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Post by Boomzilla on Jan 2, 2023 23:40:26 GMT -5
A question for Mr. KeithL, Mr. audiobill, or others knowledgable in vacuum tube power amplifiers: Keith has posited (and I think, probably VERY accurately) that my Heathkit tube amplifiers sound so dynamic because their distortion rises linearly with their (very meager) output capacity. The increased second-order distortion on peaks makes them SOUND louder (even though they really aren't). The distortion is interpreted by the ear as "loudness," thus providing a built-in "dynamic range expansion." My question is whether this linearly-rising distortion (an unavoidable artifact of my low-powered Heathkits) can be synthesized on demand in a higher-powered tube amplifier by changes in bias? Conventional bias lore is that insufficient bias will cause the sound to be thin while excess bias will make the sound rough and edgy. These choices are helpful, sometimes, in musical instrument amplifiers where the musician wants to customize the tone. But musical instrument amplifiers are normally played at a significantly higher percentage of their wattage output than would be an audio reproduction amp. Obviously, I wouldn't want to reduce or increase tube bias by any significant percentage of the wattage recommended by the manufacturer, but other than increasing or reducing tube life slightly, is there any hazard in doing bias experiments? I ask because I like the sound of the Heathkits, but they have insufficient power to drive my current speakers. My Black Ice Audio F22 has 50WPC, and even if I threw away half the power output with reduced bias, it would still have twice or thrice what the Heathkits put out. Further, the Heathkits can be noisy if not given AC-polarities and audio cables that they like; the Black Ice isn't picky. If bias adjustments won't give me "the Heathkit sound," would adding a 1-ohm resistor inline with the speaker increase second-order distortion or only reduce bass damping? Thanks - Glenn |
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Post by donh50 on Jan 3, 2023 0:19:08 GMT -5
Reducing bias current will almost certainly increase the distortion but also reduce gain and feedback which could lead to instability (bad). Guitar effects boxes can add distortion so perhaps that is a better solution for you? Adding a series resistance will change the frequency response of the speakers but will not add distortion, at least not the type you are after. That said, it is possible the Heathkit has higher output impedance (lower damping factor), and that is changing the response in a pleasing way so adding a resistor is worth a try. Otherwise you may well be liking the overdriven tube response and a "distortion box" may be your best solution. There are simple boxes up to DSP units that emulate (overdriven) tube amps you could try.
HTH - Don
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Post by 405x5 on Jan 3, 2023 10:30:51 GMT -5
“Heathkit”?? I recall some of that gear from my childhood but they are not still around are they??
I DO think you still can pick up a Heath Bar in the candy department or the little bites in a bag?
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Post by Boomzilla on Jan 3, 2023 11:02:04 GMT -5
“Heathkit”?? I recall some of that gear from my childhood but they are not still around are they?? I DO think you still can pick up a Heath Bar in the candy department or the little bites in a bag? Heathkit has not been made in decades. |
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Post by donh50 on Jan 3, 2023 11:04:28 GMT -5
“Heathkit”?? I recall some of that gear from my childhood but they are not still around are they?? I DO think you still can pick up a Heath Bar in the candy department or the little bites in a bag? They are, or were, still around though nothing like "the old days" in terms of their line. They have been reincarnated a few times but never to their former glory AFAIK (I have not kept track). I used to have a bunch of Heathkit gear, mainly Ham stuff, ad also built (or finished  ) a lot of kits for other folk. Someplace in our storage shed I still have a few small pieces, an SWR meter and dummy load, maybe a couple of generators, but I sold most of my stuff many years ago. |
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Post by 405x5 on Jan 3, 2023 11:13:53 GMT -5
What is there a connection to Tandy corporation or RadioShack or is it only the time. I’m thinking about?? I still have several of my RadioShack devices that get used on a fairly regular basis. One is a circuit tester with a plug-in module to any wall outlet and a sending unit and the other is my police scanner that has the weather banned, much more dependable than the Internet national weather service rebroadcast
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Post by donh50 on Jan 3, 2023 11:26:18 GMT -5
