Dual Rectifier tech question....

[lespaul6]

I had a friend of mine tell me that dual rectifier amps- both the solo head and tremoverb- have had problems with gradual loss of gain and eq characteristics. He said his friends had to send theirs back to Mesa to have the "LDR's" replaced.....WTF I havent heard about any problems relating to gain loss etc, and resistors needing replacement,,,,is this for real?????


thanks!

 

[Boogiebabies]

The early Tremoverbs had a bulletin for LDR replacements and an increase in two LDR voltage supply resistors. The DR did not.

 

[JimAnsell]

heh, those stacks of Light Dependent Resistors on boogie circuit boards is a bit scary to some techs.

 

[lespaul6]

Thanks guys, the information here has been great! I think I have an early one....attached plug, leather, ac ground switch etc; should I be worried? Is this an easy fix that can be done by a local tech? thanks again!

 

[AdmiralB]

Replacing them is not particularly difficult, but it is very tedious. They're about $7 per piece, and there are twenty of them in there. It's easier to 'shotgun' the amp and replace them all than it is to try to find the one or two that are trouble.

Could be worse...could be a Trem-o-verb.

The early DR/TOV design, as far as the LDR network goes...sucks. It derives its power supply rail from the bias supply, so there's a big (5W) resistor that knocks the voltage down, and it gets HOT.

The later models (with the 561140 power transformer) added a 12VAC winding dedicated to the LDRs. Much smarter design.

 

[Commander Coo1]

so about what year did the tremoverb become more reliable?

 

[lespaul6]

Replacing them is not particularly difficult, but it is very tedious. They're about $7 per piece, and there are twenty of them in there. It's easier to 'shotgun' the amp and replace them all than it is to try to find the one or two that are trouble.

Could be worse...could be a Trem-o-verb.

The early DR/TOV design, as far as the LDR network goes...sucks. It derives its power supply rail from the bias supply, so there's a big (5W) resistor that knocks the voltage down, and it gets HOT.

The later models (with the 561140 power transformer) added a 12VAC winding dedicated to the LDRs. Much smarter design.

I'm going to have to check my transformer...I'm hoping the number matches...I would hate to have to send it to mesa for repair. If there are twenty nine at seven dollars a peice, thats two hundred right there in parts alone.

 

[AdmiralB]

The transformer doesn't really affect the LDR reliability...the earlier ones run hotter internally, but LDRs are kind of finicky things - they're an LED and a photocell molded into a little cube. The photocell has high resistance when it's dark and low resistance when it's lighted. They're used as 'switches' to affect the circuit configuration.

Sometimes, they just...quit.

Like I said, they're not hard to replace, but each one has four leads, and Mesa likes to stack them atop each other...I think the regular DR doesn't go higher than three per stack, the TOV has at least one stack of four.

Couple that with the large number of flying wires inside, and you can see that it's a tedious, time-consuming process to replace them.

There are twenty in a two-channel DR, but it's unlikely that more than one or two need replaced.

Looks like I overstated the cost, too - here's the part:

http://www.alliedelec.com/Search/ProductDetail.asp?SKU=980-9951&SEARCH=&MPN=VTL5C9&DESC=VTL5C9&R=980%2D9951&sid=47042D006499617F

 

[Commander Coo1]

oh wow, thats the part that has been messed with in my old tremoverb i bought off of ebay.

very interesting, and some of my switching doesnt work, i wonder if its all screwed up becasue someone tried to fix the switching problem, or they messed with them and caused the switching problem...

 

[MesaENGR412]

could be the problem, i'd get it checked out by a Mesa-authorized tech. Switching problems suck!! I've been having some trouble occasionally with my Triple trying to switch between distortion channels. I think it might be the 7-pin cable, because when i switch the channels manually from the back of the amp, they work fine and stay in that channel, but sometimes after a while, the amp tries to switch by itself, and both ch2 and ch3 lights light up, and the amp starts cutting out. could there be another, more serious problem with mine, or is it likely the cable (i know they don't last forever and i'm not the lightest on my cables.) Thanks

-AJH