Vox V125 Assistance?

[phydauex]

Howdy All,
I'm currently going thru an early 80"s Vox V125 combo, that differs from the only schematic I can find. The V125/Climax schematic from the Vox website shows a normal/bright input into 2 FETs then into the first tube stage->Sensitivity control. This one has the two inputs joined into (1) FEt stage then into the first tube. After that it goes to a "Distortion" control and then into the second tube. Any idea what this circuit was supposed to be originally? I'm curious, because someone along the way added an effects loop, around this part of the circuit and before I remove it (owner would like this amp stock), I'd like to know what might have been changed.
I'm also rewiring the power transformer to use 115v primary, it came from the UK with their funny plug and the voltage switch on the chassis only had a 220/240v option. I found a taped off lead inside coming from the transformer that seems to be the 115v lead, I'm basing that from measuring the resistance of the 3 primary leads. So I decided to wire it up to the switch so it will be 115 or 220v. Any input, pics or a schematic to this beast would be hepful. Also, if anyone has had any experience with amp and it's shortcomings, if any would be appreciated.
Matt

[Enzo]

Are there any identifiers on the circuit board? Either silk screened on the top side or written in solder on the underside?

Try CONTACTing Vox and asking if there were revisions not covered in their web site offerings.

Just an opinion, but unless this amp is going back to the UK, I think the 115/230 switch is a bad idea. over here it won;t help anyone, and it offers the potential to be knocked to the wrong position and causing problems. Rather just wire it up for 115 and leave the switch unwired.

[phydauex]

Hey Enzo, the top side of the board is marked V125-3, that's about it. I was considering not wiring the switch, but it's not accesible to fiddling hands unless one removes the chassis from the cabinet, so accidental switching is tough. Not impossible, but not like it could be messed with while one's playing it. Your probably right about making it idiot-proof though.
Matt

[Indigo]

@phydauex Maybe you have move on? Do you require additional help with the wiring of the transformer - or any other queries reference the V125. I can help.
Indigo

[Indigo]

Apologies - why didn't I just state this in the first place!

To change the V125 from a main supply of 230V (nominal) to 115V (nominal) do the following.

1. Locate the insulated (orange) wire on the mains transformer.
2. On the Mains ON/OFF switch locate the black wire going to the transformer and unsolder.
3. Solder the orange wire to the switch to take the place of the black wire.
4. Insulate the black wire and tuck back into the wiring.
5. Change the labels on the selector switch from 220V to 110V and from 240V to 120V

Job done. Set the selector switch to suit the supply voltage in your region.

[phydauex]

No need to apologize, what you described is what I ended up doing and it works fine. I understand it's probably best to keep voltage switching a non-user adjustment, but where the switch was located, one has to take the entire chassis out to even get at it, so accidental switching is not an issue.

Thanks for the detailed info.
Matt

[Indigo]

No Problem. Glad you got it sorted.

[wcieslik]

No Problem. Glad you got it sorted.

I know this is an old thread but ...What is old is new again ...
I also have a V125 that is being troublesome.
Yes... the cct inside bears only a passing resemblance to the only schematic availabe. (especially w.r.t. the inputs and the final output).
Mine is exactly as you have described. No FETs to be seen, and the inputs are sort of wired together and go directly to the 1st ECC83. (I think this looks like the inputs on the AC120)...

Really hard to work out what's connected to where in this thing !

cct board is labeled :
Manufactured by Faraday group of companies
V125 lb ISS 3
SCN 2 V125-3

Does any one have a parts overlay (or even a tube position overlay ?)
I'm guessing that the output pairs are V5/V6 and V7/V8 .... would be keen to have that confirmed by someone who knows about these things.. ?

Cheers,
Witto..

[Indigo]

I know this is an old thread but ...What is old is new again ...
I also have a V125 that is being troublesome.
Yes... the cct inside bears only a passing resemblance to the only schematic availabe. (especially w.r.t. the inputs and the final output).
Mine is exactly as you have described. No FETs to be seen, and the inputs are sort of wired together and go directly to the 1st ECC83. (I think this looks like the inputs on the AC120)...

Really hard to work out what's connected to where in this thing !

cct board is labeled :
Manufactured by Faraday group of companies
V125 lb ISS 3
SCN 2 V125-3

Does any one have a parts overlay (or even a tube position overlay ?)
I'm guessing that the output pairs are V5/V6 and V7/V8 .... would be keen to have that confirmed by someone who knows about these things.. ?

Cheers,
Witto..

Hi wcieslik
You definitely have a VOX V125. I would suggest that you have a V125 BASS because this model did not have the FET input. The amplifier is designed as as single input amplifier with a user choice of either Bright OR Normal channel. V1 is a ECC83 double triode valve and is located near the input jacks.You are correct in assuming V5,6 7,8 are the EL34 output valves.
However that has not solved your problem. Can describe the symptoms?
Indigo

[vintagekiki]

... No FETs to be seen, and the inputs are sort of wired together and go directly to the 1st ECC83 ...

This Amplifier is Vox V125 Bass

http://www.korguk.com/voxcircuits/circuits/v125bass.jpg

http://www.korguk.com/voxcircuits/

https://images.talkbass.com/attachments/v125l-7-jpg.1754551/

[wcieslik]

Thanks Indigo,

Just waiting on a new set of el34 to arrive (at least one of the old set is faulty and blowing the HT fuse).
HT fuse is fine with no EL34 installed and remains fine with my two 'good' tubes in either pair 1 or pair 2 position, so I am assuming there is nothing else bad going on in that stage other than the faulty valve.
(Incidentally, that tube looked a bit 'rusty' inside and all of the silver in the crown had disappeared as was replaced with a white cloudy look. (It also fell apart in my hand when I removed it !!)).

There is a decent amount of hum and a bit of microphonic crackling going on, but I will address those later. (The board is full of dry joints and the wiring is a mess ! I also found a broken CAP).

I get that this is a bass unit but am still puzzling over the schematics.
The input jacks are wired much like a single channel of an AC120 (not like the V125 bass). I found 2 x signal diodes on the board too, so these are a puzzle for later on ... As is the final output to the speaker through that switch.
Again I'm guessing that the switch options of "OR" and "AND" mean :

OR: means internal speakers unless an external speaker is jacked in (thus disconnecting the internals)
AND: means both internal AND external are live. (the switch, 'switches' another tap to the jack, and allows both internal and external use at the same time )

I'm going to start trying to document what I find as I go ....




Thanks for your reply.

[wcieslik]

Thanks vintagekiki,
I have been comparing what I've got in the voxbox, with the V125, V125 BASS and AC120 schematics. What I have looks like a blurring of all three plus other mods ...

I will try to document the speaker switch, and connections around the EL34's tonight.

[g1]

'Whilst'. Not very often you'll see that on the back of an amp.

[Enzo]

I shan't expect to see it anon.

[vintagekiki]

[ATTACH=CONFIG]45914[/ATTACH]

Can you carefully remotely the plate above the number and see what's written below it?

Obviously, some unfinished custom was made on vox.
Try to draw schematic how the current wired input tube (V1a / b)