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OTL Asylum OTL, Output Transformerless Amplifier User Group. |
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In Reply to: Re: Gizmological Heresy? posted by DK on December 18, 2000 at 16:55:07:
There is a minor effect where using carefully matched tubes reduces the output impedance slightly, and the output power goes up a little as well.We of course have other issues to worry about- the most important being reliability and ease of use. Here are the issues:
1) The biggest marketing problem any OTL manufacturer has to face is the Futterman/NYAL legacy of poor reliabiliy (plus poor load stability and poor power curves). So it is vitally important that our amps be easy to live with and not go down so as to assure anyone of that reliability. *IF* we shipped matched tubes, and one of them failed in the field, we would not have a good idea of how the tube measured up after it had been in use before failure, so providing a replacement properly matched to the remaining tubes would suddenly be a big challenge.
I should note here that while we do cull miscreant tubes from our shipments, we don't do much to match them. This is because the amp will do what it does without the matched tubes PLUS, the longer the tubes run, the more they tend to drift to a tighter center. This is a phenomena of differential circuits in general. What's happening is the hotter tubes are wearing faster until the cooler tubes catch up. We've measured this in the field: a random selection of tubes wind up being almost identical on a good tester after a year of operation.
2) To assure the customer that our amps are in fact not the reliablilty nightmare of a Futterman amp, we have a one year warranty on tubes. This is the longest tube warranty in the world (save for 'salon' style tubes like the KRs). We do this because we can, What better way to disprove the Futterman legacy (all OTLs are unreliable)?
3) What do you want your tubes to cost? There are 16 tubes in M-60s, 28 in MA-1s...right now, retubing an MA-1 is cheaper then retubing a lot of 300b amps with only one tube per channel! Matched tubes would quadriple the cost without substantial gain over time (see #1). The amp *has* to be easy to live with!
4) And finally as I inferred earlier, if a tube fails in the field (usually the result of shipment- that's the time that most failures occur), shipping a replacement is a breeze. Its also easier for the customer who buys a new set from whatever source- just go ahead and put the tubes in the amp- no muss no fuss,
Again, this is stuff Harvey never listened long enough to find out. Sure, you can get better performance with better matched tubes but there are *two* sections in a 6AS7. If you read Harvey's blather and apply a little logic you see that he is trying to have it both ways in his arguments: on the one hand he is saying that less tubes sounded better, on the other, that the sections inside a single tube are poorly matched. So, with less tubes the amp should get *WORSE* not better (since the descrepencies are exacerbated). The fact is: it is not about matching when the less tubes are used. It is about output impedance and tonal coloration (which might be offseting a coloration elsewhere in the system).
I tried to be honest with Harvey once about this issue- that what he claimed he was hearing was caused by something other then what *he* thought it was- so he wrote a diatribe about how I was like a lover scorned. It seems like he wants to be some sort of god or something and it just not happening for him, so he lashes out at the truth.
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Follow Ups
- Re: Gizmological Heresy? - Ralph 20:55:58 12/19/00 (0)
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