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US Navy 803 tubes for home brew audio amp - opinions wanted

Discussion in 'Tube Audio' started by infullview, Nov 5, 2018.

  1. kward

    kward AK Subscriber Subscriber

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    What price point are you trying to achieve? Even if you do a one off conventional amp (say KT88 push pull at 60 watts output), the biggest cost outlays are iron, chassis, and tubes. Just those three items alone will be north of $500, and that's using all off the shelf parts. If you go custom anything, price shoots up significantly from there.
     
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  2. infullview

    infullview Active Member

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    Basic specs can be found here: https://www.radiomuseum.org/tubes/tube_803~3.htm
    I'm not yet a member so I can't download the full spec sheet. This is a power pentode.
     
  3. infullview

    infullview Active Member

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    Yep. Was hoping to adapt these to off the shelf iron, but as you can see from the discussion it's probably not a workable solution.
     
  4. primosounds

    primosounds SE KT120 w/ 6J5G drivers. Subscriber

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    It is a pentode. I think it is the precursor to the 813, which is a beam pentode, but slightly shorter in length, the tubes are kinda close in their requirements.
     
  5. Retrovert

    Retrovert AK Subscriber Subscriber

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    Correct. Here's why, immensely simplified.

    The output transformer in a tube amplifier is a step-down device which converts voltage into current. When the output device is a high-voltage tube (like 2,000 VDC instead of 600 VDC) the turns ration is significantly higher to scale the voltage.

    The low-frequency (bass) frequency response (F1) is controlled by the primary's impedance (a function of wire) and inductance. The higher the primary impedance the greater the number of turns, so the higher the required inductance. L = Z1 / (2Pi x F1).

    The high-frequency response (F2) is controlled by the primary impedance (again wire) (ZT) and parasitic inductance (LP), as this forms a filter. F2 = ZT / (2Pi x LP) But ZT is more than just the sum of the impedance of the primary (Z1) and secondary (Z2), because the secondary impedance (again, a function of wire) must scaled by the square of the turns ratio: ZT = Z1 + (N1 / N2)^2 x Z2)

    Increasing primary inductance requires a high number of turns, but that would increase the impedance so thicker wire must be used, and the core material must also change to a more expensive type, and the laminations must be altered. Reducing the parasitic inductance in a high-turns transformer, furthermore, requires complex interleaving techniques. The parasitic capacitance is also of concern.

    It may not be possible to balance the two goals, even with increased copper thickness, a different core material, a different lamination type, and different winding/layering techniques. Not to neglect linearity across the range, and at the high end and low end.

    The transformer gods giveth and the transformer gods taketh away.

    You, me, and a host of others. We all stand in awe of the cathode, grid, and plate structures, drooling and saying, ooooooh, shiny!

    Then reality sets in and we realize why such tubes only appear in boutique amplifiers costing nearly the price of a nice car.

    The problem, in short, is that anything you build using a stock output transformer will not have the correct output impedance, won't have the load line, and certainly won't deliver the power you stated as a goal. Beyond that, the distortion will be very high. Not to neglect the issue of building a regulated supply running at 2,000 VDC.

    Pretty much. Sorry to be the one to dash cold water all over the transmitting-tube amplifier project. :(

    If it's any consolation before I ruined your project I ruined my own. :(

    The big brand names are expensive, but some of the console pulls will run you a lot less and you can have great results with those. Magnavox made some nice iron, as did Stromberg-Carlson. Neither has the brand-name appeal of McIntosh, Marantz, Fisher, Dynaco, EICO, etc.

    Yeaaaah..... While I do not have direct experience with the Korean kits, I suggest reading the complaints and reviews, which suggest the quality is reportedly quite poor. I would not purchase one of those kits as a result. You can make your own with better quality components.

    Dude!!! Back in the day I used to buy from John Mesha, Jr. by mail order! Do you remember when he was selling the rotating magnetic drum storage units, surplus from aircraft? I still have a few of those catalogs! I bet you also remember PolyPacks!

    As far as a suggestion, try looking at the Pete Millet amplifier projects, as well as the other projects at diyAudio. Lots of easily assembled tube amplifier kits are available, with lots of high-quality tech support at an unbeatable price! (Free!!!)

    See: http://www.pmillett.com/

    Plus diyAudio.com where the boards and detailed commentary and reviews are available.
     
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  6. Retrovert

    Retrovert AK Subscriber Subscriber

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    Output transformers is what really makes or breaks any amplifier.

    It's not the size of your engine (tube), or the mightiness of its cylinders (voltage), it's the transmission (voltage-to-current conversion in the output transformer) which controls how the rubber meets the road.
     

