Wanted: Vox Essex V-4 bass amp schematic (Not V-4A)

[So80s]

Does anyone have:
* The schematic or Service Guide to Vox Essex V-4 bass amp? (Not the V-4A). The Schematic is likely from 1965. The Service guide is likely 1965, possibly early 1966.

The V-4, not the V-4A. The V-4A has too many transistors. The V-4A schematic is widely available, but I cannot find the V-4 documentation. Any help would be greatly appreciated. Have a nice day.

[So80s]

My comment about the V4A having too many transistors may be incorrect; it's unclear until comparing V4 & V4A schematics. If you have the V4 schematic you could share that would be great. I have the V4A schematic, but not the V4. Thank you..

[DrGonz78]

I fully support buying this book by RG Keen. He is a great member of many forums and MEF. He clearly has all the schematics and huge knowledge base on Vox amps.

[DrGonz78]

Oh btw there is always a chance this thread pops up on his radar. Last few days I have been restoring a Vox Jaguar keyboard. Just the smell alone is nostalgic.

[R.G.]

Yeah, finally got to my radar. 8-)
he
So - what seems to be the problem? Are you repairing a known failure or reviving a closet/basement/barn find?

edit.>> I looked at the repair supplement for the Essex series and it seems that the V4A and V1041 are the same animal, nearly as I can tell. The extra transistors in the V4A/V1041 are the fixed limiter. See my complaint below about things being mixed and matched.

As a side note, I got into researching and writing about Thomas Vox amps because (a) I'm a bit dotty about them and (b) the factory service guides are so uniformly terrible, at least as viewed from 60+ years on. edit>> I had a devil of a time digging out which model has what circuit variants inside. It took a couple of weeks of cross-comparing and sanity checking the factory schematics to figure out which model had what features and cabling, and then I got to start drawing schematics and writing about them. This was a bigger PITA than the whole "Big Head" set of models in many ways.

It's even worse as many of them have been the recipients/victims of lesser-skilled repair attempts and many of the "Big Head" amps have had parts swapped around between models of amps.

[So80s]

Thank you for your response. Regarding your question I'm simply reviving an amp bought from a gentleman allegedly the second owner which has a loud hum.

I've attached additional photos as my father and I opened up the top cabinet from underneath to see the additional circuit.
Could it be a V4 or V104? It has Tone-X if that's an indicator of the model; not sure when they added that. Thanks again. Have a nice day.

[R.G.]

OK, I understand more now. I think you have the plain-vanilla V4 as you thought. I have attached a page from the Essex repair supplement that shows the differences between the V4 and V4A. They just kept the original V4 preamp's single transistor circuit, and added on a two-transistor limiter circuit. From your photos, the limiter is not present, so you do have a V4. The schemo shows the V4 and the V4A/104.

Your hum issues probably come from one of only a few places. First, use your multimeter to check continuity on all of the grounding wires. A broken or loose ground wire will cause hum. Second, I strongly advise that you replace the power supply main filter capacitors in the power amplifier assembly. If they have not been replaced since the amp was built, they may be dying and the hum can be 120Hz power supply ripple getting into the preamp circuit. If replacing these caps does not fix the hum, then proceed with more debugging. Let me know what happens and we can dig some more.

By the way - your photos are very nice. May I have your permission to use them in a future update of the Essex repair manual?

[So80s]

Thank you RG. My father who's 96, PhD electrical engineering will really appreciate this information. As do I. Yes please feel free to use the photos. If you want any more photos just let me know. I can always take more photos when I go back over to his house. Have a good day. Thanks Niko

[R.G.]

My respect and congratulations to your father, both on his choice of professions and his longevity. Value that - I lost my father at 78. It wasn't long enough.

Can you contact me by private message?

[So80s]

Sure will do.

[So80s]

Hello,

Hope everybody had a nice weekend.
* My father checked all the ground connections and he doesn't see any issues.
* He also checked the power supply capacitors for a second time and he says the waveform is normal. He sees no leaking or damage.

He says he is going to test and determine if the hum is coming from the preamp circuit or Poweramp circuit. Basically a process of elimination to try and narrow down the cause.

He really appreciates all of your information, suggestions and welcomes input.

Thanks, Niko

[DrGonz78]

Had to post this since I don’t see these ever. One for $250. That seems low. It’s in great shape too. I can only find one that sold for $475 on reverb. Well someone is going to snatch it up.