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I neglected to add that in removing the metal-tubed coupling caps one removes some 50pF of grid-common capacitance - which plays some role in NFB h.f. stability. (you might  be aware of all this, mike) Some compensates for this by adding ceramic caps grid-ground. but I prefer using 'leading...

Folks faithfully replace capaciors when not always necessary, but what about the reistors! Those ceramic tube encased ones were not the best ever, and you might consider looking at those as well. in some instances a voltage measurement would indicate whether all is kosher.

Where are you, Livesound?

Oh Boy . . . I do not see how valve manufacturers in Russia can stay afloat then.  Finally, the end of the valve era?  Unless someone can take care of . . . . . or folks can find a way of clandestinely getting stuff out to the west . . . . There are of course Chinese manufacturers who might...

? ? ? ?  A thermionic valve operates basically off the intensity of electrons 'released' by the cathode. This is a function of the temperature or then 'wattage' of the heater, which consists equally of voltage and current values! and yes, kind sir! The spec-ed voltage was applied (I did pass...

During the years 1974 - 1990, while employed by the CSIR, I was the official dumping site for UFO-sightings by the armed forces, SAP and the like. We have long since stopped guessing regarding this subject - there is just too much evidence.  We even know how they work, but cannot yet make one...

As said above. Also, the stand dimensions are too small to cause much diffraction/whatever at the frequencies the sub is going to give any output at.

I did not do arithmetic, but much of the reason would lie in Radford having cathode-biased output stages compared to the fixed bias in the ST70. (The cathode drop voltage must therefore be subtracted from the h.t. for the actual EL34 cathode-anode voltage in the Radford.) That is assuming the...

Moonraker, Yes - but that does not explain why the ECC88 heaters should often draw currents more than 15% off the spec.value!  One would expect the heater wire to be of the same gauge!?? My point with series connecting heater(s) is that it is easier to design a high-voltage lower current d.c...

I posted this problem years ago and cannot now locate the thread. I had the inconvenient experience to discover that there is an unacceptable current variation in heaters of certain ECC88 valves. Trying to operate heaters in series I found  from 5,7 - 6,9V drop across certain heaters. This...

I have long since given up on keeping up with the plethora of modern power amplifier designs, particularly the switching power amplifier scene. But I will echo that one must be careful of simply using  bridging arrangements. Depending on exactly how the D-A side works, some quite nasties can...

No, the 'architecture' is not the same; at least not what is evident on the outside. Both controls om the errant model come out on the front panel, not the sides. There is in fact no 'discreet' volume control and on-off switch: All part of the printed circuit 'mechanics'. Not to generalise but...

Usually hum.  This could be quite soft, however, so also confirmed with an oscilloscope. (I have used a few other triode-pentodes without this symptom. Yes, the 7199 was never universally accepted; too many other similar but less expensive valves on the market.  (Although most have been...

Apology! Not desiring to overwhelm - but I found the often encountered cathode leakage --to-heater in many ECF82s troublesome.  (Where I used them as input stage I had to resort to grid leak bias (20 meg  G1-common  resistance) and the cathode tied directly to common (or with a very low cathode...

Grrrrr . . . The nightmares of the various un-pentode executions of input pentodes!  First year basics fly out the back door as the screen grid is bypassed  - -  to common in the presence of relatively large nfb. ! This leaves a lamish kind of operation as in the equivalent circuit the nfb...

Yes, one has to take off the back, damaging the label on the bottom which 'loudly proclaims '230v. I imagine that is fixed locally.  As said the trouble can be spotted by a hot spot on the cabinet, left hand upper corner. The warrantee will then by cancelled; i never really place much value on...

I was given this radio as a present end-of-last year.  Apart from an obvious cheap execution, some of them come with a hidden malady:  It is fitted with a 115VAC mains supply instead of the required 230V option for RSA! It appears to have been assembled locally by Nu-World Enterprises from...

Alleycat opened this subject on September 25, 2021 by referring to a similar-titled article by Mr Roger Skoff.  The contents of said article merits further discussion  but I was sadly not available at the time to contribute. I now quote most of the article with my comments in blue: I...

Your post #5,  Fdlsys: Brave bold words those Mike - - but they overlook one of the basics of human hearing:  The fact that said hearing has limitations; that distortion (in its broadest sense) can only be detected if AUDIBLE! Thus it is in fact quite easy to design a "blameless amplifier". to...

Joffieb and general: I would so like to support you, but as said previously, I am cursed with being limited by reality: OK, to perhaps put it better: Again I am concerned with attracting enough advertising for a 'mixed grill' or worse. but one matter not mentioned, particularly regarding...