Join me on a magical journey: Metro Plexi Superlead Build

[FourT6and2]

So, I have a few issues:

1. Half the board is populated. But I can't continue because I'm missing two caps. Metro is mailing them out to me.

2. Back when I wired the heaters, I checked the joints with a meter to make sure they were good. I had noticed that the heaters/filaments were getting continuity to ground on all sockets. Didn't think anything of it at the time since the power transformer's center tap and one side of the bias supply are grounded (as they're supposed to be). But, I was speaking to someone from Metro when I called about the missing caps and they informed me that the heaters are NOT supposed to have continuity to ground...

And, I've gone over everything and checked my wiring and it all looks good. So, I'm not sure what to do about that...

3. I got a 100k metal oxide resistor to replace the 47k in the feedback section of the board (along with placing the negative feedback wire on the 4ohm tap). This will bring the amp closer to mid-late 70's JMP. The only thing is, after I installed on the board and was checking continuity, I noticed the resistor is measuring 4.5k and NOT the 100k it's supposed to be. The color code is: brown, black, yellow, red. This is what a 100k (2%) value should be.

Can resistors go bad and/or measure false values? Because this thing is WAAAAY off.

 

[cyndicate]

So, I have a few issues:

1. Half the board is populated. But I can't continue because I'm missing two caps. Metro is mailing them out to me.

2. Back when I wired the heaters, I checked the joints with a meter to make sure they were good. I had noticed that the heaters/filaments were getting continuity to ground on all sockets. Didn't think anything of it at the time since the power transformer's center tap and one side of the bias supply are grounded (as they're supposed to be). But, I was speaking to someone from Metro when I called about the missing caps and they informed me that the heaters are NOT supposed to have continuity to ground...

And, I've gone over everything and checked my wiring and it all looks good. So, I'm not sure what to do about that...

3. I got a 100k metal oxide resistor to replace the 47k in the feedback section of the board (along with placing the negative feedback wire on the 4ohm tap). This will bring the amp closer to mid-late 70's JMP. The only thing is, after I installed on the board and was checking continuity, I noticed the resistor is measuring 4.5k and NOT the 100k it's supposed to be. The color code is: brown, black, yellow red. This is what a 100k value should be.

Can resistors go bad and/or measure false values? Because this thing is WAAAAY off.

For 3. If the resistor is placed in the circuit already and installed, its not going to read 100k

 

[FourT6and2]

So, I have a few issues:

1. Half the board is populated. But I can't continue because I'm missing two caps. Metro is mailing them out to me.

2. Back when I wired the heaters, I checked the joints with a meter to make sure they were good. I had noticed that the heaters/filaments were getting continuity to ground on all sockets. Didn't think anything of it at the time since the power transformer's center tap and one side of the bias supply are grounded (as they're supposed to be). But, I was speaking to someone from Metro when I called about the missing caps and they informed me that the heaters are NOT supposed to have continuity to ground...

And, I've gone over everything and checked my wiring and it all looks good. So, I'm not sure what to do about that...

3. I got a 100k metal oxide resistor to replace the 47k in the feedback section of the board (along with placing the negative feedback wire on the 4ohm tap). This will bring the amp closer to mid-late 70's JMP. The only thing is, after I installed on the board and was checking continuity, I noticed the resistor is measuring 4.5k and NOT the 100k it's supposed to be. The color code is: brown, black, yellow red. This is what a 100k value should be.

Can resistors go bad and/or measure false values? Because this thing is WAAAAY off.

For 3. If the resistor is placed in the circuit already and installed, its not going to read 100k

Funny, ever other resistor I already installed measures what it's supposed to...

 

[cyndicate]

So, I have a few issues:

1. Half the board is populated. But I can't continue because I'm missing two caps. Metro is mailing them out to me.

2. Back when I wired the heaters, I checked the joints with a meter to make sure they were good. I had noticed that the heaters/filaments were getting continuity to ground on all sockets. Didn't think anything of it at the time since the power transformer's center tap and one side of the bias supply are grounded (as they're supposed to be). But, I was speaking to someone from Metro when I called about the missing caps and they informed me that the heaters are NOT supposed to have continuity to ground...

And, I've gone over everything and checked my wiring and it all looks good. So, I'm not sure what to do about that...

