Qb5 1750 amplifier kits
Site Management Clement Perry. Ad Designer: Martin Perry. I later read through the product review and responses listed in the Audiogon Forum that was referenced in the enclosed link contained within the advertisement. The Audiogon Forum response on this contact enhancer seemed different. What started as a small thread became one of the largest threads with the most views on Audiogon.
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These pages represents an ongoing process. Comments are always welcome and if you have a favorite amplifier you would like to share with us, please write to me at: amplifiers at gmail. If you happen to have some pictures of the amplifiers in this compendia, please do not hesitate to contact me. The pictures will be accredited in your name. It is impossible to get around Mr. Futterman in an analysis of the history of audio amplifiers.
I fully understand why the thought of getting rid of the large and expensive output transformer emerged. The famous and best known amplifiers by Futterman were based upon pentodes as output tubes. The circuit above is actually another Williamson.
But from a AC point of view they are in parallel — and that is the trick. The exact opposite operation. But even this is very far from the 16 Ohm speaker load, hence Futterman added further output tubes.
Some k Ohms — three of these in parallel makes about k Ohm and again parallel with the other stack some 1 to 1,5k Ohms. There is still a loong way down to a regular speaker Ohms load and this is where the OTL designers plays their final card; lots and lots of global negative feedback and we now understand why Futterman wanted all that gain to begin with.
The cathode of the lower tubes are grounded, hence fixed. But the cathode of the upper tube are riding on top of the plate at the lower tube. This means that upper drive should ad the AC swing of the lower tube in order to be balanced. In reality the lower tube works fine, but the upper produced the weirdest possible distortion signature — lots of constantly changing very high upper harmonics.
Futterman partly solved it with the use of two HV supplies. The open loop distortion of single end PP amplifiers are dramatic, due to the just as dramatic unbalanced drive. Feedback is not a choice, tons of fb are mandatory. It is ironic that the unbalanced drive could have been solved by a two secondary winding transformer.
But I guess that this would have ruined the concept OTL. The Futterman designs are crazy difficult to adjust and no one, besides Futterman himself apparently learned to do the job. The final adjustments were carried out with the help of friends or the actual customer, as Julius Futterman himself had a hearing issue. In case of service or change of tubes, the customer had to sent the amplifier back to Futterman himself. But rumours has it that Futterman constantly changed the circuits — small, but significant details in the design.
Due to this and the difficulties in adjustment, hence stability, these companies cancelled the production. It have to be mentioned, that the amplifiers that were build by Julius himself , according to the saying are very reliable and stable.
Futterman was on a constant look for tubes better suitable for OTL. He changed output tubes every so often. The original designs of Futterman were all class B. Due to the excessive global feedback they acted as Voltage output sources, just like solid state amplifiers and op-amps. This meant that the available power depended highly upon the impedance of the speakers. From 16 Ohm and up, they do 4 times better and so on. The perfect match to the Futterman designs are electrostatic speakers, I am told.
OTL is a dead end in my opinion. Do as Futterman always dreamt of. I would personally prefer a genuine tube amplifier, but that is an endless and uninteresting discussion without winners or losers. The Futterman, Philips etc. These circuits are notoriously asymmetric and the open loop distortion are extreme. Perhaps the best solution are inverted power grid applications.
See Stephie Bench. Despite all this, I am a dedicated fan of Julius Futterman. I love his circuits and insisting design. I like the way he dealt with his passion and customers. Tremendous imagination and excellent ingenuity. But after all, the end goal was audio, not clever engineering. And OTL amplifiers are a difficult specimen. Would good and poor at the same time be a suitable phrase? The more iron the better.
Julius — you meant well and you did GOOD…. Unfortunately I do no longer remember if it is an original design by Futterman or one of the countless Futterman based versions from my hand — or if it is indeed a Futterman version I have copied from someone else? If you have info about this, please do not hesitate to contact me.
The 16 Watts specification are rather optimistic, despite the 16 Ohms load. Never the less, it is a Futterman design and it looks nice. This British made PA amplifier is a beauty and school example of good build quality. In the schematic above I have stripped the amplifier of the entire preamplifier section and all garniture. That is a little sad, as it is such a good looking amplifier.
