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  1. J M Fahey

    Speaker wattage for D class power amp question

    You are searching for a rule of thumb which does NOT apply elsehere. Fender is playing tricks but not telling you what they do. You can NOT cut paste "Fender says that 100W Class D = 22W Tube watts" and use it on other amps. I (roughly) know what they do, I do it myself , my own Fahey DB7 amp...
  2. J M Fahey

    Does the number of transistors in a power amp mean anything?

    With absolutely no extra data, think 100W per pair. Might rise to 150 per pair using real beefy ones (MJ15023/15024 or MosFets BUZ901/905) and down to 60perpair if conservative or old Tech (say 2N3055 class). Please measure that transformer core (W - H - L) i can pproximate the VA it can...
  3. J M Fahey

    5F1 Voltages -- deviations from specs on the preamp side

    Maybe they are actually measuring the tubes they use? :eek: Heretics!!! :mad: Everybody and his brother uses the same old worn photocopies of photocopies of datasheets made by long dead Manufacturers in opposite Countries as if they were valid now. Opposite per Cold War standards, that is. ;);)
  4. J M Fahey

    Stewart World 1.2 power amp seems anemic for the specs

    Nice amp, but remember that bridged it will only drive the single 8 ohm 15" speaker. Not that PLUS the coaxial. Stereo/Biamped we are back to square 1 .
  5. J M Fahey

    5F1 Voltages -- deviations from specs on the preamp side

    Leo said: "Voltages +/-20%" and I found no reason to doubt HIM :) You are REAL close.
  6. J M Fahey

    Compatibility question

    By all means mount that spare 8 ohm speaker there so cabinet has the proper impedance and each speaker receives 1/4 of total power evenly..
  7. J M Fahey

    How much voltage flows through the v2a section of a marshall plexi?

    Tube curves tell the truth. Manufacturers publish them to make our life easier. :)
  8. J M Fahey

    Can't get this damn Swedish cab open!!

    Good deduction Sherlock!! Yes, those old speakers were on a shelf, face back (hint hint) for years and cabinet seller mounted any junk he could find to make them "sellable".
  9. J M Fahey

    How much voltage flows through the v2a section of a marshall plexi?

    No NEED for , say, 25V caps, but every parts supplier stocks them and they are found at good price, so why not? It´s slightly harder finding 16V ones (in smallish values) and they cost about the same, and forget about 10V or 6V ones , so it´s more of an availability issue than anything else.
  10. J M Fahey

    Stewart World 1.2 power amp seems anemic for the specs

    Thanks. It sort of confirms my guesses: a usable system, but by no means wall shaking. And doubt replacing amp with a similar one changes results much. Not sure about the 15" cabinet, I guess using TWO 15" in a large cabinet (like old school Pvy and similar) will have way more "authority" but...
  11. J M Fahey

    Low Power Twin 5e8 build - distance P12N to chassis / tubes to low?

    FWIW and to get some real world comparison about magnetism and electron beam deviation, when I started studying Engineering in 1969 (Yea, I know) our Teachers were mostly Military Engineers :o , and they were way into the *practical* side of things (I still do things that way) , so every...
  12. J M Fahey

    Stewart World 1.2 power amp seems anemic for the specs

    Well, THAT one is the fuse. Specs posted are normal, no "Car amp" by any means. "Numbers" look "possible": 200/8 ; 350/4 ; **presumably 500/2** and IF so capable, why not print it in the spec sheet? Bridged: 700/8 (derived from number above), so far so good (as in being mathematically...
  13. J M Fahey

    Converting 59 Reissue Bassman from Export to North American Power

    Thanks, that´s more reasonable. Don´t worry about today´s voltages, this is just a test setup, 120V on a 240V winding and to boot further loses through bulb limiter. Keep us updated when you get the new PT.
  14. J M Fahey

    Can't get this damn Swedish cab open!!

    Pity, those must have been quite good speakers, Hagstrom were no fools, at all. Yes, look VERY MUCH like CTS/Eminence. Same frame, electrophoresis paint and the unique 8-10 mm hole punched on the back plate to hang it from a hook inside the paint bath.
  15. J M Fahey

    How (much) does the skill-level/expertise of an amp builder effect the overall performance and tone of a Hand-Wired Tube Amp?

    :p Don´t give them ideas o_O Throwing a ton of cold solder on top of an already bad joint will only make things worse ;) Best is to ensure metal to be soldered cleanliness (wire - part leg - terminal - turret - eyelet - socket), a good hot soldeing iron with enough tip mass, good solder...
  16. J M Fahey

    How (much) does the skill-level/expertise of an amp builder effect the overall performance and tone of a Hand-Wired Tube Amp?

    Suppose 2 units of the exact same amp are built, exact same circuit, parts, layout, by 2 different builders, one with 60 years experience, a Major EE degree, worked 45 years at NASA, has written 5 books on Amp building, etc.; the other a young Mexican farmer who has been trained for 3 Months on...
  17. J M Fahey

    Converting 59 Reissue Bassman from Export to North American Power

    Same here. Since you will pay full price for a new transformer, if available and about same price I´d buy a dual primary one (2 x 120V windings) so it can be used in USA and IF it eventually travels back to EU, can easily be rewired for 240V without major surgery. If going back is very unlikely...
  18. J M Fahey

    Converting 59 Reissue Bassman from Export to North American Power

    Oh, it´s basically that, but for safety. NOBODY wants mains connected and active wires with exposed ends dancing around, you holding one wire with one hand, another with a second one, 3rd and fourth with 2 extra hands, meter probes with fifth and sixth, etc. Techs look at octopuses and sometimes...
  19. J M Fahey

    Adding turrets to a PCB

    I use "shoulder" pins similar to Harbin but those require big hole drilling (1.78mm); I am using Argentine made 1.25mm ones, which still leave *some* copper ring around, but of course remove plating if present. https://www.disipadores.com/accesorios2.php# My supplier makes some "conical" shaped...
  20. J M Fahey

    Stickies are gone?

    If gone, good riddance!!! I always hated them robbing space at the beginning of every Forum area. If anything, post **one line** stating "click here for useful/indispensable information" or something like that.
  21. J M Fahey

    Converting 59 Reissue Bassman from Export to North American Power

    Thanks. WEIRD but if there is still continuity between all wires, then all were different taps of the same long continuous winding ... and joining two of them, (as in Grey joining Brown) should SHORT one winding and destroy transformer, yet it was apparently working. There is no logic there. I...
  22. J M Fahey

    Adding turrets to a PCB

    In theory you can; in practice typical PCB holes are 0.7 to 1 mm and pads match that , say 2mm diameter or so, minimum practical in a guitar amp being 1.6mm (62 mil : thousandths of an inch) while typical turrets are 2.3 mm diameter at the base. Even if pad is 2.5mm , and you enlarge the...
  23. J M Fahey

    Amp left on for weeks! Should I be concerned?

    No big deal. Think Airport/Bus/Train terminal PA system left ON 24/7/365 forever. Radio/TV stations, Industrial equipment, etc. In the old days, *everything* was tube powered, even garage door openers, Boiler/industrial ovens/Police-hospital 2 way radio, etc. an d left continuously ON...
  24. J M Fahey

    Converting 59 Reissue Bassman from Export to North American Power

    Sorry, I said Blue by mistake, probably thinking Fender OTs in the back of my mind. Now I reread from the beginning and see: My mistake. So the correct instructions are : >>>>>>>>> Currently Black and White are connected to CP6 and CP7 respectively. 1) turn OFF and UNPLUG amplifier from...
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