3. I got a 100k metal oxide resistor to replace the 47k in the feedback section of the board (along with placing the negative feedback wire on the 4ohm tap). This will bring the amp closer to mid-late 70's JMP. The only thing is, after I installed on the board and was checking continuity, I noticed the resistor is measuring 4.5k and NOT the 100k it's supposed to be. The color code is: brown, black, yellow red. This is what a 100k value should be.

Can resistors go bad and/or measure false values? Because this thing is WAAAAY off.

For 3. If the resistor is placed in the circuit already and installed, its not going to read 100k

Funny, ever other resistor I already installed measures what it's supposed to...

Is it in series with another resistor for the 100k? If you are measuring it inside the circuit it will look at the resistance of all the resistors in the path.

 

[cyndicate]

Also for No. 2, I thought since the CT is grounded like you mentioned there will always be continuity to ground with the heaters which I think is correct? I remember when I built my amps I was wondering the same thing, maybe someone can chime in.

 

[FourT6and2]

So, I have a few issues:

1. Half the board is populated. But I can't continue because I'm missing two caps. Metro is mailing them out to me.

2. Back when I wired the heaters, I checked the joints with a meter to make sure they were good. I had noticed that the heaters/filaments were getting continuity to ground on all sockets. Didn't think anything of it at the time since the power transformer's center tap and one side of the bias supply are grounded (as they're supposed to be). But, I was speaking to someone from Metro when I called about the missing caps and they informed me that the heaters are NOT supposed to have continuity to ground...

And, I've gone over everything and checked my wiring and it all looks good. So, I'm not sure what to do about that...

3. I got a 100k metal oxide resistor to replace the 47k in the feedback section of the board (along with placing the negative feedback wire on the 4ohm tap). This will bring the amp closer to mid-late 70's JMP. The only thing is, after I installed on the board and was checking continuity, I noticed the resistor is measuring 4.5k and NOT the 100k it's supposed to be. The color code is: brown, black, yellow red. This is what a 100k value should be.

Can resistors go bad and/or measure false values? Because this thing is WAAAAY off.

For 3. If the resistor is placed in the circuit already and installed, its not going to read 100k

Funny, ever other resistor I already installed measures what it's supposed to...

Is it in series with another resistor for the 100k? If you are measuring it inside the circuit it will look at the resistance of all the resistors in the path.

One side is connected to the 4ohm tap on the impedance switch. The other side is connected to the presence pot. Every other resistor on the board measures what it's value is supposed to be (even though they're all connected to other caps and resistors).

Also for No. 2, I thought since the CT is grounded like you mentioned there will always be continuity to ground with the heaters which I think is correct? I remember when I built my amps I was wondering the same thing, maybe someone can chime in.

That's what I thought as well. But the guy from Metro said the heaters are not supposed to see ground...

 

[novosibir]

2. You don't measure continuity, but almost continuity. From the CT to one outside of the heater's secondary it's only about 0.2...0.3 ohms - less than the resistance of your meter leads. It's impossible, to measure the heater secondary resistance with a regular DMM

3. When mesuring the NFB resistor already soldered into the circuit, then you're measuring inside a circle. The circle is from the NFB-R through the OTs secondary to ground and from there into the 4.7K parallel to the presence circuit. So think about, what you've done! Parallel to the 100K is the secondary + the 4.7K in series. The secondary almost is zero-point-nothing, so you've measured 100K parallel to 4.7K, resulting in 4.5K

Larry

 

[novosibir]

That's what I thought as well. But the guy from Metro said the heaters are not supposed to see ground...

Correct, the heaters (filaments) inside the tubes aren't grounded.
But the heater's secondary CT definitely is - at least should be.

Larry

 

[FourT6and2]

2. You don't measure continuity, but almost continuity. From the CT to one outside of the heater's secondary it's only about 0.2...0.3 ohms - less than the resistance of your meter leads. It's impossible, to measure the heater secondary resistance with a regular DMM

3. When mesuring the NFB resistor already soldered into the circuit, then you're measuring inside a circle. The circle is from the NFB-R through the OTs secondary to ground and from there into the 4.7K parallel to the presence circuit. So think about, what you've done! Parallel to the 100K is the secondary + the 4.7K in series. The secondary almost is zero-point-nothing, so you've measured 100K parallel to 4.7K, resulting in 4.5K

Larry

For the heaters, I set my meter to read shorts. It beeps. When I place one lead on the chassis and the other at a heater pin on a socket, the meter reads a connection and beeps. I thought this was supposed to happen, as the PT center tap is grounded. But all I'm saying is the guy I spoke to at Metro said otherwise...