What is there a connection to Tandy corporation or RadioShack or is it only the time. I’m thinking about?? I still have several of my RadioShack devices that get used on a fairly regular basis. One is a circuit tester with a plug-in module to any wall outlet and a sending unit and the other is my police scanner that has the weather banned, much more dependable than the Internet national weather service rebroadcast Not that I recall, but that was a long time ago, and none of them are really around anymore (at least anything like they were). There were a few other kit companies around "back then", like Dynaco, Eico, Lafayette, etc. but I don't think any have survived. There are new companies filling the void a bit but they do not have the breadth and such of Heathkit, again IME/IMO. |
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KeithL
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Post by KeithL on Jan 3, 2023 13:46:17 GMT -5
I'm afraid that the answer to that question is not at all simple... and will depend on the design of the specific amplifier involved... Different amplifier designs are affected differently if the bias is non-optimal... And, specifically, if the bias is wrong on output tubes, the result can be very bad... If the bias is too high you could get rather nasty distortion; and, if it's too low, you could burn up the output tubes, or even the power supply. (A lot of the non-linearity on smaller amps may not necessarily occur in the output tubes... which is the only place you're going to be able to adjust the bias.) Also, since on most big amps the output tubes are either pentodes or beam power tubes, they're going to have a sharper and steeper distortion curve. (And, being push-pull, on most amps, when they do start to distort noticeably, you're more likely to end up with more third and higher harmonics too.) If I was looking to deliberately introduce distortion in a power amp I would think about changing the operating point on the INPUT tubes. By adjusting the plate resistors and operating current of the input tubes you can change things like the distortion curve. They're probably triodes, and probably single ended, so you can reduce the gain there, which will also reduce the amount of overall feedback. That should make the overall distortion higher and the onset more gradual. To be quite honest, if I was looking to deliberately add distortion, I would probably put a separate tube buffer before the power amp. That way you can play around with the bias current, operating points, and gains of the tubes in the buffer... without risking damage to the big amp. Start with a nice simple single-stage triode "preamp"... You can then adjust the open loop gain by changing the plate and cathode resistors... Or add attenuation at the output to push it higher into its distortion curve... Or even swap tubes to try different gain characteristics... (A nice simple triode, which can use 12AX7, or 12AU7, or 12AT7, which are equivalent tubes with very different amounts of gain, would be my starting point... ) Many of the low cost ones you see on eBay use a relatively low plate voltage - which is another way to start the distortion curve lower. Just remember that not all tubes will run at really low plate voltages at all. (Remember that we're talking about "a preamp" - so nothing with output transformers.) Here's another interesting thought.... If you REALLY like the sound of those Heathkit amp so much... Then you could simply connect the output of each channel of the Heathkit to a big fat load resistor (maybe 25 watts at 8 Ohms... on a nice big heat sink)... Then use a voltage divider to use part of THAT output to drive a bigger amp (perhaps a nice big solid state amp)... Just pick values so that, when the Heathkit is at its maximum output power, the output of the voltage divider will drive the "main amplifier" to full power... You can even adjust their relative levels so that full output on the Heathkit equates to "pleasant listening level" on the other amp. (Musical instrument amps often use a similar arrangement, with multiple level controls, so you can "overdrive the driver", and such...) Incidentally, as per your last question... Adding a 1 Ohm resistor in series with the output of a solid state amp will give you the DAMPING FACTOR of a typical tube amp. (But it won't affect the distortion significantly otherwise.) A question for Mr. KeithL , Mr. audiobill , or others knowledgable in vacuum tube power amplifiers: Keith has posited (and I think, probably VERY accurately) that my Heathkit tube amplifiers sound so dynamic because their distortion rises linearly with their (very meager) output capacity. The increased second-order distortion on peaks makes them SOUND louder (even though they really aren't). The distortion is interpreted by the ear as "loudness," thus providing a built-in "dynamic range expansion." My question is whether this linearly-rising distortion (an unavoidable artifact of my low-powered Heathkits) can be synthesized on demand in a higher-powered tube amplifier by changes in bias? Conventional bias lore is that insufficient bias will cause the sound to be thin while excess bias will make the sound rough and edgy. These