Distorted output need Vox V1083 service manual

[mojotronix]

Hey folks,

I managed to eliminate the hum by replacing the main filter caps, but now I'm getting heavily distorted output. Traced it down to one of the vintage transistors testing open — a bit of an oddball type.

Looks like I'll need to replace the outputs and probably the drivers too. I'd really appreciate a schematic if anyone has one handy, and some guidance on how to properly mount its sub, the NTE390.

Thanks a lot for your time and help!
– Stan

[Pedro Vecino]

Look at the bottom of this file to see if it is useful to you.
https://www.voxshowroom.com/ct/schematics/BK.pdf

[The Dude]

Which transistors are you replacing (original part number, case style, etc.)? There may be a better cross than the NTE part.

[R.G.]

The Berkeley III uses the same stacked-NPN output as the bigger amps: Viscount, Buckingham, Guardsman, and Beatle, just lower supply voltages. The output stage is driven by a single NPN transistor driving the primary of a an interstage driver transformer. The NTE390 is OK-ish if you have already bought them, but there are others that work, too. The biggest issue is the mounting. The original package for the outputs isn't made any more; today's plastic TO3s are mildly different, so some tinkering is needed. The single driver transistor on the primary would best be replaced with a TO-220 driver transistor, not a "replacement" type from NTE or whatever.

I'm a Thomas Vox mania... er, enthusiast , and I wound up writing a detailed repair/maintenance manual for most of the Thomas Vox amps. The one for the 1083 has suggestions for transistors and the output mounting tinkering. Not trying to advertise the booklet, but it's there if you need or want it. For the outputs, look at On Semi NJW0302G; for the driver, KSC2073 is known to work. It works for the reverb driver too.

[mojotronix]

The Berkeley III uses the same stacked-NPN output as the bigger amps: Viscount, Buckingham, Guardsman, and Beatle, just lower supply voltages. The output stage is driven by a single NPN transistor driving the primary of a an interstage driver transformer. The NTE390 is OK-ish if you have already bought them, but there are others that work, too. The biggest issue is the mounting. The original package for the outputs isn't made any more; today's plastic TO3s are mildly different, so some tinkering is needed. The single driver transistor on the primary would best be replaced with a TO-220 driver transistor, not a "replacement" type from NTE or whatever.

I'm a Thomas Vox mania... er, enthusiast , and I wound up writing a detailed repair/maintenance manual for most of the Thomas Vox amps. The one for the 1083 has suggestions for transistors and the output mounting tinkering. Not trying to advertise the booklet, but it's there if you need or want it. For the outputs, look at On Semi NJW0302G; for the driver, KSC2073 is known to work. It works for the reverb driver too.

Just ordered some NJW0302G. Looks like the OEM’s emitter lead has an intermittent connection at the body—appears fine visually, but I have to tweak it just right to get a reading. Thanks so much for the valuable info, R.G.! You're a legend in my book. Speaking of books, I’m definitely grabbing your Vox Owner's Safety Net ASAP!

Cheers!

[mojotronix]

Which transistors are you replacing (original part number, case style, etc.)? There may be a better cross than the NTE part.

Thanks for the reply, Dude! See R.Gs post.

[mojotronix]

Look at the bottom of this file to see if it is useful to you.
https://www.voxshowroom.com/ct/schematics/BK.pdf

Thanks, Pedro!

[R.G.]

The Safety Net is an overall family book. The Berkeley III repair manual is similar information but pointed directly at the V1083. Unless you have more of the Thomas Line, you might prefer the Berk III manual.

[J M Fahey]

Thaks RG, Pedro and others, I also love those old VOX amps.
In fact, I should build one, just for kicks.

The diode Tremolo modulator is crazy

Those NJW transistors are beasts .... nothing to complain about by the way

In general, "Plastic TO3" (although those shown are actually TO247) can carefully be mounted in place of metallic TO3.

Pin spacing is the same, it takes bending legs down 90 degrees to fit though original BE holes (maybe you need ¨slightly* enlarging them) and you already have *one* mounting transistor hole in the proper place.