6j7 trio de amplifier
By continuing to use the forum you conform your acceptance of these. If you are not happy to accept these you must stop using the forum and delete our cookies from your browser. EF37A as AF pre-amp. This valve was apparently used before the advent of the EF Can anyone point me in the direction of some useful old schematic diagrams? I thought it might have had one of the grids strapped to run as a triode.
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By continuing to use the forum you conform your acceptance of these. If you are not happy to accept these you must stop using the forum and delete our cookies from your browser. EF37A as AF pre-amp. This valve was apparently used before the advent of the EF Can anyone point me in the direction of some useful old schematic diagrams?
I thought it might have had one of the grids strapped to run as a triode. To drive a 6V6, or EL84 if there is not enough gain. Input approx mV, from ceramic cartridge or home made TRF circuit. The EF37A is a nice old valve and works well. Some of the 40's record players used it along with a CL One noteable record player of the time was the Collaro Microgram and the microgram delux, the Amp is nice although the heater supply is odd but works well.
The EF37A will work in starvation mode and used along with a EL33 will make an excellent amp with similar performance to the Mullard I have very sensitive amplifiers in organs that use one or more of the above types, with the EF37A preferred for the front end.
For demanding applications they need to be 'auditioned' for microphony as they do vary but for your mV I suspect all will give good results. One design from uses a KTZ63 triode-connected as a concertina phase-splitter to drive a pair of KT66s. According to my scribble here the loads are 10k with an additional 2. It's driven by another '63 as a voltage amp.
The HT must be about V. This circuit was superseded in a later version by a paraphase using a 6SN7. Flipping over a chassis that happens to be standing next to the desk I see the EF37A first stage has a k anode load and 3. Find More Posts by Lucien Nunes. The amplifier pre-dates the modern preferred values. What uf is the bypass on the cathode? They evolved from the general purpose EF36 specifically for audio use, but in practice they could be used everywhere an EF36 could and replaced it completely.
You would find them everywhere in the 40s - the Colossus computer at Bletchley Park was full of the things, and lots of industrial and lab equipment used them. They continued to be manufactured into the 70s because of the replacement demand from the large installed base of old equipment. Find More Posts by paulsherwin. The bypass is 50uF but that seems to be because every cap is 50uF! I have a stock of these for maintenance purposes and it's funny how just replacing the red valve with a silver one suddenly makes the amp look non-domestic.
Rarely have to replace them though. Or some such factor that made the move to EF37A necessary? Originally Posted by paulsherwin. Last edited by glowinganode; 4th Dec at pm. Reason: faulty link. Yes, typo now corrected Rob. Originally Posted by Lucien Nunes. The EF37 is not a common valve - most people seemed to use the EF37A I guess if you are working at low level, you'd want both low hum and low microphony.
However, there is an EF37 in Gerry Wells's valve store, so it does exist! Originally Posted by Neil Purling. I have two EF37's here, I didn't realise they were unusual! I also have about a dozen EF37A valves as well. I have never had an EF37A fail and it is one of my favourite valves. Location: St. Then there's an ECC35 feeding the 6V6 p-p final stage. Cheers, Pete. Mullard originally envisaged the EF36 being used as a superhet IF amplifier but the development of the variable mu EF39 displaced it from that application.
Originally Posted by Tractorfan. Originally Posted by kalee Apparently it also made a good electrometer valve, although not designed as such - the top cap grid connection gave a really low leakage current figure for super-high impedance circuitry. It maybe worth looking at the posts for the Mullard in the following link as this includes the circuit for the and the earlier one based around an EF40 and EL41 this would be the best design for using the EF37 strapped to run as a triode.
The focus is nearly always on the Power Amplifier and the Preamplifier gets overlooked. Doing these also this gave me chance to get my Adobe Acrobat distiller working properly again as it went west recently!
Lucien: That amplifier you had on the bench What was it's role? I am just wondering what the expected input level would be. When I start construction I will complete the RF stage first and 'scope the audio output to assess the p-p signal strength. I remember from a previous incarnation of the circuit that mV was typical, depending on what valve you used. The way the circuit diagram is drawn and the European valve designations would suggest that it might be Australian and so perhaps not widely know in the UK.
Interesting book that- lots of typos with valve types and mislabelled table columns for resistor and capacitor ratings. The amp I mentioned is from an electric organ - see first picture. It takes signal directly from the electromechanical tone generators typically at a few millivolts. The source impedance is also rather high and totally capacitive, resulting in a rather ticklish input arrangement that will hum or buzz given the slightest opportunity. The whole ground line for the first stage is isolated from the chassis and connected only at the source.
The EF37A does OK, although the overall performance of the amp depends on the particular valve's microphony, especially as it is not resiliently mounted in the chassis. This is actually quite a serious shortcoming, as when not actually playing music, even with good valves you can hear many ambient sounds reproduced from the loudspeaker. Playing the pedals, the rumble of the tone generator mechanics, even kicking one's heels against the bench all get picked up by the two EF37As.
Incidentally those are not mains transformers above the EF37As which would be a disaster they are outputs, unusually large for KT66s due to the requirement for full power all the way down to 16Hz.
In this model the first stage picks up the motor vibration quite nicely, creating a higher level of 50Hz hum than the circuit itself. Again some careful mechanical decoupling should have been a no-brainer. When I get to building my replica multi-generator instrument, I'll have to think carefully about the choice of front ends, whether to stick with the authentic octal bottle or something slinky like the 6BS7 that can be snuggled in a little foam nest inside a tin can right up near the generator output.
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Re: EF37A as AF pre-amp Quote: Originally Posted by kalee20 Apparently it also made a good electrometer valve, although not designed as such - the top cap grid connection gave a really low leakage current figure for super-high impedance circuitry. Posts: Find More Posts by Valvepower.
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RELATED VIDEO: Top 5 Best Amplifiers In 2020 - Vacuum Tube Amplifiers ReviewWelcome, Guest. Please login or register. Home Help Search Login Register. If i understand correctly: you are using a 2-stage amplifier 6SJ7 into a 2A3. You like the sound without the 6SJ7 in the signal path. BUT you need a driver tube otherwise you will never get any decent levels out of the amp.
Hello, Thomas. I was looking for info on the 6J5 tube, and your site did not disappoint. I was always interested in tube technology and have thought about building an amplifier for a stereo hi-fi system for records. Looks like a lot of work, though. Anyway, thanks for your efforts. Hello Thomas, Hi, I have just come across a stash of 7A4 tubes. RCA manual says the same as this tube.
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