Vox 4120 or 7120 schematics

[vintagekiki]

Does anyone know where I can get a schematic for Vox 4120 or 7120 ?

Thank you

vintagekiki

vintagekiki@yahoo.com

[vintagekiki]

To raise the topic.
Does anyone know where I can get a schematic for preamplifier Vox 4120 or 7120 ?

Thank you

[R.G.]

I'll check - I have a bunch of the 4- and 7- series schemos in the backup disks somewhere.

I'm sure you've checked this, but the first thing that occurs to me is that Vox was heavily into using a common preamp and changing the power amp in the 4- and 7- series. Do you know that for instance the 7120 did not use the same preamp as the smaller 7-s?

[vintagekiki]

Vox Series 7 (UL715/ 730/ 760/ 7120) uses the same SS preamp, but power amps is different.
My Vox 760 preamp
Vox Series 7 (UL715/ 730/ 760/ 7120) preamp
Using the analogy, that the same rule is for preamp Vox Series 4 (UL430/ 460/ 4120).
Vox Series 7 and Series 4 used the same tube power amp, but preamps is different. Vox UL730 used 4xEL84/ 760 used 2xKT88 and 7120 used 4xKT88.
Diference between preamps and Vox Series 4 and Vox Series 7, is that Vox Series 4 does not reverb and tremolo. Most probably that Vox series 4 has a different capacitors.
Vox UL705 and UL710 are different constructive. Its completely SE and PP tube amps.
I would be grateful for preamp schematics for bass Vox Series 4.

[Robert M. Martinelli]

Hi vintagekiki, Hi R.G.!
I just opened my UL4120 to take some pics to show/send to a potential buyer, so I took the chance to clean the inside and to check that everything was OK.
I can tell you that the "normal" channel shares the preamp with the "normal" channel of a 7120, I haven't checked the "bass" channel, but at a glance some difference indeed exists with the capacitors.

About the power and the PS stage, I found that - 1 - the cathode resistors are indeed 10 Ohms 1W ones ( despite the added hand writing on the schematic telling they should be 47 Ohm - 2 - close to the stand-by switch, there was a polarity switch (not shown on the schematic), together with its cap. (my amp should be a late '66 model). I disconnected it and duly earthed the amp, but I left the switch there for "aesthetic" reasons, as the idea of leaving the hole there with "POLARITY" stamped in white close to it horrified me some.

Hope this helps

Best regards

Bob

[Robert M. Martinelli]

Hi guys!
I just spotted another difference, the schematic calls for four 330 Ohms screen grid resistors, but the amp has 470 Ohms (2W) ones.
Hope this helps
Best regards
Bob

[vintagekiki]

Vox 460 or 4120 preamplifier schematics

Tnx Bob

Vox Series 7 and Series 4 used the same tube power amp, but preamps is different. Difference is in capacitors and probably in some detail.
Therefore, the preamplifier schematics would be useful, to amplifier returned in its original form.

Does anyone have schematic for preamplifier Vox 460 or 4120?

[vintagekiki]

I'll check - I have a bunch of the 4- and 7- series schemos in the backup disks somewhere.

Still looking for Vox 460 or 4120 preamplifier schematic.

Thanks in advance.