choices are helpful, sometimes, in musical instrument amplifiers where the musician wants to customize the tone. But musical instrument amplifiers are normally played at a significantly higher percentage of their wattage output than would be an audio reproduction amp. Obviously, I wouldn't want to reduce or increase tube bias by any significant percentage of the wattage recommended by the manufacturer, but other than increasing or reducing tube life slightly, is there any hazard in doing bias experiments? I ask because I like the sound of the Heathkits, but they have insufficient power to drive my current speakers. My Black Ice Audio F22 has 50WPC, and even if I threw away half the power output with reduced bias, it would still have twice or thrice what the Heathkits put out. Further, the Heathkits can be noisy if not given AC-polarities and audio cables that they like; the Black Ice isn't picky. If bias adjustments won't give me "the Heathkit sound," would adding a 1-ohm resistor inline with the speaker increase second-order distortion or only reduce bass damping? Thanks - Glenn |
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KeithL
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Post by KeithL on Jan 3, 2023 13:52:08 GMT -5
At one point Tandy Corp owned Radio Shack... (According to Wikipedia Tandy bought Radio Shack in 1963.) Dynaco and Heathkit were the two biggest audio kit companies... Heathkit had LOTS of different products, including audio gear, radio gear, and test equipment kits. ( en.wikipedia.org/wiki/Heathkit ) Eico also made kit versions of their amps (and test equipment too)... Some speaker companies also offered their speakers in kit form. (And Dynaco has been brought back to life... under very new management... and again has tube amp kits...) What is there a connection to Tandy corporation or RadioShack or is it only the time. I’m thinking about?? I still have several of my RadioShack devices that get used on a fairly regular basis. One is a circuit tester with a plug-in module to any wall outlet and a sending unit and the other is my police scanner that has the weather banned, much more dependable than the Internet national weather service rebroadcast Not that I recall, but that was a long time ago, and none of them are really around anymore (at least anything like they were). There were a few other kit companies around "back then", like Dynaco, Eico, Lafayette, etc. but I don't think any have survived. There are new companies filling the void a bit but they do not have the breadth and such of Heathkit, again IME/IMO. |
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Post by audiobill on Jan 3, 2023 15:19:48 GMT -5
Glenn, what are the “small” tubes in your amps? If 12a series, agree with Keith regarding swapping different gain tubes (12au7, 12at7 or 12ax7….. See also en.m.wikipedia.org/wiki/Exciter_(effect)Hate to say it, but most likely little special in those Heathkit output transformers, and as you know the transformer to speaker interface is important with tube amps. Both speakers and transformers are reactive devices. You may even like low powered SET amps, many do despite their limitations. |
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Post by donh50 on Jan 3, 2023 16:31:42 GMT -5
At one point Tandy Corp owned Radio Shack... (According to Wikipedia Tandy bought Radio Shack in 1963.) Dynaco and Heathkit were the two biggest audio kit companies... Heathkit had LOTS of different products, including audio gear, radio gear, and test equipment kits. ( en.wikipedia.org/wiki/Heathkit ) Eico also made kit versions of their amps (and test equipment too)... Some speaker companies also offered their speakers in kit form. (And Dynaco has been brought back to life... under very new management... and again has tube amp kits...) Not that I recall, but that was a long time ago, and none of them are really around anymore (at least anything like they were). There were a few other kit companies around "back then", like Dynaco, Eico, Lafayette, etc. but I don't think any have survived. There are new companies filling the void a bit but they do not have the breadth and such of Heathkit, again IME/IMO. I thought he was asking if there was a connection between Heathkit and Tandy/Radio Shack, I may have misunderstood. RS existed more or less on its own until near the end when Tandy started introducing products under the Tandy name, but by then RS was pretty much in its death throes. Heathkit had no relationship with Tandy/RS AFAIK. I still have unkind thoughts about assembling a Heathkit TV... Not their best product. I had an old Eico 'scope, long gone, but still have an EL34 amp someplace in the black hole "storage" room in the basement. I completely spaced the new Dynaco; brain fart. |
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Post by audiobill on Jan 3, 2023 16:46:52 GMT -5
AFAIK, there are no current makers of components under the Dynaco name. Radial Engineering attempted to sell an overpriced unit several years ago but no longer. A Canadian company.
