Please help me out. 1969 100w build

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no0sand1s
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Re: Please help me out. 1969 100w build

Post by no0sand1s » Tue May 15, 2018 4:40 pm

neikeel wrote:
Wed May 09, 2018 1:44 pm
Ok so the 100-460 is:
I REMOVED THE HT FUSE AND READ -.38VDC - 0.0VAC I NOTED BOTH GREEN WIRES FROM PT (FILAMENT PRIMARY AND BIAS) GOING TO GROUND LUG NEXT TO CAP F6

REPLIES BELOW IN CAPS:
CURRENT PHOTOS: https://www.flickr.com/gp/wedinbordeaux/58Uz78

Primary
orange is common to power switch which when on goes to the selector switch (or neutral if no voltage selector - is that black in US cords?). NO VOLTAGE SELECTOR. ORANGE GOES TO MAINS FUSE, RED TO POWER SWITCH. EUREKA MOMENT?!? The red wire to the other half of the switch goes to one end of the mains fuse, the other end of which gets feed from power cord live (US = white?). YES Other power cord wire I presume is green which is ground? WHITE=HOT, BLACK=COMMON, GREEN=GROUND

Check you have 120vac across the mains switch 6.7VAC

Secondaries
Blue/white and grey go to each half of the standby switch with the yellow centre tap to the junction of the mains cans (looks correct in pics) YES. NEW PHOTOS ADDED.

check you have 350vac across the lugs of the standby switch 177.8VAC

the feed to the cans comes to them via the red wire from the apex of the rectifier with another spur to the HT fuse which then via the fuse feeds the turret on the corner of the board. YES

check at this corner lug point (and on the fuse and red wire of mains filter cans) measure between ground and you should have about 460vdc. -.39VDC

Then follow the B+ line from that corner lug to the one where the choke feeds the screens (two yellow wires and choke wire) you will get a slight drop here - maybe 450vdc. -.39VDC

Chase along the droppers (to the lug where the 10k MO resistor hooks to the black wire and blue wire) you will get a 20-30v drop here. -.46VDC

Do these checks an post back

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neikeel
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Re: Please help me out. 1969 100w build

Post by neikeel » Wed May 16, 2018 4:05 pm

It seems at first pass that there is a problem with the wiring of your PT.

You should get 177vac on either side of the centre tap (between blue/white and yellow and between grey and yellow) so you have half your HT, pre-rectifier. You might see 177vac between ground and each stand by lug?

If not the wiring from the PT is off.

To be sure you will have to unsolder all the PT secondary wires and screw them into a terminal strip (colloquially called a chocolate block connector) just to keep the wires safe from hands and touching.

Then measure between wires, then you know it is not your wiring to the amp.
Neil

Tazin
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Re: Please help me out. 1969 100w build

Post by Tazin » Wed May 16, 2018 6:15 pm

6.7Vac at the mains switch (ON/OFF) is way off. Use your Multimeter to check the outlet for 120Vac (between the narrow blade slot and the ground hole). If that checks out fine then plug the amp in (but leave it off) and check between the black wire that connects to the mains (ON/OFF) switch and ground (chassis) for 120Vac.

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Re: Please help me out. 1969 100w build

Post by no0sand1s » Sat May 19, 2018 5:53 pm

Tazin wrote:
Wed May 16, 2018 6:15 pm
6.7Vac at the mains switch (ON/OFF) is way off. Use your Multimeter to check the outlet for 120Vac (between the narrow blade slot and the ground hole). If that checks out fine then plug the amp in (but leave it off) and check between the black wire that connects to the mains (ON/OFF) switch and ground (chassis) for 120Vac.
Last edited by no0sand1s on Sat May 19, 2018 7:05 pm, edited 1 time in total.

no0sand1s
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Re: Please help me out. 1969 100w build

Post by no0sand1s » Sat May 19, 2018 5:53 pm

a
Last edited by no0sand1s on Sat May 19, 2018 7:04 pm, edited 1 time in total.