     

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  7. primosounds

    primosounds SE KT120 w/ 6J5G drivers. Subscriber

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    The problem as you are discovering is getting some output trannys . They will be big and they will be expensive since they will be a custom order. Using these large transmitting tubes for audio usually becomes a "statement" amp. And as the name implies a "cost is no object" design. Or at least cost is something that you have already budgeted.
    So, i would put your tubes away, start checking around for someone to wind the output transformers and budget around 300 + for each tranny, and start saving your money to pay for them.
     
    Last edited: Nov 8, 2018
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  8. Retrovert

    Retrovert AK Subscriber Subscriber

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    Yeah, I surely agree with that. The problem with a statement is money talks.

    That may be optimistic. Given some of the pricing I've seen for simpler transformers, I suspect the base price would be twice that the off-the-shelf price, and the premium price would be four times that estimate. Remember these are peculiar core designs, with less common material and interleaved windings.

    Remember, the OP wants Class A which is going to double the cost to avoid saturation, and 50 Watts per Channel requirement which is going to greatly increase the diameter of the windings and thus require some clever winding, and need a high winding ratio because of the voltage. All of that really adds up fact.

    I'd expect a transformer manufacturer at the Lundahl level would charge a Cleveland apiece, certainly a McKinley. I don't know how many other houses could wind such a transformer. Transendar is another one, probably 50% of Lundahl. Hashimoto Onetics is likely in the same price range. I don't know enough about the capabilities of Edcor and Jensen, which are far more affordable (probably 25% of the Lundahl priceing), to make such a transformer with unusual characteristics but my understanding is the offerings of both are conventional steel cores without the interleaved winding, but specialty cores (materials and shape) and windings are available at an extra charge.

    NB: this is not intended to disparage Edcor or Jensen which are high-quality producers at the lower-end of performance; if I needed a replacement OPT for a conventional device I would have it would by one of those two as Lundahl's pricing is stratospherically out of my range.

    But for that high-ratio transformer? I don't know who could reliably fabricate one with the desired characteristics. This is when and why I realized that having a giant glowing transmitting tube was, in my case, just a project driven by aesthetics and not a sound.

    All of this could easily be cleared up with a phone call by the OP to the various vendors.

    The bigger problem is even having built it, if one wanted to sell it the value would likely be below parts cost. Different, of course, if it were a boutique project form a small, typically Japanese, amplifier house.

    Another good approach would be a single-ended Class A using a modern 300B clone. Probably cost less for the transformers, and have good marketability.
     
  9. Selmerdave

    Selmerdave Well-Known Member

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    When you're referring to "class A" do you mean single-ended? I'm not aware of class A push pull having those requirements.
     
  10. infullview

    infullview Active Member

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    Absolutely. You missed out on something special if you never made it to the warehouse. A pack rats dream. All kinds of stuff that was in limited quantity that never got listed. It was a long time ago but he had a lot of old stuff that was army surplus that looked like it was from WW2 or the Korean war. At the time I was restoring antique radios and was more interested in components; he had things like Mil spec high voltage, glass sealed caps. On my last visit there, I picked up a Grundig AM/FM stereo chassis for about $5 that went into many consoles. I shopped Polly packs too. They were both cheap and great for parts.
     
  11. infullview

    infullview Active Member

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    I click on the link and looked through a lot of the designs - he definitely has some interesting and unique ideas as well as fabricated circuit boards to make things easier and cleaner on the build. His ebay stored is closed until after 11/23 so I wasn't able to get pricing. This looks very promising. Thank you.
     

     

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  12. infullview

    infullview Active Member

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    For my original idea, yes, singled ended.
     
  13. Retrovert

    Retrovert AK Subscriber Subscriber

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    Now that is a very good question and one I asked myself when I first discovered Class A push-pull.

    Let me rephrase the question in two pieces:
    (a) When does push-pull Class A turn into Class AB? (Solely in terms of crossover overlap, not in terms of bias or idle current, of course.)
    (b) What happens to the higher-order harmonics as current increases through the transformer?
    The answer is, well, it depends.

    I seem to have prematurely posted this (some inadvertent combination of keyboard clicks) so I'll finish in a separate post.
     
    Last edited: Nov 9, 2018
  14. primosounds

    primosounds SE KT120 w/ 6J5G drivers. Subscriber

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    I have gotten Single ended transformers from Electraprint that are "reasonable" for hand wound one-off. If one is serious about their passion and determined to see a project through then you just do what you need to do. As for me , i don't spend money on a new car or fancy home theatre preferring to spend it on my audio obsession.
     
