1973 50W JMP - 2563E

neikeel · Post by **neikeel** » Sat Jun 16, 2007 10:36 am

Update?

On edge of seat here

OdgeUK · Post by **OdgeUK** » Mon Jun 18, 2007 1:33 am

Yes, sorry for the extended delay! I went on holiday a couple of weeks ago and things have been pretty full on since I got back. No further progress at the moment on the amp. Hope to continue with a good soldering session next week (finishing late all this week from work

)......

Thanks for watching!

Stay tuned......

neikeel · Post by **neikeel** » Mon Jun 18, 2007 4:21 am

OdgeUK · Post by **OdgeUK** » Wed Jun 20, 2007 4:21 am

neikeel wrote:D and E are your earthed centre taps (remember it is AC)

C and E are red wires to the hot side of the standby switch (plus white wire to bias feed)

F is the common to your input (voltage) selector.

The wires to the heaters should be heavy gauge (preferably solid core) and twisted neatly together.

The other wires can be std gauge (same as rest of amp).

Bit confused. I have always though that Heater Wires refers to the twisted red/black pair that go to each of the pre-amp sockets. Presumably, this pair make their way back to the PT at some point. So are they Black/Red when they leave the PT? Is this from the A and B tags on the PT?

So for the wires from C,D,E and F, I can use standard guage wire? What would be the normal wire colour convention for this? I can then order the correct colours, in standard guage (22? Non-solid core?), from George.

Is it:

C&E = Red.
F = Blue
D&E Green/Yellow striped

Anf G,H and I? Not used at all?

neikeel wrote: Not sure what options there are on your voltage selector but suggest you connect all the ones that you have, cut the others at 2-3cms, fold them back on themselves and cover in heat shrink (George usually sends some with his MV kit).

My voltage selector was originally hardwired for 240V. The other voltage options were not wired up. Quite happy to keep it this way as I don't think I'll be using the amp outside the UK! (The 'Conquering America' tour is a way off yet....

)

neikeel · Post by **neikeel** » Wed Jun 20, 2007 7:57 am

D and H are the earthed centre taps for the AC

D=earth for the HT. 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.

G & I are the heater wires (heavy gauge) usually pair of blue, green or yellow single strand (to withstand 3A AT LEAST) H=earth for the heaters. After the first power tube (V5) the parallel connections (red/black) go to each valve socket in turn (make sure in parallel and twisted to avoid ac hum)

A & B you will not use as they are heater wires for a GZ34 valve rectifier.

The common wire is usually black and goes to to the mains on/off switch (if you are using a DPST switch you strip the wires back to extend the wire to use both rows of the switch. The other two terminals on your mains switch are hooked up to the mains fuse via a yellow wire (normal gauge stipped bcak in the same way). The other end of the mains fuse holder goes to the live feed in from the mains socket (are you bulgin or IEC?). If you ar hard wiring for 240v then use the yellow wire from your PT to go straight to the neutral terminal on your socket.

Pics of my JMP 50 are here but I used my selector switch

Hope this helps. My common wire is the blue one on the underside of the on/off switch the yellow is bundled and goes tothe fuse holder. You can see what I mean by extending the wires to both terminals? My HT feeds are red wires (on underside of standby with white wire). The other terminals go to the diodes.

http://s76.photobucket.com/albums/j2/ne ... mps023.jpg

OdgeUK · Post by **OdgeUK** » Wed Jun 20, 2007 8:49 am

GREAT

Any tips for soldering to G,H and I? These are not tags like the other connections but are, instead, solid metal bars. Wrap wire around the bar a couple of times and then solder?

Where do you like to earth your Centre taps? I see one often to the ground of the corner filter cap. What bout the other?

And you know....I'm looking at this pic from the net:

And thinking.....why have they put the PT in that way round? Surely 180 degrees turn would be best? Then the terminals for the Heaters are closer and the standby/mains terminals are closer to the switch?

neikeel · Post by **neikeel** » Wed Jun 20, 2007 9:58 am

They can be a little tricky!

Suggest you use a little emery cloth or dry wire wool to roughen up surface to make sure it is grease free. 'Tin' the wires with a little solder first (a good soldering iron is important - 40watts helps).

'Tin' the wires you are going to solder to them for the same length as teh terminals on the tranny and lay the two together with long point of contact and then apply heat to the tranny terminals not the wires. This should give you a god joint once the solder has flowed without melting your wire insulation. I recommend running a piece of shrink wrap over each terminal to cover it up as much as possible on each of these joints. I find that using a soldered ring type terminal (Halfords again!) for the earths to one of the tranny bolts works well, you can run your earth wire from the bus rail on your control pots to this too. Do not earth your mains terminal here, use a wire to one of the filter cap star washers (you may have kept that in place already?)

OdgeUK · Post by **OdgeUK** » Wed Jun 20, 2007 10:40 am

Neil,

What do you think about the rotation of the PT? (see my last post)

neikeel · Post by **neikeel** » Wed Jun 20, 2007 10:45 am

Don't know!

I asked the same question when I put my JTM45/100 together!!

That's just how they went on originally so that is how I did it. It makes no difference to transformer hum either way.

OdgeUK · Post by **OdgeUK** » Thu Jun 21, 2007 4:24 am

Will this be ok for the Heater wires from PT to power tube?

http://store.metroamp.com/product_info. ... cts_id=310

It's solid core 20guage. Not sure if it's power rating is sufficient though?

neikeel · Post by **neikeel** » Thu Jun 21, 2007 5:10 am

It's too fine for first run from PT.

Ideal for preamp tubes tho'

Wire from 3core domestic solid core 5A would be fine if you are struggling, bit more difficult to twist

OdgeUK · Post by **OdgeUK** » Thu Jun 21, 2007 6:15 am

neikeel wrote:
Wire from 3core domestic solid core 5A would be fine if you are struggling, bit more difficult to twist

You mean standard electrical flex? George doesn't seem to do wire specific for Heater wire from PT to Tube. Even in his Full amp-wire set ?

neikeel · Post by **neikeel** » Thu Jun 21, 2007 7:15 am

Yes that is what I mean.

You could use a pair of blues or blacks twisted, preferably keeping the wires short but not under any tension. I would run them forwards first and sideways (at 90 degrees) and run them around the PT (like the JTM100 in your pic above) in the groove of the mounting bracket, keeping them away from the 'signal' wires as much as possible. The different power tap wires you are not using can be cut back and shrink wrapped.
What is your warning lamp? Is it 6.3v? If so that should be hooked directly to your heater terminals on the PT and again twist the wires together for hum rejection. Keeping the wires close to the front of the chassis.

OdgeUK · Post by **OdgeUK** » Mon Jun 25, 2007 3:06 pm

Going to wire up the input jacks tonight, now that the kids are finally in bed

In the meantime. I thought I'd share with you a picture of the Power Transformer that was in the amp when I bought it.

Do you like the way that the last tech to work on this amp (when I had it serviced) clamped the PT down tight onto all those wires? Nice.

neikeel · Post by **neikeel** » Mon Jun 25, 2007 4:04 pm

Once you've done it all plug her in and give it a big open Em through a 4x12 with volumes at about 6 or 7 bridged about 3am and get assaulted by your wife..........