Hoffman Amplifiers Tube Amplifier Forum
Other Stuff => Solid State => Topic started by: FranciscoPerez on July 20, 2009, 03:32:25 pm
-
Hello!!
I'm building a jtm45 2x12 combo (1962 bluesbreaker) from scratch using 1960's components like the original.
(mustard, hunts and radiospares caps, bulgin hardware, radiospares transformers...).
After some time, and having most of the components and hardware I almost finished the board, but I can't find the 2G374 old pnp transistor used in the tremolo section.
Do you know any NOS replacement for this transistor with the same packaging?
What new transistor could I use?
I haven't been able to find any datasheet for 2G374 transistors.
Any ideas would be really helpful!!
Here you have a picture of the transistor I look for:
http://www.thefellowshipofacoustics.com/images1/Marshall%20JTM45%20SuperTremelo%20Combo%20Bold%20042.jpg
Thank you very much!!
Regards,
Francisco Pérez
-
Do you have a schematic?
-
link to datasheet here (http://www.swastikittens.com/AMPS/germanium-datasheet.pdf) and here (http://www.swastikittens.com/AMPS/germanium-datasheet-2.pdf)
these may work....
http://cgi.ebay.com.my/ws/eBayISAPI.dll?ViewItem&item=260447300232&ssPageName=MERC_VIC_RSCC_Pr4_PcY_BID_Stores_IT&refitem=380017410983&itemcount=4&refwidgetloc=closed_view_item&usedrule1=StoreCatToStoreCat&refwidgettype=cross_promot_widget&_trksid=p284.m183&_trkparms=algo%3DDR%26its%3DS%252BI%252BSS%26itu%3DSI%252BISS%252BUCI%26otn%3D4
-
> these may work....
Oh, man, way too new! :grin: Like a 1973 DuraSpark in a 1968 Mustang.
> transistor with the same packaging?
Who are you trying to fool?
If only yourself, use any modern Silicon PNP, they really are better and there is no "tone" in a tremolo oscillator. Then get a "display" old-style Ge transistor, bust out the base, swab the white goo out (it is just thermal grease), hide the modern transistor inside.
Those 2N404 parts will work fine. I know they are slightly newer than the photo you posted, but most folks won't know, and it really could be a factory part: the "S02"(?) case went out of style, the TO5 case was VERY common, as was the 2N404.
-
Thank you very much!!
I'm only trying to fool myself, so I will try using one modern transistor and hiding it inside an old one. :grin:
It's a great idea!!
I'm following an old schematic of a 1962 type jtm45 amp. Here it is:
http://www.schematicheaven.com/marshallamps/jtm45_lead_45w.pdf
I didn't know I could take out the packaging of an old transistor that easy!!
Thank you ISOtone for the datasheet, and sorry for posting the topic in the wrong section :embarrassed:
I'm really impressed on how you all help other people and share your knoweldge in this forum.
You are far too kind!!
Best regards,
Francisco Pérez
-
i think the OC44 was also used in there. that might be better available for you. =]
-
i like the black ones... :glasses9:
http://semiconductormuseum.com/MuseumStore/MuseumStore_2N404_Index.htm
-
> schematic of a 1962 type jtm45 amp. Here it is:
{excerpt}
(http://i26.tinypic.com/33lgm4w.gif)
Oooops.
That's NOT the usual way to use a transistor.
Tube V2 makes the oscillation. The transistor C-E path is used to short-out the audio.
A modern Silicon transistor "will" short-out audio; this connection is often used to mute hi-fi outputs at power-up/down.
But can it "fade" between open and short?
The old-old Germanium devices were so leaky, that they never got fully ON or OFF. Marshall may have used this "fault" as a "feature".
Also the old devices were pretty symmetrical, not much difference between C-B junction and E-B junction. Since audio swings both ways, this may be important. And I do not see why it is PNP, except PNP was most common at the time. NPN should work very nearly the same. (If you had two audio paths, one NPN one PNP, fed from the same oscillator, you would know they work on opposite sides of the trem wave; but that does not matter to a guitar amp.)
It might still work with modern devices. National Semi published an app-note for a $13-class cassette tape recorder which used a "modern" Si transistor to partially short-out the microphone for automatic record level control.
Experiment.
Also try a JFET. They were rare in Ge, but are a natural for a scheme like this, and are now real cheap.
-
> might still work with modern devices
A quick-crack with modern Si (PNP or NPN) "works" but brutally.
(http://i27.tinypic.com/2mze32p.gif)
-
Wow, that's really useful information for me. :wink:
I will try different components. It's funny that I've been looking for a 2g374 for a long time, and the same day I post this topic I found it on ebay, so I will be able to experiment also with the original one.
I have some mullard oc44 transistors at home as well.
Thank you very much!!!!
Best regards,
Francisco Pérez
-
I would be interested to know how the circuit finally worked out ... it is an odd one where, more than just about any, the characteristics of the specific transistor matter a lot, germanium will need a much lower base drive voltage than silicon, and differences between various transistors may make the tremolo effect softer or harder (switching between completely on and mostly off without much middle state). I do have a few 2G374's plus some similar transistors if anyone else is experimenting.
I will try different components. It's funny that I've been looking for a 2g374 for a long time, and the same day I post this topic I found it on ebay, so I will be able to experiment also with the original one.
-
Hello to all,
I am building the JTM45 with Tremolo (like FranciscoPerez :-) ). I have problem with this helly transistor 2G374 sourcing. Is there anybody who would provide any info where to buy that, please?
-
... I have problem with this helly transistor 2G374 sourcing.
....use any modern Silicon PNP, they really are better and there is no "tone" in a tremolo oscillator.
{also} Those 2N404 parts will work fine.
-
Thank you very much. One question, can I use also transistor AC153 for the tremolo section? This looks good and also is available in my country. :-)
https://alltransistors.com/transistor.php?transistor=21269
-
This is not a tricky job. Try any transistor you have.