Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: dude on March 01, 2014, 03:15:47 pm
-
Hello all,
I taking a modded 1992 Fender Champ SE amp back to stock. Some of the Diodes were taken out, I have the schematic and parts list and it calls for a few Diodes-(1n4448 75PRV SIGNA). What does the 75PRV SIGNA mean? The Fender part number is #006260
Mouser doesn't seem to have them but I might not be searching right and don't know what values I need, guess the 75PRV says something...?
I don't know what kind of diodes these are or what they do, the amp has a tube output and SS preamp from the early 90's.
Any help locating the correct parts appreciated. I'm not much at repairing SS state stuff and have no idea what this diode does. The diodes are in the gain and contour EQ stage in the preamp section. I'm just following the schematic and parts list.
Thanks in advance,
al
-
... I have the schematic and parts list and it calls for a few Diodes-(1n4448 75PRV SIGNA). ... Mouser doesn't seem to have them but I might not be searching right ...
Google "1N4448". Digikey sells em (http://www.digikey.com/product-detail/en/1N4448TR/1N4448VSCT-ND/3104300).
What does the 75PRV SIGNA mean?
75v Peak Reverse Voltage. May also be seen as "Vr" or "Voltage, reverse"; Vrrm or "Volts, reverse repetitive maximum"; etc.
"SIGNA" is very likely short for "Signal" as in, it's a signal diode not a rectifier diode. Which also makes sense when you consider the low voltage rating.
-
I would guess that your 1N4448 is actually a 1N4148, by far the most common and widely used "small signal diode". This spec sheet in fact lists them the same and rates them the same, voltage-wise and everything elsewise. 100% the same.
Just like virtually any small signal plastic-cased transistor can typically use a 2N3904 (NPN) or 2N3906 (PNP)...teeny little bit more power, use 2N2222... (NPN)..... little bit more power (but lower gain) 2N2219 (NPN) There are zillions of transistor type numbers but as long as the beta, voltage ratings, and dissipation are adequate and you are not doing gigahertz frequencies, 3904's and 3906's can be used for just about any TO-92 small signal transistor. This appears to be the case with 1N4148/1N4448.
There are many transistors with different type numbers that are 100% identical to other types except they have preformed leads (2N4125/2N4126) or their pinouts are ECB instead of EBC. In general, these are freely interchangeable.
http://www.nxp.com/documents/data_sheet/1N4148_1N4448.pdf (http://www.nxp.com/documents/data_sheet/1N4148_1N4448.pdf)
-
AES has the 1N4148's in stock, I did check out the spec's they are indeed almost the same and it's they are like you say, interchangeable.
AES has the older nineties Fender snap-in pots for this amp and the 1N4148's in stock but not 1N4448, now I can get everything I need from AES.
Upon further reading these are fast acting signal cap diodes. SS is another world for me, I'd rather stick with tubes :laugh:
Thanks, all
-
4148's will work fine.
Tubes are fun and heartwarming, but you could spend days building up the guts of even a single long-ago obsolete 74LS74 flip-flop or a divide-by-ten counter chip (or even a simple AND gate for that matter, not to mention a quad of them) that you can buy for a quarter from individual parts! Obviously...it's the application. One thing about transistors and chips is the ease of building stuff, once you have perf board and the basic chops. You really can't use a tube without a socket, and the socket has to mount on something, so using a tube/tubes implies having to cut or punch a big hole and drill two small holes in something with modest precision to hold the socket...then you can wire up the heater....and you've done a fair amount of work and the thing isn't even capable of doing anything yet except light up.
I like 'em both. I often wish tubes could be thrown together with the ease of transistors without all the mechnical rigamarole. Hence the desirability of a tube breadboard if you like to tweak.