As for the NFB resistor...

Thanks! I'm glad it's supposed to be that way... I was freakin' out

 

[FourT6and2]

Well, everything's pretty much done. I'm just waiting on two capacitors that are in the mail before the board is 100%. After that, I'll wire up the power cord, form the filter caps and test for all the voltages. Then I'll rock some faces off with mah toanz!

I figured out the special "trick" to getting those nice blobs of solder on the turrets. Just tap dat thang!

I also seem to have a lot of extra parts left. That worries me. 17 resistors, one electrolytic cap, and two other caps. I guess they're included so you can experiment with different values in the tone stack?

 

[briango2000]

Beautiful job...I'm sure it will sound great.

 

[novosibir]

I'm just waiting on two capacitors...

You're still waiting for the two .68/160V SoZo cathode caps. Right?
Don't forget to put the 2.7K cathode resistor in!
And yes, that's normal, that there are a lot of components left over with the MetroAmp kits.

Hey, I wish you a lot of fun with the beast!

I'm sure, that 'she' will be sounding killer!

Keep in mind, that the SoZo's need about 8-10 hours of playing, before they start to open up the nice, shimmering highs and before they loose their first dullness. Also the OT needs its time, before it's loosing its first edgyness and becomes sounding rounder and meatier after 20-30 hours of playing. After about 30-50 hours of playing (depending on the loudness) 95-98% of the burn in processes are finished and from here on only fun is remaining.

Just a tip: Swap the JJ preamp tubes with TungSol reissue - or/and try to get a nice NOS pre for the 1-st place.
Tungsram, Mullard, Valvo, RCA or Philips are good choices for this

Larry

 

[FourT6and2]

I'm just waiting on two capacitors...

You're still waiting for the two .68/160V SoZo cathode caps. Right?
Don't forget to put the 2.7K cathode resistor in!
And yes, that's normal, that there are a lot of components left over with the MetroAmp kits.

Hey, I wish you a lot of fun with the beast!

I'm sure, that 'she' will be sounding killer!

Keep in mind, that the SoZo's need about 8-10 hours of playing, before they start to open up the nice, shimmering highs and before they loose their first dullness. Also the OT needs its time, before it's loosing its first edgyness and becomes sounding rounder and meatier after 20-30 hours of playing. After about 30-50 hours of playing (depending on the loudness) 95-98% of the burn in processes are finished and from here on only fun is remaining.

Just a tip: Swap the JJ preamp tubes with TungSol reissue - or/and try to get a nice NOS pre for the 1-st place.
Tungsram, Mullard, Valvo, RCA or Philips are good choices for this

Larry

Yeah, I'm waiting for the .68 Sozo caps. And yeah, I have that 2.7K resistor ready and waiting! I think I'm going to go with Chinese Shuguang HG+ preamps because of their longevity and low-noise. For power tubes, I'll probably go with the JJ E34L's initially, and after I know the amp is working correctly, I'll go with either SED =C= or Ruby BHT.

Thanks for all the help!

 

[FourT6and2]

This thing is insanely, ridiculously, incredibly, ear-splittingly LOUD...

I still have a few kinks to work out, though. I need to change one of the caps to a different value, remove the bright cap, and install one of the missing .68uF caps that is still in the mail. But that cap is not required to operate the amp.

It's all biased up and ready to rock. But it's WAY too loud to play in my apartment, even on like... 2 or 3. So I'll have to wait until I can get into the practice space to crank it.

Oh, and the presence pot seems like it's bad. It makes an audible low-rumble when you move it. Other than that, it works fine.

Will report back when I have more time to play with it. Gotta break it in.

 

[LP Freak]

This thing is insanely, ridiculously, incredibly, ear-splittingly LOUD...

I still have a few kinks to work out, though. I need to change one of the caps to a different value, remove the bright cap, and install one of the missing .68uF caps that is still in the mail. But that cap is not required to operate the amp.

