NAD - MESA Boogie Mark IV

The_Nuge

Senior Member
Joined
Dec 12, 2010
Messages
1,934
Reaction score
1,450
Hi!
This somehow followed me home today :cool2:
20191119_221111_2.jpg

Had to drive for 2 1/2 hours to check it out, but got it at a very good price including flight case. Didn't work very well when I checked it out (humming, noises...), but a good hour spent cleaning pots, replacing the mains plug and attaching the grounds properly did wonders!
It's a wee bit complicated inside...

20191119_2052352_2.jpg

...but possibly more outside!
There isn't much that can't be adjusted, and I'll need to spend some serious time with it I think!
 

ErictheRed

Senior Member
Joined
Dec 8, 2009
Messages
5,403
Reaction score
6,657
Sweet! I have only recently come to appreciate Mesas (I associated them with "dad rock" types or super high gain metal), but I've really come to love a lot of Mesa's products in the last year. I've also become a dad in the last year, so that might be related...?
 

The_Nuge

Senior Member
Joined
Dec 12, 2010
Messages
1,934
Reaction score
1,450
Thanks!
It's been sat in the flight case for maybe 15-20 years, and the foam has deteriorated and somehow reacted with the tolex, rendering it gummy. I may have to recover it in snakeskin tolex :hmm::thumb:
 

Robotechnology

V.I.P. Member
Joined
Jun 4, 2014
Messages
141
Reaction score
173
I owned 2 heads in the past. The first one sounded better than the second but, I can’t remember which was which A or B version (original and revision). Shouldn’t have sold my 1st one.
 

The_Nuge

Senior Member
Joined
Dec 12, 2010
Messages
1,934
Reaction score
1,450
Hi again,
I had a longer play with the amp yesterday, and had a few weird problems:
1. The amp has a "Tweed" feature on the power switch, which, as I understand, acts as a kind of fixed Variac, lowering the mains voltage. When using this feature, and SOVTEK LPS tubes in V1-3 and V5 (V4 is a 12AT7 for the reverb), the amp significantly loses volume and gain after running for maybe 10 minutes. When this happens, the footswitch also malfunctions... When using JJs or TAD 7025 in the preamp, everything is fine! What could be the cause of this? Surely all 4 LPS's can't be defective? I read somewhere that some "Russian Tubes" can have problems with the voltages in the amp, but that sounds strange to me!
2. The power tranny has taps for 220V and 240V mains (I live in Germany), however our mains voltage is usually at about 230V here. Which would be better to use? Advice elsewhere was to go for the 240V tap, but I'm wondering if it would be better to use something like the heater voltage (6.3V AC?) for reference?

Another question: is there a way of testing the filter caps with a multimeter that can read capacitance?

The amp does sound really great with the tubes (TAD 7025 in V1, JJs in the rest) I threw in there! I also think I now comprehend most of the features :thumb:
 

The_Nuge

Senior Member
Joined
Dec 12, 2010
Messages
1,934
Reaction score
1,450
Hi!
I think I've traced the issues to the area of the board with the 3 brown caps (in "front" of the 3 blue ones) - couple of blown resistors and a dodgy diode. I've managed to remove the offending parts, but in order to solder the new ones in, it would be good to remove the PCB. Is there a practical way of doing this?
I was thinking of unscrewing the pots and then unsoldering the wires on the tube side of the board. Still seems like a major pain, so I'd be grateful for any advice!
Cheers
Es
 

HogmanA

Senior Member
Joined
Jan 2, 2009
Messages
1,101
Reaction score
849
Well, it looks like the pcb is a 'plated through-hole' type, and if so you should be able to solder from the top, leaving the leads a bit longer than usual. The solder will flow through to the other side.
But if you must solder from the other side, I would remove the pots and the board with the sliders and rotate the board up. Looks like there would be just enough room to get access.
 

bblooz

Senior Member
Joined
Oct 8, 2014
Messages
3,142
Reaction score
1,673
..foam has deteriorated and somehow reacted with the tolex, rendering it gummy. I may have to recover it in snakeskin tolex
Try Naptha (old-fashioned lighter fluid) or denatured solvent alcohol to try and clean the tolex first. I found these two solvents to work wonders on stain and glue removal.
..in order to solder the new ones in, it would be good to remove the PCB. Is there a practical way of doing this?
If you turn the amp on its' side and carefully apply the solder to the pre-heated joint, you may not have to remove the PCB.

Good Luck!
 

The_Nuge

Senior Member
Joined
Dec 12, 2010
Messages
1,934
Reaction score
1,450
Hi Guys.

the "flowing solder from the top trick" does work, as I've used it for the filter caps, but there is one of the pin holes that looks very dodgy. Also, I'm not sure how much shorter the new radial caps are - I'm still hoping that soldering from the top will work!
Cheers

Es
 

grumphh

Senior Member
Joined
Oct 9, 2015
Messages
1,105
Reaction score
884
2. The power tranny has taps for 220V and 240V mains (I live in Germany), however our mains voltage is usually at about 230V here. Which would be better to use? Advice elsewhere was to go for the 240V tap
I live in Denmark, so have the same voltage problem, and well, to be on the absolutely safe side, set it to 240 V, as that will lower internal voltages, which should be easier on the amp rather than having to high internal voltages.

At least that is my reasoning - and if i have a choice, i set my amps input to 240 V.
...but older amps that were still designed for 220 V do still run fine, even on ~230 V, so i guess that those 5-10 % in voltage difference don't matter all that much...
 

EndGame00

Senior Member
Joined
Aug 31, 2013
Messages
1,649
Reaction score
1,587
Yep... My first Big Boy amp.... I find the Mark IV was much easier to dial in compare to Mark V....

You can substitute the outside power tubes from 6L6 with El-34 and set to triode mode (it's on the manual)... Or with 5881's if you want a little darker tone....
 

bgh

Senior Member
Joined
Oct 22, 2016
Messages
403
Reaction score
449
Yep... My first Big Boy amp.... I find the Mark IV was much easier to dial in compare to Mark V....

You can substitute the outside power tubes from 6L6 with El-34 and set to triode mode (it's on the manual)... Or with 5881's if you want a little darker tone....
I use EL34s on the outside tubes in mine. Like the way it sounds.
 

The_Nuge

Senior Member
Joined
Dec 12, 2010
Messages
1,934
Reaction score
1,450
I got the parts today, except they forgot one of the caps....
I did manage to replace the suspect diodes and resistors, and also 2 of the 3 caps, soldering from the top side.
I wired in one of the old caps and fired the old girl up using my newly acquired variac - NO SMOKE!
It's got stable 15V DC to the footswitch and sounds fine, as in also quieter than before, so I'm pretty confident I've found the issue.
Hope to get it all done on friday, will retube it with new JJ 6L6s, TungSol in V1 & PI, JJ 12AT7 in V4 (reverb) and gold-pin EH 12AX7s in V2 and V3 as well!

Cheers

Es
 




Top