Blog of Ian Parr

Well I have been waiting weeks for Marshall to give me a formal quote for the components for my 2203.

Half hearted (from several Marshall staff) email communications over several week resulted in a quote of £16.63 for (almost) all the bits and pieces I needed.

Quote from Marshall:
“The only problem that we have is that the 2pin plugs that you require are obsolete as they are not deemed as safe to use anymore.

If both of these are damaged or missing the only options that you have are to replace for this new switching type that I offered you originally (unfortunately this will mean increasing the hole size in the chassis)or to have the original ones hardwired to the voltage and impedance that you use by an engineer.”

Bah ! these are the impedance and voltage selector plugs I needed. Health and safetly gone mad !

I’m certainly not going to replace the switches for mordern replacements so I’ll stick with the hardwired mods I have made myself for now until I can source an alternative.
So for £16.63, I’ll get the stap handle with gold endcaps,  the four M6 chassis bolts and cagenuts and the four bolts that hold the circuit board to the steel chassis.

I could go to town having it recovered, replacing the corners etc. but its a vintage amp and I want to keep it looking well used.
1. New strap handle for the top of the amp. The old one has rusted and snapped at one end.

2. New ceramic valve bases for the EL34′s, one has cracked and another is chipped.

3. New valve bases for the ECC83 pre-amp valves. These are actually riveted to the chassis and one in particular has rivets that have worn so that the valve base is now loose.

4. Two new chassis cage nuts and bolts – for some reason the front pair are missing.

5. Impedance selector for speaker output

6. Mains input voltage selector.

Some pictures:

The broken handle – a replacement necessity.

This is one of the two broken EL34 valve bases

The impedance and voltage selection switches – missing the selector plugs. I have temporarily soldered the connectors on the inside of the chassis.

The rivet holding the valve base to the chassis has rusted and is broken. A new valve base is in order.

A matched quad set of Electro Harmonix valves arrived yesterday.

Had to wait until the wife and children were out of the house this morning before I could plug them in and test the amp with all four valves.

I did remember to set the output impedance back to 8 Ohms before testing.

A warm, satisfying orange glow from all four valves was all the encouragement I needed to plug the Les Paul in and give it a whirl.

I tried the low sensitivity input on the amp first and cranked the pre and master volume up half way – quite a disappointing output level, so I cranked the pre-amp up to 10 and the master to 8. A little better but not the crunch I was expecting and certainly no where near the volume
Pulled out and plugged into the high sensitivity jack – Christ ! it nearly took my legs out from under me.

Have you ever seen those films of test pilots in the centrifuge G-Force testing devices, where their faces ripple with the extreme force they are under ? Well, thats what I felt like stood in front of this amp and a 4×12 cab after whacking a power cord out
Had to leap for the master volume control before the patio doors blew out.

It works then.

Apart from the cosmetic ‘problems’ with the amp:

• Shoddy looking tolex cover
• Broken top strap handle
• Rustly looking internal chassis
• Cobwebs inside !

I wasn’t actually sure whether the amplifier was in working order.

With replacement transformers costing around £100+ each, all the power amp valves (EL34) missing, voltage selector and impedance selectors missing etc etc. It may turn out to be an uneconomical repair job.

I decided to do the bare minimum to see if the amp was in working order. I set about getting some power into the amp and at least testing up to pre-amp stage.

First job was to check the two externally accessible fuses – the mains input fuse and the HT circuit fuse.

HT fuse rated at 1A was fine, the mains fuse rated at 2A had blown
, this was easy to replace.

I then needed to replace the missing transfomer input voltage selector and speaker output impedance selector.

These are of the external plug in vintage variety and had been long gone. I will replace these but in order to make progress I removed the amplifier chassis from the cabinet and soldered bridging connectors between the common and 240V (UK spec) voltage pole. For teh impedance selectorI soldered a connection between the common and 8 Ohm impedance selector to match my Marshall cabinet impedance.
I now had power into the amplifier.

Interestingly the red neon power light sits before the fuse and so illuminates on switch on regardless of the state of the mains fuse.

Next job was to check the power output from the mains input transformer through to the pre-amp valves. I only had a very poor hand drawn circuit schematic so it was difficult to look at measurement points. I decided instead to look at the preamp valves and see if I could detect any glimmer of light coming from their heaters – a sure sign of input power. Nothing.

The pre-amp valves (3 off) are all Mullard (a good sign) ECC831, I wasn’t actually sure whether I should be able to see any glow on these (I’m still not !)
I was also not sure whether these valves were in working order.

In the absence of my long lost analogue electonic skills I decided I’d just try and limit my expense by geting hold of just TWO cheap EL34 power valves and testing the head at half power load (50W).

I could see some Electro Harmonix (EH) EL34′s from Watford valves in the UK for just £8 each but being an impatient sort and with a public holiday weekend coming up I decided to try my local music store.

Two EH EL34′s at £17.99 each – ouch!.

Still, onwards.

In order to run the amp at half load on two rather than four valves
, the output impedance needs to be halved – Ohms law apparently.

I had to resolder the output impedance selector to 4 Ohms.

Valves now in place, 4 Ohm speaker connected, all knobs turned to minimum – time to power up.

A warm satisfying orange glow from the EL34′s – a good sign.

I felt brave enough to plug a guitar cable into one of the front jacks, tweak the master volume knob to 3 and the same for the pre-amp knob.

A lovely clean crisp Em chord from the cabinet !

Cranked the pre-amp knob clockwise – fantastic filthy tone !

Not wanting to get too optimistic, I have powered down for now and found a matched quad set of EH EL34′s on Ebay for just £30.

I’ll wait until these cheap valves arrive before testing again.

Must remember to reset the impedance slector back to 8 Ohms….

I have had a Mk 2 1978 Marshall Master model 100W head sitting around for ages (about 9 years!) as a restoration project. Well, now I have finally got around to starting the restoration job.

I’ll document my progress here over the coming weeks.