Let us look at this from a different angle. You have 3 resistors, R1A, R1B and R2. You should have R1A = R1B, this provides the same current into either transistor or tube. The sum R1A + R1B sets the

Hi Morris, when I repaired my 7904 some years ago I replaced these transistors with BU208A in TO-3 package, with good result. Göran

Hi, yes I agree. I had a similar 7904 problem years ago. In tic mode there was also a hissing sound. The problem was the HV multiplier. Göran

Hi, one shall never place a magnetic circulator on top of an instrument having a CRT. You would get a permanent damage. Göran

Hi, what about using freezing spray? A quick shower on one component at a time. This will tell you, hopefully, where the problem not is. Göran

Hi, U350 is a high frequency ECL circuit. I cannot see any decoupling capacitor placed close to the circuit. This is I believe the cause for the marginal stability. Perhaps a small cap shall be placed

it is a ferrite core which prevents high frequency oscillations, I believe. Göran

Sorry, they dont have them that size. Göran

I´ll do that later this evening. Göran

Try this one: https://www.sifvert-skruv.com/ biggest store in Stockholm. Göran

I assume U4110 pin 3 is at approximately 0V. Connect +1V to pin 2 through a 10k resistor. Pin 6 shall go negative a couple of volts. Change to -1V instead and pin 6 shall go positive several volts. In

Hi, I agree with John, there is a controlled feedback system as he describes. Nevertheless the opamp U4110 runs at maximum gain, there is no local feedback. To this you have more gain from Q4105/Q4115

Hi, I would like to comment on this, the U4110 gain is infinite (or 100 000) since there is no feedback resistor from pin 6 to pin 2. The value -0.01V is not significant. At pin 2 you should have clos

Hi, I have not followed this discussion very closely but my guess is that you are looking in the wrong direction. You need to check U3105 pin 2, BAL SENSE, where the voltage should be 0V in normal ope

Hi Colin, you need to measure the voltage at each node in the -15V supply, evaluate where the currents go. CR1478 is ok since the output voltage is +0.63V. Göran

Hi, No you can not. You need a load of some 50W. There is a document in the archive describing the various loads you need on the different outputs. Pulsing may be caused by a load too heavy or too lig

My memory tells me that the Germans in the 1930s (?) made calculations to figure out if there would be a certain characteristic impedance that would give you the lowest possible cable losses and found

hp 465 A amplifier!

Hi, if your amplifier is able or not to reduce noise at its input is not related to the amplifiers noise figure. However, the Transfer Function is the one to be used. Göran

Gentlemen, I have been following this splendid discussion with great interest. There are so many ways you can discuss amplification and noise, negative feedback or no feedback, hopefully not positive