January 11, 201610 yr Author go ahead and try other compatible tubes. whats the worst that can happen, fried tubes or blown parts. i have tried kt88, 6550 and 6l6, all end up the same way with G3 toasted.
January 11, 201610 yr i have ordered 4 X 20B-V4 for GG. Does anyone want to buy it ? Maybe a Group buy can get nice price.
January 11, 201610 yr I'd be interested if the price cut's good, though I imagine it'll still be prohibitively expensive. Have you contacted them about it already?
January 12, 201610 yr 10 hours ago, nopants said: I'd be interested if the price cut's good, though I imagine it'll still be prohibitively expensive. Have you contacted them about it already? Yes.if we order at least 10pics,it can be a low price.
January 12, 201610 yr So to expand on Dr. GIlmore's point. With few exceptions, tube amplifiers use output transformers. An audio output transformer with a very high turns ratio is more difficult to design and build, so for output tubes you want a relatively moderate voltage (say 300-550 volts) with relatively high current (say 80-150 mA). That way a moderate turns ratio will supply a reasonable output voltage with adequate current. For a stat headphone amp, on the other hand, you want a high voltage to supply enough voltage swing, but you don't need nearly as much current (10-20 mA is enough). As spritzer has noted, you seldom if ever approach the full voltage swing that a stat amp is capable of - enough to fry the diaphragms in all likelihood. But having that large voltage swing means that at tolerable dB levels, the outputs are staying well away from the voltage limits where device linearity goes to pot.
February 14, 201610 yr Continued the rebuilt. Emission Labs DHT Tubes, EML 20B-V4. To the left is variac. Its purpose is to set the two small transformers to appropriate voltage for the filament.
February 14, 201610 yr 1 hour ago, JoaMat said: Continued the rebuilt. Emission Labs DHT Tubes, EML 20B-V4. To the left is variac. Its purpose is to set the two small transformers to appropriate voltage for the filament. not much O'Hara ...
February 14, 201610 yr You are right. Even when completely dark the tubes can be barely seen. Very disappointing, but the sound is OOOK!!! Maybe I should turn up the variac, it’s only at 67% percent...
February 16, 201610 yr On 2016-02-15 at 1:21 AM, nopants said: any ac hum problems? I can’t hear any AC hum – doesn’t mean that there isn’t any though. The filament transformer gives [email protected] out. In order to reduce voltage for tube heating (5.0V +/-5%) I’ve put wire wound resistors in series with heater. Below shows the small board with terminals and resistors mounted to Kevin’s main board on two stand offs. For info I followed this link and bought some SiTubes filament supplies. They work OK for a quarter of an hour or so than the voltage drops to a few tenths of a volt. After some cooling down they are fit for fight again. I should have red data sheet. Maybe this would do if you really want DC heating. Probably overkill??
February 16, 201610 yr I wonder if we can use thermistor for the job, Lower the inrush current and thus prolong the heater's life. And also add time delay for HV. but but but I don't know how to calculate. Edited February 16, 201610 yr by joehpj
February 16, 201610 yr I’m actually reading the information Emission Labs sent me with the tubes. Regarding filament they say: “The filament voltage must be exactly as specified, under all circumstances. Slow-start filament electronics taking longer than 10 seconds, are not allowed, otherwise this may damage the tubes” “Stand-by mode should not be used with directly heated tubes.
February 17, 201610 yr Here is a Blue Hawaii I built a couple of years ago. Just removed the EL34 (left channel) and put the EML 20B-V4 tall base in place. Held my breath, closed my eyes, pulled the trigger and…. it works
February 17, 201610 yr Life is short. Would T2 accept EML 20B-V4 tall base? Yes, she does! For how long?
February 18, 201610 yr that was what I was planning to ask, seems like the dht is a straight sub for the el34 for most of the designs
February 18, 201610 yr Author don't let any of the idiots over there know about this, the first thing that will happen is that someone will plug the tubes into a bhse directly and destroy $2k in tubes and probably trash the rest of the thing. these dht's have virtually identical curves to 6ca7 in triode mode.
February 18, 201610 yr yeah the price of the tubes is kind of a problem, I wonder how they compare though. hybrid dht sounds too interesting to not try.
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