Golborne Vintage Radio

Hi All,
I recently could not resist buying this Marshall amplifier cabinet (Marshall Class 5 - single EL84 with 2 x ECC83's) as a project. It was advertised as a "dummy' cabinet but looked original and I managed to negotiate a price of £60 which I thought was cheap considering it was one with red tolex material being quite rare. The person I bought it from had no idea whether it had a proper chassis or any board etc but I took it as read that it may not have anything inside.

When it arrived, on examining this the chassis is marked as 'dummy" but it is a real model and it does have a circuit board which is the same as the one as the one in my other Class 5 that my late mother bought me on my 50th birthday (near 13 years ago). The challenge I have, hence ask for some advice/thoughts is that the chassis appear to be designed for a later board (which cannot be purchased and are never seen anywhere for sale) where the valve are positioned at the edge of the chassis (see the photo below). The board I have has the valve positioned on the rear of the board and as such have holes drilled in the middle of the chassis to position them. The reason for the change was to do with a major rattling issue with this amp which eventually led to it being sold as a head and cabinet and not a combo, which had the issues.

I don't want to spend masses of time working on this one at the moment so what I have been thinking is:
- can I use the board I have (yes, it looks a wee bit cheap!) and position the valves at the edge of the chassis by adding appropriate leads from where the valve socket mounts in the middle of the board outwards?
- drill holes in the middle of the chassis and mount the bard with no changes as it stands with no modification?
- prepare a handwired board and modify the whole thing albeit my expertise here is very weak indeed (I can't seem to understand still(!!??) how to convert a schematic into a circuit board layout). I've look everywhere and cannot find anyone or anything that explains this in easy terms.

Thanks in advance for any help.

Rob

Hi Rob, it looks like a good board, but would need the transformers to go with it. Well worth a lash up with any old transformers to see if it operates before buying expensive transformers for it.

Plenty of programmes available to design boards out there, but should not be necessary if the original works.

I use easy PC, which is similar to most programmes. First you enter the schematic with component details etc. You then "translate" it via the software onto the size of PCB you wish to use. The components are then normally dumped as a "rat's nest heap" on a corner of the board.
You ten drag/drop the parts in the positions you want them and place the "rubber banded" tracks onto the board where you want them, again by drag and drop.

I suspect your board is of moderate complexity so would be long winded to layout manually, but would it be worth the time to learn the software?

Cheers, Ed

The board is standard modern Marshall style. It will work fine. As mentioned you do need the "right " transformers.
You can fit old ones if you have some, and I would suggest that they will probably be better than the new chinese ones.
Yes the sign that says made in England is true. Its about the only thing thats English. The rest is chinese.
These little amps work OK and for practice or even low level recording.

I am watching this post.

Regards
Joe

This is the circus diafragm[attachment=21524]

Joe

You have two options Rob, either dill holes in the bottom of the chassis for the valve to pop though or use flying leads to join the PCB to side mounted valve bases. With the latter you could use three B9A plugs to plug into the PCB valve bases. One issue though, I think the valve bases are on the bottom of the board so you'd either have to swop them to the top of the PCB or drill hole is the bottom of the chassis, which is a faff, I'd just swop them to the top. See attached.

The first way is quicker, 3 octal size holes punched in the bottom of the chassis, job done. I have some punches you can borrow if you don't fancy drilling em out. Either way the amp not having any tfmr's is a bit of a downer though they're easily sourced. BTW, what the dickens is "class 5" ?

Andy.[attachment=21525]

(30-07-2022, 07:49 AM)Diabolical Artificer Wrote: [ -> ]BTW, what the dickens is "class 5" ?

Andy.

I didn't know either but finding out was easy. It's simply a model name: https://www.musicradar.com/reviews/guita...mbo-218428

Many thanks to all for your thoughts and comments

I originally bought the Marshall Class 5 to use at home, it was cost effective at the time (£299 in 2009) and was still being made in England. Its a good small amp but alas it rattles due to the cost saving in the chassis design and build and also the position of the valves for the first model which are position very close to the speaker (see 1st photo below) which is why I believe the valves were repositioned at the bottom of the chassis (see 2nd photo albeit this is a modified amp with an extra valve as seen).
The down side is that it is a wee bit on the loud side for home use but that is not an amp design issue.

The 2nd model has a different board with leads at one edge leading to the valves.

[attachment=21526][attachment=21527]

I do think the easiest thing to do is to drill holes in the chassis body and leave the circuit board "as is". I have some suitable transformers I am sure to use. 
I am also planning to strengthen the chassis by adding two small bars of metal (mild steel or aluminium, is strong enough for the size) either side of the bottom of the chassis to lock it together and at least stop this from potential rattles. I have seen someone else do this and they indicated that it did make an improvement.

Best Regards

Rob

Do it with standoffs and if necessary build up the chassis with another plate.
It looks as if it should be quite straight forward and yes use that PCB.
Good luck.

I'd agree, use existing PCB unmodified. adapt chassis.

Class 5 means its a 5 watter. 

Joe