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Re: Please help me out. 1969 100w build

Post by no0sand1s » Sat May 19, 2018 6:24 pm

no0sand1s wrote:
Sat May 19, 2018 5:53 pm
no0sand1s wrote:
Sat May 19, 2018 5:53 pm
Tazin wrote:
Wed May 16, 2018 6:15 pm
6.7Vac at the mains switch (ON/OFF) is way off. Use your Multimeter to check the outlet for 120Vac (between the narrow blade slot and the ground hole). If that checks out fine then plug the amp in (but leave it off) and check between the black wire that connects to the mains (ON/OFF) switch and ground (chassis) for 120Vac.
I get 125VAC between ground and the black wire to mains switch. The indicator light turns on - I get 125VAC on the red wire to the lamp, but no reading on the black wire - this leads to the mains fuse and there's no voltage showing on either terminal.

I unsoldered secondary wires and attached to terminal strip. See VAC I'm reading : https://www.flickr.com/gp/wedinbordeaux/L614UY

There are 2 green wires showing different voltages - should I be surprised there are no individual identifiers for these...

What's the next step? Call Mercury?

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Re: Please help me out. 1969 100w build

Post by Tazin » Sat May 19, 2018 7:43 pm

Well, you have the correct wall voltage (apprx. 120Vac) at the mains (ON/OFF) switch...The black wire from the Indicator lamp should not have voltage since it is connected to the Mains Fuse along with the White wire (neutral) from the AC power cord. The Metroamp instructions puts the Mains Fuse inline with the Neutral wire (just like Marshall did back in the day) rather than the Hot wire (black wire). The two secondary Green wires don't require identification from one another since they are both used as Grounds in this application. You could run both the Green secondary wire back to ground again and re-check the AC voltages at the terminal block but with the numbers I see that you listed from your initial test tells me something is wrong with the PT. Perhaps neikeel has some insights or a new "plan of attack"...I'd wait for him to chime in.

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neikeel
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Re: Please help me out. 1969 100w build

Post by neikeel » Sun May 20, 2018 4:54 am

Can I just double check.

Meter set to ac volts, add probe to wires I mention (not to ground unless I say)

Your input voltage is 120v into the orange and red pair of wires only? The other wires are turned back and shrink wrapped?

Heaters
Measure between thick black and black wires should equal about 6.5vac (half that between black/green and green/black)

Bias
Measure between white and green bias wires (check for continuity first) should get around 95vac.

High Tension

Measure between grey and blue/white wires should get 350vac (and half that between these and the yellow CT).

What have you done with the brown and brown accessory wires (hopefully folded back and shrink-wrapped away?

Let us know what happens.

If you do these tests and don't get these readings the PT needs to go back to Mercury.
Neil

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Re: Please help me out. 1969 100w build

Post by no0sand1s » Fri May 25, 2018 9:35 pm

Hello all.

122VAC between red and orange pair of wires (which are currently soldered into the switch and mains fuse, respectively). All other wires from the PT are wired to my connecting block, and extra (2) brown, violet, and blue wires are shrink wrapped and tied away.

Between both black wires, I read 6.8VAC

Between 1st black wire and (2) green wires, I read 3.4VAC and 18.8VAC. Between 2nd black wire and (2) green wires, I read 3.42VAC and 15.8VAC

Between white and (1) green wire, I get no continuity, but 99VAC. Between the white wire and the other green wire, I get resistance and 13.3VAC

Between grey and blue/white wire I get 356VAC

All extra wires have shrink tubing around the end and are bundled.

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neikeel
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Re: Please help me out. 1969 100w build

