LDR'S in 2:90

Triaxis, Quad Preamp, Stereo Power series, Recto Preamp

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Henz
Mark II
Posts: 83
Joined: Wed May 18, 2016 11:05 pm

LDR'S in 2:90

Post by Henz » Sun Oct 01, 2017 1:59 pm

Greetings. What function do the two LDR's do in my 2:90? And, what are some of the symptoms when they start to fail? Thanks, Jim
MKIIC+
2:90
4x12 Recto Cab w/ Eminence and V30's
Home made 2x12 half open cab w/ Eminence and V30's
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MesaMad1378
Mark II
Posts: 56
Joined: Tue Sep 15, 2015 4:49 pm
Location: Gold Coast, Australia

Re: LDR'S in 2:90

Post by MesaMad1378 » Fri Oct 13, 2017 12:22 am

Hi Henz,

The 2 ldr’ s are for 1/2 Drive. If they fail you won’t have it or it will be stuck in half Drive. They switch an extra resistor in and out of the circuit. They add a 470 in parallel to the 15k. This changes the voltages in various circuits.
Mesa Dual Rectifier, TriAxis, Recto Recording,
2:90, 2:100, SUS-4 16ru Case,
Flux Five, Throttle Box EQ, 5 Band EQ,
Straight Traditional 4x12 Cabs.
And other stuff!!

Henz
Mark II
Posts: 83
Joined: Wed May 18, 2016 11:05 pm

Re: LDR'S in 2:90

Post by Henz » Fri Oct 13, 2017 11:00 pm

Hey, I just replied to ur other post. I measured the voltages on the pins of the 12ax7's. they are ok. Man, I wud love to solve this issue with my half drive. Question: On a cold power up, shud all of the voicing led's be off? Oh , on your other post, the same happens to mine ( while all 3 are on, 1/2 drive is dim, then after a while brightens). With ur post here, my half drive seems stuck when first powering up but never have lost it. (sigh). Thanx for the reply, James.
MKIIC+
2:90
4x12 Recto Cab w/ Eminence and V30's
Home made 2x12 half open cab w/ Eminence and V30's
Rocktron Patchmate, Rocktron Intellifex, TS10 Tubescreamer

MesaMad1378
Mark II
Posts: 56
Joined: Tue Sep 15, 2015 4:49 pm
Location: Gold Coast, Australia

Re: LDR'S in 2:90

Post by MesaMad1378 » Wed Nov 01, 2017 3:43 pm

The LDR's should be open by the looks of the diagram, close when shorted. My 1/2 drive is bright when on by itself or with only 1 other function, only dull when all 3 on.
Have you tried making shorting plugs? I'm wondering if your cables that you are using or the source you are using for switching is doing it. Are you using instrument cable or are you using speaker cable? Maybe try swapping cables around to see if it is one particular cable that isn't quite sending enough signal.

Cheers Brett
Mesa Dual Rectifier, TriAxis, Recto Recording,
2:90, 2:100, SUS-4 16ru Case,
Flux Five, Throttle Box EQ, 5 Band EQ,
Straight Traditional 4x12 Cabs.
And other stuff!!

Henz
Mark II
Posts: 83
Joined: Wed May 18, 2016 11:05 pm

Re: LDR'S in 2:90

Post by Henz » Wed Nov 01, 2017 10:44 pm

Thanx for the reply... I never thot of the shorted plug option. Thanks. Im using a R. Patchmate to activavate voices. You know its been so long , I know that I tried both cables. Not sure what they are now ( shame on me). I'll check and let you know. My led's act just like yours. Half very brite by its self. On a cold power up, shud all of the led's be off? my half stays on a lil, then flickers then goes out with patchmate noet switched in yet. Blessings, Jim
MKIIC+
2:90
4x12 Recto Cab w/ Eminence and V30's
Home made 2x12 half open cab w/ Eminence and V30's
Rocktron Patchmate, Rocktron Intellifex, TS10 Tubescreamer

MesaMad1378
Mark II
Posts: 56
Joined: Tue Sep 15, 2015 4:49 pm
Location: Gold Coast, Australia

Re: LDR'S in 2:90

Post by MesaMad1378 » Sat Nov 25, 2017 2:56 am

All should be off when powering on, dependant on what signal is being sent to the 2:90. If the patch is being sent with half Drive on, then the half Drive light will be on.
My half Drive is on with every patch except clean tones. If I want more volume then I turn half Drive off.
Mesa Dual Rectifier, TriAxis, Recto Recording,
2:90, 2:100, SUS-4 16ru Case,
Flux Five, Throttle Box EQ, 5 Band EQ,
Straight Traditional 4x12 Cabs.
And other stuff!!

