1973 50W JMP - 2563E

OdgeUK · Post by **OdgeUK** » Wed Sep 05, 2007 4:18 am

Could this be the problem? :

My mains and standby switches appear to be 'On-On' DPDT switches with 6 lugs. But I've still bridged the mains feed across the top two tabs and the PT common across the next pair down as though it were a DPST switch.

I'm not certain that a DPDT switch should be wired like this?

Struggling to find a decent DPDT wiring guide at the moment, but it looks like only two of the DPDT tabs are for input, so bridging lugs would be bad news....

neikeel · Post by **neikeel** » Wed Sep 05, 2007 4:49 am

Look at this picture to see if it helps, forget the diode board (the blue wires from the standby are the same as yours, the red to the rectified HT can just be seen too. On this amp I have not put a voltage selector in (Georges std chassis did not have a hole for one) and have shrink wrapped them all in the far corner. This is a std Heyboer 118 PT from George. You should be able to clearly see how I have run the wires and the arrangement of the power supply in. Mac's pic of a really clean 72er is excellent, you probably just need to blow the picture up - when I do it gets all pixellated. On my pic the orange is live between plug and fuse, the yellow from the body of the fuse goes to the 'hot' side of the mains switch. The other side of that switch happens to be the yellow to the PT secondary. The black wire (neutral from the plug) goes to the other secondary of the PT (rather than going to the common of the selector (and then to the other wires via the selector as you should have). I susoect your problem lies partly in your on/off switch hook up. Have you ringed out which terminals are which (ie switched, common etc) as the switches are non stock items.

MacGaden · Post by **MacGaden** » Wed Sep 05, 2007 5:05 am

Hope this is useful.

OdgeUK · Post by **OdgeUK** » Wed Sep 05, 2007 5:21 am

MacGaden - Thank you.

neikeel wrote: I suspect your problem lies partly in your on/off switch hook up. Have you ringed out which terminals are which (ie switched, common etc) as the switches are non stock items.

This is my suspicion too. I have assumed that my 6 lug switches are simply the same as a 4-lug DPST switch and then ignored the bottom pair. I think that it is not this simple and that the DPDT switch I have does not switch in this way. Consequently, I have probably, by bridging the Live feed across two terminals, put the amp in a constant state of 'ON'. Whether or not this would explain the dodgy voltage readings on the pre-amp tube sockets, I don't know.

Looking forward to getting out the office today and seeing if this is just a simple fix

I honestly didn't realise these were non-original switches!

neikeel · Post by **neikeel** » Wed Sep 05, 2007 1:31 pm

MacGaden wrote:Hope this is useful.

You are right that is a really clean amp!

The switches on that are not like any others that I have seen on a Marshall before.

Are they Scandinavian issue for Marshall or replacements? The amp looks like it has been in a museum

Keep us posted........

OdgeUK · Post by **OdgeUK** » Wed Sep 05, 2007 5:17 pm

ok. Permanent power on is sorted now I think but still wrong voltages on V1. Pin1 is 385v! As is Pin6.

No voltage on pin1 one when I switch on amp with standby. Then, when I flick on standby, voltage races up to 385v. If I flick standby back on, voltage very slowly decreases. So that seems to be right.

Continuity test fine on heaters back to the PT.

What else can I check? Been over the wiring diagram a million times, and all looks good??

OdgeUK · Post by **OdgeUK** » Wed Sep 05, 2007 5:29 pm

Getting 333vac on each HT terminal on the PT.

2.8vac on the PT connections for the heaters

240vac on mains switch and voltage selector common.

neikeel · Post by **neikeel** » Wed Sep 05, 2007 5:50 pm

You have the correct HT AC

what is the dc between earth and your red lead off the diode block?

You should get a voltage drop from here through your 10k resistors and the on board links to the plate resistors on V1

Having valves in will bring these voltages down but it does seem a little high to me

Take a reading from that red wire (it is linked via the filter caps to your board (yellow wire to grids and wire from choke there too). Then follow the reading from there to the far end of that big (20k?? 5watt resistor) then to the grey 10ks and to the confluence of the 100k plate resistors on V1 and to the valve pins themselves.

I must say that if I had no shorts and I was sure of my wiring I would put in some ok but not precious preamp valves in to see what happens, see if they bring the voltages down. Chek that you have -30-40V on pin 5 of V4 and v5 if so put your not best power valves in too.

If no good put up a really clear pic of your board and tidied up power supply wiring on the forum to let others (and me) see what you have done if I can't see there are plenty of talented people here who can if you ask nicely

Do not forget to hook up a speaker cab to your amp if you fire up with them in

OdgeUK · Post by **OdgeUK** » Thu Sep 06, 2007 3:12 pm

OK.