Post by neikeel » Sat May 26, 2018 4:23 am

no0sand1s wrote:
Fri May 25, 2018 9:35 pm
1). 122VAC between red and orange pair of wires (which are currently soldered into the switch and mains fuse, respectively). All other wires from the PT are wired to my connecting block, and extra (2) brown, violet, and blue wires are shrink wrapped and tied away.
1). Ok so your input is correct and other primaries and the extra pair of secondaries are secure.
no0sand1s wrote:
Fri May 25, 2018 9:35 pm
2). Between both black wires, I read 6.8VAC
2).That is correct as these are your heaters, the centre tap should be a green wire of same gauge which follows on to :
no0sand1s wrote:
Fri May 25, 2018 9:35 pm
3).Between 1st black wire and (2) green wires, I read 3.4VAC and 18.8VAC. Between 2nd black wire and (2) green wires, I read 3.42VAC and 15.8VAC
3). That is odd. If you have half of 6.8vac between a black and green wire that green wire must be the centre tap, therefore between that green wire and the other black wire you MUST have 3.4vac, by definition (from the 6.8vac reading in (2) on each so bundle the two black wires and the green wire that gives those readings.
no0sand1s wrote:
Fri May 25, 2018 9:35 pm
4).Between white and (1) green wire, I get no continuity, but 99VAC. Between the white wire and the other green wire, I get resistance and 13.3VAC
4). That is ok, pair up the 99vac green and white - these are correct as bias wires.
no0sand1s wrote:
Fri May 25, 2018 9:35 pm
5). Between grey and blue/white wire I get 356VAC
5). That sounds correct

So the PT sounds like it is doing what it should, and if your other wiring is correct you wire each aspect of your secondary to the correct places it will all work. Leave each set of wires isolated to your block until we are ready for them.

I suggest first you wire the black heater wires to pins 2 and 7 of the socket V7, with the corresponding ground wire to a good solid lug on the chassis (in Larry grounding you run the ground from your input jacks to this point but lets get it working first.
Now check you have heater readings to each socket, if not inspect to see where mistake is.

Next is your bias wire, again ground the green wire (I tend to do this to one of the output tube ground lugs (any round will do),
Now check you have bias voltage on the 220k resistors and the orange and green wires to pin 5s of your outputs (-40 to -50vac is ballpark).

Finally wire the HT (high tension wires from the PT to either half of the DPST standby switch so that when you throw the switch they connect to the pair of wires that go to the rectifier.

Take a picture of where you are wiring to at each stage and check your readings step by step. Also make sure you have the correct rated SLO blow (T rated) fuses in place - check fuses with a resistance/continuity meter not by eye.

If all is correct put your preamp tubes in (don't need a load yet) and recheck your voltage chart.

If still good hook your amp up to cab with speaker cable, drop in your output tubes and see if it works, check your bias is not too hot (in fact adjust your bias resistor to max - voltage you can get initially before dropping tubes in to avoid red plating/trashing them.

Post back later please.

Sorry I can't hand hold each step but there is a time difference and I am working on call all weekend!
Neil

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Re: Please help me out. 1969 100w build

Post by Tazin » Sat May 26, 2018 10:09 am

The above post is why neikeel is hailed as a mighty amp guru when it comes to Marshalls...The man knows his stuff!

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neikeel
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Re: Please help me out. 1969 100w build

Post by neikeel » Sat May 26, 2018 1:39 pm

No not true!
It is just common sense and basic wiring
Neil

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Re: Please help me out. 1969 100w build

Post by no0sand1s » Tue May 29, 2018 3:13 pm

I've reconnected the (2) black wires to V7, pins 2 and 7. Can you confirm what you're referring to by 'corresponding ground' wire'? Should I reconnect the (2) green wires from the PT to the ground lug I have bolted to the chassis?

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Re: Please help me out. 1969 100w build

Post by Tazin » Tue May 29, 2018 4:00 pm

In order to find out which Green wire is the center tap for the heater winding you need to use your meter set to Ohms and measure between one of the Black heater wires and each Green wire. The correct 'corresponding' Green wire should have a very low Ohms reading and should also read just about equal (ohms wise) between either Black heater wire and the Green wire. The low ohms reading is due to the fact that the heater winding is made up of a rather thick wire so it has a pretty low resistance.

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neikeel
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Re: Please help me out. 1969 100w build

Post by neikeel » Wed May 30, 2018 4:13 am

no0sand1s wrote:
Tue May 29, 2018 3:13 pm
I've reconnected the (2) black wires to V7, pins 2 and 7. Can you confirm what you're referring to by 'corresponding ground' wire'? Should I reconnect the (2) green wires from the PT to the ground lug I have bolted to the chassis?
Yes that will work for now
Neil

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