Should this be bulging like that? - Valve amp restoration.

[Circuitbenders]

Ok, so i'm restoring my WEM Dominator mkIII valve amp and i've come accross this wierd dark blue component labelled 'ARCOL V7 100R' which turns out to be a 7 watt Vitreous Enamelled resistor, presumably wirewound at that wattage.

What i'm wondering is, is it actually meant to be bulging in that disturbing manner? I think that dried brown goop around it is ancient glue to hold what appear to be insualtors in place but i'm not 100% sure, it could be something leaking although i wouldn't have thought there would be anything to leak from a resistor.





It measures at 100 ohms so it appears to be working alright for now and it has been there for about 40 years, but i'm a bit wary of a catostrophic failure.

While i'm at it, does anyone recognise the logo on those blue electrotytics? I'm just trying to work out how old they are. the smaller 47uF one is obviously a replacement as its meant to be 50uF on the schematic so i'm assuming that the big one is as well but for all i know they were replaced 20 years ago. It looks like GIE to me but i can't find any manufacturers under that name.



sorry the photots are a bit shit, i had to take them on my phone

[LoFi-Ninja]

Perhaps http://www.gieinc.com/ but they seem to be more into valves. But you never know what a compagny might have manufactured 30 years ago.

I'm pretty shure that resistor is leaking enamel.. I would just replace it with say a 10 or higher Watt ceramic resistor. They're pretty expensive around here so I usually grab them from filters out of busted speakers or TV's..There's a reason the original resistor is 7 watts.

Let's hear your amp when you finished it.. Myself I'm restoring an old Montarbo 453 powered mixer with a tape drum echo it even has a green glowing vacuum tube.. Pretty rare item.. Can't find any info on it and the PSU is completely burnt out.. Many component values can't be identified..

[Gordonjcp]

Yes, those ones are kind of cigar-shaped.  The brown stuff is flux, left over from soldering it.

[LoFi-Ninja]

Yes, those ones are kind of cigar-shaped.  The brown stuff is flux, left over from soldering it.

I've never seen a wirewound resistor bulge like that.. And I do have a couple floating around.. But if you say so.. Well then the solder that was used must be the most flux containing solder ever..

[Gordonjcp]

Those resistors and really messy flux were very common in 60s and 70s British amps.

[Circuitbenders]

Any guess on the age of those electrolytics Gorden?

I've had the amp for about 12 -15 years and i've never changed them although they do look newer that the rest of the board.

[Gordonjcp]

No idea.  If they're working, leave them alone.  I know people harp on about failing electrolytic capacitors, but that's only a problem with enormously old (>60 years) or cheap Chinese motherboards.  I think I've replaced maybe two or three failed electrolytic capacitors in equipment in about 25 years of poking electronic stuff.

Resistors going high in value, now that's a very different story.  Watch out for high value resistors (typically more than about 100k, but it happens to lower value ones too) that are used in high-voltage circuits just mysteriously creeping up in value.  Another favourite is disc ceramic capacitors becoming very leaky or even failing dead short, and tantalum bead capacitors failing dead short and emitting huge amounts of magic smoke all out of proportion to their size.

[Circuitbenders]

I think I've replaced maybe two or three failed electrolytic capacitors in equipment in about 25 years of poking electronic stuff.agic smoke all out of proportion to their size.

I was thinking this might be one of those cases like guitarists claiming to hear differences in tone between a box of identical valves. Word has it that valve amps sound better with new caps but i'm suspecting the difference might be undetectable to my ears.

Having said that, a while back i was repairing an amp from the 70's and a couple of the bigger electrolytics were actually rattling, but then they didn't look to good on the outside.

[Gordonjcp]

I was thinking this might be one of those cases like guitarists claiming to hear differences in tone between a box of identical valves.

Any cheap modern valve is likely to have closer tolerances than a "matched pair" from 20 years ago ;-)

You used to have to buy push-pull amp valves in matched sets, which were bloody expensive.  Any two off the pile these days are often a closer match!

[LoFi-Ninja]

I was thinking this might be one of those cases like guitarists claiming to hear differences in tone between a box of identical valves.

Any cheap modern valve is likely to have closer tolerances than a "matched pair" from 20 years ago ;-)

You used to have to buy push-pull amp valves in matched sets, which were bloody expensive.  Any two off the pile these days are often a closer match!

The trick was to buy chinese military valves.. They where cheap as hell compared to US based valve manufacturers..

But yeah old valves is like old germanium transistors.. No two are the same.. So yeah if your an audiophile guitarist or producer you can hear a difference. But the regular listener would never have a clue..

[Circuitbenders]

I do recall that swapping the cheap chinese valve in my ART Studio V3 preamp for an old Mullard ECC83 made it go from sounding noisy and plastic, to nicely warm and rounded. It seemed to lose a tiny amount of definition but personally i prefer weight to precision. 

[LoFi-Ninja]

But the millitary ones where different than the regular chinese.. I'll bring it up next time i speak to the guy I used to buy them from.. He used to be a sound engineer, not sure why he's not any more.. But yeah the sound was different..