1973 50W JMP - 2563E

[LordAli]

BTW: What's the JMP50 plate voltage with 1202-118 PT ?

[OdgeUK]

BTW: What's the JMP50 plate voltage with 1202-118 PT ?

Bout 420v I think.

[OdgeUK]

Neil. Pics as per PM....

[OdgeUK]

For C&E I would use std gauge wire for these (a pair of red or blue twisted wires that go to your stand by switch one of these has the bias feed to the 220k resistor on your board.

Does it matter which one is the bias feed? C or E?

[neikeel]

Hi Odge

No it does not matter which one goes to the bias feed, it is just the high tension AC at this stage from the power transformer secondary, just hook up the white wire to one of the 'hot wires at the switch. Remember to twist the wires quite tightly and lay them forwards from the tranny into the corner of the chassis and run the wires right in the corner before bringing them up to the switch.
Two different coloured wires then come from the switched side of your standby to the first diodes or your diode block if you are going to use it. Remember if you can to run the wires to the selector switch around the chassis in the corner if you can, under the fuse holders, idealy bundled with bootlace (takes practice) or ratchet cable ties (easy but a bit of a giveaway that it has been rewired).
Looking at the dreadful lead dress and fitting of the previous tranny makes me glad you are doing this all properly.

[OdgeUK]

Hi Odge

No it does not matter which one goes to the bias feed, it is just the high tension AC at this stage from the power transformer secondary, just hook up the white wire to one of the 'hot wires at the switch. Remember to twist the wires quite tightly and lay them forwards from the tranny into the corner of the chassis and run the wires right in the corner before bringing them up to the switch.
Two different coloured wires then come from the switched side of your standby to the first diodes or your diode block if you are going to use it. Remember if you can to run the wires to the selector switch around the chassis in the corner if you can, under the fuse holders, idealy bundled with bootlace (takes practice) or ratchet cable ties (easy but a bit of a giveaway that it has been rewired).
Looking at the dreadful lead dress and fitting of the previous tranny makes me glad you are doing this all properly.

That's cool ta. I think I'm nearly there now. I've got the HT's twisted and going to the bottom tabs on the Standby switch, with the bias feed from the board terminated to one of them also. The HT's are, like you suggested, twisted and run round the inside edge and corner of the chassis (although, I might have to re-run them as I think the twisted pair is a little tight as it comes of terminals C&E.

The bias feed I have simply run in a straight line to the standby switch. It goes under the board a little, with some slack.

Now.....looking at the way the mains switch was originally wired, I see a discrepency between how this was done:



and your suggestions in your PM. Your '70 JMP has the live from the mains socket going to the fuse, and then a wire from the fuse to the mains switch, where it is terminated across two tabs by extending the exposed wire and bridging the terminals. And you suggest that my neutral from the mains socket should go to the selector switch. As you can see in the picture of the original PT wiring <shudder> the neutral from the mains socket is wired directly to the mains switch with a wire from there to the selector. And the live from the mains does NOT bridge two terminals at once. Is this the same thing?

And finally..... ..........the earths from the PT. I have the HT earth still to ground somewhere, and the Heater wire earth to ground also. Any reason why I can't bunch these two grounds together and terminate them on the filter cap screw which connects to the filter cap earth? If so, where should I terminate the earth from the Mains socket? I think you said that I shouldn't ground the mains socket in the same place as the other PT earths?

and finally, finally.... I have two wires coming from my indicator lamp. Where do they terminate?? The original wiring had these going to the mains switch, but I have seen other amps with these joined to the Heater wires terminated on V4 and V5??

Thanks for your patience!!

[neikeel]

That's cool ta. I think I'm nearly there now. I've got the HT's twisted and going to the bottom tabs on the Standby switch, with the bias feed from the board terminated to one of them also. The HT's are, like you suggested, twisted and run round the inside edge and corner of the chassis (although, I might have to re-run them as I think the twisted pair is a little tight as it comes of terminals C&E.

The bias feed I have simply run in a straight line to the standby switch. It goes under the board a little, with some slack.

All good!

Now.....looking at the way the mains switch was originally wired, I see a discrepency between how this was done:

]

and your suggestions in your PM. Your '70 JMP has the live from the mains socket going to the fuse, and then a wire from the fuse to the mains switch, where it is terminated across two tabs by extending the exposed wire and bridging the terminals.

Yes and the other swiched side goes to the PTsecondary common

And you suggest that my neutral from the mains socket should go to the selector switch.

Yes the centre common terminal

as you can see in the picture of the original PT wiring <shudder> the neutral from the mains socket is wired directly to the mains switch with a wire from there to the selector. And the live from the mains does NOT bridge two terminals at once. Is this the same thing?

Yes, you complete the circuit by selecting a connection to a PT primary tap with the switch to your other wires to the PT (orange yellow red black etc).

And finally..... ..........the earths from the PT. I have the HT earth still to ground somewhere, and the Heater wire earth to ground also. Any reason why I can't bunch these two grounds together and terminate them on the filter cap screw which connects to the filter cap earth? If so, where should I terminate the earth from the Mains socket? I think you said that I shouldn't ground the mains socket in the same place as the other PT earths?

