Ugg, New Gold Lions, JTM45 with a VVR

yodermr · Post by **yodermr** » Sat Oct 24, 2009 1:24 pm

Hey guys
So I built a Metro JTM45 a few years ago. Worked great, no problem. Loud as hell, year later, I installed a VVR (Dana) between the first cap and the choke and between the Bias trim and the 220K resistors. Worked great, no problem. Zoom forward about a year...

Loud hum, then back to normal. Switched it off. Back on and watched the tubes, spark shower storm inside one tube. Shut her down. K, Figured it was time for new tubes...

Got a pair of Gold Lions, installed. Going from suggestions on this board, tried to bias at .033 but I didn't have the needed range to go that low (got down to .039). So I change the bias resistor.

Biased her in at .034mV. Sounded great. Here is where it got weird on me.

So I'm playing along with the bias meter on, letting it get warmed up to readjust the bias. Turned down the VVR and it didn't drop the volume like it used to. Umm, strange...then playing along, Red Plate (on both tubes). Looked at the bias reading, it was .157. Shut it down (I didn't recheck the plate voltage & bias voltage when it was down...assumed, as designed, they track together).

So now, I turn it on with the VVR all the way up, bias in at .034, sounds great but after a few minutes I get this toxic smell happening (thought maybe something on the new tubes, but the smell get strong) and I hear a high pitched buzz in the amp (not from the speakers). Not even going near turning the VVR down at this point

Check all voltages, seem in range. My novice brain is tapped

Help?

Thx
Mark

MBD115 · Post by **MBD115** » Sun Oct 25, 2009 6:14 pm

I don't know but my guess would be to remove the VVR and wire the amp back right and test it then. I have no idea on how to test the amp with that device in the circuit.

Good luck.

Structo · Post by **Structo** » Sun Oct 25, 2009 8:32 pm

I'll bet you fried the MOSFET in the VVR.

Even though it is stated that it can handle 50 watts, it seems to me the people having problems with them are the ones with 45-50 watt amps.

And of course once distortion kicks in you are probably well over the wattage an amp is rated at.

yodermr · Post by **yodermr** » Sun Oct 25, 2009 9:35 pm

Yup one of the mosfets was toast. With that, I guess the VVR knob becomes just a raw bias control. Like a light bulb dimmer

The maker of the VVR board (Dana) to the fact that I didn't have a heat sink on it as why it probably blew to begin with.

Swap it out, add the heat sink and we'll see what we get.

Thx
m

yodermr · Post by **yodermr** » Sat Nov 07, 2009 2:43 pm

Hey just letting everyone know...got it all up and running. Replaced the Mosfet, added a nice heat sink on it, biased it up and away we go.

On the Gold lions...very nice. Certainly an improvement over the Valve Arts. I won't throw out a bunch of meaningless marketing descriptors, just saying, I'd definately pick GL over the VA

All said and done, my JTM45 (Sozo, Mercury Magnetics, Weber Blue Dog, etc...all the goodies) sounds/feels a better than my Fuchs, Bogner and my equally pimped out home brew TrainWreck.

Thanks for all the help
M

Roe · Post by **Roe** » Sun Nov 08, 2009 12:40 pm

My 45/100 just blew a gold lion after 150 hours or so

yodermr · Post by **yodermr** » Sun Nov 08, 2009 1:17 pm

So, guess I need some additional guidance....The amp is up and running, playing and sounding great. Played it for a few hours over the last few days...One thing I notice though and have no idea what to do with it is that the smell is still there. Not as bad as before.

So I searched around (transformer, caps, resistors) but it seems for my expertise level I'm poking around in the dark.

Any thoughts on if this is an actual problem?, will it become one?, what I can to to diagnosis it?

Thx, much appreciated
Mark

Structo · Post by **Structo** » Sun Nov 08, 2009 1:44 pm

Not sure about the smell but be sure to feel the PT and OT after you have been playing for a while.
They shouldn't be so warm that you can't leave your hand on them for a minute.
If they are too hot to touch then you have a problem with the amount of current the amp is drawing.

In that event I would double check your bias setting.

New amps will have a bit of a smell when they are new but I wouldn't classify it as a burning smell.
Just the smell of new components getting warm.

yodermr · Post by **yodermr** » Mon Nov 09, 2009 2:52 pm

Well let it run and run, played for a few hours and the OT PT never really get past warm.

Tough smell to describe, its more metallic, chemical not really a burning smell.

Started only after the inital Mosfet failure, I've had the amp running many many hours prior to this so don't think its a new component smell.

The smell was very strong when the mosfet failed and my VVR control acted like a bias control, red plating fun. Now its much less but there.

Could I have pushed something to "sweat" bad stuff out but not actually fail? When it heats up is "burning" off whatever?

In the end it plays great....just worried about something else (the smelly part?) failing later and taking down a few more dominos

M

Structo · Post by **Structo** » Tue Nov 10, 2009 11:45 am

How do the resistors on the VVR board look?
Any of them discolored from heat?

It may just be one of those things where you have to wait until something goes belly up to figure out what's wrong.

Did you feel the PT to see how warm that is getting?

Remember the louder you play the more demand that is being put on the components.

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