tube fanatic Posted February 22, 2019 Share Posted February 22, 2019 I haven't posted any simple, relatively inexpensive, flea power amp circuits in a while and have received a number of requests from DIYers who want to build something new to use with their Klipsch speakers. So, here it is! One of the requests was for something using a "less typical" looking output tube and the first one which came to mind is the 6GC5. It was registered by Sylvania in June, 1960 for use in the audio output stage of TVs. Although it is a 9 pin miniature type, its very large globe allows for substantial heat dissipation as may be encountered in a small, closed, TV cabinet. Power output in this circuit is about 1 watt @ 32 Hz which can drive the more efficient Klipsch speakers (especially higher efficiency types like the Heresy, CW, La Scala/Belle, as well as many of the Reference Series) to very loud levels in smaller size rooms. The pinout of the tube also allows the socket to be wired so that a totally different tube can be used if desired, the 6DB5 (a venerable TV type tube from the same era). The latter is more conventional looking and gives the user the opportunity to roll either type as the mood dictates! This build features revamped p/s AC wiring to further increase isolation from the signal circuitry, and an externally adjustable "ear bleed" filter to set the high frequency response to taste. If you haven't experienced a pair of mono amps (as opposed to a stereo amp which shares the p/s rail between both channels) you are in for a treat as crosstalk between the channels is limited to that of the source resulting in a huge sound stage if the recording was done that way. Bottom end response is excellent and should satisfy those who like lots of bass. The midrange and top end approach that of a good SET (at least in my opinion!). The amp runs very cool and can be used all day without getting hot or heating the room. Conservative operating parameters ensure extremely long tube life. I'll post the schematic separately so it doesn't get lost among pictures. Maynard 5 Quote Link to comment Share on other sites More sharing options...
tube fanatic Posted February 22, 2019 Author Share Posted February 22, 2019 THIS AMPLIFIER OPERATES ON VOLTAGES WHICH CAN KILL YOU! DO NOT BUILD THIS CIRCUIT IF YOU ARE NOT EXPERIENCED IN WORKING WITH SUCH VOLTAGES IN A SAFE MANNER!!! 4 1 Quote Link to comment Share on other sites More sharing options...
thebes Posted February 23, 2019 Share Posted February 23, 2019 Looks like another terrific build Maynard. Cost to build should be very reasonable too. I may have to try this one. I have one question. We may have discussed this before but I seem to have forgotten your answer, and that's the type of power supply rectification. I do believe you use solid state rectification in most of your amps. Is this simply a cost factor or do you favor this approach for other reasons? Wait, I remembered another couple of questions. Do you use mostly braided wire or single strand wire in your builds and what brand do you favor? 1 Quote Link to comment Share on other sites More sharing options...
tube fanatic Posted February 23, 2019 Author Share Posted February 23, 2019 Yes, I only use SS diodes for the cost factor. If going with a tube rectifier, it's necessary to use a choke instead of a filter resistor in order to get the ripple down to what I consider acceptable levels since the input filter cap has to be a fairly low value to prevent exceeding the peak current rating of the rectifier tube. So, we're talking about a $15 or $20 choke for each chassis (which would need to be larger to accommodate the choke) instead of some 10 cent resistors as well as the cost of the rectifier tubes and sockets. You can see where I'm going with this. For wire I generally use #22 stranded with plastic insulation for the p/s AC runs, and switch to #22 stranded silvered copper/teflon insulated for the rest. I don't use the latter because I think it sounds better, but rather because it's easier to bend the small lengths used between the terminal strips and controls since the insulation is so much thinner than that of the former. Besides, the insulation of the teflon doesn't "crawl" when heated! As for brand, I usually buy whatever John's Teflon Wire Shop offers on Ebay. The plastic insulated wire is just excess lengths cut off of the Hammond power and output xfmrs! No point in wasting it... Maynard 1 Quote Link to comment Share on other sites More sharing options...
thebes Posted February 24, 2019 Share Posted February 24, 2019 All of the above makes perfect sense to me. I'll have to get some of that teflon coated stuff. I asked the question about the stranded wire because on most old equipment I have they used single solid wire except for the transformers and chokes which came from the factory with stranded wire. Quote Link to comment Share on other sites More sharing options...
thebes Posted February 24, 2019 Share Posted February 24, 2019 Well I just ordered 50 feett in five different colors, for $15 with shipping. Quote Link to comment Share on other sites More sharing options...
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