Exactly, earth the centre taps together on a star earth on a filter cap mount next to the PT and the mains to a different star earth on a filter cap mount next to the chassis (almost under the mains plug).

and finally, finally.... I have two wires coming from my indicator lamp. Where do they terminate?? The original wiring had these going to the mains switch, but I have seen other amps with these joined to the Heater wires terminated on V4 and V5??[/quote]

DEpends on its rating Yours sounds like a 120 or 240v light. Put one terminal onto the switched terminal of the on/off switch and run another directly to the appropriate lug on your PT. If these are hard wired inside teh transformer then you need run the wire to the correct lug on your voltage selector (the PT primary acts as a voltage divider so you do not need to be running the amp on 120v for the warning light to see 120v as long as you have run that appropriate wire from the PT to the switch rather than cutting and shrinking) if that is what it is hooked up to. If 240v lamp the wire should go to the 240v terminal). I personally would use all yout PT wires to all the available terminals on your selector-it will be just as neat and at least they are not flapping around - even if they are insulated an dit will be more original.
Are you keeping the kettle or going to risk death with a bulgin I use bulgins with right angle clamped cable but you may need the kettle to get your PAT testing for some gigs (I mark my own!!!)
Good luck
Neil

[OdgeUK]

Yes, you complete the circuit by selecting a connection to a PT primary tap with the switch to your other wires to the PT (orange yellow red black etc).

Ok. Sooooooooo.....the way I see it....you can do this two ways? (See crude diagram)

Are you keeping the kettle or going to risk death with a bulgin I use bulgins with right angle clamped cable but you may need the kettle to get your PAT testing for some gigs (I mark my own!!!)
Good luck

Hmmm. Keeping the kettle. The Bass amp I just got is still Bulgin, and I was going to use that as is, until you mentioned the whole death thing? Is a Bulgin socket inherently dangerous? I just assumed that people swapped them out in case they lost their orginal bulgin lead and were left with no way to connect the amp to the mains? I have noted Georges disclaimer about the original mains connectors. Tell me more?

[MacGaden]

Hi Odge: I

[neikeel]

The diagram on the right is what I use and that is how they are made.

Regarding Bulgins I put them in my builds and have just put one back in my superbass after junking the kettle lead.

The theory is that there are two issues:

1) a bulgin socket is wide enough for a finger to slip into when the mains are unplugged when you pack it away and you can get a kick back from the filter caps

2) the straight plugs never clamp the cable very well and you get twisted and bared wires with the pulling in and out all the time. Not an issue if you unplug from the wall first but people have got mains shocks from pulling the plug and getting the exposed wires. The straight sockets also stick out so you do have to unplug them.

I use the angled plugs which clamp the cable up because:
You cannot pull on the cable to unplug them.
I often leave them plugged in day to day as the rightangle plug does not stick out appreciably.

If you are keeping both amps using the same sort of lead makes sense, but of course when you use two a amps rig (you know you want to!) you need two cables anyway.

[OdgeUK]

I think I've done all the soldering for now. PPIMV will go in once I've confirmed it's working in un-modded form, as it was before I started.





The indicator lamp is 240v, so I have put one leg on the mains switch (where the live from the kettle socket terminates) and the other leg where the kettle socket neutral joins the yellow 240v feed from the PT, on the voltage selector. Hope this is right?

Tommorow night I will make some sort of attempt to plug it in and hear the result of all my dry solder joints and reversed wiring With a bit of luck, the PT won't explode again and the chassis won't inexplicably become 240v live as soon as I touch it!!

You think I should just plug it in and see if I get any sound? Or should I measure some voltages first with the tubes all out etc? If so, where can I get a guide for what I should be measuring and where?

Will let you know what happens.......

[neikeel]

Look up Georges instruction booklet for his kit. The penultimate couple of pages explain the voltage checking process.

Print yourself an expected chart and there is a blank chart to fill in what you measure.

If you fire up without valves first at least you can check the power supply first (heaters ac/ht ac and your output valve voltages). If you have done something daft you should not blow anything up that way.

Got a spare box of correctly rated slo blo fuses ready

Good luck!

[OdgeUK]

Just having a final look at the amp before I put power to it. Noticed that my NFB wire is going to the 4-ohm tap not the 8ohm like in my schematic. I put it on the 4ohm 'cos that's how it was when I bought the amp. Thought the amp sounded sweet just as is. Any harm in leaving it on the 4 ohm tap for now?

[OdgeUK]

Bugger.

Turned power on and indicator lamp came straight on. Switched power switch, but still on.

Then I decided to test voltages on first two pre-amp sockets. Way high voltages!

V1:

1 374v
2
3 0v
4
5
6 160
7-
8 0v

V2:

1 386v
2
3 0v
4
5
6 426v
7 0
8 0

To measure, I put the multimeter on 600V DCm stuck one lead to the chassis and then probed each of the pins with the other multimeter lead. That's the right way to do it?

These voltages seem present whether Standby is on or not. Seems like I've got permanent power on??

I've discharged the filter caps from 300v to 1.9v now. And will look over the amp for any obvious mistakes.......

[neikeel]

Bugger.



These voltages seem present whether Standby is on or not. Seems like I've got permanent power on??

I've discharged the filter caps from 300v to 1.9v now. And will look over the amp for any obvious mistakes.......

Yup! Trace power into mains fuse to PT common to on/off switch to various selectors.
Check ac on heaters
Check ac on HT (yopu'll only get half)
check ht on v4 and v5

Take care!