Well — nothing is ever perfect. An easy modification for lower gain would be to triode couple the EF86 valve. It might also be worth to fiddle a little with the feedback resistor and possible to decrease the fb? Note the use of two smoothing chokes. The smoothing capacitors are quite small and it would be no problem to double these with modern capacitors. The separate fb winding insures the amplifier against instability in case of capacitive loading.
Parmeco are still in business today and still makes transformers and other electromagnetic components. In the company split in to two and changed the name to Parmeco. It is interesting that while most American HiFi companies based their designs upon the Williamson circuit, most British HiFi companies stock to the well known Mullard design.
The Tannoy here is an exception to that rule and indeed a very well designed one. Boy — yes, we need some Klangfilm here. I have cleaned the typical mess of wires, that German designers seemed to love back then. Every damn piece of wire would be drawn at the diagram I can not read the values of the components, but the design comes through well enough, I think.
Klangfilm made a lot of fancy designs. Caps and plate Voltage at the socket shield! Schou, Jensen, Radiometer and a few others…. Collected they may pass as the Danish Western Electric…Huh.? Right then, back to business….. If you happen to have such a in your possession you better mod that amp to something like — say.. ECC83 as phase splitter as well as driver..? Plenty of free windings at the main trannie.
Siemens made good quality iron, all worth the effort. This Klangfilm one might very well end up as your top amp. This group of amplifiers was referred to as the EL series. The Power Amplifiers of the EL64 00 series were all class B service at anode voltages close to max ratings. EL is a typical example of such amplifier. It is a class B power amplifier rated at Watts and it runs at about Volts. The weight of this monster is kg. Despite all of this, the EL was only a micro dwarf from the EL series.
The largest power amplifier in this exotic family, was a kW giant mammute monster. The EL is a simple and very efficient circuit. It is all balanced Differential even the feedback loop.
The input signal is taken to the input transformer, The input transformer may be connected as a SE input or balanced input. The ratio is with a centre tap for phase splitting. This means that the full signal is maintained to each grid of the E80CC. In other words if a mV RMS input signal is applied to the entire windings of the input transformer it will transform this to 2 00mV RMS at the secondary winding. The cathode resistors has not been decoupled, hence local feedback is established.
Local fb is usually a good thing, from a sonic point of view as it improves the linearity. It comes, however, at the price of higher internal impedance of the device and lower gain.
In this case it is a good deal, and after all, we cant decouple the cathode resistor entirely as we want the overall feedback to be connected here.
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100 Amplifiers – Part 3 , 1955 – 59
QRZ Forums. Homebrew linear using C tetrodes? Hi , I've almost achievd my first RF linear amp using a pair of C. Why using this tube? I have more than 24 left NOS or in a good shape I wanted the exercise to be cheap , using lots of unusued parts from shack microwave oven xformers and so on Anyway, it's working!
Bristol Sound & Vision Show 2011
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Homebrew linear using 715C tetrodes ?
It is only 11" wide, 4" high, and 9" deep. The amplifier features fast warm up and Watt RF output with Watts of drive. The unit is considerably over designed as can be seen in the pictures documenting the construction [ Hits: Votes: 11 Rating: 6. Settings can be made on a 7-inch touch screen, and on this screen you can see a lot of useful information during operation, such as output power, temperature, SWR, and so on. The amplifier also contains several types of protection functions like too high current, too high swr, too high temperature, etc. This, very compact, dual version will deliver about watts output.
Wzmacniacze lampowe i inspiracje
Order by:. Available to:. Tesla Coil. Produced s by Ryasan Tube Factory. All tubes are new. Carbidized,direct heating, Application field, power amplification up to 50 MHz, Brief application, amplification.
Linear Amplifier 2 x QB5/1750 3200 W OUT
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These pages represents an ongoing process. Comments are always welcome and if you have a favorite amplifier you would like to share with us, please write to me at: amplifiers at gmail. If you happen to have some pictures of the amplifiers in this compendia, please do not hesitate to contact me. The pictures will be accredited in your name. It is impossible to get around Mr. Futterman in an analysis of the history of audio amplifiers.
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