Henz
Mark II
Posts: 83
Joined: Wed May 18, 2016 11:05 pm

Re: LDR'S in 2:90

Post by Henz » Sun Nov 26, 2017 11:41 pm

Thanx for the reply. Does that mean that it needs repaired? When powering up cold, the half drive led stays on, but not as long and no flickering. I(seem) to not notice any difference in tone. From my research, it may be a resistor in the LDR supply. I have noticed that my pilot lite flickers. You may be rite, i need those connectors instead of power tube socket pins. The green wires from power tranny does supply the 6 volts for both ( i think-all tubes too). Please reply if u can help me. Blessings. James
MKIIC+
2:90
4x12 Recto Cab w/ Eminence and V30's
Home made 2x12 half open cab w/ Eminence and V30's
Rocktron Patchmate, Rocktron Intellifex, TS10 Tubescreamer

MesaMad1378
Mark II
Posts: 56
Joined: Tue Sep 15, 2015 4:49 pm
Location: Gold Coast, Australia

Re: LDR'S in 2:90

Post by MesaMad1378 » Wed Nov 29, 2017 8:12 am

Hi Henz,

I’m not sure if you are any good with a soldering iron? If you are, I’d do it myself.
I’d say there may be a problem with a transistor as the led should only be able to light up if it has an earth. The only way I see it gets its earth is through the transistor Q5 in the wiring diagram. It is a 2N6426, as are all the transistors in the switching circuits.

Unless the LDR or capacitor are leaking and switching the transistor, thus providing the earth.

Does it do it with nothing plugged in except the speakers?

Cheers Brett
Mesa Dual Rectifier, TriAxis, Recto Recording,
2:90, 2:100, SUS-4 16ru Case,
Flux Five, Throttle Box EQ, 5 Band EQ,
Straight Traditional 4x12 Cabs.
And other stuff!!

Henz
Mark II
Posts: 83
Joined: Wed May 18, 2016 11:05 pm

Re: LDR'S in 2:90

Post by Henz » Wed Nov 29, 2017 11:53 pm

Thanx for the reply, yes i'm good on soldering. The Half drive comes on with nothin plugged in on cold power up. Tho, it has been acting differently recently. It doesn't flicker no more. It stays on for, about 3 to 5 mins. then goes out. How can i find out if those components are leaking? Shud i get a ldr transistor and install it ? You're a God send . Ty! I know i can fix it. I just need a little guidance. Blessings. James
MKIIC+
2:90
4x12 Recto Cab w/ Eminence and V30's
Home made 2x12 half open cab w/ Eminence and V30's
Rocktron Patchmate, Rocktron Intellifex, TS10 Tubescreamer

MesaMad1378
Mark II
Posts: 56
Joined: Tue Sep 15, 2015 4:49 pm
Location: Gold Coast, Australia

Re: LDR'S in 2:90

Post by MesaMad1378 » Fri Dec 15, 2017 7:39 pm

Hi there Henz,

I'm thinking of changing all my LDR's, mine does crackles for a good couple of minutes when I turn the standby on (running mode). My lights don't come on or anything though.

I've got to try to find a replacement as the are VTL5C9's and these are not made any more.

I've found these, they seem to be a fit:

Luna Optoelectronics NSL-28

https://www.alliedelec.com/luna-optoele ... /70136793/

Luna Optoelectronics NSL-32

https://www.alliedelec.com/luna-optoele ... /70136794/

Advanced Photonix NSL 32

http://uk.farnell.com/advanced-photonix ... dp/3168773

Does anybody else have any better matches?
Mesa Dual Rectifier, TriAxis, Recto Recording,
2:90, 2:100, SUS-4 16ru Case,
Flux Five, Throttle Box EQ, 5 Band EQ,
Straight Traditional 4x12 Cabs.
And other stuff!!

Henz
Mark II
Posts: 83
Joined: Wed May 18, 2016 11:05 pm

Re: LDR'S in 2:90

Post by Henz » Fri Dec 15, 2017 11:41 pm

Thanx for the reply. I wud love to do the same. keep in touch. James.
MKIIC+
2:90
4x12 Recto Cab w/ Eminence and V30's
Home made 2x12 half open cab w/ Eminence and V30's
Rocktron Patchmate, Rocktron Intellifex, TS10 Tubescreamer

Henz
Mark II
Posts: 83
Joined: Wed May 18, 2016 11:05 pm

Re: LDR'S in 2:90

Post by Henz » Wed Mar 07, 2018 12:39 am

Im using guitar, shielded cables for my switching jacks. Shud i be using short speaker cables? Thanx! James
MKIIC+
2:90
4x12 Recto Cab w/ Eminence and V30's
Home made 2x12 half open cab w/ Eminence and V30's
Rocktron Patchmate, Rocktron Intellifex, TS10 Tubescreamer

MesaMad1378
Mark II
Posts: 56
Joined: Tue Sep 15, 2015 4:49 pm
Location: Gold Coast, Australia

Re: LDR'S in 2:90

Post by MesaMad1378 » Wed Jul 18, 2018 1:38 am

Hi Henz, in the manual it says uninsulated speaker cables.
Mesa Dual Rectifier, TriAxis, Recto Recording,
2:90, 2:100, SUS-4 16ru Case,
Flux Five, Throttle Box EQ, 5 Band EQ,
Straight Traditional 4x12 Cabs.
And other stuff!!

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