It's all biased up and ready to rock. But it's WAY too loud to play in my apartment, even on like... 2 or 3. So I'll have to wait until I can get into the practice space to crank it.

Oh, and the presence pot seems like it's bad. It makes an audible low-rumble when you move it. Other than that, it works fine.

Will report back when I have more time to play with it. Gotta break it in.

The LarMar does wonders.

 

[cyndicate]

For a stock I like the LarMar, have one in my JTM45 atm, if you decide to mod it and cascade the gain stages a pre-pimv works great.

 

[novosibir]

Oh, and the presence pot seems like it's bad. It makes an audible low-rumble when you move it.

When the presence pot is wired in old fashion as original, then it's normal, when you have a scratchy noise by dialing.
There's DC across the pot, what causes the scratchyness.

Larry

 

[gibson08]

Wow, you have moved right along on the build, was it harder or easier than you thought? Def looking forward to some clips!!!

 

[FourT6and2]

This thing is insanely, ridiculously, incredibly, ear-splittingly LOUD...

I still have a few kinks to work out, though. I need to change one of the caps to a different value, remove the bright cap, and install one of the missing .68uF caps that is still in the mail. But that cap is not required to operate the amp.

It's all biased up and ready to rock. But it's WAY too loud to play in my apartment, even on like... 2 or 3. So I'll have to wait until I can get into the practice space to crank it.

Oh, and the presence pot seems like it's bad. It makes an audible low-rumble when you move it. Other than that, it works fine.

Will report back when I have more time to play with it. Gotta break it in.

The LarMar does wonders.

Yeah, I'm definitely ordering one.

Oh, and the presence pot seems like it's bad. It makes an audible low-rumble when you move it.

When the presence pot is wired in old fashion as original, then it's normal, when you have a scratchy noise by dialing.
There's DC across the pot, what causes the scratchyness.

Larry

You're my hero, Larry. Is there another way of wiring up the presence control so it doesn't see DC?

While I have your attention I have two other concerns:
1. There's a bit of hum, even without a guitar plugged in. I think it's 60 cycle hum from the mains. I have the neutral lead from the mains plug bundled with the power transformer's primaries and secondaries (running to the power switch). Should I unbundle it and just leave it running up in the air, straight to the switch? Any other causes of hum I should look at?

2. The middle and treble pots add a fair amount of noise (slight hum and some hiss) when I turn them up. It's contributing to most of the noise I hear. Any way of getting rid of this noise or is it normal?

Thanks!

Wow, you have moved right along on the build, was it harder or easier than you thought? Def looking forward to some clips!!!

I think it was pretty much as easy (or hard) as I thought it would be. I didn't have too many moments of concern. I think there were a couple of times when I had to do a bit of searching online to find a certain way of doing something. And I think the biggest hassle was wiring up the heaters and the impedance selector. I turned the amp on and all the numbers looked good. I did have two scary moments, though:

1. The instructions say NOT to flip the amp out of standby while taking measurements. But this is incorrect, as there's no high-voltage running while in standby. So I was getting strange numbers on all the tube socket pins. I thought it was my meter, so I ran out and bought another one.

2. While measuring the power tube sockets I accidentally shorted pin 3 and pin 2 on V7. Caused a big spark and the HT fuse blew. Scared the shit out of me. But I replaced the fuse and all is well.

Also I'm a bit frustrated at the missing parts. I'm still waiting for them to arrive.

All in all, it was a good build and I already know what is next for me: SLO Clone!

 

[Anonymous]

This thing is insanely, ridiculously, incredibly, ear-splittingly LOUD...

I still have a few kinks to work out, though. I need to change one of the caps to a different value, remove the bright cap, and install one of the missing .68uF caps that is still in the mail. But that cap is not required to operate the amp.

It's all biased up and ready to rock. But it's WAY too loud to play in my apartment, even on like... 2 or 3. So I'll have to wait until I can get into the practice space to crank it.

Oh, and the presence pot seems like it's bad. It makes an audible low-rumble when you move it. Other than that, it works fine.

Will report back when I have more time to play with it. Gotta break it in.

The LarMar does wonders.

+1 My fav for NMV amps...

Steve