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Post by donh50 on Jan 3, 2023 16:51:14 GMT -5
AFAIK, there are no current makers of components under the Dynaco name. Radial Engineering attempted to sell an overpriced unit several years ago but no longer. A Canadian company. Ah, you are right, this is the company I had in mind: www.dynakitparts.com/ -- not the same. Hard to believe it's been almost 20 years since David Hafler passed away.  |
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Post by audiobill on Jan 3, 2023 16:54:28 GMT -5
Dynakit Parts, Triode Electronics and VTA/ Tubes4hifi all supply kits and parts, but no components representing “Dynaco”. Radial owns the name now afaik.
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KeithL
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Post by KeithL on Jan 3, 2023 17:07:08 GMT -5
I never did any complete Heathkit products... (I did buy one of their later SQ4 decoder boards and assemble it into a separate box - it was intended as an option for one of their receivers)... Their later TVs had a reputation for being "technically very advanced" - but very difficult to assemble and get to work. (That's a nice way of saying that they supposedly got a really nice picture if you could get them to work.) I did know someone who purchased one of their most modern solid state receiver kits. It was supposed to be really advanced technically... but I don't think he ever managed to assemble it and get it working. (This was all long after their vacuum tube days.) At one point Tandy Corp owned Radio Shack... (According to Wikipedia Tandy bought Radio Shack in 1963.) Dynaco and Heathkit were the two biggest audio kit companies... Heathkit had LOTS of different products, including audio gear, radio gear, and test equipment kits. ( en.wikipedia.org/wiki/Heathkit ) Eico also made kit versions of their amps (and test equipment too)... Some speaker companies also offered their speakers in kit form. (And Dynaco has been brought back to life... under very new management... and again has tube amp kits...) I thought he was asking if there was a connection between Heathkit and Tandy/Radio Shack, I may have misunderstood. RS existed more or less on its own until near the end when Tandy started introducing products under the Tandy name, but by then RS was pretty much in its death throes. Heathkit had no relationship with Tandy/RS AFAIK. I still have unkind thoughts about assembling a Heathkit TV... Not their best product. I had an old Eico 'scope, long gone, but still have an EL34 amp someplace in the black hole "storage" room in the basement. I completely spaced the new Dynaco; brain fart. |
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Post by leonski on Jan 9, 2023 14:08:52 GMT -5
The WIFE of a buddy of mine DID successfully build a Heathkit TV. And it lasted for years.
The FIRST thing you built in the kit? A built-in METER which made the rest of the assembly more.....possible.....
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Post by mgbpuff on Jan 10, 2023 13:37:13 GMT -5
KIts I have built; A Heathkit receiver and speakers (for our local pastor); A Heathkit color tv (was in a big console and lasted 1970 to 1982). A Heathkit cassette recorder. I had Dynaco tubed pre and FM tuner, but I bought them ready built.
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Post by leonski on Jan 10, 2023 20:29:12 GMT -5
Persons HERE and in another forum are big on the VTA amps. Basically, derived and improved versions of the Dynaco Stereo 70....an EL34 amp. they make a 60x2 version and 125 a side MONO amps.....
They make a point of the Stainless chassis, beefy transformers and a good selection of capacitors and 'other' parts.
I've got some of the build directions around here somewhere and THEY look pretty good, too....
Back in the 60s I build a couple Knight Kits......I wish I still had the VTVM which was very nice for its time and I suspect still useful...
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) a lot of kits for other folk. Someplace in our storage shed I still have a few small pieces, an SWR meter and dummy load, maybe a couple of generators, but I sold most of my stuff many years ago.