At the red lead you mention, I've got 457v DC. Then it drops across my single 16k resistor (where most people have a 10k and 8.2k in series) to 441v.

At the end of the pair of 10K resistors (which are actually 8.2k resistors on my amp) the voltage is 434v.

Finally, at the end of the 100k resistors, to V1, we get 396v. At Pin 1 and 6, this is very slightly lower, at 393v

So I'm dropping about 64v from end of HT fuse to V1.

neikeel · Post by **neikeel** » Thu Sep 06, 2007 3:42 pm

That all sounds about right.

Suggest you check your V4 and V5 voltages and if they are about right as in pin 3 and pin 5 then lob in some valves

OdgeUK · Post by **OdgeUK** » Thu Sep 06, 2007 3:44 pm

neikeel wrote:That all sounds about right.

Suggest you check your V4 and V5 voltages and if they are about right as in pin 3 and pin 5 then lob in some valves

Ok.

But isn't 390v on pin1 of V1 a bit worrying, seeing as the voltage chart expects 180v?

OdgeUK · Post by **OdgeUK** » Thu Sep 06, 2007 3:58 pm

Right, just started checkin again. After discharging caps. Noticed that this time, the voltage at the HT fuse was a little higher than before (bout 470v). Measured pins on v4:

pin 3 - 465 (expected 380)
pin 4 - 465 (expected 390)
pin 5 - -33 (expected -30)

Then I started checking v5 on pin5 and put the probe on pin 6 instead (little bit of spark).Fairly certain I didn't actually cause pin5 and pin6 to touch. Took the probes away, few seconds later, fuse pops. Power dies.

Discharging caps again now and will check HT fuse. And no, I' don't have any more fuses

EDIT *** Oh bugger!! It was the mains fuse that went. And I've just managed to bust the fuse holder getting the fuse out! Think I might call it a night......

neikeel · Post by **neikeel** » Thu Sep 06, 2007 4:03 pm

It's getting volts, why worry

The only things that drop the volts from your B+ line are your voltage dropping resistors (which appear to be doing what they are supposed to do) and the valves.

My latest squeeze (JTM45 clone pics to follow with a story [duff component

] included) did EXACTLY the same. Checked and double checked made sure my power valve voltages were right - they were not as I had a faulty bias cap and was not getting the right voltages in that circuit due to open BC 10uF cap

. I tracked it down and put in a replacement and all good.

Check your bias circuit, V4 and V5 voltages and stick some inexpensive (not your cherished Blackburn 163 Mullards and twin halo xf2 EL34s) and give it a spin (I have some spares if it all goes HORRIBLY wrong

)

neikeel · Post by **neikeel** » Fri Sep 07, 2007 3:51 am

Our posts crossed.

Pain about the fuses.

Make sure they are slo blo, get a pack each of 0.5 and 2amp. (I keep a spare of each taped inside the back panel of each amp when I go out).

Give it a whirl your voltages are about right and your power valves will bias up in that range.

Good luck

OdgeUK · Post by **OdgeUK** » Mon Sep 10, 2007 5:23 pm

Quick Update:

Stuck tubes in tonight and put guitar in channel 1, input 1. Turned power on, then flicked standby off. Vol I and Vol II turned completely down to zero. Lots of hissy noise. Much worse as I raised the volume to about 1. Change guitar input to Channel 1, input 2 and hiss went RIGHT UP. Then started building up into something that sounded like Mic feedback at a gig. Quickly turned off power switch and squealing continued to build up for a moment before dissapating.

Woke up one of the children so had to pack it in. Going to spend a good afternoon one day soon with everything setup and to hand (I dont have a proper workspace at all and have to second the dining room whenever I need to do this stuff, then pack it away before the morning!

).

Just been through the wiring with my Bass head next to it for comparison. Input Jacks, pre-amp sockets, power tube sockets, filter caps, all wired the same. Continuity testing shows heater wires connected all the way from PT to V1 and all wires from sockets passing continuity test back to board, or between sockets. Choke wiring checked for reverse polarity too (well....the red goes to the same power tue socket as on my bass head, and the white respectively)

Bit stumped. I suppose it's got to be a bad solder joint? Or bad earth somewhere?

Quick question too. I was getting about 457v on the tip of the HT fuse holder. Is this the B+ voltage? If so, is this a little high considering the Marstran specification for this PT states that it produces 420v ? Or is that 420v the expected plate voltage? (pin3 on V4?).

EDIT****** The amp was NOT in it's head case when i did this. Would this really make a difference? I've kinda got it set up like the amp in this vid at the moment: http://www.youtube.com/watch?v=ltD2B34_jNQ