started working with the 2A3 and 300B, I jury-rigged this radio such that I could drive the power amp section with a CD player and a reworked Dynaco PAS2. I attached it to a Mirage 190is and then to an 8" Utah Celestia in a custom made cabinet. This amp sounded quite nice through both of these speakers. It is probably very similar to this 71A amp we are talking about here. I tested the frequency response and it did not show up to be very good (about 70hz to about 8Khz with fast roll off at each end of that spectrum). Still, the amp sounded really good to my ears as well as other people's ears that I let hear it. In fact, a couple people wanted to know if I could build them a stereo version of the radio's power amp. My point is, don't discount any design until you listen to it. This amp obviously took a lot of work and looks very professional. This was a very nice job. Aren't Klipsch speakers great? Man, all you need is a couple of watts and you can fill a room with sound. My 2A3 parallel amps are single ended and deliver around 7 watts a channel. I tried them through a pair of Klipsch speakers and boy were they loud. Bill |
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#23
Posted to rec.audio.tubes
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71A amp
flipper wrote:
On Sun, 03 May 2009 18:11:19 -0500, Raymond Koonce wrote: Hi RATs, I finally got my 71A amp up and running and in a proper chassis. It's a push-pull design with transformer coupled 56s driving the 71As. It has transformer input with a pair of Newcomb microphone transformers. Really nice sound, zero hum in Klipsch Cornwalls. I used, at Al Marcy's suggestion (thanks Al) Blumlein Garters. I found the bass to much improved over a standard bias method. Nine tubes and sixteen transformers for 2 watts/channel :-). I posted a photo on alt.binaries.pictures.radio. I will have a web page up tomorrow. Happy listening! Raymond Gorgeous I'm curious, what technique did you use for the socket blind screw mounting? Thanks, I built the amp on a sub-chassis and mounted it from underneath. You can see more details at http://www.timebanditaudio.com/71A/71a.html. Raymond |
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#24
Posted to rec.audio.tubes
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71A amp
flipper wrote:
On Mon, 04 May 2009 09:10:35 -0500, Raymond Koonce wrote: flipper wrote: On Sun, 03 May 2009 18:11:19 -0500, Raymond Koonce wrote: Hi RATs, I finally got my 71A amp up and running and in a proper chassis. It's a push-pull design with transformer coupled 56s driving the 71As. It has transformer input with a pair of Newcomb microphone transformers. Really nice sound, zero hum in Klipsch Cornwalls. I used, at Al Marcy's suggestion (thanks Al) Blumlein Garters. I found the bass to much improved over a standard bias method. Nine tubes and sixteen transformers for 2 watts/channel :-). I posted a photo on alt.binaries.pictures.radio. I will have a web page up tomorrow. Happy listening! Raymond Gorgeous I'm curious, what technique did you use for the socket blind screw mounting? Thanks, I built the amp on a sub-chassis and mounted it from underneath. You can see more details at http://www.timebanditaudio.com/71A/71a.html. Raymond Thanks. I figured it was likely a sub chassis but the sockets top mounted is what threw me off. I found some pan-head screws which allowed me to mount the sub chassis closer to the external chassis. Raymond |
Hybrid Mode
