Early 60s Shaftesbury 516 combo

[stephenhartley]

I've posted about this amp before.

It's early sixties British with tremelo. It has an EF86, ECC83, EL84 and an EZ81. I recapped it and changed a few resistors and it sounds awesome albeit a bit trebly.

The tremelo was producing a rhythmic thumping and I was advised on here that it might be related to the biasing of the tremelo circuit. I changed a few resistors and now it doesn't work at all.

I've finally got round to drawing the schematic. Can anyone advise me what I might do to get the tremelo working.

I'm unable to put up pics at the moment (I've attached the schematic) - I keep getting an error message. Is anyone else having this problem?

[stephenhartley]

Shaftesbury SE combo advice?

Any advice greatly appreciated - I've been searching for original schematics but can't find any.

I've posted about this amp before.

It's early sixties British with tremelo. It has an EF86, ECC83, EL84 and an EZ81. I recapped it and changed a few resistors and it sounds awesome albeit a bit trebly.

The tremelo was producing a rhythmic thumping and I was advised on here that it might be related to the biasing of the tremelo circuit. I changed a few resistors and now it doesn't work at all.

I've finally got round to drawing the schematic. Can anyone advise me what I might do to get the tremelo working.

I'm unable to put up pics at the moment (I've attached the schematic) - I keep getting an error message. Is anyone else having this problem?

[Ted]

It's quite an unusual arrangement to have the EF86 as the tremolo oscillator and the ECC83 as preamp.
Its usually the other way around. e.g. Vox AC4
Vox AC4 Amplifier - 1960 Schematic

But what you've drawn makes sense.

Tremolo thump has precisely nothing to do with the biasing of the tremolo oscillator circuit. In amps like this its caused by changing the bias point of the output stage.
There isn't a whole lot you can do about it. Reducing the tremolo drive gets rid of it, but also reduces the trem.

Suggest you try changing the resistors back to their original values. (You did take note of what they were and where they went didn't you?)

Pin 8 of the ECC83 shows no connection. That is almost certainly not correct, but won't have any effect on the trem.

The circuit around the EF86 is wrong. It shows the screen grid (pin 6) connected into the trem signal via that 0.47 uF cap. The cap should probably go to the next point on the tagstrip instead which is the EF86 anode, pin 1.

This is probably not an exhaustive list.

[stephenhartley]

Thanks very much.

As far as I can make out, the 0.047 cap is already attached to pin 1. Did you mean the other way round?

I don't have the amp here at the moment. I decided that I'd reached the limits of my ability & I've taken it to a repairer.

When I get it back, I'll redraw and repost the schematic.

I knew that early voxes used EF86s and I thought that they might be similar circuits, but now you've explained why they're not.

[Ted]

Yes sorry thats right.

The more I look at it, the whole oscillator circuit appears to be wrongly wired. It should be pretty simple to sort out for someone who knows what they're doing. If you're near London I'd be happy to sort it out for you.

[stephenhartley]

Thanks - that's very kind. I'm in Burnley.

it would be easy just to leave it as it is, as it sounds great but I'm determined to get it back to original spec. I've started building amps with great results so far and I've bought the odd one off e-bay to try and learn from it. I use my first build for every rehearsal and gig.

[Valvewhiz]

Hi Stephen,

You haven't got the large size copy of the diagram have you? I have a Rangemaster 526 here, same preamp - push pull output stage with a faulty trem.

[WelshFungus]

Hi Stephen,
I've tried clicking on the link for the schematic but its unavailable. Would it be possible to get a copy please ?

Best,
Steve