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  15. infullview

    infullview Active Member

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    I want to thank everyone for their input on my original question. I am still looking at pmilliet.com to see all the different designs available and reviews of same. I also looked at a few kits offered on ebay to see what was reasonable and available. I see a lot of Dauk audio kits and also people on AK that have them. Does anyone have any idea about the quality and efficacy of these kits? They claim class A and seem to be reasonably priced, but none of them go much over 10 watts. Not enough power in my book, but for $200, you could buy two and bridge both channels for a "theoretical" 4x power (ya, I know and that's why it's in quotes). In the mean time, since I'm getting back into tube tech again, I picked up a 1934 Philco 118 cathedral to restore - that should be fun. I'm still a go for some kind of tube amp, but I'm going to do due diligence before I make a move to build. Thanks again for all the comments, you've all been very helpful.
     
  16. Retrovert

    Retrovert AK Subscriber Subscriber

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    I would advise against purchasing any kit with an output transformer because the output is going to be the single most expensive, and the single most important, component and the one component where the kit producer is going to pick a lower-quality component to maximize its profit.

    The kit manufacturer may reduce the cost of the circuit board by using thinner copper. It may reduce the cost of capacitors by using poor quality capacitors, including electrolytics instead of film, or poor quality film instead of better quality film. It may reduce the cost of resistors by using carbon composite or carbon film instead of metal film or wirewound. It may reduce the cost by using lower-quality tubes. But if it wants to save a pile of money the best way to do that is to use a transformer with a lighter core and thinner copper wire.

    You are far, far better off to purchase the components yourself and spend a small amount extra to obtain a superior kit. That's why I suggested the Millett designs. You can pick everything to be wonderful quality and get the best possible sound for about the same cost.

    If you price out a good (second-tier, non-custom) Class A single-ended transformer at that output power level you'll find a pair costs nearly half as much as that kit. That ought to tell you something. You can tell the value of an output transformer by its weight.

    Bridging amplifiers will not yield the power you want. If it did, we'd always bridge Class A and just bridge together smaller transformers. The flux is not shared and the performance is not identical.
     
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  17. Selmerdave

    Selmerdave Well-Known Member

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    I think Pete Millet's designs are generally very highly respected.

    If you're going to go single-ended you're basically looking less than10W. If you need more power than that you should go push-pull, which would give you anywhere between 15 and 60 watts fairly easily, just a matter of what your needs are. If you want >10W single-ended, be prepared for the costs of transformers, output tubes and high-voltage parts as well as the significant dangers of high voltage, which may not be the ideal project to get back into it on.
     
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  18. Retrovert

    Retrovert AK Subscriber Subscriber

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    Very true. This is sound advice.The incremental cost per watt is going to be far higher for Class A SE than anything else. BTW, you also have the option of SET vs. SEP, and I'm soooooo not going in that land of flamewars. But it is something to investigate. If one is going single-ended, the linearity of the output tube also matters, which is why the typical SE tube costs a lot more than a random TV power tube used single-ended.

    To the above advice I would add the suggestion that you spend as much as you can afford on the output transformer, and carefully investigate how the transformer is wound as this will greatly affect your sound quality. The other issue to consider is if you want to use the amplifier with headphones instead of speakers the high and low end may not be as critical and you can save money on the transformer.

    The way I suggest thinking of this is: if you keep the amplifier for twenty years, that's 240 months. Amortizing an extra fifty dollars over that time period works out to be 21 cents per month.
     
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  19. primosounds

    primosounds SE KT120 w/ 6J5G drivers. Subscriber

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    I don't think you should give up on building your own amplifier. I have owned, and still do, many of the classic amps from the golden age, Scott, Harman Kardon, EICO, Fisher, etc, and to me the best sounding of all of them are the custom designed amps where i can make the power supply the way i want. I can use the type of resistors and capacitors that i want, and the circuit and tubes that i want. It is much more satisfying when you can design an amp from top to bottom.
    So perhaps starting with to 803 tubes is not practical now, but i would eagerly await a post about your 803 amp when you can build it.
     
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  20. infullview

    infullview Active Member

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    If I were to go ahead with the 803 project I would have to invest in a lot of test equipment and do some experimentation to discover if they can be run at a much lower voltage and how much that affects the plate resistance; I would need to determine if it's possible to use a stock OPT. I haven't ruled this out I'm just looking at other options and thinking about how deep into the weeds I want to wade. This is a hobby not a job. If it were possible to make a living doing this my attitude might be different. I just got done restoring a pair of vintage Wharfedales. They sound great, but my next impulse is to invest in software, reference mic, and USB ATD to see what the actual frequency response is. After I have this set up, it could also be used to test frequency response and distortion for an audio amp. Honestly, it's been years since I've done electronics work so I feel like I've got to focus on some realistic goals at the moment. It doesn't mean I won't get there, but I'm not going to drive headlong into a project without first having the tools to do it right.
     

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